Radio Measurements in LTE

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Radio Measurement in LTE

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Radio Measurements in LTE

  1. 1. * http://id.linkedin.com/in/sofian/ http://babakhalid.com/
  2. 2. 1 LTE MEASUREMENT - LIST - List of detected preambles The eNB shall report a list of detected PRACH preambles to higher layers. Higher layer utilize this info for the RACH procedure Transport BLER The ACK/ NACKs for each transmission of the HARQ process are reported to the MAC. Based on these ACK/NACKs the higher layers compute the BLER for RRM issues. TA The eNB needs to measure the initial timing advance (TA) of the uplink channels based on the RACH preamble. Average RSSI Measured in UL by eNB. It can be used as a level indicator for the UL power control. The RSSI measurements are all UE related and shall be separately performed for ( TTI intervals) · UL data allocation (PUSCH) · UL control channel (PUCCH) Sounding reference signal (SRS) Average SINR In UL the eNB measures SINR per UE. The average SINR can be used as a quality indicator for the UL power control UL CSI Channel state information per PRB for each UE. The CSI shall be the received signal power averaged per PRB.
  3. 3. 2 LTE MEASUREMENT - LIST - Intra LTE measurements ( from LTE to LTE) UE measurements • CQI measurements • Reference Signal Received Power (RSRP) • Reference Signal Received Quality (RSRQ) eNB measurements • Non standardized (vendor specific):TA, Average RSSI, Average SINR, UL CSI, detected PRACH preambles, transport channel BLER • Standardized:DL RS Tx Power, Received Interference Power, Thermal Noise Power Measurements from LTE to other systems UE measurementsare mainly intended for handover • UTRA FDD:CPICH RSCP, CPICH Ec/No and carrier RSSI • GSM:GSM carrier RSSI • UTRA TDD:carrier RSSI, RSCP, P-CCPCH • CDMA2000:1xRTT Pilot Strength, HRPD Pilot Strength
  4. 4. 3 LTE MEASUREMENT SAMPLES REFERENCE SIGNAL RECEIVED POWER (RSRP) The received power on the resource elements that carry cell-specific reference signals
  5. 5. 4 LTE MEASUREMENT SAMPLES REFERENCE SIGNAL RECEIVED POWER (RSRP) There is dependency between RS power and Max Total Tx Power. The relation is given by PRS = PTx, Max – 10* log (NRB *12)+ 10*log (Pb+1) where PRS = RS power per RE (dBm) PTx, Max = Max eNodeB power per Tx (dBm) NRB = number of resource block Pb = RS power boosting constant (actual value range = 0~3) recommended value: single antenna = 0, double antenna =1) • The higher the maximum transmit power of eNodeB, the higher is the RS power. • Besides, the RS power also affected by the RS power boosting constant, Pb. A larger value of Pb results in larger increase in RS power, better channel estimation & PDSCH demodulation performance. Huawei recommended setting for Pb is 0 (single antenna) & 1 (dual antenna)
  6. 6. 5 LTE MEASUREMENT SAMPLES Reference Signal Received Quality (RSRQ) The relation of N times the Reference Signal Received Power divided by the total received power in the channel bandwidth. Within the RSRQ also the noise and interference contributions are considered.
  7. 7. 6 LTE MEASUREMENT TIMING ADVANCE TIMING ADVANCE (TA) When UE wish to establish RRC connection with eNB, it transmits a Random Access Preamble, eNB estimates the transmission timing of the terminal based on this. Now eNB transmits a Random Access Response which consists of timing advance command, based on that UE adjusts the terminal transmit timing. 3GPP TA Requirements • Timing Advance adjustment delay UE shall adjust the timing of its uplink transmission timing at sub-frame n+6 for a timing advancement command received in sub-frame n. • Timing Advance adjustment accuracy The UE shall adjust the timing of its transmissions with a relative accuracy better than or equal to ±4* TS seconds to the signalled timing advance value compared to the timing of preceding uplink transmission. The timing advance command is expressed in multiples of 16* TS and is relative to the current uplink timing. In GSM Dist = TA * bit-period * light-speed / 2 bit-period = 48/13 (3.69) μs light-speed = 300000 km/s
  8. 8. 7 LTE MEASUREMENT SAMPLES In LTE No DL TA Maintenance of Uplink Time Alignment The UE has a configurable timer timeAlignmentTimer which is used to control how long the UE is considered uplink time aligned • When a Timing Advance Command MAC control element is received then UE applies the Timing Advance Command and start or restart timeAlignmentTimer. • When a Timing Advance Command is received in a Random Access Response message then one of following action is performed by UE. - if the Random Access Preamble was not selected by UE MAC then UE applies the Timing Advance Command and starts or restarts timeAlignmentTimer. - else if the timeAlignmentTimer is not running then UE applies the Timing Advance Command starts timeAlignmentTimer; when the contention resolution is considered not successful then UE stops timeAlignmentTimer. - else ignore the received Timing Advance Command. • When timeAlignmentTimer expires UE flushes all HARQ buffers, notifies RRC to release PUCCH/SRS and clears any configured downlink assignments and uplink grants.
