PowerPoint-Prsentation

1LTE INITIAL ACCESS Power Management andMobility Management in LTE

2Overview

Power Conservation in UEHigh Power: Connected Mode when UE has both its transmitter and receiver always on.Low Power: Idle Mode when UE turns off it transmitter. It turns on its receiver periodicallyTransition between the statesMobility in Idle ModeCell Selection and Re-selectionTracking Area UpdateMobility in Connected Mode: Handovers3Power Management in LTEHigh Power ModeConnected Mode

Network controls UEs movement through handover.Location of the UE is known to the network at granularity of a cell.Mobility

UEs radio is in ON state.UE is constantly communicating with the network.Low Power ModeIdle ModeNetwork does not control UEs movement. UE autonomously selects new cell as it moves.Network only knows the location of the UE to the granularity of a tracking-area.

Tracking Area 24Mobility

UEs radio is in low-power state. UEs transmitter is off.UE only listens periodically to control channel. If UE enters a new location area, based on hearing information from base-station, the UE informs the network of the new tracking area it has entered.

UE is like a dog without a leash enclosed in an electronic fenceTracking Area 1UE is like a dog on a leash Activity State ManagementA UE in LTE can be in two states:Connected Mode: The UE is transmitting and receiving data from the network.Idle Mode: The UE is only monitoring the paging and broadcast channel.After the UE stops transmitting/receiving data/signal for a period of time, called inactivity period, the network moves the UEs state to idle-stateData/SignalactivityYes

No

TimeUEsStateConnected

Idle

TimeConnected -> Idle Inacitivity TimerConnected -> Idle Inacitivity Timer5Irfan Ali 5UEs Activity States for AS and NASASNASEMM-IDLEEMM-ConnectedRRC connectionEstablishedRRC connection ReleasedRRC-IDLERRC-ConnectedRRC connection EstablishedRRC connection ReleasedEMM-IDLEEMM-ConnectedNAS connection EstablishedNAS connection ReleasedS1-MMEUEeNBMMEEMM NAS AS RRCEnhanced Mobility Management Non Access StratumAccess StratumRadio Resource ControlRRC StateRRC-ConnectedRRC-IdleEMM StateMME Request eNB to setup data radio bearersEMM-ConnectedEMM-Idle

TimeEventsTimeTimeMME Request S1 connectionto be torn downeNB tears down RRC ConnectionUE has a packet to sendUE sets up RRC ConnectioneNB sets up data radio bearersUEs State MachineRRC idle:- Memperoleh sistem informasi dari Broadcast Control Channel- Menggunakan DRX untuk memonitor paging message- Cell reselection di bawah kontrol UERRC Connected:- Transfer data dari/ke UE- Proses Handover dan Cell Reselection dikontrol oleh network- Memperoleh sistem informasi dari Broadcast Control ChannelReferensi: 3GPP TS 36.331, lteworld.org, LTE in Bullets

