LTE – RRC - 3G Network Solutions3gnets.in/files/documents/LTE-Protocol-Stack-RRC.pdf · LTE –...

LTE Protocol Stack- 1 [email protected]

Development, Conformance Testing, Optimization

Certification Course – Amateur Level (3PCA-RRC)

3PCA-RRC

LTE – RRC

LTE Protocol Stack

Author: Surya Patar Munda

----------------------------------------------------------------------------------------------------------------------------- ---------LTE Protocol Stack- 2 email: [email protected] – Page - 2 . .

Preface:

Dedication – This book is dedicated to my family who has given me support to complete this book.

The colleagues in office have given me encouragement to start and complete this book. My hearty

thanks to all of you. The first release is printed with many terms unexplained and even sentences are

shortened but intended to cover in this book. They will gradually be expanded in next release. Please

do write me on the email given in the pages below to improve.

Who is this book for?

Over the years I have seen the telecom industry struggling to get right people with sufficient domain

knowledge in 2G or 3G or 4G. The specification is very huge and it is often horrendous to go through

the details. This book is referring most of the time with respect to LTE 3GPP specification, Rel-10.

This is an effort to consolidate information in an organised way to give a methodical way of

understanding LTE. This is a very good start for an engineer who is either going to pursue:

LTE Protocol Stack Development

LTE ConformanceTesting

LTE Network/RF Optimization

LTE entities (UE and Network both) troubleshooting

If you need 3GNets LTE Physical Layer for Amateur Level (3PCA-RRC), you need this course.

This knowledge and level is required for the next level – Professional Level (3PCP-RRC) where you

can be trained for higher level with Hands on Projects and real implementation. Full Amateur level

courses are:

LTE Physical Layer - (3PCA-L1)

LTE L2 Layer - MAC, RLC, PDCP - (3PCA-L2)

LTE RRC – (3PCA-RRC)

LTE NAS – (3PCA-NAS)

About Author:

Surya Patar Munda has been in Telecommunications Since 1987 and has gone through the life cycle

of Software Development, Software Testing, Network Deployments, Integration, Testing,

Troubleshooting, Handphone Testing with Specification etc.. a full round of the Telecom industry. He

has worked with Motorola, Nortel Networks, Spirent Communications, Sasken etc. companies with full

round cycle. The Software engineers midset and Testing engineers mindsets are different and so is

the mindset of an RF optimization engineer. This book will cater to all.

Author also conducted many trainings for Telecom industry and has a very good understanding of

what kind of requirement is there for engineers. The goal is not just what and how does it work, but

also the goal is how do I start implementing and how do I test.

Edition: July 2013

Price: Rs.149

mailto:[email protected]


Contents

1. Access Stratum – RRC L3 .............................................................................................................. 5

1.1. Radio Resource Controller – Idle ............................................................................................ 5

1.1.1. PLMN and Cell Selection ................................................................................................ 5

1.1.2. PLMN Selection............................................................................................................... 5

1.1.3. Cell Selection .................................................................................................................. 6

1.1.4. Cell Reselection .............................................................................................................. 6

1.1.5. Cell Access Restrictions .................................................................................................. 8

1.1.6. Closed Subscriber Group (CSG) ..................................................................................... 8

1.1.7. Neighbour Monitoring and Cell Reselection .................................................................... 8

1.1.8. Paging ............................................................................................................................. 9

1.1.9. RRC Messages and Controls ........................................................................................ 10

1.1.10. System Information Broadcast (SI) ............................................................................... 10

1.2. Cell ReSelection & PLMN Selection Design-Development .................................................. 13

1.2.1. Cell Re-Selection (CRS) Description ............................................................................ 13

1.2.2. CRS Actions: ................................................................................................................. 13

1.2.3. CRS Process Inputs: ..................................................................................................... 14

1.2.4. Internal Messages Design ............................................................................................. 14

1.2.5. CRS Outputs Message(Internal): .................................................................................. 15

1.2.6. IPC-Design Diagram: .................................................................................................... 15

1.2.7. Cell_Selection_Function() ............................................................................................. 16

1.2.8. Cell_Re-Selection_Function() ....................................................................................... 16

1.2.9. PLMN Selection Process Design .................................................................................. 20

1.2.10. PLMN Selection Actions ................................................................................................ 20

1.2.11. PLMN Selection Inputs .................................................................................................. 20

1.2.12. PLMN SelectionOutputs(Internal) ................................................................................. 20

1.2.13. PLMN Selection IPC-Design ......................................................................................... 21

1.3. Measurement and Reporting ................................................................................................. 23

1.3.1. LTE Measurements ....................................................................................................... 23

1.3.2. Measurement Objects and Management ...................................................................... 23

1.3.3. NON-LTE Measurements .............................................................................................. 24

1.3.4. Measurement Report Triggering ................................................................................... 25

1.3.5. Measurement Reporting ................................................................................................ 25

1.3.6. Measurements when Camped on LTE ......................................................................... 25

1.3.7. LTE Mobility in RRC_CONNECTED ............................................................................. 26

1.4. Radio Resource Controller – Connected .............................................................................. 31

1.4.1. Connection Control within LTE ...................................................................................... 31

1.4.2. Security KeyManagement ............................................................................................. 31



1.4.3. Connection Establishment and Release ....................................................................... 32

1.4.4. RRC_CONNECTED Messages .................................................................................... 33

1.4.5. Mobility Control in RRC_IDLE and RRC_CONNECTED .............................................. 34

1.4.6. Message sequence for handover within LTE ................................................................ 35

1.4.7. Connection Re-Establishment Procedure ..................................................................... 35

1.4.8. Connected Mode Inter-RAT Mobility ............................................................................. 36

1.4.9. Handover to LTE ........................................................................................................... 36

1.4.10. Major HANDOVER Steps (Intra-LTE) ........................................................................... 37

1.4.11. Handover to UMTS........................................................................................................ 38

1.4.12. Handover to GSM.......................................................................................................... 38

1.4.13. Other RRC Signalling Aspects ...................................................................................... 39

1.5. Radio Resource Management .............................................................................................. 41

1.5.1. UE Mobility Activities Overview ..................................................................................... 41

1.5.2. LTE Cell Search ............................................................................................................ 41

1.5.3. UMTS Cell Search......................................................................................................... 42

1.5.4. GSM Cell Search........................................................................................................... 42

1.6. MU-Scheduling & Interference Coordination ........................................................................ 45

1.6.1. Resource Allocation Strategies ..................................................................................... 45

1.6.2. Scheduling Algorithms .................................................................................................. 46

1.6.3. Performance of Scheduling Strategies.......................................................................... 47

1.6.4. Considerations for Resource Scheduling in LTE .......................................................... 47

1.6.5. Interference Coordination and Frequency Reuse ......................................................... 47

1.7. Sample Call Flows ................................................................................................................ 51

1.7.1. Basic Call Flow – Attach Procedure .............................................................................. 51

1.7.2. Basic Call Flow – Incoming Call with Handover ............................................................ 52

1.7.3. Call Flow example from tool .......................................................................................... 53



1. Access Stratum – RRC L3

1.1. Radio Resource Controller – Idle Radio Resource Controller (RRC) performs Control Plane of Access Stratum (AS). AS interacts with NAS, which handles PLMN_selection, Tracking Area update, paging, authentication, EPS bearer establishment, modification and release. RRC is in either RRC_IDLE or RRC_CONNECTED state. UE in RRC_IDLE performs cell selection, reselection – select best cell to camp. Consider priority of frequency, RAT, radio link quality, cell status, speed, CSG and MBMS. An RRC_IDLE UE monitors paging to detect incoming calls, acquires system information (SI). SI consists of parameters for cell (re)selection, Paging.

Fig 5.1.0 – Idle Mode Processes

In RRC_CONNECTED, eNB allocates RB to UE to transfer data via shared data channels. UE monitors PDCCH for allocated transmission resources in time and frequency. UE reports buffer status and DL channel quality (CQI), neighbouring cell (including other freq/RAT) measurement to select most appropriate cell for UE. UE continues to receive SI. To extend battery lifetime, UE may be configured with a Discontinuous Reception (DRX) cycle. RRC performs security, inter and intra RAT mobility, establishment and reconfiguration of radio bearers to carry control and user data.

1.1.1. PLMN and Cell Selection Once UE is switched on, first it selects a PLMN, then it performs cell selection –searches for a suitable cell to camp on with help of acquired SI parameters. Subsequently, UE registers in the tracking area if not done in that TAI, then it can receive paging for incoming calls. UE may establish RRC connection either to establish a call or to register. In Idle mode, UE regularly verifies if there is a better cell (cell reselection). Detected Cells can be:

Suitable cell (normal service), Acceptable cell ( „limited service‟, emergency calls), Reserved cells (normal service but with special rights like for operators or AC >=11) or Barred cells (No service at all).

1.1.2. PLMN Selection NAS handles PLMN selection based on available PLMN list provided by AS. NAS indicates selected PLMN together with list of equivalent PLMNs. After registration, selected PLMN becomes R-PLMN. AS may autonomously indicate available PLMNs after full search. For all the PLMNs UE receives, it searches for the strongest cells(PLMNs are retrieved from SI) on each carrier frequency. PLMNs are reported as high quality or ; just reported with their quality.



1.1.3. Cell Selection In Cell selection, UE searches for strongest cell on all supported carriers of each supported RAT until it finds a suitable cell. After switch on, first selection is Cell Selection. To speed up, UE may use stored information and NAS may indicate RATs associated with selected PLMN. Cell selection criterion is known as S-criterion and is fulfilled when Srxlev > 0 dB, where

Srxlev = Qrxlevmeas − (Qrxlevmin − Qrxlevminoffset) where Qrxlevmeas = measured cell receive level value(RSRP), Qrxlevmin = minimum RSRP in cell, Qrxlevminoffset = configured offset to prevent PLMN ping-pong.

Cell selection parameters are broadcast in SIB1.

1.1.4. Cell Reselection Once UE camps on a suitable cell, it starts Cell Reselection to go to the „best‟ cell of selected PLMN/e- PLMNs. UE first evaluates frequencies of all RATs based on their priorities. Secondly, compare cells on that frequency based on radio link quality, using ranking. Verify cell‟s accessibility before comparing. UE may re-trigger cell reselection only after having camped for at least one second on the current serving cell. Measurement Rules Minimize measurements required by UE. Firstly, measure intra-frequency only if S-Cell S <= „SintraSearchP‟. Measure other frequencies/RATs of lower or equal priority only when S-Cell S <= „SnonintraSearchP‟). Always measure frequencies/RATs of higher priority. Frequency/RAT Evaluation E-UTRAN configures an absolute priority for all frequencies of each RAT. Cell-specific priorities are optionally provided by SI. eNB can assign UE-specific priorities via dedicated signalling. S Criteria must be valid for Treselection for Re-selection. When reselecting to new freq/RAT, reselect to highest-ranked cell. Thresholds and priorities are configured per frequency, while Treselection is configured per RAT.

UE reselects higher priority freq cell if T-Cell S> ThreshX-High.

UE reselects lower-priority freq/RAT cell if S-Cell S < ThreshServing-Low & T-Cell S > ThreshX-Low, while no higher-priority freq/RAT cell available.

From Release-8 onwards, LTE, UMTS and GERAN support same priority-based cell reselection. Any differences are managed by different offsets. Cell Ranking UE ranks the intra-frequency cells and cells on other frequencies of equal priority which fulfil S-criterion with R-criterion. R-criterion generates rankings Rs and Rn. For Serving cell: Rs = Qmeas,s + Qhyst,s

For Neighbour cells: Rn = Qmeas,n + Qoff s,n

Qmeas is measured cell RSRP & Qhyst,s is degree of hysteresis for ranking, and Qoff s,n is offset between SCell and NCell on frequencies of equal priority (cell-specific + frequency-specific offsets). UE reselects to the highest-ranked candidate cell if best ranked for at least Treselection. Treselection and Qhyst, may be rescaled based on speed.



Fig 5.1.4 – Cell Reselection process flow diagram

Accessibility Verification If best cell is barred or reserved, exclude it from candidate list. If barred, UE may consider other cells on same frequency unless barred cell indicates Intra-Freq-Not-Allowed in SI, except for CSG cells. If, however the best cell is unsuitable for other specific reasons, UE should not consider any cell on concerned frequency for 300s. Speed Dependent Scaling UE scales cell reselection orHandover parameters depending on its speed. UE speed is categorized by a mobility state (high, normal or low), which is determined by number of cell reselections/handovers within a defined period, excluding consecutive reselections/handovers between the same two cells. The state is determined by comparing the count with thresholds for medium and high state, while applying some hysteresis. Parameters are signalled in SIB3. Any Cell Selection



When no Suitable cell found at all in PLMN, perform „any cell selection‟. In this case, perform normal idle mode operation: monitoring paging, acquiring SI, cell reselection . UE is not allowed to receive MBMS.