  9. 9. 8 LTE MEASUREMENT SAMPLES Timing Advance Command MAC Control Element 3GPP 36.321 The Timing Advance Command MAC control element is identified by MAC PDU subheader with LCID value = 11101 (Timing Advance Command) • R: reserved bit, set to "0" • Timing Advance Command: This field indicates the index value TA (0, 1, 2… 63) used to control the amount of timing adjustment that UE has to. The length of the field is 6 bits.
  10. 10. 9 LTE MEASUREMENT SAMPLES Signalled granularity = 16 Ts = 0.52 μsec (corresponding to 78 m). In GSM we got about 553m granularity. Ts is basic time unit defined by 3GPP Ts. = 1 / (2048 x 15000) sec = 1 / 30.720.000 = 0.0325520833 e-6 - 15000 = 15 kHz is passband for a subcarrier in LTE - 2048 FFT-size Radio frame Tf = 307200 x Ts = 10ms = 20 timeslots (in FDD) 1 timeslot = 15360 Ts 2048 x Ts = 1/15kHz UMTS bandwidth is 5 MHz and it operates at a high chip rate 3.84 Mcps/s, which contributes to the better resolution in timing measurements compared to GSM. The timing resolution in UMTS with one sample per chip is ∼0.26 µs which corresponds to the propagation distance of ∼78 m. The frequency of TA is sent dependent on speed of the UE. If UE speed 72km/h = 20m/s  update every 4s 500km/h = 130m/s  max every 2s NodeB measuring TA based on Recevide PUSCH on TTI basis CQI reports on PUCCH
  11. 11. 10 LTE MEASUREMENT CQI
  12. 12. 11 LTE MEASUREMENT Cell Selection/ReSelection When the UE is switched on, it attempts to establish a contact with a public land mobile network (PLMN) using a certain radio access technology. The overall process is divided into three sub-processes: • PLMN selection and reselection to search for an available mobile network. • Cell selection and reselection to search for a suitable cell belonging to the selected PLMN. • Location registration to register the UE’s presence in a registration area
  13. 13. 12 LTE MEASUREMENT PLMN Selection PLMN Selection When an UE is switched on, it attempts to make contact with a PLMN. The selection of the PLMN could be either automatically or manually. • Automatic mode: Utilizes a list of PLMN to be selected in priority order. • Manual mode: The mobile station indicates available PLMN to the user. Normally the UE operates on its home PLMN. At home PLMN, the MCC & MNC match with PLMN identity stored in USIM. If the UE loses its present PLMN coverage, a new available PLMN is selected automatically or manually.
  14. 14. 13 LTE MEASUREMENT PLMN Selection PLMN Selection Service types LIMITED SERVICE: emergency calls on an acceptable cell. UE may camp to obtain limited service like emergency call. The minimum set of requirements for initiating an emergency call in a UTRAN network are: • The cell is not barred. • The cell selection criteria are fulfilled. NORMAL SERVICE: for public use on a suitable cell. UE may camp on to obtain normal service. Such a cell shall fulfill all the following requirements: • The cell is part of the selected / registered / equivalent PLMN • The cell is not barred • The cell is not part of a forbidden registration area • The cell selection criteria are fulfilled • In case of CSG cell it is part of the white list OPERATOR SERVICE: For operators only on a reserved cell. Reserved cell: When the cell status "reserved for operator use" is indicated and the Acces Class of the UE is 11 or 15 the UE may select/re-select this cell if in Home-PLMN Barred cell: When cell status "barred" is indicated the UE is not permitted to select/re-select this cell, not even for limited services. This information is set by office data.