RRC message digunakan untuk signaling antara UE dan NodeB sedangkan NAS antara UE dan MME.6Key Points about UEs AS (RRC) and NAS State MachinesThe RRC state machine transitions are very clearWhen the RRC Connection is setup, the UE transitions from RRC-Idle to RRC-Connected, and vice-versaThe NAS state machine transitions are based on RRC eventsThe NAS specification (TS 24.301), does not have EMM-Connected and EMM-Idle shown in a state-transition diagram. TS 24.301 has more detailed NAS state machine diagrams, with states such as EMM- Registered, EMM-Deregistered, etc. The following two statements buried deep in 24.301 provide details of state-transitions:In S1 mode, when the RRC connection has been released, the UE shall enter EMM- IDLE mode and consider the NAS signalling connection releasedIn S1 mode, when the RRC connection has been established successfully, the UE shall enter EMM-CONNECTED mode and consider the NAS signalling connection established.Details of NAS specifications for MME are not explicitly provided in TS24.301. One needs to infer these from TS 24.301, which is written from a UE implementation point of view.7Activity States of UEEMM-IDLERRC connection establishedRRC connection releasedEMM-IDLEEMM-CONNECTEDNASConnectionestablishedNAS Connection releasedUEMMEIdle ModeUE monitors paging channels periodically (DRX cycle) and some System Information channelNo NAS signalling connection between UE and MMEUE (independently) performs cell selection/re-selection based on broadcast informationNo UE information in the eNBLocation of UE is known to the MME at granularity of Tracking Area.UE performs TAU when UE enters a new TAI or when the periodic TAU timer expires.UE enters connected mode when RRC signaling connection is established.For MME there is no clear indication when the UEs state transitions to EMM-Connected. Typically this happens when the S1-MME connection is established for the UE.Connect ModeUE monitors System Information channel and control channels associated with shared data channels.NAS signalling connection between UE and MMENetwork (eNB) controls UEs movement through handover.UE context in the eNBLocation of the UE is known to the MME at granularity of eNB.UE performs TAU when UE enters a new TAI broadcastUE enters idle mode when RRC connection is released.For MME there is no clear indication when the UEs state transitions to EMM-Idle. Typically this happens when the S1-MME connection is released for the UE.EMM NAS RRCEnhanced Mobility Management Non Access StratumRadio Resource ControlBoth the UE and MME keep track of the state of the UEEMM-CONNECTEDState in Network for Connected and Idle modeUEMMEeNBSGWPGWNAS(logical)S1-MMES1-uS11S5DRBSRBUEMMEeNBSGWPGWS11S5No UEContextUE ContextNo S1-UtunnelConnected ModeIdle ModeDRB SRB9Data Radio Bearer Signaling Radio BearerTransition from Connected to Idle State S1 Release ProcedureSGWHSSPGWUEeNBMMESRB-0 SRB-1 SRB-2Data Radio Bearer-10GTP-U-10 TunnelS1-MMEGTPU-10 TunnelGTPC TunnelGTPC TunnelUE reamains inactive for sometimeS1 UE ContextRelease RequestEMM-ConnectedGTPCRelease Access Bearer Resp. (IMSI, TEIDs)Release Access Bearer Req. (IMSI, TEIDs, )S1 UE ContextRelease CommandDL-SCH:DCH SRB1RRC Connection ReleaseS1 UE Context Release CompleteEMM-IdleRRC-IdleEMM-IdleNo UEContext in eNBGTPC-1 Tunnel GTP-U-10 TunnelGTPC TunnelSGW does not have DL S1-U TEIDs for UERRC-IdleIrfan Ali10Packet arrives at Serving GW for idle UE: Where to page the UE?10Concept of Tracking Area-1Tracking Area consists of a set of eNBs.The concept of tracking area is introduced to reduce the amount of location reporting (Tracking Area Update TAU) signaling that a UE does when in idle- stateThe UE only signals to the network (MME) when the UE enters a TA to which it is not admitted.The MME knows the location of the UE to the granularity of TAs.Tracking areas are non-overlapping in LTE.The identity of each tracking area is called Tracking Area Identity (TAI).Each cell in a eNB can belong to only one TAI.Each cell advertises in broadcast message the TAI to which it belongs.The MME tells the UE which Tracking areas the UE is registered in.This is done in EMM-Connected mode.TA-112TA-2TA-3TA-4TA-5TA-6TA-7

Concept of Tracking Area-2A UE in LTE can be admitted to multiple tracking areas. The list of tracking areas to which the UE is admitted is called the tracking area list (TAI List) is provided to the UE.When a UE is idle and the MME needs to locate the UE, the MME pages the UEs in the set of eNB which belong to the TAI that the UE is registered in.Larger the tracking area, less frequent will be the UEs need to signal to the network; however larger the number of eNBs that the UE will need to be paged in.TA-1TA-2TA-3TA-4TA-5TA-6TA-7UE-1 is admitted to TAI-1UE-2 is admitted to {TAI-2, TAI-4}Perimeter-crossing where UE-2 performsTAUArea to page UE-2Area to page UE-1Perimeter-crossings where UE-1 performs TAU14Tracking Area Identity (TAI)WorldUSTurkeyIndiaTurkcellVodafoneAveaIzmirIstanbulAntalyaMCCMCCMNC

