WO BT1002 E01 1 UMTS Key Technologies

UMTS Key TechnologiesZTE University

ContentRAKE ReceiverHandover ControlCompressed ModeAdmission ControlLoad ControlCode Resource AllocationCapacity Features

Multi-path characteristics of radio channelElectromagnetic propagation: direct radiationreflectiondiffraction and scatteringSignal attenuation:Path loss Loss of electromagnetic waves in large scope of the spread reflects the trend of the received signal in the spreadingSlow fadingLoss because of being blocked by the building and hill in the propagation pathFast fadingElectromagnetic signals rapidly decline in a few dozens wavelength rangesDescription of Fast fading distributionRayleigh distributionnon line-of sight(NLOS) transmissionRician distributionline-of sight(LOS) transmission

Multi-Path Effectssending signal

Frequency off-set caused by the movement of mobile that is Doppler effectCharacteristics of Radio Propagation

RAKE Receiver can effectively overcome the multi-path interference, consequently improve the receiving performance.RAKE ReceiverThe multi-path signals contain some useful energy , therefore the UMTS receiver can combine these energy of multi-path signals to improve the received signal to noise ratio. RAKE receiver adopts several correlation detectors to receive the multi-path signals, and then combines the received signal energy.

RAKE Receivingd1d2tttd3transmittingReceivingRake combinationnoise

Multi-finger receiverTraditional receiverMulti-path signals are treated as interference.The receiving performance will decline because of the Multi-address Interference (MAI).Precondition of Multi-finger receiver Multi-finger receiver utilizes the Multi-path Effect.Multi-finger signals can be combined through relative processMulti-finger time delay is larger than 1 chip interval, which is 0.26us=>78m.

Multi-finger receiverreceivertransmittercodingdecodingDirect signalReflected signalDispersive time < 1 chip intervalMulti-finger receiver cant supply multi-finger diversitydecodingDirect signalReflected signaltransmitterreceiverDispersive time > 1 chip intervalMulti-finger receiver can supply multi-finger diversity, signal gain is improvedcoding

RAKE ReceivingreceiverSingle receivingSingle receivingSingle receivingsearchercalculatecombiningtts(t)s(t)signalRAKE Receiving overcomes multi-finger interference, improves receiving performance

Combination of Multi-fingersMaximal ratio combining (MRC)at each time delay phase shifting by adding Finger 1

Finger 2

Finger 3

Whats When UE is moving from the coverage area of one site to another, or the quality of service is declined by external interference during a service, the service must be handed over to an idle channel for sustaining the service. Handover is used to guarantee the continuity of service.Handover is a key technology for mobile networking.

Category of Handover Intra-RNC, inter-Node B Inter-RNCSoft handover (SHO) Same Node B, Inter-sectorSofter handover Intra-frequency Inter-frequency Inter-system (UMTS&GSM) Inter-mode (FDD&TDD)Hard handover (HHO)UMTS system support multiple handover technology

Handover DemonstrationHard HandoverSoft Handover

Soft Handover/Softer HandoverSoft HandoverSoft-Softer HandoverSofter Handover

Hard HandoverDuring the hard handover procedure, all the old radio links with the UE are abandoned before new ones are established, so there must be service interruption during the HHO.Hard handover may occur in the following main cases When the UE is handed over to another UTRAN carrier, or another technology mode.When soft handover is not permitted (if O&M constraint)Hard HandoverNode BSRNCRNC or BSCCNNode B or BTS

Soft/Softer HandoverThe soft/softer handover allows to migrate from one cell to another without service interruption or without deleting all old radio links.UE can connecte to more than one cell simultaneously and take benefit from the macro-diversity. Soft HandoverSofter HandoverCNCNIurThe two Node Bs may belong to the same RNCThe two Node Bs may belong to the Same RNCSoft HandoverSofter HandoverSRNCDRNCCNNode BSRNCCNSoft HandoverSofter HandoverNode BCN

UMTS General Handover TrilogyMeasurement ControlUTRAN demands the UE to start measurement through issuing a measurement control message.Handover decisionUTRAN makes the decision based on the measurement reports from UE. The implementation of handover decision is various for different vendors. It impacts on the system performance critically.Handover executionUTRAN and UE execute different handover procedure according to the handover command.