  15. 15. 14 LTE MEASUREMENT PLMN Selection
  16. 16. 15 LTE MEASUREMENT Cell Selection/Reselection Cell Selection Upon PLMN selection, UE uses “cell selection” for fast cell searching to camp on. To receive system information UE tunes to the control channels. This procedure is known as "camping on the cell”. The UE will then register its presence in the registration area of the chosen cell by NAS (Non Access Stratum) registration procedure. NAS registration procedure means the upper layer information is transmitted from UE to CN via AS (Access Stratum). The NAS offers the E-UMTS service to the users. Cell selection is performed in RRC idle mode. The cell will be decided as suitable if it fulfils the cell selection criteria. The purpose of camping on a cell is: • To enable UE reception of system information from the selected PLMN • To allow UE an RRC connection, accessing the network on the cell control channel. • To receive paging and respond to paging messages on a tuned control channel in the registration area. The PLMN knows the tracking area of the cell in which the registered UE is camped. Control Plane Protocol Stack
  17. 17. 16 LTE MEASUREMENT Cell Selection/Reselection Cell RE-Selection If the UE finds a "better" cell, UE reselects it and camps on it. After camping on, UE monitors the system information to get the quality threshold and performs measurements for the cell reselection evaluation procedure. The UE evaluates whether or not a better cell exists. The E-UTRAN controls the quality measurements for cells to be reselected. The UE measurements are triggered according to the serving cell quality level and the threshold indicated in the system information. The measurement must satisfy different requirements for intra frequency, inter frequency or inter RAT (Radio Access Technology) quality estimations. Cell selection is performed in RRC idle mode. The camping on a cell in idle mode enables the UE to receive information from the network. UE stays in idle mode until it transmits a request to establish an RRC connection. After receiving the RRC connection set up, the mode changes into connected mode.
  18. 18. 17 LTE MEASUREMENT CRITERIA Selection PLMN Selection The UE scans all RF channels in the UTRAN band according to its capabilities to find available PLMNs. On each carrier, the UE searches for the strongest cell according to the cell search procedure (refer cell searching) and read its system information in order to find out which PLMN the cell belongs to. If the UE can read the PLMN identity, the PLMN and the measured signal strength is reported to the NAS: if: signal >= - x dBm (high quality PLMN); without the measured signal strength if < x dBm.
  19. 19. 18 LTE MEASUREMENT CRITERIA Selection PLMN Selection
  20. 20. 19 LTE MEASUREMENT CRITERIA Selection CELL Selection After selecting a PLMN, the cell selection process starts. The UE selects a suitable cell and the radio access mode based on idle mode measurements and cell selection criteria. The UE searches a suitable cell of that PLMN to camp on according to the following steps: 1) The UE creates a candidate list of potential cells to camp on by using one of the two search procedures: • Initial Cell Selection UE scans all RF channels in the UTRAN band to find a suitable cell. On each carrier, UE searches for the strongest cell and reads its system information. Once the UE has found the suitable cell for the selected PLMN, the UE creates a candidate list consisting of this cell and its neighboring cells as received in measurement control information. • Stored Information Cell Selection (optionally) This procedure requires information stored from previously received measurement control information elements (cell parameters, carrier frequencies, etc). After the UE has found a suitable cell for the selected PLMN, candidate list is created same as the initial cell selection process. 2) Each cell on the candidate list is evaluated according to the selection criteria S as described below. 3) After selecting a suitable cell (S criterion fulfilled) for camp on, UE reports this event to NAS for registration procedures. If the registration is successful, the UE enters into "camped normally“ state.