Uniquely identifies an operatorMCC: Mobile Country Code3 digits2-3 digitsMNC: Mobile Network Code2 OctetsTAC: Tracking Area Code310286404010203TAI: Tracking Area Identifier15Source for MCC and MNC codes: www.wikipedia.org1-400401-20003000-3500MCCMNCTACIdle-mode: When to page the UE?16In the next few set of slides we figure out when the UE turns on its receiver to figure out if the network is paging the UE.DL Frame Structure Type 1 (FDD)1 subframe = 1ms10 subframes make up Radio FrameEach subframe consists of 14 symbolsDL control signalling is in the first 1-3 symbolsThe rest of the symbols (11-13) are used for data and dedicated control channels.#0#1 One Radio Frame (10 ms)Sub-frame (1 ms)CCH 1RB 2CCH 2CCH 3CCH 4RB 0RB 1RB n-1...CCH 1 RB 2CCH 2CCH 3CCH 4RB 0RB 1RB n-1...TimeFrequencyIndication of page message for UE will be contained in the Common Control Channel (CCH)Pages may only be present in the subframe {0, 4, 5, 9}CCH RB17Common Control Channel Resource Block#9RB 0RB 1CCH 1RB 2...CCH 2CCH 3CCH 4RB n-116UEs DRX cycle in idle mode: Paging DRXThe UEs paging DRX cycle period is one of the following:{32, 64, 128, 256} frames (each frame is 10 msec), i.e{0.32, 0.64,1.28, 2.56} seconds

The UE determines its idle-mode DRX paging cycle eitherFrom the information in System Information Block (SIB)Or is provided to the UE via dedicated signal before UE goes idle.

Not all radio frames contain page messages.Paging Occasion (PO) is a subframe that contains paging messagePaging Frame (PF) is a radio frame that contains one or more paging occasions.

The UE needs to monitor only one paging occasion per DRX cycle.Changes in the system information are indicated by the network using a Paging message.Hence UE only monitors PDCCH.If there is a page message, the ID in the PDCCH is P-RNTI. All UEs share the same P- RNTI (FFFE).Once the UE finds PRNTI, it looks at the appropriate Resource Block in the PDSCH pointed to by the PDCCH message. If it finds its P-TMSI in the PDSCH, then page is destined for the UE.When the Paging message indicates system information changes then UE shall re- acquire all system information.PDCCH DRXP-RNTI S-TMSIPhysical Downlink Common Control Channel Discontinuous ReceptionPaging Radio Network Temporary Identity S Temporary Mobile Service Identity17Low Power (Idle Mode)UEs radio is in low-power state. UEs transmitter is off.UE listens periodically to control channel.To receive pages from the network.DRX CycleON DurationUE MontiorsPDCCH

UEs ReceiverDRX SleepIrfan Ali18Formula to determine which radio frame number (SFN) and which subframe within the SFN for UE to monitor for page messageSFN mod T = (T/N) X (UE_ID mod N) i_s = floor(UE_ID/N) mod NsT = min (Tc, Tue)N = min (T, number of paging subframes per frame X T) Ns = max (1, number of paging subframes per frame(Nf) )where,Tc Tue NUE_IDi_s N_fcell specific paging cycle {32,64,128,256} radio frames UE specific paging cycle {32,64,128,256} radio framesnumber of paging frames within the paging cycle of the UE IMSI mod 1024index to a table containing the subframes with a radio frame used for paging number of paging subframes in a radio frame that is used for paging.{4, 2, 1, 1/2, 1/4, 1/8, 1/16,1/32}SFNSystem Frame NumberTable to determine the subframe within a radio frame that is used for pagingSource: 36.304 Section 7.1NsPO when i_s=0PO when i_s=1PO when i_s=2PO when i_s=319N/AN/AN/A249N/AN/A40459Irfan Ali19Transition from Idle to Active: Network Triggered Part 1 of 1SGWHSSeNBUEPGWInternMMERRC-IdleGTPC-1 Tunnel GTP-U-10 TunnelGTPC TunnelSGW does not have DL S1-U TEIDs for UE.EMM-IdleGTPCDownlink Data Nofic. AckDownlink Data Notificatione eNBNBS1AP Page (S- TMSI)DL-SCH: Common CC: SRB0