Handover Flows

General Procedure of Handover Control (I)MeasuringThe measurement objects are decided by RNC. Usually, either Ec/Io or RSCP (Received Signal Code Power) of P-CPICH channel is used for handover decision.ZTE RNC adopts Ec/Io measurement, because Ec/Io embodies both the received signal strength and the interference. The relation of Ec/Io and RSCP is shown as follows:Ec/Io RSCP/RSSIIn the above equationRSSIReceived Signal Strength Indicatoris measured within the bandwidth of associated channels

FilteringThe measurement results should be filtered before being reported. Measurement filtering can be regarded as a low pass filtering procedure. The following equation is applied for filtering.Fn=(1-a)Fn-1a*MnVariants definitionFnfiltered measurement resultFn-1last filtered measurement resultMnlatest Ec/Io or RSCP measurement result received from physical layer;a = 1/2(k/2), k means the Filter coefficient, which is included in the Measurement Control message. It is decided by the UTRAN.F0 is initialized by the first measurement result M1.General Procedure of Handover Control (II)

General Procedure of Handover Control (III)ReportingPeriod report triggered handoverBase on the filtered measurement resultEvent report triggered handoverBase on the event

Soft HandoverHard HandoverPeriodEventMeasurement result filtered in UEEvent decided in RNCHandover decided in RNCMeasurement result filtered in UE Event decided in UEHandover decided in RNC

General Procedure of Handover Control (IV) Handover algorithmAll the handover algorithms including soft handover, hard handover and so on are implemented on the event decision made according to the measurement reports. Events defined in 3GPP specificationsIntra-frequency events1A~1FInter-frequency events2A~2FInter-RAT events3A~3DNote: RAT is short for Radio Access Technology, e.g. UMTS&GSM

Concepts Related to Handover Active Set: A set of cells that have established radio links with a certain mobile station.User information is sent from all these cells.Monitored Set: A set of cells that are not in the active set but are monitored according to the list of adjacent cells assigned by the UTRAN. Detected Set:A set of cells that are neither in the active set nor in the monitor set.

Soft handover event

EventDescription1AQuality of target cell improves, entering a report range of relatively activating set quality1BQuality of target cell decreases, depart from a report range of relatively activating set quality1CThe quality of a non-activated set cell is better than that of a certain activated set cell1DBest cell generates change1EQuality of target cell improves, better than an absolute threshold1FQuality of target cell decreases, worse than an absolute threshold

An Example of SHO ProcedurePilot Ec/Io of cell 1timePilotEc/IoConnect to cell1 Event 1A Event 1C Event 1B add cell2replace cell1 with cell 3remove cell3Pilot Ec/Io of cell 2Pilot Ec/Io of cell 3ttt

RNS RelocationCore NetworkCore NetworkServing RNSTarget RNSServiing RNSTarget RNSIuIuIurRNSRadio Network Sub-systemRNS relocation can :Reduce the Iur traffic significantlyEnhance the system adaptability

Hard HandoverHard handover measurement is much more complex for UE than soft handover measurement.Inter-frequency hard handover requires UE to measure the signal of other frequencies.UMTS employs compressed mode technology to support inter-frequency measurement.

Purpose of Compressed ModeIn order to support inter-frequency and inter-RAT handover, UE is required to perform inter-frequency and Inter-RAT measurement periodically.The UE with one transceiver does not have the opportunity to perform inter-frequency measurement during the service period (especially the voice call) , because the transceiver is busy in transmitting and receiving the signals all the time.Compressed mode can provide idle slot based transmission time window, which can be used for inter-frequency measurement, for the UEs in connected state, e.g. CELL_DCH.