  21. 21. 20 LTE MEASUREMENT CRITERIA Selection CELL Selection If the UE is unable to find any suitable cell in the selected PLMN, the UE enters to "any cell selection" state. Camped normally state : UE obtains normal service and performs the following tasks: • Select and monitor the PCH of the cell. • Performs system information monitoring. • Performs necessary measurements for the cell reselection evaluation procedure. • Execute the cell reselection procedure If after cell reselection evaluation process a better cell is found, the cell reselection is performed. If no suitable cel is found, the UE enters to next state “any cell selection” Any cell selection: UE searches an acceptable cell of any PLMN to camp on. If an acceptable cell is found, the UE reports to NAS and camp on this cell obtaining limited service. And UE enters to “camp on any cell” state. If the UE can’t find any acceptable cell, it stay in this state. Camped on any cell state: UE obtains limited service and periodically searches for a suitable cell in the selected PLMN. If a suitable cell is found the states changed to Camped normally.
  22. 22. 21 LTE MEASUREMENT CRITERIA Selection PLMN, CELL Selection & ReSelection Flowchart
  23. 23. 22 LTE MEASUREMENT CRITERIA Cell Selection S-CRITERION The cell selection criterion S is a pre-condition for suitable cells.
  24. 24. 23 LTE MEASUREMENT CRITERIA Cell Re-Selection R-CRITERION The cell reselection evaluation process depends on whether Hierarchical Cell Structure (HCS) is used or not. In order to perform cell reselection UE measures and ranks the neighbor cells. For each type of neighbor cells (Intra-Frequency; Inter-Frequency; Inter-RAT, i.e. GSM) thresholds are definable. Measurements of neighbor cells will be triggered if these thresholds are reached. HIGH MOBILITY / MEDIUM MOBILITY / NORMAL MOBILITY: For faster moving UEs the procedure alters - speed dependent scaling rules are applied. If the number of (different cells) cell reselections during the past time period TCRmax exceeds NCR_H, high mobility has been detected. If the number exceeds NCR_M, and not NCR_H, medium mobility has been detected.
  25. 25. 24 LTE MEASUREMENT CRITERIA Cell Re-Selection R-CRITERION In high/medium-mobility states, a UE: • multiplies Qhyst by "Speed dependent ScalingFactor for Qhyst for high/medium mobility state" if sent. • multiplies TreselectionRAT by "Speed dependent ScalingFactor for TreselectionRAT for * mobility state for RAT cells. (RAT = EUTRAN, UTRAN, GERAN).
  26. 26. 25 LTE MEASUREMENT CRITERIA Cell Re-Selection Neighbor Cell Measurement For inter-frequency and inter-system measurements, depending on the UE capability, the network allocates measurement gaps during which no data are sent for the UE, so that the UE could perform the necessary measurements using a single receiver. During the measurement gaps, the particular UE cannot be scheduled for data transmission, but the vacant resources could still be used for other UEs, because of the shared channel mechanism. FOR INTRA-FREQUENCY AND EQUAL PRIORITY INTER-FREQUENCY CELLS: (Re-) Selected cell is a suitable cell (e.g. fulfills the S criterion) and is the best ranked cell (has the highest R). The UE shall however reselect the new cell, only if the following conditions are met: • The new cell is better ranked than the serving cell during a time interval Treselections • more than 1 second has elapsed since the UE has camped on the current serving cell. The cell-ranking criterion R is defined as shown below: Note, s – indicates the serving cell, n – indicates the candidate cell.
  27. 27. 26 LTE MEASUREMENT CRITERIA Cell Re-Selection Neighbor Cell Measurement
  28. 28. 27 LTE MEASUREMENT CRITERIA Cell Re-Selection Neighbor Cell Measurement FOR INTER-FREQUENCY AND INTER-RAT NEIGHBOUR CELLS: If UE camps longer than 1 sec in the serving cell and: - a higher priority neighbor fulfills (during TreselectionRAT): SnonServingCell,x > Threshhigh 􀃆 reselect neighbor cell. - no cell fulfills SnonServingCell,x > Threshhigh : SServingCell < Threshserving,low and SnonServingCell,x > Threshx,low 􀃆 reselect neighbor cell.