RRC Paging (S-TIMSI)UE Trigerred Service Request ProcedureIP PacketEIMrfMa-CnoAnnleicted20Transition from Idle to Active: UE Triggered(1 of 2)DL-SCH: Common CCRandom Access PreambleRACHRandom Access PreambleUL-SCH: SRB0RRC Connection RequestDL-SCH: Common CC: SRB0RRC Connection SetupUL-SCH: SRB1RRC Connection CompleteNAS MSGSGWHSSeNBUEPGWInternMMERandom AccessProcedureRRC Setup ProcedureRRC-IdleRRC-ConnectedUE needs to send dataGTPC TunnelGTPC-1 Tunnel GTP-U-10 TunnelSGW does not have DL S1-U TEIDs for UE.EMM-IdleIrfan Ali 21Transition from Idle to Active UE Triggered (2 of 2)SGWeNBUEPGWInternetMMEInitial UE MessageNAS MSG: Service Request, GUTI, UE Network CapabilityMME looks up EMM Context based on GUTIInitial Context Setup Request(UE Context Info: UE SecurityCapability, KeNBDL-SCH:CCH SRB1RRC Security Mode Command, AS AlgorithmUL-SCH: SRB1RRC Security Mode Complete

AS Security

DL-SCH:CCH SRB1RRC Connection ReconfigUL-SCH: SRB1Initial Context SetupCompleteSRB-2Data Radio Bearer-10S1-MMEGTPU-10 TunnelGTPC TunnelRRC Reconfig CompleteSRB-0 SRB-1GTPCModify Bearer Resp(IMSI, TEID)Modify Bearer Req.(IMSI, eNB TEIDs)EMM-ConnectedTracking Area Update, Inter-MME Part 1 of 3Random Access PreambleRandom Access PreambleUL-SCH: SRB0RRC Connection RequestDL-SCH: Common CC: SRB0RRC Connection SetupUL-SCH: SRB1RRC Connection Complete NAS MSGRRC-Connected EMM-ConnectedSGWHSSRandomProcedureRRC Setup ProcedureTA-3TA-5MME-2eNBMME-1MME-2UEPGWInternRRC_IdleMME-1UE reads the TAI advertised by eNB and realizes that it is in a new TA.Irfan Ali24PGWSGWTracking Area Update, Inter-MME Part 2 of 3SGWHSSeNBMME-1MME-2UEPGWInternInitial UE MessageNAS MSG: TAURequest, GUTI, UENetwork CapabilityMME-2 does DNS lookup based onGUTIContext Req (GUTI) NAS MSGMME-1 checks msg integrityContext Resp (IMSI,MM Cntxt, SM Cntx)(IMSI, TEIDs)Modify Bearer Resp (IMSI, S1U TEID)

GTPC Tunnel

Location Update Request IMSI, Cancel Location Request (IMSI,..) Cancel Location Resp (IMSI,..)Location Update Response Subscription Data

MME-2 allocates new GUTI to UEGTPCModify Bearer Req.Downlink NAS transportNAS: TAU Accept( new GUTI, TAI,..)DL-SCH: Dedicated CC: SRB1DL Information TransferNAS: TAU AcceptS1-MMEIrfan Ali25Tracking Area Update, Inter-MME Part 3 of 3SGWHSSeNBMME-1MME-2UEPGWInternUL-SCH: SRB1UL Information TransferNAS: TAU Accept Complete