1.1.5. Cell Access Restrictions Each UE belongs to an Access Class (AC) in range 0–9. In addition it may belong to one or more high-priority ACs in the range 11–15. AC10 is used for emergency access. UE considers access to be barred if access is barred for all its applicable ACs. SIB2 includes AC barring for MO calls and/or MO signalling. This barring has a probability factor and a barring timer for AC0–9 and a list of barring bits for AC11–15. For AC0–9, if UE initiates a MO call and relevant AC is barred, UE draws a random number. If this number exceeds probability factor, access is not barred, otherwise access is barred for a duration which is randomly selected centred on the broadcast barring timer value. For AC11–15, if UE initiates a MO call, access is barred whenever the bit corresponding to all of the UE‟s ACs is set. The behaviour is similar in the case of UE-initiated MO signalling. For cell (re)selection, UE is expected to consider Suitable Cells.UE with AC=11–15 shall consider reserved cell in HPLMN also suitable. UE can not make even emergency calls in barred cells.

1.1.6. Closed Subscriber Group (CSG) UE maintains a CSG white list (CSG identities where UE is granted Access), received from NAS or updated upon successful access of a CSG cell. UEs support „manual selection‟ request by NAS for CSG cells(text sent) not in CSG white list.

1.1.7. Neighbour Monitoring and Cell Reselection All LTE mobility procedures in RRC_IDLE state are performed autonomously within the UE and extreme care is taken for sufficient UE mobility performance without sacrificing power-efficiency. By being autonomous, UE minimizes transmission of resource in inactive UEs. In fact, over-the-air signalling is only required for Tracking Area Update in RRC_IDLE and thus saves UE power. In RRC_IDLE UE just camps on a serving cell where paging reception is sufficiently reliable with good cell quality for an incoming call. UE is not required to perform any frequent neighbour cell monitoring (cell search and measurements) unless S-Cell quality drops below a specified threshold.

Priority-Based Cell Reselection In LTE Priority-based cell reselection is adopted to improve cell reselection in multiple RATs. This reduces the need to monitor all available intra-system and inter-RAT carriers defined by a set of priority rules provided to UE. Following steps are carried out in cell reselection and camps on a new cell while in RRC_IDLE:

1. Decode broadcast information. A UE decides to camp on a cell if cell selection criteria S are met the best. Then it will receive all relevant system information on BCH, like cell-specific paging and random access parameters, cell bandwidth, serving cell minimum quality threshold (S-threshold), UMTS neighbour cell list, GSM neighbour cell list etc. Neighbour cell priority is provided to the UE through RRC dedicated signalling (not broadcast).

2. Tracking Area Update. If UE has moved to a cell belonging to a different tracking area, it will establish a brief signalling connection with eNodeB to inform MME about its new location before it can enters the paging reception stage.

3. Paging reception. UE determines paging DRX cycle (min(Cell default cycle, UE specific paging cycle)) and other paging parameters broadcast. Henceforth, unless UE is being paged or cell reselection occurs, UE will periodically wake up on every paging occasion to check for paging messages. Same time, the UE can measure its S-cell quality.

a. When S-cell quality is poor (RSRP < S-threshold), UE risks losing S-cell, it must attempt to identify and reselect a new suitable cell. All possible PLMNs are searched and measured regardless of their priority, and UE camps on the highest priority (R) PLMN detected cell which meets suitability criteria (S). The search rate will be frequent (small multiple of the paging DRX period, min 1 second).

b. If S-cell quality (S Criteria) is good enough, then searching for lower priority layers is not done, but still searches for higher priority cells at a reduced rate and UE must



reselect a higher priority cell if it meets S-criteria. If S-cell quality is good, search rate can be far less frequent to reduce UE power consumption (may be order of 60 s).

4. Cell reselection evaluation. On every paging occasion S-criterion is evaluated. If S-cell quality is poor (RSRP < S-threshold) and N-cell meets S-criterion then cell reselection towards N-cell is initiated and UE restarts cell-specific configuration on the new cell by updating new cell broadcast.

Measurements in Idle Mode N-cell search, measurement rates and S-Criteria evaluation rates are function of configured paging DRX cycle, the layer being measured (search and measurement rates LTE intra-frequency cells > LTE inter-frequency cells > inter-RAT cells) and S-cell quality (RSRP < S-threshold). Frequency of measurement (rate) can be set inversely proportional to S-cell quality.

1.1.8. Paging Paging process start with an incoming call at MME. MME sends paging to all the cells who belong to the TAC where UE is at the moment of paging: Here is the figure explaining the flow:

Fig 5.1.8.1 – Paging distribution in relevant TAC‟s

Fif 5.1.8.2 – Paging Protocol Stack

To receive paging, UEs in idle mode monitor PDCCH for P-RNTI on specific subframes(called Paging Occasion –PO) within specific frames (Called Paging Frames- PF). At other times, It may apply DRX(switch off its receiver to preserve battery power). eNB configures PF and PO for paging by broadcasting a default paging cycle for all UE‟s. Upper Layers may use dedicated signalling to a UE for specific paging cycle. If both configured, UE applies the lowest value. UE calculates PF and PO as follows: SFN mod T = (T/N) × (UE_ID mod N) i_s = (UE_ID/N) mod Ns T = min(Tc, Tue) N = min(T , number of paging subframes per frame × T ) Ns = max(1, number of paging subframes per frame) (3.1) where: Tc cell-specific default paging cycle {32, 64, 128, 256} radio frames, Tue UE-specific paging cycle {32, 64, 128, 256} radio frames,



N number of paging frames with the paging cycle of the UE, UE_ID IMSI mod 4096, with IMSI being the decimal rather than the binary number, i_s index pointing to a pre-defined table defining the corresponding subframe, Ns number of „paging subframes‟ in a radio frame that is used for paging. Below are the steps for paging processing in eNB.

Fig 5.1.8.3 – Paging buffering until PF and PO in eNB

1.1.9. RRC Messages and Controls RRC covers following functional areas.

System information- handles broadcasting of SI, for NAS, RRC, L2 and PHY.

RRC connection control- covers (re)establishment, modification and release of RRC connection, paging, initial security activation, establishment of SRBs & DRBs, inter/intra-RAT handover including context, configuration of L1 & L2, AC barring and radio link failure (RLF).

Network controlled inter-RAT mobility besides mobility, security activation and context information transfer.

Measurement configuration and reporting for intra/inter-frequency and intra/inter-RAT mobility, with measurement gaps management.

Miscellaneous functions – Perform transfer of dedicated NAS & access capability information.

RRC messages are transferred across SRBs, mapped via PDCP and RLC onto logical channels – either CCCH or DCCH. SI is mapped to BCCH and Paging is mapped to PCCH. SRB0 is used for CCCH, SRB1 is for DCCH, and SRB2 is for NAS messages using DCCH. All DCCH messages are integrity-protected and ciphered by PDCP (after security activation) and use ARQ for AM RLC. CCCH messages are not integrity-protected and no ARQ in RLC. NAS independently applies integrity protection and ciphering. For low transfer delay parameters, MAC signalling is used when no security concerns applies.

1.1.10. System Information Broadcast (SI) SI broadcast is structured by three types of messages: MIB, SIB1 and SI (SIB2-SIB16) messages. Each contains function related Parameters:

• Master Information Block (MIB), most frequently Params, essential for UE‟s initial NW access.

• System Information Block Type 1 (SIB1), cell selection, time domain scheduling of other SIBs.

• System Information Block Type 2 (SIB2), common and shared channel information.



• SIB3–SIB16, control intra/inter-frequency/RAT cell reselection, inter-RAT Handover, ETWS, MBMS etc.

Fig 5.1.10 – SIBs summary

SI message includes one or more SIBs which have the same scheduling periodicity. SIB2 is always the first entry in SI messages. Scheduling of System Information MIB and SIB1 messages Transmission tine is fixed: periodicities of 40 ms and 80 ms respectively. Scheduling of SI messages is dynamically flexible: each SI is indicated in which subframes within this window the SI is scheduled. SI-windows are consecutive (i.e. neither overlaps nor gaps between windows) with common length. SI-windows can include subframes in which no SI messages can be sent. For illustration, please refer to the diagram in the physical layer processing of PBCH. SI messages may have different periodicities. In some clusters of SI windows all SI messages are scheduled, while in other windows only SIs with shorter repetition periods are transmitted. SI Validity and Change Notification SI changes only at specific SFN, where SFN mod N = 0, whereN = modification period. LTE provides two mechanisms for indicating that system information has changed:

1. A paging with SystemInfoModification flag set. 2. A value tag in SIB1 which is incremented every time one or more SI messages

change.

UEs in RRC_IDLE use first mechanism, while in RRC_CONNECTED can use either mechanism. To ensure reliability change notification, paging is repeated a number of times during BCCH modification period. Modification period is expressed as multiple of cell-specific default paging cycle. UEs in RRC_CONNECTED try paging message the same number of times per modification period as in RRC_IDLE using default paging cycle. Connected mode UEs can utilize any of IDLE mode paging subframes to receive change indications. If UE receives SI change notification, it considers all SI to be invalid from the start of next modification period. UE operations may be restricted until UE has re-acquired SI, especially in RRC_CONNECTED. UE considers SI valid if it was received within 3 hours & value tag matches.



Here is an example of how SI is scheduled:



1.2. Cell ReSelection & PLMN Selection

Design-Development This sample design process helps you how you may attempt to design various protocol stack

modules. This chapter takes you to the level of pseudo code. The overall software design design

depends on your rest of the software architecture and how the inter-process meassage and

information flow is planned. This can give you an idea how to connect your theory knowledge to

practice of software design.

1.2.1. Cell Re-Selection (CRS) Description All the times in Idle mode, UE performs measurements for cell selection and reselection. NAS can

control RAT(s) in which the cell selection should be performed, by indicating RAT(s) associated with

the selected PLMN. UE also maintains a list of forbidden registration area(s) and a list of equivalent

PLMNs. UE selects a suitable cell based on measurements and cell selection criteria.

Stored information for several RATs are maintained in the UE to speed up the cell selection process.

When camped on a cell, UE regularly searches for a better cell according to the cell reselection

criteria. If a better cell is found, that cell is selected. The change of cell may imply a change of RAT.

NAS is informed if the cell selection and reselection results in changes in the received system

information relevant for NAS. This is an autonomous function in the UE and network may not be

congested by any message for this.

1.2.2. CRS Actions: 1. Measurement process will perform Measurement and keep it in each cell structure – Shared

Memory. CRS should be able to access measured information.

2. NAS controls RATs with PLMN selection and provides to PLMN-RAT to CRS.

3. Maintain fb_PLMN and e_HPLMN list and select PLMN from there.

4. In the selected PLMN – select suitable cell, based on measurement and CRS criteria.

5. Start the selection with Stored information.

6. Camp on a cell, and continuously select a better cell after 1000ms.

7. Once cell is changed, camped - changes in SI are informed to NAS.

a. Receive SI in the cell – TAC

b. If registered, receive paging and Notifications

c. If NAS requests – initiate Connected Mode.

8. Maintain state – Idle or Connected.

9. If state=Idle do CRS else suspend CRS until it comes back from Connected to Idle.

10. On every PLMN change, start CRC at #1 (START_CELL_RESELECTION).

11. If Store_Info available then StoredInfo_CRS else Initial_CRS.

12. Maintain CampState = Normally, Anystate, Connected, Nowhere. Initially

CampState=Nowhere.

13. Maintain list of following type of cells- Barred Cells, Reserved Cells, Acceptable Cells and

SuitableCells, CSG/Hybrid cells.

14. Arrange the cells in these lists with priority application.

a. If any CSG, CSG priority.

b. Carrier Priority

c. Ranking Priority

d. All the cells within the same PLMN should be considered.

e. RAT, TDD/FDD is not considered and does not affect the priority.

15. Traverse among the Suitable cells and pick the best ranked Suitable cell. If not found Suitable

Cell, Try searching from Acceptable Cells and camp but not more than 10s on AnyCell.

