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Radio Bearer Control & DRX/DTX Management

LTEPAR Pilot Düsseldorf CW 22 2010

LTE Radio Parameters RL10

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Radio Bearer Control & DRX/DTX Management

• After completing this learning element, the participant should be able to:

• State different connection / activity states of an LTE UE in comparison to UMTS

• Identify performance related aspects of the feature

• Describe different transitions and relevant triggers as e.g. activity/inactivity detection

• State the possible configuration choices for DRX/DTX in RL09

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States in UTRAN, GERAN, E-UTRA

• The 3 transitions supported by the RL 09/10 LTE Inter working features

Handover

CELL_PCH

URA_PCH

CELL_DCH

UTRA_Idle

E-UTRA RRC_CONNECTED

E-UTRA RRC_IDLE

GSM_Idle/GPRS Packet_Idle

GPRS Packet transfer mode

GSM_Connected

Handover

Reselection Reselection

Reselection

Connection establishment/release

Connection establishment/release

Connection establishment/release

CCO, Reselection

CCO with optional

NACC

CELL_FACH

CCO, Reselection

Supported by feature

RL20

3G LTE GSM

Supported RL10

Supported by feature

RL10

Supported by feature

RL10

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Definition of main EPS Mobility Management states• EMM-DEREGISTERED

– The UE is not reachable by a MME.

– UE context can still be stored in the UE and MME

• EMM-REGISTERED– UE enters to EMM-Registered with Attach or Tracking Area Update procedure

– The UE location is known with accuracy of the tracking area list

– UE has at least one active PDN connection

– After Detach procedure the state is changed to EMM-DEREGISTERED

UE state handling :Mobility Management States

Attach accept

DetachAttach rejectTAU Reject

All Bearer Deactivated

EMM-DEREGISTERED EMM-REGISTERED

EMM states in UE

Attach acceptTAU Accept

DetachAttach rejectTAU Reject

All Bearer Deactivated

EMM-DEREGISTERED EMM-REGISTERED

EMM states in MME

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Definition of EPS Connection Management states• ECM-IDLE

– UE is in ECM-IDLE state when no NAS signalling connection between UE and network exists.

– In the EMM-REGISTERED and ECM-IDLE state, the UE shall perform: Tracking Area Update Periodic Tracking Area Update Service Request Answer to paging from MME with Service Request

– UE and MME enter the ECM-CONNECTED state when signaling connection is established.

• ECM-CONNECTED– UE location is known in the MME with an accuracy of a serving eNodeB.

– For a UE in the ECM-CONNECTED state, there exists a signalling connection between the UE and the MME.

– The S1 release procedure changes the state at both UE and MME from ECM-CONNECTED to ECM-IDLE.

UE state handling :Mobility Management States

RRC Established

RRC Released

EMM-IDLE EMM-CONNECTED

EMC states in UE

S1 Established

S1 Released

EMM-IDLE EMM-CONNECTED

EMM states in MME

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DRX/DTX – General Motivation is the Challenge –> Battery Capacity Increases only Slowly Compared to Moore’s Law

Joseph A. Paradiso Massachusetts Institute of Technology Media Laboratory, Thad Starner Georgia Institute of Technology, GVU Center “Energy Scavenging for Mobile and Wireless Electronics”, Pervasive Computing, IEEE Volume 4, Issue 1, Jan.-March 2005 Page(s):18 - 27 Digital Object Identifier 10.1109/MPRV.2005.9

CPU by Moore’s law = double

every 18 months

Battery capacity double every 12

years

Battery savings

are a must and

are proportional to

active/inactive ratio

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Normal eNB initiated Transition to ECM-IDLE (e.g. due to user inactivity)

eNBUE MME S-GW

S1AP: UE Context Release Command

S1AP: UE Context Release CompleteRRC: RRC Connection Release

Release all UE related resources,

remove UE context

Set UE to RRC-IDLE

Set UE to ECM-IDLE

Detect user inactivityor other eNB trigger

S1AP: UE Context Release Request

S11 interaction to inform S-GWabout connection release

UE inRRC-CONNECTED

L2 ACK

Main impact –> UE- consume less battery power in idle mode and there

Is less active UEs which network have to handle. Fast going to inactivity

Has drawback of longer connection setup time (transition idle<->connected)

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UE_INACTIVITY DETECTION/MEASUREMENT

T_INACTIVE

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In-Actvity Timer

Parameter, abbreviated Name

Description Access

RWR

Parameter Type

O: Operator configurableV: Vendor configurable

Range, Step size / Granularity, Units, Special Value

Default Value

Parameter Scope(PLMN, RAN, Nb, Cell, Chl),Proposed MOC

Reference e.g. 3GPP name or other

Multiplicity

(mand) (mand) (mand) (mand) (mand) (opt) (mand) (opt) (mand)

T_INACTIVE Time period for UE inactivity detection; the same value is used for UL and DL direction.