S1 UE ContextUL NAS TransportS1-MMERelease CommandDL-SCH:DCH SRB1RRC Connection Release

S1 UE Context Release Complete

RRC-IdleEMM-IdleEMM-IdleNo UEContext ineNBNAS MsgIrfan Ali26Idle mode procedures in network: Selecting an MME and finding context of UE in MMEIrfan Ali27Tracking Area and MME Service AreaMME Service Area is defined as the set of TAIs served by the MME.MME Service Area consists of complete TAI(s).The Service Area of two MMEs can be overlapping.TA-1TA-2TA-3TA-4TA-5TA-6TA-7MME-1MME-2Service Area of MME-1 {TA-1, TA2, TA-3, TA-4}

Service Area of MME-2 {TA-3, TA-4, TA-5, TA-6, TA-7}Irfan Ali28?UE performing Tracking Area UpdateUE in idle-mode informs the MME about its current location by performing Tracking Area Update eitherWhen the UE enters a new Tracking area (not in the UEs TAI List), orThe new tracking area may be under the same MME serving the UE current TAI, or served by a new MME.When the periodic Tracking Area Update timer expires (to let the network know that it is alive)Routing to get to the old MME.For periodic TAU, the UE should provide sufficient information to the eNB to route the UEs message to the MME that currently holds the UEs context.For normal tracking area to a new MME, the new MME should be able to identify the old MME inorder to get the UEs context from the old MME.The identity used to perform routing is the UEs temporary identity, called Globally Unique Temporary identity (GUTI)The next few slides provides and overview of how GUTI is used to route to the MME that containsthe UEs context.MME-1MME-2MME-3(Periodic) TAU messageMME-1MME-2MME-3MME-4?(normal) TAU messageMME-5TAI-1TAI-2Irfan Ali29MME Pooling ConceptS-GWeNBeNBeNBCellCellCellCellCelleNBCellCelleNBCellCellPDN GWTA1TA2S-GWeNBCellCellMMEMMES-GWMMEMME Pool-1MME Pool-2Pool areas can be overlapping.A cell in an eNB belongs to only one TA.A eNB (single cell) can be connected to multiple MMEs (belonging to more than one MME pools).TA3TA4Pool Area-1Pool Area-2Irfan Ali30MME Identification in a poolS-GWeNBeNBeNBCellCellCellCellCelleNBCellCelleNBCellCellPDN GWTA1TA2S-GWeNBCellCellMMEMMES-GWMMEMME Pool-1 MME Group ID = 1MME Pool-2 MME Group ID = 2MMEC=1MMEC=2MMEC=3MMEGI(MME Group ID)MMEC(MME Color) Code16 bits8 bitsMME Pool #MME #within PoolTA3TA4Pool Area-1Pool Area-2MMEC cannot be 1 or 2 due to overlapping pool areaIrfan Ali31UEs NAS Temporary ID in LTE3 BCDdigits2 or 3 BCDdigits32 bitsGlobally Unique Temporary IDS-TMSIM-TMSIMMEC 1 18 bits40 bitsAn M-TMSI is the unique part of a GUTI within the domain of one MME.lMCCMNCMMEI (MME ID)M-TMSIUEs ID usedfor PagingIn Signaling24 bitsIrfan Ali30A GUTI is globally unique.A GUTI is allocated to eachUE by the serving MME.An M-TMSI is theuniqueness part of a GUTI within the domain of one MME.An S-TMSI is unique within the domain of an MME Pool.A UE is paged with its S- TMSIThe UE identifies itself in a service request with the S- TMSIS-TMSIGUTIGUMMEIUEs ID used8 bits16 bits8 bits1MMEGI(MME Group ID)MMEC(MME Code)MME Pool #MME #within PooRouting parameters provided by UE and used by eNB for Selecting MMEUEeNBMMERRC Connection Setup Complete ( selectedPLMN-Identity,registeredMME: plmn-Identity, mmegi, mmec dedicatedInfoNAS )Select MME:Service request/periodic TAU: based on S-TMSI Attach w GUTI or TAU in new TA: MME ID+PLMN Attach w/o GUTI: selected PLMN-ID