Compressed Mode Compressed Mode Transmission Diagram

1 frame10ms

10ms

Transmit gapsMaximum 7 slots = 4.7ms

Generation of Compressed Mode Frame PuncturingLower the symbol rate of physical channel when processing the rate matching procedure SF halvingEmploy half SF, e.g. employ SF64 to replace SF128 High layer schedulingDecrease the bit rate from up layer

Admission ControlThe admission control is employed to admit the access of incoming call. Its general principal is based on the availability and utilization of the system resources.If the system has enough resources such as load margin, code, and channel element etc. the admission control will accept the call and allocate resources to it.

Purpose of Admission ControlWhen user initiates a call , the admission control should implement admission or rejection for this service according to the resource situation.The admission control will sustain the system stability firstly and try the best to satisfy the new calling services QoS request, such as service rate, quality (SIR or BER), and delay etc. basing on the radio measurement. Admission control is the only access entry for the incoming services, its strategy will directly effect the cell capacity and stability, e.g. call loss rate, call drop rate.

Admission Control in UplinkItotal_old+I >Ithreshold The current RTWP (Received Total Wide Power) value of cell, which is reported by Node B AccessThresholdInterference capacityService priorityReserved capacity for handoverIown-cellIother-cellThe forecasted interference including the delta interference brought by the incoming service is calculated by the admission algorithm, and its result depends on the QoS and transmission propagation environment

Different ultimate user numbersDifferent interference threshold under different ultimate user number conditionsDifferent ultimate throughputs

Ultimate Situation for different service rateAdmission Control in Uplink

Quantity of Subscriber

Quantity of Subscriber-- The Total Bandwidth Received by Node B

The Total Bandwidth Power Received by Node B (dBm)

Throughput

Throughput -- The Total Bandwidth Received by Node B


Admission Control in DownlinkPtotal_old+P>=Pthreshold Access ThresholdThe forecasted TCP value including delta power required for the incoming service is calculated by the admission algorithm, and its result depends on the QoS and transmission propagation environment.The current TCP value of cell, which is reported by Node BTransmitted Carrier Power*PmaxMax TCP of cellService priorityReserved capacity for handover

Redlow speed serviceBluehigh speed serviceThe above figure illustrates the relation between ultimate user number corresponds to different service rate and distance under equidistant distribution conditionAdmission Control in Downlink


The Total Transmission Power (dBm)

The service can be either one-direction or bi-direction type. For bi-direction service, it is admitted only after both uplink and downlink are admitted. Admission control is the only access entry for the incoming services, its strategy will directly effect the cell capacity and stability, e.g. call loss rate, call drop rate.Admission Control Analysis

Load controlThe purpose of load control is to keep the system load under a pre-planned threshold through several means of decreasing it, so as to improve the system stability.The speed and position changing of UE may worsen the wireless environment.Increased transmitted power will increase the system load.Purpose of Load Control

Overload control

Serious overload threshold

Overload recovery threshold

Admission control threshold

Common overload threshold

Cell load

Overload control

Normal state

Common overload state

Serious overload state

4. The load is smaller than the overload recovery threshold

3. The load exceeds the serious overload threshold

6. The load is smaller than the serious overload threshold. but greater than the common overload threshold

5. The load exceeds the serious overload threshold.

1. The load exceeds the common overload threshold

2. The load is smaller than the overload recovery threshold

Load Control FlowsStartDecisionLight loadedOver loadedNormal loaded1.Handover in andaccess are forbidden2. TCP increase isforbidden3. RAB service ratedegrade4. Handover out5. Release call (call drop)1. Handover in and access are allowed2. Transmitted code power (TCP) increase is allowed3. RAB service rate upgrade is allowed1. Handover in and access are allowed2. TCP increase is allowed

Load Control in UplinkTriggersRTWP (Received Total Wide-band Power) value from measurement report exceeds the uplink overload threshold;Admission control is triggered when rejecting the access of services with lower priority due to insufficient load capacity in uplink.Methods for decreasing loadDecrease the target Eb/No of service in uplink;Decrease the rate of none real time data service;Handover to GSM system;Decrease the rate of real time service, e.g. voice call;Release calls.Methods for increasing loadIncrease the service rate.