16. Camp on a cell, and continuously select a better cell after 1000ms.



17. Maintain a timer for Tsearching_for_suitable (10s required to search intra, after expiry, do

inter-freq) and Treselect1s(1s-minimum required before subsequent CRS initiated)

1.2.3. CRS Process Inputs: a. SI parameters input – Shared Memory

1. cellReselectionPriority 2. Qoffsets,n , Qoffsetfrequency 3. Qhyst , Qqualmin, Qrxlevmin

4. TreselectionRAT , TreselectionEUTRA, TreselectionUTRA

5. TreselectionGERA, TreselectionCDMA_HRPD, TreselectionCDMA_1xRTT

6. ThreshX, HighP, ThreshX, HighQ, ThreshX, LowP

7. ThreshX, LowQ, ThreshServing, LowP, ThreshServing, LowQ

8. SIntraSearchP, SIntraSearchQ 9. SnonIntraSearchP, SnonIntraSearchQ 10. TCRmax, NCR_M, NCR_H, TCRmaxHyst 11. Speed dependent ScalingFactor for Qhyst 12. Speed dependent ScalingFactor for TreselectionEUTRA 13. Speed dependent ScalingFactor for TreselectionUTRA 14. Speed dependent ScalingFactor for TreselectionGERA 15. Speed dependent ScalingFactor for TreselectionCDMA_HRPD 16. Speed dependent ScalingFactor for TreselectionCDMA_1xRTT

ii. PLMN Shared Memory iii. NAS Shared Memory iv. Meas. Shared Memory

1.2.4. Internal Messages Design v. From PLMN Message – Change the PLMN now. Either initiated by NAS or on CRS

request. vi. From CSG Message – Any change in current available CSG list, vii. From TAU Message – from NAS response if any PLMN, forbidden_PLMN to be

changed.



viii. From MBMS Message – If any session is current (within start-end time), them MBMS priority.

ix. From Meas. Message - ?? x. From SI Message – Change of SIB3 or CRS related parameter change. xi. From RRC Message – Inform CRS of success or failure of tuning to new Cell. If failure,

stick to the same cell. If success, update the variables and lists. xii. From RRC Message – redirectedCarreerInfo of RRCConnectionRelease

1.2.5. CRS Outputs Message(Internal): a. Updates in Parameters

a. PLMN Message – Request for new PLMN as no suitable cell in the current PLMN for last 10s.

b. Internal Output Messages a. To PLMN Message – Request for new PLMN as no suitable cell in the current PLMN

for last 10s. b. To TAU Message – There is a change in TAC and that TAC is not in the TAI list.

Subsequently TAU should update that to NAS. c. To Meas. Message(Based on design) – Schedule measurement for the neighbour

cells as received from SI SIB4. (Add/Mod/Del for MO+MI+RC internal). It may be done by SI itself, depending on your overall design.

d. To RRC Message – Inform RRC of New cell selection and Camp on that new Cell. Tune as per CRS info on Freq/Cell-Id information. RRC should scan PSS, SSS, RS and BCCH signals and channels in that new Cell.

i. If successful, inform CSR of Success. ii. If Fail, inform CRS of failure and stick to the old existing Cell and continue

CRS.

1.2.6. IPC-Design Diagram:



Functions:

1.2.7. Cell_Selection_Function() Please refer to the flow diagram in 36.304 – Idle mode processing. This module excludes the design of PLMN selection and that is assumed to be done by another process. Cell_selection_function()

{ If stored_Info StoredInfo_CRS – Carrier freq and cell parameters from prev measured cell. Find the strongest suitable cell and camp. If ((no stored_Info) OR (no suitable cell from stored_Info)),

Initial_CRS - Scan all RF channels to find suitable cell. On each carrier – find strongest cell. Among suitable cells, hook to strongest cell.

Srxlev = Qrxlevmeas – (Qrxlevmin + Qrxlevminoffset) – Pcompensation

Squal = Qqualmeas – (Qqualmin + Qqualminoffset)

Cell SelectionCriteria(&Srxlev, &Squal) if (Srxlev>0 && Squal>0) S=1 else S=0; Use offsets only for higher priority PLMN while camped normally in VPLMN. If manually CSG cell is selected, select that cell, if suitable.

}

1.2.8. Cell_Re-Selection_Function() Cell_reselection_function() {

0) Keep measuring the serving cell.

1. Measure RSRP and RSRQ of Serving cell and find S at least every DRX cycle.

2. Filter at least 2 measurements spaced by, at least DRX cycle/2.

1) Execute CRS evaluation process when:

1. When (Srxlev < SIntraSearchP || Squal < SIntraSearchQ,) in Nserv consecutive DRX cycles,

trigger CRS (after min 1s from last camping Normally).

2. When CRS parameters in BCCH is modified in CRS SIBs.

2) UE internally triggers CRS, to meet performance, if anyone above happens;

3. initiate neighbour cells measurement

4. Evaluate CRS Criteria for cells.

5. Find a Suitable Cell or AnyCell and Camp either Normally (preferred) or in AnyCell.

3) If for 10s, no new Suitable cell found in intra-freq, inter-freq and inter-RAT, initiate PLMN

selection.

Reselection priority handling – freq.Priority.SI and freq.Priority.ded 1. Maintain Carriers list and their priorities – from SI(freq w/o

cellReselectionPriority), release(freq with priority), or inter-RAT CRS. 2. If dedicated signalling priority, that is taken, else SI priority taken. 3. If in AnyCellState – Apply SI priority. 4. If CSG cell, consider this freq priority as Highest. 5. If Normally camped on non-CSG cell, consider this as lowest priority

freq. 6. If MBMS session is on (calculate from start and end time), consider

MBMS freq to be of highest freq. 7. Delete priorities when – RRC Connected, 8. When priority validity(T320) expires, PLMN selection is done. 9. Exclude black listed cells from priority calculations.



Measurement rules for CRS 1. If (!(Srxlev > SIntraSearchP and Squal > SIntraSearchQ, )), perform Intra-freq

Measurement. 2. If (any Intra & Inter-RAT frequency priority > current freq), Perform

measurement. 3. If (any Intra & Inter-RAT frequency priority <= current freq)

a. If (Srxlev > SnonIntraSearchP and Squal > SnonIntraSearchQ) No measurement.

b. Else Measure lower freq. Cell Mobility states – scaling rules

4. If (TCRmax, NCR_H, NCR_M and TCRmaxHyst) available, mobility=1; 5. Keep counting #CRS within last TCRmax . 6. Initially lasttolast=-2, last=-1, current=current_PCI; then Store –

lasttolast=last, last=current, current=new; 7. If new == lasttolast, don‟t count. 8. If within TCRmax , ((#CRS > NCR_M ) & (#CRS < NCR_H )) Mstate=

MEDIUM. 9. If (#CRS > NCR_H ) Mstate=HIGH. 10. If (Mstate!=HIGH && Mstate != MEDIUM) during TCRmaxHyst,

Mstate=NORMAL 11. If Mstate==HIGH (Qhyst += sf-High; TreselectionEUTRA*= sf-High)

for respective RAT. 12. If Mstate==MEDIUM, (Qhyst += sf-Medium; TreselectionEUTRA*= sf-

Medium) for respective RAT. 13. Roundup the above TreselectionEUTRA results to nearest seconds.

Barring, Reservation, restrictions or unsuitable filtering 1. Make a list of candidate cells – excluding restricted cells 2. Store highest rank cell. If Highest rank cell changes- remake

candidate list. 3. Check if access restricted for the best rank cell. 4. If the best rank cell is Not suitable – Forbidden TAC or not ePLMN to

RPLMN a. Consider this cell and others in this freq Not Suitable for

300s. b. After 300s, they may be in the candidate list and check if still

forbidden. 5. If CRSstate==Anycellselection, No restrictions apply. 6. If CSG cell and CSG-Id is not in CSGWhitelist, consider not suitable,

but other cells may be suitable of the same freq. Inter-Freq or Inter-RAT CRS Criteria

If for 10s, no new suitable cell found intra-freq, inter-freq and inter-RAT, initiate

PLMN selection.

Scale TreselectionRAT as per Mstate= medium or high If threshServingLowQ in SIB3, & candidate cell freqPrio > Serving, CRS if

{Candidate LTE cell Squal > Threshx,HighQ for Treselection-RAT, OR

Candidate non-LTE cell Srxlev > Threshx,HighP for Treselection-RAT.

AND current Cell camping time>1s.- Check 1s camped timer expired} Else if

{Candidate cell Srxlev > Threshx,HighP for Treselection-RAT.

AND current Cell camping time>1s.- Check 1s camped timer expired} If priority is equal, select on the basis of Ranking if Rn > Rs.

If threshServingLowQ in SIB3, & candidate cell freqPrio < Serving, CRS if

{Serving cell Squal < Thresh,servingLowQ && Candidate Squal >

Threshx,LowQ for Treselection-RAT, OR

Serving cell Squal < Thresh,servingLowQ && Candidate Srxlev >

Threshx,LowP for Treselection-RAT,

AND current Cell camping time>1s.- Check 1s camped timer expired} Else if

{Serving cell Srxlev < Thresh,servingLowP && Candidate Srxlev >

Threshx,LowP for Treselection-RAT.



AND current Cell camping time>1s.- Check 1s camped timer expired} The Higher priority candidate Cell takes priority over Lower.

If freq priority is equal, select on the basis of Ranking if Rn > Rs. ...Current design leave out the CDMA2000 and CDMA_HRPD Cells. Among all the above selected cells, prioritise them as follows: First - Highest priority freq from E-UTRA cells. Next – Highest priority freq from other RAT cells. For Other RAT, if Squal(RSRQ) supported, CRS is based on Squal Else CRS is based on Srxlev.

Intra-frequency and equal priority Ranking criteria

1. Rn=0; 2. if S==0(if Suitable), Rdturn(Rn=0) 3. Rs = Qmeas,s(SRRP) + Qhyst 4. Rn = Qmeas,n(RSRP) - Qoffset 5. Select CellN if

a. Rn > Rs. During TreselectionRAT

b. More than 1s elapsed since last camp on Scell. CRS with CSG/Hybrid cells Procedures(Rules) – CSG is an autonomous process maintaining shared CSGav cell list, CSGwhite cell

list, including inter-RAT frequencies. Consider only current PLMN cell ids. Maintain a shared variable for CRS to know if CSGav cell list is empty. Disable this function if the CSGav cell list is empty; This process is expected to be designed separately and it updates the respective list and variables.

i. With Hybrid Cells 1. if cell in CSGwhite list

a. Treat the Hybrid cell as CSG cell, 2. Else

a. Treat the Hybrid cell as Normal Cell ii. Candidate is CSG (CSG/non-CSG -> CSG)

1. CSG cell of Current freq will be ranked higher than other freq priority. 2. If more than one CSG cell within same frequency, apply ranking

rules. iii. CSG to NonCSG rule.

1. Apply normal CRS rules. Actions in Camped Normally-Suitable cell

a. Monitor Paging Channel – Independent Process b. Monitor SI - Independent Process c. Continuously perform CRS every 1s or if CRS parameters change(from SI).

CRS at leaving connected to Idle state i. Store status if idle-to-connected was from AnyCell or Suitable Cell. ii. Attempt to CRS as per redirectedCarreerInfo in RRCConnectionRelease.

1. If CRS fails to directed cell – still try any suitable cell in that RAT. 2. If idle-to-connected=AnyCell, Allow to select AnyCell in that RAT.

iii. If No redirectedCarreerInfo, CRS on current or other E-UTRA carrier. iv. If non above successful, do StoredInfo CRS to find suitable cell. v. If still not camping on any suitable cell, Select_PLMN and search for any

Acceptable Cell. Any Cell Selection state Keep attempting all PLMN‟s from Higher priority PLMN to lower. Try finding

Suitable Cell. At least remain camped on Any Acceptable Cell. Stay in this state until at least Acceptable Cell is found and camp on it. Camped on Any Cell

a. Monitor Paging Channel – Independent Process b. Monitor SI - Independent Process c. Perform necessary measurements



d. Continuously perform CRS in all RATs and camp at least Any Acceptable Cell.

e. If suitable Cell found, move to Suitable Cell and Camp normally. f. If UE supports voice call and current cell doesn‟t support emergency, perform

CRS to any RAT regardless of priority and move to voice supporting cell. g. If Cell does not support IMS emergency call, do not do CRS on that cell.

Access Control Check for CellStatus, Barred and Reserved in SIB1

a. cellBarred – common for all PLMN b. cellReservedForOperatorUse - (per PLMN). c. If !cellBarred and ! cellReservedForOperatorUse, treat cell

for CRS. d. If cellBarred

i. No CRS allowed, even for emergency NO. Select Another cell

ii. If CSG cell, 1. select another suitable cell in same freq

iii. else 1. if SIB1->cellAccessRelatedInfo-

>intraFreqReselection = “allowed”, select another suitable cell (including same frequency cells and any RAT);

2. Bar only for 300s and recheck after 300s if it is still barred.

3. if SIB1->cellAccessRelatedInfo->intraFreqReselection = “Not allowed”, select another suitable cell (excluding same frequency) in any RAT;

4. Bar only for 300s and recheck after 300s if it is still barred.

Check for AC 0-15 where it belongs. It may have one or many AC’s. a. Depending on AC‟s b. reserved cell may be marked as barred or acceptable for a

UE. c. If !cellBarred && cellReservedForOperatorUse

i. If AC ==11 or 15 in H/eH-PLMN, treat cell as Suitable for CRS.

ii. If AC ==0-9 or 12-14 in H/eH-PLMN, treat cell as barred.

1. AC 12-14 valid only in home country.

Emergency Call ac-BarringForEmergency in SI indicates emergency restriction.

1. If cell-AC[10]=barred a. If UE-AC[0-9]=barred or without IMSI - Ecall not allowed. b. Else if UE-AC-11-15]=barred && cell-AC[10]=barred and cell-

AC[11-15] barred – Ecall not allowed c. Else Ecall are allowed.