Attach request S1-MME for UERRC Connection Request ( UE Identity: S-TMSI or rand,..)Signaling channel- SRB0RRC Connection SetupSignaling channel- SRB1S-TMSI is only provided by upper layer if the cell belongs to UEs registered TA.If S-TMSI is not provided UE generates random numberThe registered MME ID is not provided by upper layer if the cell is in a TA the UE is already registered to, i.e in service request or periodic TA. [Ref: Section 5.3.1.1 TS24.301]MME Code: uniquely identifies an MME in case of over-lapping pools. Selected PLMN is used for MOCN to get to the right MME.Irfan Ali33Cell-Selection and Cell-Reselection in Idle-mode: Which cell should UE camp on?Irfan Ali34Low Power (Idle Mode)MobilityLocation Area 1Location Area 2Network does not control UEs movement. UE autonomously selects new cell as it moves.Network only knows the location of the UE to the granularity of a location-area.Cell Reselection Instances

UEs radio is in low-power state. UEs transmitter is off.UE only listens periodically to control channel. If UE enters a new location area, based on hearing information (SIB) from base-station, the UE informs the network of the new location area it has entered.DRX CycleON DurationUE MontiorsPDCCH

UEs ReceiverDRX SleepTAUTAUIrfan Ali35Cell Selection vs Cell ReselectionCell selection or cell-reselection is the process of UE choosing a cell.Camped on a cell: UE has completed the cell selection/ reselection process and has chosen a cell. The UE monitors system information and (in most cases) paging information.Return from Out- of-CoverageRRC-Connected to RRC-IdleCamped on a CellCamped on a different CellCell SelectionIrfan Ali36Cell Re-SelectionWhat does the UE measure to determine if it cancamp on a cell? (1 of 3)Reference SymbolsIn order for receiver to estimate the channel, known reference symbols also referred to as pilot symbols are inserted at regular intervals within the OFDM time-frequency grid.Using knowledge of the reference symbols the receiver can estimate the frequency- domain channel around the location of the reference symbolThe reference symbols should have sufficient high density in time and frequency to provide estimates of the entire time/frequency grid.There are four resource elements per resource block that are dedicated to Reference Symbols.The location of Reference Symbols depends on the Physical layer cell identity of the cell.Once the UE has decoded the Primary and Secondary Synchronization Signals and consequently identified the Physical Layer Cell Identity, the UE is able to deduce the resource elements allocated to the Reference Signal.7 symbols = 0.5 ms (Slot)12 subcarriers = 180 kHzResource BlockResource Elements used for Reference SymbolsIrfan Ali37What does the UE measure to determine if it cancamp on a cell? (2 of 3)Reference Signal Received Power (RSRP)The RSRP is the average power (in watts) received from a single Reference Signal resource elementThe power measurement is based upon the energy received during the useful part of the OFDMA symbol and excludes the energy of the cyclic prefix.Knowledge of absolute RSRP provides the UE with essential information about the strength of cells from which path loss can be calculated for power-control calculations.Reference Signal Received Quality (RSRQ)RSRP on its own it gives no indication of signal quality.The Received Signal Strength Indicator RSSI parameter represents the entire received power including the wanted power from the serving cell as well as all co-channel power and other sources ofnoise.where N is the number of Resource blocks over which the RSSI is measuredRSRQ is always less than 1 (< 0 dB, actually < -3dB)7 symbols = 0.5 ms(Slot)12 subcarriers = 180 kHzResource BlockResource Elements used for Reference SignalsRSRP= Energy in one Reference Signal Resource ElementRSSI = Total energy in OFDMA symbol containing Reference Signal REOFDMA SymbolRSRQ =RSRP RSSI / NIrfan Ali38What does the UE measure to determine if it cancamp on a cell? (3 of 3)Cell Selection CriteriaCell is selected if:Srx > 0, and Sq > 0Measured Rx Level (dBm)Time (s)Measured Cell Quality (dB)Time (s)Srx = Rx_measured P_comp Rx_minSrxP_compensationRx_minSq = Q_measured Q_minQ_minSqCell SelectedCell Not SelectedIrfan Ali39Power savings in active state: DRX in connected mode in LTEIrfan Ali40Irfan Ali39OverveiwDRX allows UE to not continuously monitor the PDCCHLeads to power-savings for UE in active state.Configured using RRC signaling by the eNBPer UE mechanismThe eNB keep track of UEs DRX cycle, so that it transmits DL data to the UE only during the subframe when the UE is listening to PDCCH.DRX Cycle: Specifies the periodic repetition of the On Duration followed by a period of sleepTwo types of DRX cycles: Long DRX cycle, and (optional) Short DRX cycle. The Long DRX cycle is a multiple of short DRX cycle.On Duration Timer: Specifies the number of consecutive PDCCH-subframe(s) at the beginning of a DRX CycleDRX Sleep