  29. 29. 28 LTE MEASUREMENT CRITERIA Cell Re-Selection Neighbor Cell Measurement Cell Reselection from WCDMA to LTE UE must measure the LTE frequencies and detect the available LTE cell in order to perform cell reselection to LTE. • UE measures two physical properties called for WCDMA signal. One is CPICH RSCP and CPICH EcNo. RSCP determines Srxlev and EcNo determines Squal. • Srxlev = Qrxlevemeas - qRxLevMin. Qrxlevemeas is RSCP level measured by UE and qRxLevMin is the value specified in SIB. • Squal = Qqualmeas - qQualMin. Qqualmeas is EcNo level measured by UE and qQualMin is the value specified in SIB. • The detection measurement of LTE frequencies should be done at least once every 60s for higher priority LTE frequencies. • In following condition, detection measurements of lower priority LTE frequency is not required. Srxlev > absPrioCellRes.sPrioritySearch1 Squal > absPrioCellRes.sPrioritySearch2 • In following condition, UE should detect once every 30s for both lower and higher priority LTE frequencies Srxlev <= absPrioCellRes.sPrioritySearch1 Squal <= absPrioCellRes.sPrioritySearch2 • The maximum number of LTE FDD Frequencies are 4. In this case, UE should have performed measurement for detecting LTE cells on all 4 LTE frequencies once every 240 (4 x 60) s or 120(4 x 30) s depending if UE measures above or below parameter threshold absPrioCellRes.sPrioritySearch1
  30. 30. 29 LTE MEASUREMENT CRITERIA Cell Re-Selection Neighbor Cell Measurement Cell Reselection from LTE to WCDMA • Measurement Criteria (From High Priority LTE Cell to Lower Priority WCDMA Cell): When LTE cell has higher priority than WCDMA, it would stay in LTE cell but it performs measurement for the low priority WCDMA if UE is under the following condition : Srxlev of the serving cell < sNonIntraSearch (SIB3), where Srxlev = Qrxlevmeas - qRxLevMin (SIB3), where Qrxlevemeas = measured RSRP level, qRxLevMin = minimum RSRP level for camping • Measurement Criteria (From High Priority LTE Cell to Lower Priority WCDMA Cell): When LTE cell has lower priority than WCDMA (WCDMA cell priority defined in SIB6 is higher than the serving cell priority),The UE always have to perform measurements on WCDMA cell. How often UE has to measure for WCDMA depends on whether Srxlev of the serving cell is greater or lower than sNonIntraSearch(SIB3). If no parameter is set (meaning in default condition), detection of WCDMA cell should be performed at least every 60 seconds. • Reselection Criteria (From High Priority LTE Cell to Lower Priority WCDMA Cell): If UE in LTE cell is under the following condition with the duration longer than tReselectionUtra (SIB6), it should reselect to WCDMA cell. Srxlev of LTE cell (serving cell) < threshServingLow (SIB3), where Srxlev = Qrxlevmeas - qRxLevMin (SIB3), where Qrxlevemeas = measured RSRP level, qRxLevMin = minimum RSRP level for camping Srxlev of WCDMA cell > threshXLow (SIB6), where Srxlev = Qrxlevmeas - qRxLevMin (SIB3), where Qrxlevemeas = measured RSCP level, qRxLevMin = minimum RSCP level for camping Note : If more than one WCDMA meet this condition, UE should select to the cell with highest Srxlev Note : If these values are not specified in SIB and UE has to apply default values, UE has to perform reselection when LTE RSRP is lower than -145 dBm and WCDMA cell is better than -119 dBm for at least 2 seconds.
  31. 31. 30 LTE MEASUREMENT CRITERIA Cell Re-Selection Neighbor Cell Measurement Cell Reselection from LTE to WCDMA • Reselection Criteria (From Lower Priority LTE Cell to Higher Priority WCDMA Cell): If UE in LTE cell is under the following condition with the duration longer than tReselectionUtra (SIB6), it should reselect to WCDMA cell. Srxlev of WCDMA cell > threshXHigh (SIB6), where Srxlev = Qrxlevmeas - qRxLevMin (SIB3), where Qrxlevemeas = measured RSCP level, qRxLevMin = minimum RSCP level for camping
  32. 32. 31 LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW
  33. 33. 32 LTE MEASUREMENT HANDOVER HANDOVER INTRA E-UTRAN Intra E-UTRAN Handover is used to hand over a UE from a source eNodeB to a target eNodeB using X2 when the MME is unchanged. The intra E-UTRAN HO in RRC_CONNECTED state is UE assisted NW controlled HO, with HO preparation signalling in E-UTRAN. To prepare the HO, the source eNB passes all necessary information to the target eNB (e.g. E-RAB attributes and RRC context) and UE accesses the target cell via RACH following a contention-free procedure using a dedicated RACH preamble. The HO procedure is performed without EPC involvement, i.e. preparation messages are directly exchanged between the eNBs.