2. Else Ecall are allowed. }

Exercises:

Data structures – Student should try designing data structure.

C Coding – Student should try writing code as per the design.



1.2.9. PLMN Selection Process Design In UE, the AS reports available PLMNs to the NAS on request from the NAS or autonomously. During

PLMN selection, based on PLMN identities list in priority order, a PLMN may be selected either

automatically or manually. Each PLMN in the list of PLMN identities is identified by a 'PLMN identity'.

In the system information on the broadcast channel, the UE can receive one or multiple 'PLMN

identity' (upto 6) in a given cell.

1.2.10. PLMN Selection Actions 18. On NAS request, provide PLMN list or the selected PLMN to NAS and/or to CRS.

19. Accept manual selection and provide selection.

20. Receive the PLMN identities of the current cell and maintain this cell_PLMN;

21. Maintain Lists - avPLMN-list, eHPLMN list, cell-PLMN list and fb_PLMN list.

22. Maintain PLMN list in priority order – eHPLMN, fb_PLMN, av_PLMN list.

23. Maintain RPLMN and VPLMN.

24. Return the highest priority PLMN.

25. For LTE Cell:

a. Provision for NAS to stop PLMN selection anytime.

b. Receive/Use (make e/HPLMN and fb_PLMN list) the initial SIM PLMN info.

c. Check if CSG list is provided. If yes, return the highest priority PLMN with suitable

cell. If no Suitable CSG cell, no PLMN from the CSG cell.

1.2.11. PLMN Selection Inputs 1. Request – NAS, CRS – reply is expected.

a. NAS to PLMN – Request to change PLMN/RPLMN

b. TAU to PLMN – Whether there is any update of the PLMN list from NAS.

c. CSG to PLMN – If any HeNB or network is of higher priority.

1.2.12. PLMN SelectionOutputs(Internal) 1. PLMN to NAS – reply any PLMN selection request to NAS. NAS should initiate Meas with

this PLMN.

2. PLMN to CRS – Give out the selected PLMN to CRS.

3. eHPLMN update

4. fbPLMN update

5. cellPLMN update

6. avPLMN update



1.2.13. PLMN Selection IPC-Design

Flow Diagram – Student to try doing this.

Data structures – Student to try doing this.

C Coding – Student to try doing this.





1.3. Measurement and Reporting

1.3.1. LTE Measurements 1. LTE Reference Signal Received Power (RSRP)

a. RSRP measures cell-specific signal strength of Cell-specific Reference Signal(CRS). It is used to rank candidate cells according to RSRP and is used as an input for handover and cell reselection decisions. RSRP for a specific cell is linear average over the power contributions (in Watts) of Resource Elements (REs) which carry CRS within considered bandwidth. Normally the first antenna port RS are used for RSRP determination, but second antenna port can also be used if UE can determine that they are available. If receive diversity is in use, the reported value is linear average of values of all diversity branches.

2. LTE Carrier Received Signal Strength Indicator (RSSI) a. RSSI is defined as total received wideband power by UE from all sources,

including co-channel S-cells and Non-Serving cells, adjacent channel interference and thermal noise within measurement bandwidth. RSSI is not reported but used to derive RSRQ measurement.

3. LTE Reference Signal Received Quality (RSRQ) a. RSRQ is used to rank different LTE candidate cells according to their signal quality,

as input for handover and cell reselection decisions when RSRPs alone do not provide reliable mobility decisions.

b. RSRQ = N · RSRP/(LTE carrier RSSI) where N = RBs of used for RSSI measurement bandwidth.

c. RSRQ enables the combined effect of signal strength and interference in an efficient way.

1.3.2. Measurement Objects and Management E-UTRAN provides measurement config to UE in RRC_CONNECTED by RRCConnectionReconfiguration. The measurement configuration parameters are:

Fig 5.3.7 – Measurement ID for Measurement Objects and Report Configs

1. Measurement objects(MO): Objects on which UE performs measurements. It may be

a. a single E-UTRA carrier frequency. b. a list of cell specific offsets c. list of 'blacklisted' cells. d. a set of cells on a single UTRA carrier frequency. e. a set of GERAN carrier frequencies.

2. Reporting configurations(RC): RC consists of : a. Reporting criterion: triggers (periodic or once) UE to send a measurement report. b. Reporting format and c. quantities.

3. Measurement identities (M-Id): a. each ID links one MO with one RC. b. possible to link many MO to same RC, as well as many RC to same MO.



4. Quantity configurations: a. Defines quantities and associated filtering, b. One filter per measurement quantity.

5. Measurement gaps: a. Periods that the UE may use to perform measurements, b. No (UL, DL) transmissions are scheduled in between.

The following table is maintained for each measurement ID:

1.3.3. NON-LTE Measurements

UMTS Measurements 1. UMTS FDD CPICH Received Signal Code Power (RSCP)

a. CPICH RSCP is equivalent to LTE RSRP, used to rank different UMTS FDD candidate cells according to their signal strength for decisions on handover and cell reselection to UMTS. It is received power measured on the P-CPICH. If transmit diversity is there for P-CPICH, received code power from each antenna is measured and summed together in Watts as total received code power.

2. UMTS FDD Carrier RSSI a. RSSI is the received power including thermal+receiver noise, for the carrier,

within considered bandwidth. 3. UMTS FDD CPICH Ec/N0

a. CPICH Ec/N0 is the received energy per chip (Ec) on P-CPICH of a cell divided by total noise power density (N0) on UMTS. CPICH Ec/N0 is used to rank different candidate cells according to signal quality for handover and cell reselection decisions.

b. If no diversity used by UE, CPICH Ec/N0 = CPICH RSCP / RSSI. c. If transmit diversity is used on P-CPICH, received Ec from each antenna is summed

together (inWatts) to total received energy per chip on P-CPICH, before calculating Ec/N0.

UMTS TDD RSI is the received wideband power, including thermal+receiver noise, within bandwidth for UMTS TDD within a specified timeslot. P-CCPCH RSCP is defined as the received power on the P-CCPCH of a UMTS TDD cell, used to rank different UMTS TDD candidate cells for handover and cell reselection decisions.

GSM Measurements GSM Carrier RSSI GSM RSSI is wideband received power within bandwidth of BCCH carrier.

CDMA2000 Measurements CDMA2000 1x RTT Pilot Strength Pilot Strength is equivalent to RSRP, used to rank different CDMA2000 1x candidate cells for handover and cell reselection decisions. CDMA2000 HRPD Pilot Strength This also is equivalent to LTE RSRP, used to rank different CDMA2000 HRPD candidate cells for handover and cell reselection decisions.Measurement Configuration eNB configures UE to report measurements for UE mobility via RRCConnectionReconfiguration:

1. Measurement objects (MO). MO defines what should UE measure – like carrier frequency, list of cells (white-list or black-list), offsets etc.

2. Reporting Configurations (RC). Periodic or Event-triggered RC defines criteria for UE to send a measurement report and details of what UE is expected to report (quantities, RSCP/RSRP & number of cells etc.).

3. Measurement identities(MID). M-ID identify a measurement and defines MO and RC attached.

4. Quantity configurations. It defines filtering used on each measurement. 5. Measurement gaps(Meas Gaps). It defines time periods when no UL/DL transmissions will

be scheduled, so that UE may perform measurements.



Above details vary depending on LTE, UMTS, GERAN or CDMA2000 RAT/frequency. eNB configures single MO for a given frequency, but more than one M-ID may use same MO. In LTE it is possible to configure the quantity which triggers the report (RSCP or RSRP) for each reporting configuration. The UE may be configured to report either the trigger quantity or both quantities.

1.3.4. Measurement Report Triggering Depending on measurement type, UE may measure and report any of the following:

1. Serving cell;

2. Listed cells (i.e. Part of MO);

3. Detected cells on a listed frequency (i.e. unlisted cells but detected by UE). For some RATs, UE measures and reports listed cells only (white-list), while for other RATs UE also reports detected cells. Following event-triggered reporting criteria are specified for intra-RAT:

1. Event A1. SCell > absolute threshold. 2. Event A2. SCell < absolute threshold. 3. Event A3. NCell > offset relative to SCell. 4. Event A4. Ncell > absolute threshold. 5. Event A5. SCell < absolute threshold1 and NCell > absolute threshold2.

For inter-RAT mobility, following event-triggered reporting criteria are specified: 6. Event B1. NCell > absolute threshold1. 7. Event B2. SCell < absolute threshold1 and NCell > absolute threshold1.

UE triggers event when one or more cells meets a specified „entry condition‟. eNB can influence entry and exit condition by setting of thresholds, offset, and/or a hysteresis. Entry condition must be met for at least „timeToTrigger‟ parameter. UE scales timeToTrigger by speed state. UE may be configured to provide periodic reports after it triggered an event. „event-triggered periodic reporting‟ is configured by „reportAmount‟(number of periodic reports) and „reportInterval‟(time period between reports). Whenever a new cell meets the entry condition, count of number of reports is reset to „0‟. Same cell cannot then trigger a new set of periodic reports unless it first meets „leaving condition‟. UE may be configured for periodic reporting. Same parameters may be configured as for event-triggered reporting, except that UE starts reporting immediately rather than after occurrence of an event.

1.3.5. Measurement Reporting 6. In MeasurementReport message, UE includes measurement results related to a single

measurement –not combined by multiple RC. If multiple cells triggered report, UE includes cells in order of decreasing value of reporting quantity – i.e. best cell is reported first. Max number of cells in a MeasurementReport may be ‘maxReportCells’.

1.3.6. Measurements when Camped on LTE Majority of UE measurements require coherent demodulation and processing, hence it measures only after synchronization with Tcell and knows parameters (slot timing, frame timing and scrambling codes) required to perform coherent processing. However LTE RSSI, UMTS RSSI and GSM RSSI can be measured non-coherently. All UE reported measurements are obtained by averaging uniformly distributed samples over measurement period over the measurement bandwidth.Measurement model contains four different reference points.



Fig 5.3.5 – Measurement filtering layers

• Reference point ‘A’ represents physical layer („Layer 1‟) measurements like a single aggregated measurement sample of LTE RSRP in 1 ms. Actual measurements procedure is not specified, but it may be the measurement of all the RS received power averaged during 1 subframe. • Reference point ‘B’ represents measurements after L1 filtering reported to RRC („Layer 3‟). Sampling rate/periodicity is not defined, but performance objective, bandwidth and measurement period may be defined. The reporting rate at point B should be sufficient to meet the specified performance objectives. • Reference point ‘C’ represents a measurement after L3 filtering in RRC. Reporting rate is again not defined but should meet the performance objective (depends on measurement type). Layer 3 filters is standardized and configuration is provided by RRC signalling. So, result at point C is a filtered (averaged) version of the samples available at point B. • Reference point ‘D’ contains measurement reports by UE to eNodeB. Evaluation means checking if RRC measurement reporting is necessary at point D, which may be based on multiple flow of measurements (C, C‟) after L3 filtering (for example after comparing different measurements). UE maintains reporting configuration triggers, set by the network RRC by Measurement configuration message.

1.3.7. LTE Mobility in RRC_CONNECTED During RRC_CONNECTED UE is actively transmitting and receiving user data. Every effort is made to maintain the radio link, and N-cell monitoring is given priority over power saving. In RRC_CONNECTED, UE cell search and measurements controlled and configured by eNodeB. When a better cell than current one is identified, eNodeB will trigger handovers to other cells. Handover is requested by eNodeB to other cells either on same carrier (intra-frequency), to LTE cells on other carriers (inter-frequency) and to other cells of a different RAT (inter-RAT).

Monitoring Gap Pattern Characteristics During RRC_CONNECTED, if eNodeB decides UE needs to perform LTE inter-frequency and inter-RAT monitoring, it will provide UE with a monitoring gap pattern sequence. Same purpose is achieved by „Compressed Mode gaps‟ and „FACH Measurement Occasions‟ in UMTS and by Idle frames in Dedicated and Packet Transfer Mode states in GSM.

Fig 5.3.9.1 – Measurement Gap concept

During monitoring gaps, UE reception and transmission activities with S-cell are interrupted. How does monitoring gap patterns work and help?

1. Same LTE receiver is used both to perform intra-frequency monitoring and to receive data when there is no transmission gap.



2. Monitoring gaps allows the receiver to be used to receive data and to perform inter- RAT activity, but not simultaneously.

3. Even if UE has multiple receivers for inter-RAT monitoring (e.g. one LTE receiver, one UMTS receiver and one GSM receiver), for some band, monitoring gaps are still required in UL, specially when UL carrier used for transmission is adjacent to monitored band. There may be significant power difference between inter-RAT signal measured and UE signal transmitted. The receive filter may not be sufficient to filter out the transmitted signal at receiver front end, so the transmit signal leaks into the receiver band creating interference which saturates the radio front end stages. This interference desensitizes the receiver being used to detect inter-RAT cells. Uplink gaps in LTE are configured for all such scenarios.