Long DRX CycleSource: 36.300 (Section 12), 36.321 (Section 5.7)DRX SleepShort DRX CycleON DurationUE MontiorsPDCCHPDCCHPhysical Downlink Common CHannelUE MontiorsPDCCHRRC State Transition in LTE with Connected Mode DRXDRX Inactivity TimerDRXContinuous ReceptionShort DRXLong DRXInactivity TimerData TransferRRC-CONNECTEDRRC-IDLEDRX Short Cycle TimerTimer ExpirationData TransferIrfan AliCharacteristics of 4G LTE Networks, Junxian Huang, et al, 201240Source: A Close Examination of Performance and PowerEntering DRX operationInactivity Timer: Duration in downlink subframes that the UE waits from the last successful decoding of a PDCCH which contained data for UE, till entering DRX.On-duration: Duration in downlink subframes that the UE waits for, after waking up from DRX, to receive PDCCHs. If the UE receives PDCCH with data for UE, the UE stays awake and starts the inactivity timer.Inactivity timerDRX Start OffsetOn DurationLong DRX CycleDRX Short Cycle TimerAll DRX parameters are signalled by eNB during RRC Connection Setup message.The frame-number, x, and the subframe number, y, to start the On-duration is computed as follows: [x * 10 + y] mod (Short_DRX_Cycle) = DRX_Start_Offset mod (Short_DRX_Cycle), for Short DRX cycle

[x * 10 + y] mod (Long_DRX_Cycle) = DRX_Start_Offset,for Long DRX CycleDRX Start Offset: Number of subframes.Short DRX Cycle: Value in number of subframes. 2,5, 8, 10,, 320,512,640DRX Short Cycle Timer: Number of short cycles before the UE enters Long DRX CycleLong DRX Cycle: Value in number of subrame.10, 20, .. 2560 (2.56s)DRX SleepUE MontiorsPDCCHPDCCH contains DL data for UEIrfan Ali43Exiting and re-entering DRX operationInactivity Timer: Duration in downlink subframes that the UE waits from the last successful decoding of a PDCCH which contained data for UE, till entering DRX.On-duration: Duration in downlink subframes that the UE waits for, after waking up from DRX, to receive PDCCHs. If the UE receives PDCCH with data for UE, the UE stays awake and starts the inactivity timer.Inactivity timerDRX Start OffsetUE MontiorsOn DurationPDCCHLong DRX CycleDRX Short Cycle TimerAll DRX parameters are signalled by eNB during RRC Connection Setup message.The frame-number, x, and the subframe number, y, to start the On-duration is computed as follows: [x * 10 + y] mod (Short_DRX_Cycle) = DRX_Start_Offset mod (Short_DRX_Cycle), for Short DRX cycle