  34. 34. 33 LTE MEASUREMENT HANDOVER HANDOVER INTRA E-UTRAN Detailed explanation of above scenario is below. • The source eNB configures the UE measurement procedures according to the area restriction information. UE sends MEASUREMENT REPORT by the rules set by i.e. system information, specification etc. • Source eNB makes decision based on MEASUREMENT REPORT and RRM information to hand off UE and issues a HANDOVER REQUEST message to the target eNB passing necessary information to prepare the HO at the target side. • Admission Control may be performed by the target eNB dependent on the received E-RAB QoS information to increase the likelihood of a successful HO. The target eNB configures the required resources according to the received E-RAB QoS information. • Target eNB prepares HO with L1/L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source eNB. The HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container to be sent to the UE as an RRC message to perform the handover. • The UE receives the RRCConnectionReconfiguration message with necessary parameters (i.e. new C-RNTI, target eNB security algorithm identifiers, and optionally dedicated RACH preamble, target eNB SIBs, etc.) and is commanded by the source eNB to perform the HO. • The source eNB sends the SN STATUS TRANSFER message to the target eNB to convey the uplink PDCP SN receiver status and the downlink PDCP SN transmitter status of E-RABs for which PDCP status preservation applies (i.e. for RLC AM). • After receiving the RRCConnectionReconfiguration message including the mobilityControlInformation , UE performs synchronisation to target eNB and accesses the target cell via RACH.
  35. 35. 34 LTE MEASUREMENT HANDOVER HANDOVER INTRA E-UTRAN • The target eNB responds with UL allocation and timing advance. • UE sends the RRCConnectionReconfigurationComplete message (C-RNTI) to confirm the handover to the target eNB to indicate that the handover procedure is completed for the UE. The target eNB verifies the C-RNTI sent in the RRCConnectionReconfigurationComplete message. The target eNB can now begin sending data to the UE. • The target eNB sends a PATH SWITCH message to MME to inform that the UE has changed cell. • The MME sends an UPDATE USER PLANE REQUEST message to the Serving Gateway. • The Serving Gateway switches the downlink data path to the target side. The Serving gateway sends one or more "end marker" packets on the old path to the source eNB and then can release any U-plane/TNL resources towards the source eNB. • Serving Gateway sends an UPDATE USER PLANE RESPONSE message to MME. • The MME confirms the PATH SWITCH message with the PATH SWITCH ACKNOWLEDGE message. • By sending UE CONTEXT RELEASE, the target eNB informs success of HO to source eNB and triggers the release of resources by the source eNB. The target eNB sends this message after the PATH SWITCH ACKNOWLEDGE message is received from the MME. • Upon reception of the UE CONTEXT RELEASE message, the source eNB can release radio and C-plane related resources associated to the UE context. Any ongoing data forwarding may continue. Source : 3GPP TS 36.300
  36. 36. 35 LTE MEASUREMENT HANDOVER HANDOVER INTRA E-UTRAN (X2)
  37. 37. 36 LTE MEASUREMENT HANDOVER HANDOVER INTRA E-UTRAN (X2)
  38. 38. 37 LTE MEASUREMENT HANDOVER HANDOVER INTRA E-UTRAN (X2)
  39. 39. 38 LTE MEASUREMENT HANDOVER HANDOVER INTRA E-UTRAN (X2) ANR HO LTE UE can detect intra LTE neighbours without neighbour lists which simplifies network management. The UE reports other cell IDs to the eNodeB. If the target cell ID is known by eNodeB, it will proceed with the handover. If the target is not known by eNodeB and no is X2 enabled, the eNodeB asks UE to decode global cell id of the target cell. The eNodeB finds out the target cell’s IP address from O&M, enables an X2 connection to the target cell and proceeds with the handover
  40. 40. LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW (S1) PREPARATION PHASE
  41. 41. LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW (S1) EXECUTION PHASE
  42. 42. LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW (S1) COMPLETION PHASE