LTE monitoring gap patterns contain gaps every N LTE frames (gap periodicity is multiple of 10 ms) and these gaps have 6 ms duration. Single monitoring gap pattern is used to monitor all possible RATs. Different gap periodicities are used to trade off between monitoring performance, data throughput and efficient utilization of resources. Cell identification performance increases as the monitoring gap density increases, UE throughput decreases as monitoring gap density increases. Most RATs broadcast sufficient pilot and synch information to enable a UE to synchronize and start measurements within a useful period slightly in excess of 5 ms, as most RATs transmit DL synch signals with a periodicity no lower than 5 ms. In LTE, PSS and SSS symbols are transmitted every 5 ms. Therefore 6 ms gap provides sufficient additional headroom to retune the receiver to inter-frequency LTE carrier and back to S-cell and still to cope with the worst-case relative alignment between both cells. GSM requires special treatment because synch information is organized differently in the time domain.

Fig 5.3.9.2 – Measurement Gap configuration

With these restrictions the following diagram explains DCI and PHICH restrictions during Measurement Gap.



Fig 5.3.9.3 – PDCCH and PHICH restrictions due to Measurement Gap

LTE Intra-FrequencyMonitoring LTE intra-frequency monitoring perform measurements both on Scell and Ncells which use same carrier frequency. For RSRP and RSRQ measurements, UE must first synchronize to find cell ID of N-cells. LTE UE has to be able to perform search without an explicit NCL being provided. The intra-frequency measurement period is defined to be 200 ms. Even when monitoring gap patterns are activated, vast majority of time is available to perform intra-frequency monitoring. When DRX is enabled, UE can use opportunities to save power between subsequent DRX „On periods‟. Intra-frequency monitoring performance relaxations will only be defined for cases when „On period‟ periodicy > 40 ms. LTE Inter-FrequencyMonitoring LTE inter-frequency monitoring is similar to intra-frequency except that it performs in monitoring gaps. For a 6ms gap pattern only 5ms is available for inter-frequency monitoring once the switching time has been removed. If monitoring gaps repeat every 40 ms only 5/40 = 12.5% is available for inter-frequency monitoring. So, LTE inter-frequency maximum cell identification time and measurement periods need to be longer than for intra-frequency case. Within one monitoring gap, PSS and SSS symbols is guaranteed and there are also sufficient RSs to perform power accumulation and obtain RSRP, RSSI and derive RSRQ. Normal measurement bandwidth are 6 central RBs of an LTE carrier (i.e. 1.08MHz), which include PSS and SSS. An optional 50 RB configuration is also defined. GSM Monitoring from LTE GSM is the only RAT where synch information with a single 6 ms monitoring gap may not be sufficient. A monitoring gap pattern used for GSM monitoring must do: GSM RSSI measurements, initial BSIC identification and BSIC reconfirmation, by allocating every third monitoring gap to each one of the above three. Careful selection of gap repetition period to a period which is a factor of 240 ms (30, 40, 80, 120 and 240 ms) can detect synchronization burst(SB) containing BSIC and SFN within a guaranteed max-time. A control channel multiframe is 51 frames (=51*577*8µs=240ms). How/Why a gap pattern of 6 ms gaps repeating every 240 ms, guarantees initial BSIC identification and BSIC reconfirmation time, under good reception conditions? Maximum time will always involves multiple gaps. Any gap duration exceeding nine timeslots (9*577µs) = 5.19ms is guaranteed to contain a timeslot 0 regardless, which contains FB or SB. Once receive switching overhead is added, 6ms gap is sufficiently large. Moreover, a gap pattern repeating every 240 ms will be guaranteed to observe FB or SB in at most 11 consecutive gaps because there is a shift of one GSM frame with respect to the GSM 51-frame control multiframe between two adjacent monitoring gaps. Thus, a single step BSIC reconfirmation is guaranteed not to require more than 11 consecutive gaps since all it requires is decoding the SB. For the same reason, both the FB and the SB can be observed in no more than 12 consecutive gaps (12*240ms = 2880 ms). Therefore, two step initial BSIC identification single attempt is guaranteed not to require more than 2880ms. Single-step initial BSIC reconfirmation requires the same time as BSIC reconfirmation.



More complicated analysis must be performed in order to determine the worst-case initial BSIC identification and BSIC reconfirmation times when using other monitoring gap periodicities (i.e. 40, 80 and 120ms etc..). UMTS Monitoring from LTE UMTS monitoring is performed within the monitoring gaps. UE needs to read P-SCH, S-SCH and CPICH for cell identification and measurements (RSCP and Ec/No), and are guaranteed to be present within a 6 ms gap.

Measurement Reporting Two types of measurement reporting are specified by Measurement Configuration:

1. Periodic reporting: Measurement reports are configured to be reported periodically. 2. Event-triggered measurement reporting: Measurement reporting can be configured to

trigger when some conditions are met by measurements by UE. Reporting conditions are criteria to start N-cell measurements or trigger handovers due to poor cell coverage or poor quality. Once criteria is met, UE can be configured to report additional measurements even unrelated to the event condition. This report is used by eNodeB RRM algorithms to determine the best handover command.





1.4. Radio Resource Controller –

Connected Radio Resource Controller (RRC) performs Control Plane of Access Stratum (AS). AS interacts with NAS, which handles PLMN_selection, Tracking Area update, paging, authentication, EPS bearer establishment, modification and release. RRC is in either RRC_IDLE or RRC_CONNECTED state. In RRC_CONNECTED, eNB allocates RB to UE to transfer data via shared data channels. UE monitors PDCCH for allocated transmission resources in time and frequency. UE reports buffer status and DL channel quality (CQI), neighbouring cell (including other freq/RAT) measurement to select most appropriate cell for UE. UE continues to receive SI. To extend battery lifetime, UE may be configured with a Discontinuous Reception (DRX) cycle. RRC performs security, inter and intra RAT mobility, establishment and reconfiguration of radio bearers to carry control and user data.

RRC covers following functional areas.

System information- handles broadcasting of SI, for NAS, RRC, L2 and PHY.

RRC connection control- covers (re)establishment, modification and release of RRC connection, paging, initial security activation, establishment of SRBs & DRBs, inter/intra-RAT handover including context, configuration of L1 & L2, AC barring and radio link failure (RLF).

Network controlled inter-RAT mobility besides mobility, security activation and context information transfer.

Measurement configuration and reporting for intra/inter-frequency and intra/inter-RAT mobility, with measurement gaps management.

Miscellaneous functions – Perform transfer of dedicated NAS & access capability information.

RRC messages are transferred across SRBs, mapped via PDCP and RLC onto logical channels – either CCCH or DCCH. SI is mapped to BCCH and Paging is mapped to PCCH. SRB0 is used for CCCH, SRB1 is for DCCH, and SRB2 is for NAS messages using DCCH. All DCCH messages are integrity-protected and ciphered by PDCP (after security activation) and use ARQ for AM RLC. CCCH messages are not integrity-protected and no ARQ in RLC. NAS independently applies integrity protection and ciphering. For low transfer delay parameters, MAC signalling is used when no security concerns applies.

1.4.1. Connection Control within LTE Connection control involves:

1. Security activation; 2. Connection establishment, modification and release; 3. DRB establishment, modification and release; 4. Mobility within LTE.

1.4.2. Security KeyManagement Two functions provided for security: ciphering of both control and user plane data and integrity protection of control plane (RRC) only. Ciphering is used to protect data, while integrity protection detects packet insertion or replacement. RRC always activates both functions together, either following connection establishment or after handover to LTE. The key „K‟ is always in Authentication Centre (AuC) in Home Subscriber Server (HSS). At MME‟s request, HSS with RAND number, generates vector (IK,CK, RES,AUTN) and subsequently KASME

(Access Security Management Entity). Generated KASME, checksums(RES) and random number (RAND) are transferred to MME, which passes AUTN and RAND to UE. „K‟ is also in a secure part of the Universal Subscriber Identity Module (USIM) in the UE. USIM in UE then computes the same set of keys using the RAND with secret key. Verify if AUTN matches with received one. Upon connection establishment, AS derives eNB specific KeNB from KASME. KeNB is used to generate RRCINT RRCENC and UPENC. In handover within E-UTRAN, a new AS base-key and AS derived-keys are computed from AS base-key used in Scell. The use of security keys is handled by PDCP layer.



Security functions are never deactivated, although „NULL‟ algorithm may be used.

1.4.3. Connection Establishment and Release UE may be in NAS states EMM-DEREGISTERED or EMM-REGISTERED. Within REGISTERED, it may be in EPS Connection Management (ECM) state (ECM-IDLE or ECM-CONNECTED). ECM-IDLE to ECM-CONNECTED involves RRC connection and S1-connection establishment. NAS initiates RRC connection establishment prior to S1-connection establishment. Connectivity in RRC_CONNECTED is initially limited to exchange of control information between UE and E-UTRAN. UEs move to ECM-CONNECTED when becoming active within 100ms. RRC connection release is initiated by eNodeB following S1 connection release between eNodeB and CN. Connection establishment message sequence. RRC connection establishment establishes SRB1 and transfers initial UL NAS message. This NAS message triggers S1 connection, Security, establishes SRB2 and one or more DRBs (for default and optionally dedicated EPS bearers). Step 1: Connection establishment

• Upper layers in UE trigger connection establishment, which may be in response to paging. Lower layers in the UE perform a contention-based random access(RA) procedure, UE starts T300 and sends RRCConnectionRequest to Cell with initial identity (S-TMSI or a random number) and an establishment cause.

• If E-UTRAN accepts connection, it returns RRCConnectionSetup with initial radio resource configuration with SRB1. E-UTRAN may order default configuration as per specification.

Fig 5.2.3.1 – rrcConnectionSetup IE

• UE returns RRCConnectionSetupComplete with NAS message, selected PLMN and registered MME code. Based on this, eNodeB decides CN node for S1-connection.

Step 2: Initial security activation and radio bearer establishment

• eNB sends SecurityModeCommand to activate integrity protection and ciphering. Itself, it is integrity-protected but not ciphered, indicates which algorithms to be used.

• UE verifies integrity protection of SecurityModeCommand and, start applying integrity protection and ciphering to all subsequent messages (SecurityModeComplete (or SecurityModeFailure) onwards).

• eNB sends RRCConnectionReconfiguration with RB configuration, to establish SRB2 and one or more DRBs, possible piggybacked NAS message or a measurement configuration. It may be sent prior to receiving SecurityModeComplete. eNB should release the connection when one or both (Security and Configuration) procedures fail.

• UE finally returns RRCConnectionReconfigurationComplete.

• A connection establishment may fail for many reasons, such as: o Access may be barred.

o Cell re-selection occurs during connection establishment, UE aborts procedure.



o Wait timer expires. o NAS may abort on NAS timer expiry.

Fig 5.2.3.2 – rrcConnectionSetupComplete IE

Step 3: DRB Establishment

• RRCconnectionReconfiguration commands is sent to UE to establish, modify or release DRBs.

Fig 5.2.3.3 – rrcConnectionReconfiguration IE

• For DRB, eNB decides RB interface for EPS bearer which is mapped (1-to-1) to a DRB which is mapped (1-to-1) to a DTCH, further mapped/multiplexed (n-to-1) to DL-SCH or UL-SCH, which are mapped (1-to-1) to PDSCH or PUSCH. RB configuration covers PDCP, RLC, MAC and PHY layers. The main configuration parameters / options include the following: o PDCP may be configured for header compression to reduce signalling overhead. o RLC Mode (AM, UM or TM) is selected. Normally RLC-AM is applicable for reliable

transmission. o eNB assigns priorities and PBRs to control how resources and data rate. o UE may be configured with a DRX cycle. o For VoIP, semi-persistent scheduling (SPS) may be configured to reduce signalling

overhead. o Delays may be configured with a Hybrid ARQ (HARQ) profile.

1.4.4. RRC_CONNECTED Messages Here is the list of all RRC Messages:



Fig 5.2.4 – List of all RRC messages in UL and DL.