RW O 10..65535step size: 1unit: seconds0: disabled

300 Cell NA 1

INPUT

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DTX/DRX, Discontinuous Reception

• Discontinuous reception/transmission means UE transceiver is switched off for some predefined time periods. This save power consumption on one side but might consequences in longer call setup time and/or lower user throughput achievable.

• What are DRX/DTX options?

• In Idle mode for Paging – this option means UE is listening paging messages in predefined time opportunities only and sleeping all other time. Supported in RL10.

• DRX/DTX in connected mode – UE is switched off for predefined time interval. Not supported for RL10.

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Discontinuous Reception for paging (TS 36.304)

The UE may use Discontinuous Reception (DRX) in idle mode in order to reduce power consumption. One Paging Occasion (PO) is a subframe where there may be P-RNTI transmitted on PDCCH addressing the paging message. One Paging Frame (PF) is one Radio Frame, which may contain one or multiple Paging Occasion(s). When DRX is used the UE needs only to monitor one PO per DRX cycle.

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Paging Related DRX/DTX Parameters in RL09

• defaultPagingCycle– The Default Paging Cycle defines the cell specific paging DRX cycle duration. It

also determines the maximum paging DRX duration applicable in the cell. Referred to as ' T ' in TS 36.304. Value 32rf corresponds to 32 radio frames, 64rf corresponds to 64 radio frames and so on (possible vales to set are 32rf (0), 64rf (1), 128rf (2), 256rf (3), default 128rf).

– One rf means radio frame = 10ms in time– Increasing parameter value save battery capacity in idle mode as listening to

paging is less frequent, but mean call setup time is getting longer due to longer average paging time.

• pagingNb– Paging nB defines the number of possible paging occasions per radio frame,

i.e. the density of paging occasions. This parameter is used to calculate the number of paging occasions within one paging DRX duration, which in turn is used to calculate the paging occasion. (possible values to set are RL09 are oneT (2), halfT (3), quarterT (4), oneEighthT (5), oneSixteenthT (6), oneThirtySecondT (means 1/32 as per TR36.304) (7), default is quarterT).

– Side values existing in RL10 3GPP defines also possible values fourT and twoT which are not implemented in RL10. Reason – more than 1 paging occasion per radio frame seems unrealistic.

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Occasion of Paging Messages

• The cell specific DRX cycle length Tsib is broadcasted by System Information (PCCH-Config parameter defaultPagingCycle (in number of radio frames) - defined by O&M).

• The UE specific DRX cycle length Tue might be received from core network from S1AP Paging Message as Optional IE.

• The used paging DRX Cycle T (in number of radio frames) is set to:T=MIN(Tue,Tsib). (Referred to as ' T ' in 3GPP TS 36.304)

• The relationship “paging occasions - radio frame” is given by the parameter pagingNb provided in System Information (PCCH-Config parameter pagingNb). nB shall be interpreted as a calculation formula (how to derive paging occasions from T). For better understanding, the result of the calculation formula nB will be written as nB(T) in this section.Example: quarterT denotes nB(T)= 1/4*T (there is one paging occasion in every 4th radio frame).

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Occasion of Paging Messages – Explain of Variables as per SFS (UE Behavior)

• Paging capacity is not a limiting factor as the Paging Channel (PCH) is mapped dynamically on the PDSCH.

• The factor (T div N) gives the distance of radio frames with paging occasions. The calculation of the factor (T div N) is 2(i-k).

• The factor (UE_ID mod N) gives a relative index of a radio frame with paging occasions inside a Paging DRX cycle. The calculation of factor (UE_ID mod N) is a simple mask operation for the last k bits.

• The product (T div N)*(UE_ID mod N) gives the relative position of a radio frame with paging occasions relative to the start of a Paging_DRX cycle.

• (SFN mod T) provides a SFN numbering relative to the start of a Paging-DRX cycle. The calculation of factor (SFN mod T) is a simple mask operation for the last i bits.

• Example of paging with impact of mean paging time: Microsoft Excel Worksheet

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Example (as per UE Behaviour SFS, simplified, note the Tue is smaller than allowed by 3GPP):

Cell paging DRX Tsib = 32,nB(T)=halfT,UE paging DRX Tue = 8*,T = MIN(Tue,Tsib) = MIN(8,32) = 8,nB(T) = half(8) = 4,N = MIN(T,nB(T)) = MIN(8,4) = 4,Ns = MAX(1, nB(T)/T) = MAX(1, 4 / 8) = MAX(1,0)=1,UE_ID = 3, assumption for this example (it could be any number)T div N = 8 div 4 = 2,UE_ID mod 4 = 3 (assumption for this example),(T div N)*(UE_ID mod 4) = 2*3 = 6,Let next reachable SFN = 501; therefore (SFN mod T) = 5; therefore SFN for paging

is 501+(6-5)=502.

Simplified case as the Tue is smaller than allowed by 3GPP.

SFN

T div N

T (Paging DRX)Paging OccasionPO

[SFN=x*T] [SFN=(x+1)*T]

(T div N)*(UE_ID mod N)