[x * 10 + y] mod (Long_DRX_Cycle) = DRX_Start_Offset,for Long DRX CycleDRX Short Cycle Timer: Number of short cycles before the UE enters Long DRX CycleShort DRX Cycle: Value in number of subframes. 2,5, 8, 10,, 320,512,640DRX Start Offset: Number of subframes.DRX SleepActive TimeIrfan Ali44PDCCH contains DL data for UEDifference between Connected mode DRX and Idle mode DRXIrfan Ali45Typically the DRX period of connected mode DRX is shorter than that of idle mode DRXIn connected mode, there is a higher probability of data activity from UE. Longer connected mode DRX would mean higher delay in sending the first packet to the UE.Power consumption for UE in connected-mode DRX is typically greater than that during idle-mode DRX.For more details, please refer to: A Close Examination of Performance and Power Characteristics of 4G LTE Networks, Junxian Huang, et al, 2012Since smart phones generate constant dribble of traffic, with several background processes doing keep-alives, and there is too much signaling overhead in transitioning the UE to idle and then back to connected state, operators keep smartphones in connected mode for long duration of time using connected mode DRX in LTE.Mobility Management in LTEIrfan Ali46OverviewMobility Mangement in LTEMobility Management in Idle-ModeMobility Management in Connected ModeCell selection/reselectionCovered in previous slidesHandoversCovered nextIrfan Ali47Handovers, orMobility Management in Connected ModeIrfan Ali48Overview of Handovers

All handovers in LTE are prepared handoversResources are prepared in the target eNB, before the UE connects to the target eNBAll handovers in LTE are UE assisted network controlledThe UE is asked to make measurements of neighbouring cells by the source eNB and report back to the source eNB.The source eNB decides as to which target eNB the UE should be handed over to and directs the UE to that particular target eNB.Irfan Ali49Measurement(1 of 2)Irfan Ali50There is no need to indicate neighbouring cell IDs to enable the UE to search and measure a cell i.e. E-UTRAN relies on the UE to detect the neighbouring cellsFor the search and measurement of inter-frequency neighbouring cells, at least the carrier frequencies need to be indicatedeNB signals reporting criteria for event-triggered and periodical reportingEvents can be defined eg to be low Rx threshold on current cell, etc.An NCL (network cell list) can be provided by the serving cell by RRC dedicated signalling to handle specific cases for intra- and inter-frequency neighbouring cells. This NCL contains cell specific measurement parameters for specific neighbouring cells;Black lists can be provided to prevent the UE from measuring specific neighbouring cells.Measurement (2 of 2)Depending on whether the UE needs transmission/reception gaps to perform the relevant measurements, measurements are classified as gap assisted or non- gap assisted.Gap patterns (as opposed to individual gaps) are configured and activated by RRC.Intra-frequency cell measurements are non-gap assisted.Inter-frequency cell measurements may be gap-assisted based on UEs capabilities and the current operating frequency. The UE determines whether a particular cell measurement needs to be performed in a transmission/reception gap and the scheduler needs to know whether gaps are neededScenario C

current cellUEtarget cellfcfccurrent cellUEtarget cellfcfcScenario AScenario B

current cellUEtarget cellfcfcScenario D

current cellUEtarget cellfcfcScenario E

current cellUEtarget cellfcfccurrent cellUEtarget cellfcfcScenario FNon-Gap Assisted MeasurementIrfan Ali51Gap Assisted Measurement50Types of handoversIMSInterneteNB-1eNB-2eNB-3MME-AS11S-GW-1S-GW-2P-GWHSSS1-MMES1-US6aS5X2X2eNB-4eNB-5eNB-6X2S-GW-3MME-BMME-C123451X2 Handover with no SGW relocation2X2 Handover with SGW relocation3S1 Handover with MME and SGW relocationS10S104X2 Handover with no SGW relocationX2 Handovers cannot have an MME change, i.e for an X2 HO, both the source-5S1 Handover with MME and no SGW relocationIrfan AlieNB and target-eNB have to be under the control of the same MME.