1.4.5. Mobility Control in RRC_IDLE and RRC_CONNECTED Cell-reselection in RRC_IDLE is UE-controlled, while Handover, CCO, Redirection in RRC_CONNECTED is E-UTRAN controlled. Mobility mechanisms are designed to support a wide



variety like network sharing, MCC borders, HeNB and Macro/Micro/Pico/Femto cells and varying subscriber densities. Radio link quality is the primary criterion for selecting a cell on an LTE frequency. When choosing between cells, consider frequencies, RATs, UE capability, subscriber type, call type etc. Voice centric call request can be retained (or forwarded to) GSM and data centric calls may be forwarded to LTE. eNB provides neighbouring frequencies and cells for cell reselection and measurements. In general, white-list are considered and used for selection and black-list are forbidden. eNB is not required to indicate all neighbour cells that UE shall consider. UE can detect itself what cells it can move to. Mobility in idle mode. Cell re-selection between frequencies is based on absolute priorities, provided by SI. eNB may assign UE-specific values upon release, based on UE capability or subscriber type. Among equal priority freq cells, cells are ranked based on radio link quality. Equal priorities are not applicable between frequencies of different RATs. Cells without frequency priority are not considered. Mobility in connected mode. In RRC_CONNECTED, eNB decides target cell to maintain the radio link, taking into account UE capability, subscriber type and access restrictions. Although eNB may trigger blind handover without measurement report, normally it configures UE to report measurements of target cells. In LTE, handover from a Scell to Tcell is a hard handover. eNB which controls Scell requests target eNB to prepare for handover. T-eNB generates RRC message to S-eNB to order UE for handover, and message is forwarded by S-eNB to UE. In case S-Cell Radio link fails during preparation, UE by itself decides to connect to T-cell as connection reestablishment. This succeeds only if T-cell was prepared in advance for handover. UE may be redirected to another freq/RAT on release. Redirection may also be performed if Ssecurity not activated. Redirection during connection establishment is not supported, before and after is supported.

1.4.6. Message sequence for handover within LTE In RRC_CONNECTED, eNB controls mobility – to intra or inter frequency cells. Inter-frequency measurements may require measurement gaps depending on UE dual receiver capabilities. Handover may be used for change of security keys or to perform a „synchronized reconfiguration‟. The message sequence for itra-freq handover is as follows:

1. UE may send a MeasurementReport to eNB. 2. Before handover command to UE, S-eNB sends „handover preparation request‟ to one or

more T-cells. S-eNB provides UE context about UE capabilities, current AS-configuration and UE-RRM information. T-eNB sends „handover command‟to S-eNB, who will forward this transparently to UE in RRCConnectionReconfiguration message.

3. RRCConnectionReconfiguration orders UE to perform handover with mobility control information (target cell id, frequency) and common RRM information(SI with RA parameters, dedicated Resource configuration, security, C-RNTI) in T-cell. Optionally it may include measurement configuration. If no measurement configuration is included for inter-frequency handover, UE stops any inter-freq/RAT measurements and deactivates measurement gap.

4. If UE can comply with RRCConnectionReconfiguration, UE starts T304, and initiates a random access (RA) using received RACH configuration, to target cell. Note that UE does not need to acquire SI in T-cell prior to RA and resuming data communication. UE may be unable to use SPS, PUCCH and SRS from very start. UE derives new security keys and applies received configuration in T-cell.

5. On successful RA, UE stops T304. Now UL and DL, RRC, NAS communications continue.

1.4.7. Connection Re-Establishment Procedure In many failure like RLF, handover failure, RLC error, reconfiguration compliance failure - UE initiates RRCconnection reestablishment, if security is active. If security is not active, UE moves to RRC_IDLE instead. UE starts T311 and performs cell selection, prioritize searching on LTE frequencies. Upon finding a suitable cell, UE stops T311, starts T301 and initiates RA to send



RRCConnectionReestablishmentRequest including UE-Id used in failed cell, failed cell-id, MAC and a cause. Re-establishment procedure reuses/continues SRB1 and reactivates security without changing algorithms. A subsequent RRCconnectionreconfiguration is used to resume operation on radio bearers and measurements. If re-establishing T-cell is not prepared (i.e. does not have UE context), eNB will reject and UE should move to RRC_IDLE.

1.4.8. Connected Mode Inter-RAT Mobility Handover to LTE Handover to LTE is largely same as handover within LTE. Main difference is that entire AS-configuration needs to be signalled, whereas within LTE „delta signalling‟, changes to the configuration are signalled. If ciphering not activated in previous RAT, E-UTRAN activates ciphering, possibly NULL algorithm. eNB establishes SRB1, SRB2 and one or more DRBs (i.e. at least for default EPS bearer). Mobility from LTE Mobility from LTE to another RAT supports both handover and Cell Change Order (CCO or even NACC – Only GERAN), but only after security is activated. Here is the brief procedure:

1. UE may send MeasurementReport message. 2. In handover (not CCO), S-eNB sends „handover preparation request‟ to T-RAN, with

applicable inter-RAT UE capabilities and established bearers. In response, T-RAN sends „handover command‟ to SeNB.

3. S-eNB sends MobilityFromEUTRACommand to UE including either inter-RAT message from T-RAN (handover case), or T-cell/frequency and inter-RAT parameters (CCO case).

4. On MobilityFromEUTRACommand, UE starts T304 and connects to T-node, either by handover or CCOas per applicable specifications of T-RAT.

CDMA2000 For CDMA2000, additional procedures are defined to transfer dedicated information from UE CDMA2000 layers, used to register UE‟s presence in target core network before handover (preregistration) using SRB1.

1.4.9. Handover to LTE When eNB-RRC decides to initiate a handover it sends a „MOBILITY FROM E-UTRA COMMAND‟ RRC message to UE, including target RAT, frequency and relevant parameters required for UE to establish a radio link with target cell. Handovers reasons can be many:

1. Quality: Measurement report shows that UE can communicate better with a N-cell than current S-cell.

2. Coverage: Inter-RAT Handover may be initiated because UE is losing coverage for current RAT. UE could be moving away from LTE coverage and eNB hands over the connection to next preferred RAT which UE has detected, such as UMTS or GSM.

3. Load-Balancing: To spread the load more evenly between different cells or even RATs belonging to same operator, when current cell is overloaded. If LTE cell is congested then some users may be moved to nearby LTE or UMTS or GSM cells.



1.4.10. Major HANDOVER Steps (Intra-LTE) The steps are as follows:

Fig 5.2.14 – Intra RAT Handover Ladder diagram

1. UE generates and transmits measurement report to current S-Cell. At least in one

measurement, there must be one target cell(T-Cell) with higher RSRP level than the current S-cell.

2. eNB controlling S-Cell decides that a handover is necessary, identifies a suitable T-cell (assumed LTE cell) and requests access to eNodeB controlling T-cell.

3. T-eNB accepts handover request and provides S-eNB with the parameters required for UE to access T-cell, including cell ID, frequency and UL (PRACH) resources.

4. S-cell sends „RRCConnectionReconfig‟ RRC message to UE. 5. UE receives message, interrupts radio link (stops data transmission) with S-eNB and initiates

establishment of new radio link with T-eNB. There are a number of steps involved: a. DL synchronization establishment. UE will have to perform LTE PSS and SSS

synchronization steps. DL synchronization is only considered established when DL RS quality is sufficiently good.

b. Random Access: By Random access procedure, it receives uplink resource, its identity and Timing advance command. From this point onwards data reception in DL from T-eNB may take place.



c. Timing advance. It is provided by T-eNb based on received delay measured on PRACH.

d. Data transmission. UE starts UL/DL data transmitting towards T-eNB. S-eNB may forward UE data to T-eNB pending in the S-eNB.

6. Moment UL data transmission is established with T-eNB, RRC message is sent to S-eNB to notify that handover has been completed.

7. T-eNB also notifies the MME that UE has handed over to T-Cell and MME reroutes the DL data to T-eNB. S-GW Notifies S-eNB that DL data is switched to T-eNB. S-eNB then forwards rest of the pending data to T-eNB and clears the UE-Context.

8. UE now just continues the communication with T-Cell in T-eNB.. The above steps are just representative of best-case scenario and many deviations/failures are possible. Failure cases can necessitate recovery procedures. Preferred T-eNB may have no spare resources to grant to UE, DL synchronization might fail, UL RACH process might fail etc. Differences between LTE Intra- and Inter-Frequency Handover In LTE all handovers are hard handovers. The steps for inter and intra-frequency handover within LTE are very similar. Handover interruption time= time between the end of last TTI UE has received handover command on PDCCH/PDSCH and the time UE is ready to start a PRACH transmission to new uplink. Tinterrupt = Tsearch + TIU + 20 ms

where Tsearch = time required to find T-cell when not already known, else if known, Tsearch =0ms. TIU = interruption uncertainty to locate first available PRACH occasion in new cell. 20 ms is added to allow for UE processing time to execute handover.

1.4.11. Handover to UMTS This procedure can be decomposed into two stages, each of which relates to an identical stage in a single-mode handover procedure:

1. Handover initiation. In UE case, it receives “MobilityFromEUtraCommand”, within which it has the “UMTS handover command” what it would have received if it was in UMTS network. eNB through MME would have received all the information required for Target UMTS T-NB from T-RNC/SGSN.

2. Radio link establishment to UMTS T-cell. This stage is identical to UMTS inter-frequency handover. Handover execution delay requirements are very similar to intra-UMTS hard handover requirements.

Handover to UMTS may be blind or guided depending on whether or not the UE has been able to synchronize to T-cell prior to receiving „MOBILITY FROM E-UTRACOMMAND‟ RRC message.

1.4.12. Handover to GSM Similar to UMTS, Handover to GSM can also be decomposed into two separate stages:

1. Handover initiation. In UE case, similar for UMTS, it receives “MobilityFromEUtraCommand”, within which it has the “GSM handover command” what it would have received if it was in GSM network. eNB through MME would have received all the information required for Target GSM BTS from T-BSC/SGSN.

2. Radio link establishment to GSM T-cell. This stage is identical to a GSM intra-system unsynchronized handover.

Handover to GSM interruption time can be decomposed into three main contributions: Tinterrupt GSM = Tprocessing time + Tsync,blind + Tinterruption,guided , where Tprocessing time = 50 ms (different implementations to reconfigure modem for GSM) Tsync,blind =time to enable UE to synchronize to T-cell during a blind handover (100 ms). Tsync,guided = 0 ms). Tinterruption, guided = 40 ms (UE has been able to synchronize to T-cell command)

Seamless mobility is ensured in LTE, to deliver uninterrupted mobile user experience. A wide range of measurements and signalling are defined to support different handover scenarios.



1.4.13. Other RRC Signalling Aspects UE Capability Transfer Core Network stores AS capabilities when UE gets registered as EMM-REGISTERED and not each transition from RRC_IDLE to RRC_CONNECTED. Upon S1 connection establishment, CN provides capabilities to eNB. If eNB does not receive (required) capabilities (e.g. due to UE in EMM-DEREGISTERED), it may requests UE by UEcapabilityEnquiry, may be for each (LTE, UMTS, GERAN). UE responds with UECapabilityInformation. Uplink/Downlink Information Transfer UL/DL Information transfer is used to transfer only NAS/OtherRAT messages. NAS information may be included in RRCConnection-SetupComplete and RRCConnectionReconfiguration also. This applies for EPS bearer establishment, modification and release also. HandoverFromEUTRAPreparationRequest and ulHandoverPreparationTransfer are defined for CDMA2000 for preregistration.





1.5. Radio Resource Management Radio Resource Management (RRM) provide the user with mobility whereby UE and NW take care of mobility seamlessly, without much user intervention. There is a trade-off between additional UE complexity (e.g. cost, power consumption, processing power), network complexity (e.g. radio interface resource, network topology) and achievable performance. The main procedures are cell search, measurements, cell reselection and handover. RRM includes protocols for handling mobility, synchronization, cell search, mobility with LTE and other Radio Access Technologies (RATs) cells.

1.5.1. UE Mobility Activities Overview To maintain service continuity as a user moves, UEs must be connected to a S-cell and monitor neighbour cells continuously, since propagation conditions(interference) to different eNodeBs changes rapidly. UE and NW will always be directed to a preferred RAT according to preference criterion based on QoS, cost or operator. Generally UE will be requested to perform mobility decisions (handover or cell reselection) towards other cells of same RAT. But, whenever preferred network is not available (poor coverage, congestion etc), NW and UE must cooperate to identify fallback options to other NW or RATs for continuity. A fallback RAT may result in some degradation in terms of services provided, but at least continuity can be preserved. In all mobility cases UE must meet minimum performance requirements, for cell search, measurement accuracy and periodicity and handover execution delay. UE power consumption and cost are important factors. The performance requirements consists of:

1. Current serving S-Cell RAT. 2. Layer 3 state of S-Cell, e.g. LTE states RRC_CONNECTED and RRC_IDLE. 3. Monitored RAT. Camped on an LTE cell, monitor other cells on same LTE frequency

(ntra-frequency) and cells on other LTE frequencies (inter-frequency). It should monitor one or more other RATs, such as GSM, UMTS, WiMAX, TD-SCDMA, CDMA HRPD, or CDMA2000. Criteria in each RAT may be different.

Among 3GPP RATs (LTE, UMTS and GERAN1), minimum-effort are broadly the same regardless of RAT involved:

1. Serving cell quality monitoring and evaluation: S-cell quality is evaluated periodically. If S-cell quality is satisfactory (above a configured threshold), then no further action is required and stay in step 1. However, if S-Cell quality is below threshold, the next step 2 is executed.

2. Initiate periodic cell search for candidate neighbour cells: Candidate neighbour cells can be intra-frequency, inter-frequency and inter- RAT cells, and search is performed in a defined order of priority. Cell search is repeated periodically. Even if a UE has identified a N-cell (neighbour), it will continue cell search until either S-cell quality becomes satisfactory again, or UE moves to another S-cell through handover, cell reselection, redirection or cell change order. If some N-cells are identified as candidate, then the following step is performed or else continue step 1 or 2.