Load Control in Downlink TriggersTCP (Transmitted Carrier Power) value from measurement report exceeds the downlink overload threshold;Admission control is triggered when rejecting the access of services with lower priority due to insufficient load capacity in downlink. Methods for decreasing loadDecrease the downlink target Eb/No of service in downlink;Decrease the rate of none real time data service;Handover to coverage-shared light loaded carrier;Handover to GSM system;Decrease the rate of real time service, e.g. voice call;Release calls. Methods for increasing loadIncrease the service rate.

Cell breathing is one of the means for load controlThe purpose of cell breathing is to share the load of hot-spot cell with the light loaded neighbor cells, therefore to improve the utilization of system capacity.Cell Breathing Effect

Example for load controlCell Breathing EffectWith the increase of activated terminals and the increase of high speed services, interference will increase.The cell coverage area will shrink.Coverage blind spot occursDrop of call will happen at the edge of cellCoverage and capacity are interrelated

UMTS Code ResourceChannelized Code (OVSF code) Uplink Channelized CodeDownlink Channelized CodeScrambling CodeUplink Scrambling CodeDownlink Scrambling Code

Function of OVSF CodeOC1, OC2OC3, OC4OC5, OC6, OC7OC1 , OC2, OC3OC1, OC2OC1, OC2, OC3, OC4Uplink: distinguish different radio channels from the same UE.Downlink: distinguish different radio channels from the same NodeB.

Function of Scrambling codeDownlink: distinguish different CellsUplink: distinguish different UEs

PN3PN4PN5PN6PN1PN1Cell Site 1 transmits using PN code 1PN2PN2Cell Site 2 transmits using PN code 2

Why Code Resource Planning?The OVSF (Orthogonal Variable Spreading Factor) code tree is a scarce resource and only one code tree can be used in each cell. In order to make full use of the capacity, and support as many connections as possible, it is important to plan and control the usage of channel code resource.Downlink scrambling code allocation should be planned to avoid the interference between neighboring cells.The uplink scrambling codes are sufficient, but RNC should plan the codes to use for avoiding allocating same code to different users in inter-RNC handover scenario.

Code Resource PlanningThe uplink and downlink scrambling code can be planned easily by computer.The uplink channelized code does not need planning, for every UE can use the whole code tree alone.Therefore, only the downlink channelized code is planned with certain algorithm in RNC.Each cell has one primary scrambling code, which correlates with a channel code tree. All the users under this cell share this single code tree, so the OVSF code resource is very limited.The downlink channelized code tree is a typical binary tree with each layer corresponds to a certain SF ranging from SF4 to SF512.

Generation of Channelized Code

SF = 1

SF = 2

SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

OVSF Code Tree

Channelized Code CharactersCode allocation restriction The code to be allocated must fulfill the condition that its ancestor nodes including from father node to root node and offspring nodes in the sub tree are not allocated; Code allocation side effectThe allocated node will block its ancestor nodes and offspring nodes, thus the blocked nodes will not be available for allocation until being unblocked .

Strategy of Channelized Code AllocationFull utilizationThe fewer the blocked codes, the higher code tree utilization rate. Low ComplexityShort code first.Allocate codes for common channels and physical shared channels prior to dedicated channels.Guarantee the code allocation for common physical channels.Apply certain optimized strategy to allocate codes for downlink dedicated physical channels.

An Example of Code Allocation 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31SF = 4SF = 8SF = 16SF = 32SF = 4SF = 8SF = 16SF = 32Red spots represent the codes that have been allocatedGreen spots represent the codes that are blocked by the allocated offspring codesBlue spots represent the codes that are blocked by the allocated ancestor codes;Black spots represent the codes that to be allocated;Choose one code from three candidates

Planning of downlink scrambling codePN1PN2PN3PN7PN6PN4PN5PN7PN6PN4PN5PN1PN2PN3PN1PN2PN3PN7PN6PN4PN5PN1PN2PN3PN7PN6PN4PN5PN1PN2PN3PN7PN6PN4PN5PN1PN2PN3PN7PN6PN4PN5

Capacity of UMTSUL capacity is restrained by interferenceDL capacity is restrained by the power of NodeB

Power RisingPower rising occurs because of the Multiple Access Interference (MAI) resulting from the non-orthogonal code channels.