3. Neighbour cell measurement: Signal Strength for N-cells in step 2 is measured periodically until either S-cell quality becomes satisfactory again, or UE moves to another S-cell.

a. To avoid measurement fluctuations, measurement is obtained by averaging over a number of evenly spaced samples within a measurement period (Intra-frequency RSRP meas-period is 200 ms) and then next step 4 is performed.

4. Mobility evaluation: Next, decision is made UE should move to another S-cell. The eNodeB decides on handover and UE redirection/cell change orders, and UE decides cell reselection. If mobility criteria are fulfilled then mobility procedure to move towards Target T-cell is executed. The T-cell may be in same RAT (intra- and inter-frequency handover and cell reselection) or in different RAT (for inter-RAT handover and cell reselection).

1.5.2. LTE Cell Search UE‟s detects N-cells, which may belong to LTE (intra or inter-frequency) or to other RATs (inter-RAT). The cell search in LTE in summary consists of:

1. Primary Synchronization Signal (PSS) detection to obtain physical cell ID (within a group of three) and slot synchronization.



2. Secondary Synchronization Signal (SSS) detection to obtain Cyclic Prefix (CP) length, physical cell group ID and frame synchronization.

3. Physical Broadcast CHannel (PBCH) decoding to obtain critical system information (MIB(40ms periodicity), SIB1 and SIB2).

4. For new cell identification, PBCH may not be required but Reference Signal (RS) may be decoded to measure RSRP and RSRQ to be reported to NW.

1.5.3. UMTS Cell Search UE is synchronized to UMTS cell when it knows cell‟s frame boundaries timing and cell‟s primary scrambling code which distinguishes the cell‟s transmissions from other cells. UMTS synchronization process stages are:

1. Primary-Synchronization CHannel (P-SCH) search. Only one UMTS P-SCH code exists, and repeated on the first 256 chips of every slot (0.666 ms). UE performs matched filter correlation between the received signal and P-SCH sequence for all possible timing offsets within one slot and correlation peaks can be observed in those locations where a P-SCH sequence is present. This gives the slot boundary timing for each detected P-SCH. For one or more of the strongest detected peaks, next step is performed.

2. Secondary-SCH decoding. The S-SCH code sequence is one of 15 codewords present on the first 256 chips of every slot (same time as P-SCH). One S-SCH code sequence is defined for all cells belonging to the same „code group‟. Each S-SCH code sequence identifies uniquely a code group and 10 ms frame boundary position. In good signal conditions the information contained within three slots is sufficient to identify uniquely both the frame timing and the code group, but in order to reliably decode the S-SCH in difficult reception conditions longer decoding periods are required.

3. Primary scrambling code identification. The code group of S-SCH indicates a group of eight primary scrambling codes. A given cell uses one code from this group as the scrambling code for all DL channels, including Primary Common PIlot CHannel (P-CPICH). UE performs a correlation against the eight scrambling sequences, looking for known CPICH sequence (which is the same in all UMTS cells), to determine which code is being used.

4. System Frame Number (SFN) detection. Primary Common Control Physical CHannel (P-CCPCH) carries the Broadcast CHannel (BCH), encoded over a 20 ms TTI. Earlier synchronization stages only provide timing information up to a 10 ms period (one frame). The location of the even frame boundaries can be found, by trial and error by performing decoding attempts on the two possible TTI boundaries. Only the correct boundary will ensure successful channel decoding and return a correct CRC. BCH carries the SFN. This step is only required on cell reselection from LTE to UMTS and on handover to UMTS after handover initiation.

Once a UE has camped on an LTE cell it will receive a UMTS neighbour cell list containing up to 32 primary scrambling codes per UMTS carrier, used by the UE to speed up the UMTS cell search process.

1.5.4. GSM Cell Search GSM Synchronization includes: GSM RSSI measurements, initial BSIC identification and BSIC reconfirmation. When camped on LTE cell, UE will be provided Neighbour Cell List (NCL) with at least 32 GSM carrier numbers (ARFCNs) indicating neighbouring cells frequencies, and optionally an associated BSIC for each GSM carrier in the NCL.

GSM RSSI Measurements For GSM monitoring, UE will measure GSM RSSI (averaged over at least 3 samples) for all carriers in the NCL in every measurement period (usually 480ms). Once measurements for all cells in NCL are available, the strongest N cells are passed to the next step.



Initial BSIC Identification BSIC is within GSM Synchronization Burst (SB), carrying GSM Synch CHannel (SCH). The SCH also carries cell SFN. The BSIC (3 bits Base station Colour Code (BCC) and 3 bits Network Colour Code (NCC)) allows UE to distinguish two different cells which share the same beacon frequency. BCC is also used to identify Training Sequence Code (TSC) used while reading BCCH. NCC is used to differentiate between operators utilizing same frequencies, (e.g. on border when both NW have same frequency or frequencies). Initial BSIC identification is performed in for N = 8 strongest GSM carriers as follows:

a. Frequency Control Channel (FCCH) detection. To detect a Frequency Burst (FB) by FCCH, UE tunes to a beacon frequency and performs a continuous correlation against the signal contained within FB. The FB is transmitted on timeslot 0 of frames 0, 10, 20, 30 and 40 of 51-frame control multiframe. When a correlation peak is detected, coarse frame timing and coarse frequency synchronization can be acquired. If continuous correlation is performed, FCCH is surely detected in no more than 11 frames. One GSM frame duration = 60/13ms = 4.61 ms.

b. GSM SCH detection. There is always one SB (carried by SCH) exactly one frame after the FB. If initial BSIC identification is being performed within a gap in LTE signal specially created for inter-RAT monitoring and this gap is too short, then GSM SCH can be decoded later. Then decoding SCH becomes more complicated for the presence of the GSM idle frame in 51-frame control multiframe. Idle frame introduces a N/(N + 1) frame ambiguity forcing UE to perform decoding attempts at two adjacent locations after FB detection separated by one GSM frame: 10/11 frames, 20/21 frames, etc. Since SCH contains CRC, CRC check outcome determines which of the two options is the correct outcome. Once SCH is decoded, both BSIC and frame number are obtained, and position of SB can be predicted.

BSIC Reconfirmation BSIC Reconfirmation decodes the SB periodically on GSM carriers where BSIC has already been detected. Then SB position within a cell can be predicted exactly as neighbour cell SFN is acquired earlier. UE needs to check periodically that the carrier with this BSIC was previously identified with same BSIC. After many unsuccessful BSIC reconfirmation attempts, a carrier must be moved back to initial BSIC identification.





1.6. MU-Scheduling & Interference

Coordination The eNodeB is responsible for managing resource scheduling for UL/DL channels to fulfil the expectations of as many users as possible as per Quality-of-Service (QoS) requirements of their respective applications. A single-cell with K UEs communicates with one eNodeB over a fixed total bandwidth B. Each UE has several data queues for different UL channel groups, each with different delay and rate constraints. In DL also, eNodeB maintains several buffers per UE with dedicated data traffic with different QoS and broadcast services. Total BW B is divided into M RBs. Data is split into blocks of duration T = 1 subframe (1 ms, 1 TTI). Channel can be assumed stationary for the duration of each subframe, but vary from subframe to subframe and channel is assumed constant over the subcarriers in one RB, but channel gain of a user may change from one RB to another. Resource scheduling algorithm in eNodeB allocates RBs and powers for each subframe to optimize performance metrics, for example max/min/avg throughput, delay, spectral efficiency or outage probability. In DL, allocation is constrained by total transmission power of eNodeB, while in UL, constraint of power in different RBs are due to multicell inter-cell interference. Resource allocation algorithms considers orthogonal design of multiple access schemes, where only one user is allocated a particular RB in any subframe.

1.6.1. Resource Allocation Strategies Scheduling algorithms uses channel-state information (CSI) and traffic measurements (volume and priority) via feedback signalling channels. Algorithms aim is to maximize the data rate in one direction at the expense of more overhead in the other. In TDD, amplitude coherence between UL and DL may be used to assist scheduling algorithm. It is tightly coupled with adaptive coding and modulation scheme based on channel measurement and HARQ. Secondly, the queue dynamics, impacting throughput and delay, depend heavily on HARQ protocol and TB sizes. Combination of channel coding and HARQ retransmission enables the spectral efficiency. eNodeB resource scheduler manages differing requirements of all UEs in the cells to ensure sufficient RBs are allocated to each UE within acceptable latencies to meet their QoS requirements in a spectrally-efficient way. There are mainly two approaches to scheduling: Opportunistic scheduling and fair scheduling are two methods. Opportunistic Scheduling is designed to maximize total data rates to all users by exploiting channel conditions at different times and frequencies. For a multiuser system, more information can be transmitted across a fading channel than a non-fading channel for the same average signal power at the receiver, it is known as multi-user diversity. Allocating channel only to the user with the best channel condition can increase the total throughput for large active users, if UE is able to adapt the power dynamically according to the channel state. This allows some simplification and is well suited to DL where transmitted power in a given subframe is limited by dynamic range of UE receivers and the need to transmit wideband RS for channel estimation. Opportunistic Scheduling doesn‟t ensure fairness and QoS, users‟ data cannot always wait until the channel conditions are sufficiently favourable for transmission. It is important to provide reliable wide area coverage, including to stationary users near the cell edge – not just to the users which happen to experience good channel conditions by virtue of their proximity to the eNodeB. Fair scheduling, pays more attention to latency for each user than to total data rate achieved, particularly important for real-time applications like VoIP or video-conferencing, where a minimum rate must be guaranteed independently of the channel state. In practice scheduling algorithms fall between the two extremes to deliver the required mix of QoS. A Cumulative Density Function (CDF) metrics of throughput of all users is used. Ensure that the CDF of the throughput lies to the right-hand side of a particular threshold. This saves penalizing the celledge users to give high throughputs to the users with good channel conditions. In a network, individual cells



cannot be considered in isolation –eNodeBs should consider interference generated by co-channel cells.

1.6.2. Scheduling Algorithms Multi-user scheduling performs capacity-maximizing resource allocation. A capacity metric is first formulated and then optimized across all possible resource allocation solutions with predetermined constraints, may be based on bandwidth and total power or QoS.

Ergodic Capacity The ergodic capacity (Shannon capacity) is defined as the maximum data rate possible over the channel with asymptotically small error probability, averaged over fading process. When CSI is available, Tx power and CSI can be varied depending on the fading state to maximize the average rates. Ergodic capacity metric considers average data rate which can be delivered to a user when the user does not have any latency constraints. Maximum Rate Scheduling The maximum sum rate is achieved by orthogonal multiplexing where in each subchannel (each RB in LTE) user with the best channel gain is scheduled. Water-filling formulae in both frequency and time is used where we allocate more power to a scheduled user when his channel gain is high and less power when it is low. A variant of this resource allocation strategy with no power control is called „maximum-rate constant-power‟ scheduling, where only the user with the best channel gain is scheduled in each RB, but with no adaptation of the transmit power. Most of the performance gains offered by the maximum rate allocation are due to multi-user diversity and not to power control, so an on–off power allocation can achieve comparable performance to maximum-rate scheduling. Proportional Fair Scheduling The ergodic sum rate gives optimal rate for traffic without delay constraint. This is unfair sharing and when the QoS required by the application includes latency, this strategy is not suitable. A fair approach is Proportional Fair Scheduling (PFS) algorithm. PFS schedules a user when its instantaneous channel quality is high relative to its own average channel condition over time. PFS takes into account link adaptation dynamic range, power and code resources, convergence settings, signalling overhead and code multiplexing. A large time window tends to maximize total average throughput; PFS and maximum-rate constant-power scheduling result in the same allocation of resources. For small window, the PFS tends towards a round-robin scheduling.

Delay-Limited Capacity The fairness of PFS may not be sufficient for very tight latency constraint. A different capacity metric is needed like „delay-limited capacity‟ (zero-outage capacity), where transmission rate is guaranteed in all fading states under finite long-term power constraints. It is relevant to traffic classes of guaranteed throughout the connection time, regardless of the fading dips. Guaranteeing a delay-limited rate incurs only a small throughput loss in high SINR conditions when number of users is large, but requires non-orthogonal scheduling of the users in each RB, which is unsuitable for LTE. Orthogonal Delay-limited Rate Allocation: It is possible to combine orthogonal multiple access with hard QoS requirements. It finds the allocation of users to RBs which maximizes the number of served users for a given total transmit power while achieving a target rate-tuple R = (R1,R2,.. .. ..,Rk) through an orthogonal multiplexing of the users. Solution uses power adaptation across the RBs. Max-Min allocation: At any instant, minimum channel gain of any of the allocated users is the highest possible among all possible allocations and thus maximizes the minimum allocated rate when an equal and fixed power is used for all users. It is useful where no power control (like in DL) can be used.



1.6.3. Performance of Scheduling Strategies The per-user average throughput increases with the number of users, hence even under delay-limited requirements, high multi-user diversity gains can be achieved. Even under hard fairness constraints it can achieve performance very close to the optimal unfair policy; thus hard fairness constraints do not necessarily introduce a significant throughput degradation, even with orthogonal resource allocation, provided that the number of users and BW are large like VoIP users, with a latency constraint typically requiring each packet to be successfully delivered within 50 ms. For a high SINR scenario, PFS does not provide any significant gain and may even perform worse than the optimal non-orthogonal delay-limited scheduling; even if imposed fairness constraint is less stringent. For low to moderate SINR, the stricter hard-fairness constraint incurs a large throughput penalty for delay-limited scheduling with respect to PFS. Summarily, strategies assumes that all users have an equal and infinite queue length (full-buffer traffic model). For real-time services, users‟ queue lengths is necessary to guarantee system stability. If a scheduling algorithm keeps the average queue length bounded, the system is said to be stabilized. To achieve this, use the queue length to set the priority order in the allocation of RBs. This generally works for lightly-loaded systems. In wideband frequency-selective channels, low average packet delay can be achieved even if the fading is very slow.

1.6.4. Considerations for Resource Scheduling in LTE Each logical channel has a QoS description influencing eNodeB resource scheduling algorithm. QoS could potentially be updated for each service in a long-term fashion. Mapping between QoS descriptions of different services and resource scheduling algorithm in the eNodeB makes a difference. Availability and accuracy of CSI for the active UEs to the scheduler in cell is a limitation. CSI reporting differs for UL and DL. For DL, CSI is provided through CQIs by UEs, while for UL, eNodeB may use SRSs or other signals by UEs to estimate CQI. The CQI reports and SRS frequency is configurable by eNodeB, and signalling overhead is controlled to get up-to-date CSI, which if received too long ago, may degrade the decision. To perform frequency-domain scheduling, CSI needs to be frequency-specific. eNodeB may configure CQI reports to relate to specific subbands to assist DL scheduling. UL frequency-domain scheduling can be facilitated by configuring SRS to be transmitted over a large bandwidth. For cell-edge UEs, wider the transmitted BW, lower the available power per RB; this means, accurate frequency-domain scheduling is difficult for UEs near cell edge. Limiting SRS to a subset of system BW will improve CQI estimation on these RBs but restrict the ability of the scheduler to find an optimal scheduling solution for all users. In general, if CQI estimated for scheduling is greater than the intended scheduling bandwidth, a useful element of multi-user diversity gain may still be achievable. In order to support QoS and queue-aware scheduling, scheduler must have CQI and queue status, both. In DL, eNB MAC BSR to each UE is available;

1.6.5. Interference Coordination and Frequency Reuse LTE is designed to operate with a frequency reuse factor of one, which requires inter-cell interference coordination among adjacent cells to increase the data rates for users at the cell edge. This implies imposing restrictions on specific RBs available to the scheduler, or what transmit power may be used in certain RBs. If a user k is experiencing no interference, then its achievable rate in a RB m of subframe f =

R(k).no-Int(m,f) = B/M log [1 + (Ps(m,f) (Hs(m, f ))2 )/ N0]

where Hs(m, f ) = channel gain from serving cell s, Ps(m, f ) = transmit power from cell s and N0 is the noise power. Neighbouring cells are transmitting in the same time-frequency resources, then the achievable rate reduces because of these interfering cells to:

R(k).Int(m,f) = B/M log [1 + (Ps(m,f) (Hs(m, f ))2 )/ (N0+ Σ(i!=s)p

i(m,f)(H

ik(m,f))

2]



Where „i‟ is the interfering cell. The loss of rate = R(k).no-Int(m,f) - R(k).Int(m,f). For a level of interference = desired signal level, use k experiences a rate loss of approximately 40%. To demonstrate further the significance of interference and power allocation depending on the system configuration we consider two examples of a cellular system with two cells (s1 and s2) and one active user per cell (k1 and k2 respectively). Each user receives the wanted signal from its serving cell, while the inter-cell interference comes from the other cell. In the first example, each user is located near its respective eNodeB. The channel gain from the interfering cell is small compared to the channel gain from the serving cell. Maximum throughput is achieved when both eNodeBs transmit at maximum power. In the second example, we consider the same scenario but with the users now located close to the edge of their respective cells. Channel gain from the serving cell and the interfering cell are comparable. Maximum capacity is reached by allowing only one eNodeB to transmit. Optimal power allocation for maximum capacity with two base stations is binary this means, either both base stations should be operating at maximum power in a given RB, or one of them should be turned off completely in that RB. This result is exploited in the eNodeB scheduler by treating users in different ways depending on whether they are cell-centre or cell-edge users. Each cell can be divided into two parts – inner and outer. In the inner part (low interference) require less power to communicate with S-cell, frequency reuse factor of 1 can be adopted. For outer part, scheduling restrictions are applied: when cell schedules a user in a RB, system capacity is optimized if the neighbouring cells do not transmit at all; alternatively, they may transmit only at low power (to users in the inner parts of neighbour cells) to avoid creating strong interference to the scheduled user in the first cell. This effectively results in a higher frequency reuse factor at cell-edge; it is often known as „partial frequency reuse‟. To coordinate scheduling in different cells, communication between neighbours is required. If neighbours are managed by same eNodeB, a coordinated scheduling strategy can be followed without standardized signalling. When neighbouring cells are controlled by different eNodeBs, Inter-Cell Interference Coordination (ICIC) is managed in frequency domain (Not time domain, as it will affect HARQ processes). For DL transmissions, a bitmap Relative Narrowband Transmit Power (RNTP) indicator is exchanged between eNodeBs over X2. Each RNTP bit indicator corresponds to one RB in frequency domain and is used to inform neighbouring eNodeBs if a cell is planning to keep the transmit power for the RB below a certain upper limit or not. The upper limit, and validity period, are configurable and this helps the neighbouring cells to minimize interference in each RB when scheduling UEs in their own cells. The reaction is implementation dependent, but avoid scheduling cell-edge UEs in such RBs. In RNTP indicator, transmit power per antenna port is normalized by maximum output power of a base station or cell, because a cell with a smaller maximum output power, corresponding to smaller cell size, can create as much interference as a cell with a larger maximum output power corresponding to a larger cell size. For UL, two messages may be exchanged between eNodeBs (X2) for transmit powers and scheduling of users:

1. A reactive indicator, „Overload Indicator’ (OI), to indicate physical layer measurements of average uplink interference plus thermal noise for each RB. The OI may be = low, medium, or high levels of interference + noise. To avoid excessive signalling load, update frequency is not more than every 20 ms.

2. A proactive indicator, „High Interference Indicator’ (HII), to inform neighbour that it will, in near future, schedule UL by one or more cell-edge UEs in certain RB, and high interference might occur in those RBs. Neighbouring cells will then avoid scheduling their own users to limit the interference impact. The HII is a bitmap with one bit per RB, and, is not sent more often than every 20 ms. The HII bitmap is addressed to specific neighbour eNodeBs.



In addition to RB scheduling in UL, eNodeB also controls UE compensation for the path-loss when setting its UL power. This enables the eNodeB to trade off fairness for cell-edge UEs against inter-cell interference generated towards other cells, and maximize system capacity.

1. Static interference coordination: Coordination is done with cell planning and reconfigurations are rare. This avoids signalling on X2, but has performance limitation since it cannot adaptively use cell loading and user distribution informations.

2. Semi-static interference coordination: Reconfigurations are carried out in the order of seconds or longer. X2 interface is used. Traffic load is shared.

A scheduling algorithms will depend on the optimization criteria, such as traffic classes, throughput maximization for delay-tolerant apps, QoS for delay limited apps etc. Multi-user diversity is important when user density is high. System optimization requires coordination between cells and eNodeBs, to avoid inter-cell interference. Best results are realized by simple „on–off‟ allocation of RBs, where some eNodeBs avoid scheduling in certain RBs used by neighbouring eNodeBs for cell-edge users.





1.7. Sample Call Flows In this section we will list some sample representative call flows. This will make the understanding easier:

1.7.1. Basic Call Flow – Attach Procedure

Fig 5.5.1 – Attach Procedure including L1,L2,L3 Access Messages



1.7.2. Basic Call Flow – Incoming Call with Handover

Fig 5.5.2 – Call flow for incoming call and Handover



1.7.3. Call Flow example from tool

Fig 5.5.3 – A TEMS tools output showing the message sequence with Protocol and Latency



1.7.4. Sequence of inter-cell handover In general, the Inter-Cell handover is done without activation time, i.e. the timing information for

configuration of the SS and sending of the RRCConnectionReconfiguration is „Now'.

1. Transfer of the PDCP Count for AM DRBs from source to target cell: a) Source Cell: Get PDCP COUNT. b) Target Cell: Set PDCP COUNT.

There shall be no further sending/receiving of AM DRB data before the HO has been done. 2. Target Cell: Inform the SS about the HO and about the source cell id. 3. Target Cell: Configure RACH procedure either dedicated or C-RNTI based. 4. Target Cell: Activate security. For AM DRBs the PDCP count is maintained (for SRBs and UM DRBs the PDCP count is

reset). 5. Target Cell: configure DRX and measurement gap configuration (if necessary). As long as the DRX configuration is not modified by the RRCConnectionReconfiguration the

target cell gets the same DRX configuration as the source cell. Measurement gap configuration is released at the UE due to the handover, therefore nothing

needs to be configured at the target cell regarding measurement gaps unless a new measurement gap configuration is explicitly given in the RRCConnnectionReconfiguration.

6. Source Cell: Stop periodic TA. Unless explicitly specified UL grant configuration keeps configured as per default at the

source cell. 7. Target Cell: Configure UL grant configuration ("OnSR", periodic TA is not started). 8. Source Cell: Send RRCConnectionReconfiguration. 9. Target Cell: Receive RRCConnectionReconfigurationComplete. 10. Target Cell: Start periodic TA. 11. Target Cell: Inform the SS about completion of the HO (e.g. to trigger PDCP STATUS

PDU). 12. Target Cell: Re-configure RACH procedure as for initial access. 13. Source Cell: Reset SRBs and DRBs. 14. Source Cell: Release DRX and MeasGapConfig configuration.

1.7.5. Sequence of intra-cell handover For Intra-Cell handover dedicated timing information is used: the sequence starts at time T with

sending of the RRCConnectionReconfiguration. T is set to 300 ms in advance of the handover.

0. Before T: Get PDCP count for AM DRBs. 1. At T: Send RRCConnectionReconfiguration. 2. At T + 5ms: Release SRBs and DRBs. 3. At T + 5ms: Configure RACH procedure either dedicated or C-RNTI based. NOTE 1: Since the RACH procedure may require a new C-RNTI to be used it cannot be

configured before sending out the RRCConnectionReconfiguration. 3A At T + 5ms: Release MeasGapConfig configuration. NOTE 2: According to TS 36.331, clause 5.5.6.1 the measurement gap configuration is released

at the UE due to the handover, therefore MeasGapConfig is released unless a new measurement gap configuration is explicitly given in the RRCConnectionReconfiguration.

4. At T + 10ms: (Re-) configure SRBs and DRBs. 5. At T + 10ms: Reestablish security, disable TA transmission. NOTE 3: For AM DRBs the PDCP count is maintained while for SRBs and UM DRBs the PDCP

count is reset. 6. (after step 5) Receive RRCConnectionReconfigurationComplete. 7. (after step 6) Re-configure RACH procedure as for initial access, enable TA transmissions. 8. (after step 7) Restore the PDCP count for AM DRBs.

1.2.14. UL Grants used in RA procedure during handover In the Random Access Procedure a grant is assigned to the UE by the Random Access Response

and another grant, as initial grant, is assigned for contention resolution.



When UL data is pending, the UE will try to put as much data into given grants as possible, i.e. it will

segment the user data and send it e.g. with the initial grant if possible. To avoid this segmentation of

user data, the grants assigned during handover will be set in TTCN to:

Grant assigned by Random Access Response: 56 bits. Initial grant: 104 bits. 56 bits are the minimum grant which can be assigned by the Random Access Response. That is

sufficient to convey C-RNTI (3 bytes) and short BSR (2 bytes) or long BSR (4 bytes) but even with short BSR the remaining 2 bytes are not sufficient to convey any segment of the RRCConnectionReconfigurationComplete (at least 4 bytes).

The RRCConnectionReconfigurationComplete (9 bits) shall completely be conveyed in the initial grant of RA procedure. This requires a minimum of 10 bytes (1 byte MAC header + 2 bytes RLC header + 5 bytes PDCP header + 2 bytes payload). Additionally an optional PHR MAC element (2 bytes) needs to be considered since the PHR has higher priority than the MAC SDU. Any further user data would require a minimum of 5 additional bytes (2 bytes MAC header + 2 bytes RLC header + 1 byte payload).




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