UMTS network Meeting Room

Code channel transmit talk with dialectsChannel power voice tonePromised channel quality listen clearlyChannel power rise voice tone risePower climb voice climbCollapse over the range can not hear each other

Power Rising


Quantity of Subscriber-- The Total Bandwidth Received by Node B


Capacity of UMTS SystemUnder the circumstance of single services:

===

Capacity of UMTS System...XYZ++Under the circumstance of mixed services

UMTS Capacity FeaturesUMTS capacity featureUMTS capacity is Soft Capacity.The Concept of Soft CapacityThe system capacity and communication quality are interconvertible.Different services have different capacity.Different proportion of services have different capacity for mixed services.The capacity is also restricted to the allocation of code resource.

Different combination of service has different capacityDifferent service has different capacityConcept of Soft CapacitySystem capacity and QoS can be interconverted

QualityCoverageCapacityAll the key technologies adopted are used to try to achieve the optimal balance of the three factorsCrucial Factors for UMTS Network (CQC)

Coverage and CapacityUMTS performance is determined by such factors asNumber of usersTransmission rateMoving speedWireless environmentindoorsOutdoorsThe radius of cell depends on such factors as: Local radio conditions (local interference) Traffic in neighbouring cells (remote interference)Cell Radius decrease according to the Increase of user number

Coverage/capacity VS Data RateHigher data rate needs higher powerHigh data rate transmission is only available nearby the station>12.2 kbps>64 kbps>384 kbps>144 kbpsCoverage decreaseSubscriber num increase

DL/UL: Add carrier six sectorsUL Tower Mounted Amplifier (TMA) 4 Rx Div OTSRDL transmission diversity (Tx Div) high power amplifierAdd basestation last choiceOptimization methodsTo overcome Cell Breathing Effect caused by increased traffic and meet different requirements for capacity and coverage in different environment, following solutions can be applied:

Factors affects UMTS Capacity

FactorsImpact on UMTS capacityRAKE ReceiverThe advanced receiving and baseband processing technology is introduced to overcome the fast fadingPower ControlReducing interference, saving power and Increasing capacityHandover ControlImpacting the capacity through applying different proportion and algorithm of soft handover Admission ControlAdmitting a connection base on the load and the admission threshold of planned capacity Load ControlMonitoring system load and adjusting the ongoing services to avoid overloadOVSF Code The Allocation of codes impacts the maximum number of simultaneous connections.Wireless EnvironmentWireless environment such as interferences, UE position and mobility etc. can influent the cell capacity

Multipath Propagationdelay spreadangle spreadDopplerRayleighRician

Rayleigh Rician

Radio wave propagation on radio channels is characterized by much reflection, diffraction and fading of signal energy. These are due to space obstacles, such as buildings and hills, which result in multipath propagation, as shown in Fig. 1.22 Therere Two effects of multipath propagation :1.The code chip energies arrive at the receiver at distinguishable moments. The energies received constitute a multipath delay distribution, as shown in Fig. 1.22. When the chip rate is 3.84Mcps, the duration of a code chip is 0.26s. If the time difference of the multipath components is at least 0.26s, the WCDMA receiver can distinguish these multipath components and combine them into multipath diversity. 2.At a given delay location, there are usually many radio signal transmission paths with nearly the same distance. Therefore, even when the receiver moves a very short distance, there will be signal cancellation, also known as fast fading effect. WCDMA has the following solutions to counteract fading: 1.Use the Rake receiver to gather those delayed, distributed energies by multiple Rake finger peaks (related receiver). These finger peaks are allocated to these delay locations with significant incoming energies. 2.Use rapid power control to alleviate signal power fading. 3.Use convolutional coding, interleaving, and retransmission protocol to add redundancy and time diversity, to help the receiver restore subscriber data bits from fading. RayleighRician

MS(UE)IMT-20002GHz15cm40dB1!

CDMARAKERAKERAKEMRAKE

Radio wave propagation on radio channels is characterized by much reflection, diffraction and fading of signal energy. These are due to space obstacles, such as buildings and hills, which result in multipath propagation, as shown in Fig. 1.22 Therere Two effects of multipath propagation :1.The code chip energies arrive at the receiver at distinguishable moments. The energies received constitute a multipath delay distribution, as shown in Fig. 1.22. When the chip rate is 3.84Mcps, the duration of a code chip is 0.26s. If the time difference of the multipath components is at least 0.26s, the WCDMA receiver can distinguish these multipath components and combine them into multipath diversity. 2.At a given delay location, there are usually many radio signal transmission paths with nearly the same distance. Therefore, even when the receiver moves a very short distance, there will be signal cancellation, also known as fast fading effect. WCDMA has the following solutions to counteract fading: 1.Use the Rake receiver to gather those delayed, distributed energies by multiple Rake finger peaks (related receiver). These finger peaks are allocated to these delay locations with significant incoming energies. 2.Use rapid power control to alleviate signal power fading. 3.Use convolutional coding, interleaving, and retransmission protocol to add redundancy and time diversity, to help the receiver restore subscriber data bits from fading.

Rake Correlative: disrelated : Dispersive:CDMARAKERAKECDMARAKERAKEDPCCH4IS-95 AW-CDMA3W-CDMAW-CDMA8RAKE75%RAKESearcher(correlation)FingerNodeBUERAKEDPCCH4 UENodeB8RAKE75%RAKEThis is typically done with a single matched filter (or any similar device) matched to the primary synchronization code The slot timing of the cell can be obtained by detecting peaks in the matched filter output.

Intra-freq Diversity mode is different, must be hard handoverMSCmsc

GoS=Pb+10Pd PdPb

Hard handover indicates that contacts are set up between a UE and a new cell after the UEs radio link with the previous cell is broken. There is only one radio link at any moment during hard handover.Soft/Softer HO applies to dedicated physical channels and not to shared or common transport channelson the same carrier frequencySoft handover indicates a handover between two cells with the same carrier frequency. In this case, a UE will not stop the contact with the previous cell when set up contacts with a new cell. In the soft handover status, radio links can be set up between a UE and more than one cell.

*RSSI(Received Signal Strength Indicator) the wide-band received power within the relevant channel bandwidth. Measurement shall be performed on a UTRAN downlink carrier. The reference point for the RSSI shall be the antenna connector of the UE.

RSCP(Received Signal Code Power) the received power on one code measured on the Primary CPICH. The reference point for the RSCP shall be the antenna connector of the UE. If Tx diversity is applied on the Primary CPICH the received code power from each antenna shall be separately measured and summed together in [W] to a total received code power on the Primary CPICH.

Ec/N0 : The received energy per chip divided by the power density in the band. The Ec/No is identical to RSCP/RSSI. Measurement shall be performed on the Primary CPICH. The reference point for the CPICH Ec/No shall be the antenna connector of the UE. If Tx diversity is applied on the Primary CPICH the received energy per chip (Ec) from each antenna shall be separately measured and summed together in [Ws] to a total received chip energy per chip on the Primary CPICH, before calculating the Ec/No.

*1X 1ACPICH 1BCPICH 1CCPICHCPICH 1D 1ECPICH 1FCPICH 2X 2a 2b 2c 2d 2e 2f 3X 3aUTRAN 3b 3c 3d

*1A~1F 2A~2F 3A~3D1A1B1CActive SetActive Set1D1E1F

**WCDMAUEGSM1800UE1900MHz1800MHzGSM

*RTTWCDMABPSKQPSK1bite/Hz2bites/Hz5MHz3.84MHz10Mbps3G2G* 35%

*1.2.QoS1.2.

*1. 2. QoSSIR ERRORUE>Noise rise>>

Load balance: inter-handover, intra-blind handoverCDMAOVSF-OVSFCDMAC4,1C8,1C8,3C4,1

WCDMA++

RAKE;

OTSROmni Transmission Sectorized ReceiveBSC OTSRTEUTransmission enhanced unit

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WO BT1002 E01 1 UMTS Key Technologies

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