  43. 43. LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW (S1) Step 1. The source eNodeB decides to initiate an S1-based handover to the target eNodeB. This can be triggered e.g. by no X2 connectivity to the target eNodeB, or by an error indication from the target eNodeB after an unsuccessful X2-based handover, or by dynamic information learnt by the source eNodeB. Step 2. The source eNodeB sends Handover Required (Direct Forwarding Path Availability, Source to Target transparent container, target eNodeB Identity, CSG ID, CSG access mode, target TAI, S1AP Cause) to the source MME. The source eNodeB indicates which bearers are subject to data forwarding. Direct Forwarding Path Availability indicates whether direct forwarding is available from the source eNodeB to the target eNodeB. This indication from source eNodeB can be based on e.g. the presence of X2. The target TAI is sent to MME to facilitate the selection of a suitable target MME. When the target cell is a CSG cell or a hybrid cell, the source eNodeB shall include the CSG ID of the target cell. If the target cell is a hybrid cell, the CSG access mode shall be indicated. Step 3. The source MME selects the target MME and if it has determined to relocate the MME, it sends a Forward Relocation Request (MME UE context, Source to Target transparent container, RAN Cause, target eNodeB Identity, CSG ID, CSG Membership Indication, target TAI, MS Info Change Reporting Action (if available), CSG Information Reporting Action (if available), UE Time Zone, Direct Forwarding Flag) message to the target MME. The target TAI is sent to the target MME to help it to determine whether S GW relocation is needed (and, if needed, aid SGW selection). The source MME shall perform access control by checking the UE's CSG subscription when CSG ID is provided by the source eNodeB. If there is no subscription data for this CSG ID or the CSG subscription is expired, and the target cell is a CSG cell, the source MME shall reject the handover with an appropriate cause. The MME UE context includes IMSI, ME Identity, UE security context, UE Network Capability, AMBR, Selected CN operator ID, APN restriction, Serving GW address and TEID for control signalling, and EPS Bearer context(s). An EPS Bearer context includes the PDN GW addresses and TEIDs (for GTP-based S5/S8) or GRE keys (for PMIP-based S5/S8) at the PDN GW(s) for uplink traffic, APN, Serving GW addresses and TEIDs for uplink traffic, and TI. RAN Cause indicates the S1AP Cause as received from source eNodeB. The source MME includes the CSG ID in the Forward Relocation Request when the target cell is a CSG or hybrid cell. When the target cell is a hybrid cell, the CSG Membership Indication indicating whether the UE is a CSG member shall be included in the Forward Relocation Request message. The Direct Forwarding Flag indicates if direct forwarding is applied, or if indirect forwarding is going to be set up by the source side. The target MME shall determine the Maximum APN restriction based on the APN Restriction of each bearer context in the Forward Relocation Request, and shall subsequently store the new Maximum APN restriction value. If the UE receives only emergency services and the UE is UICCless, IMSI can not be included in the MME UE context in Forward Relocation Request message. For emergency attached UEs, if the IMSI cannot be authenticated, then the IMSI shall be marked as unauthenticated. Also, in this case, security parameters are included only if available.
  44. 44. LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW (S1) Step 4. If the MME has been relocated, the target MME verifies whether the source Serving GW can continue to serve the UE. If not, it selects a new Serving GW. If the MME has not been relocated, the source MME decides on this Serving GW re-selection. If the source Serving GW continues to serve the UE, no message is sent in this step. In this case, the target Serving GW is identical to the source Serving GW. If a new Serving GW is selected, the target MME sends a Create Session Request (bearer context(s) with PDN GW addresses and TEIDs (for GTP-based S5/S8) or GRE keys (for PMIP-based S5/S8) at the PDN GW(s) for uplink traffic, Serving Network, UE Time Zone) message per PDN connection to the target Serving GW. The target Serving GW allocates the S GW addresses and TEIDs for the uplink traffic on S1_U reference point (one TEID per bearer). The target Serving GW sends a Create Session Response (Serving GW addresses and uplink TEID(s) for user plane) message back to the target MME. Step 5. The Target MME sends Handover Request (EPS Bearers to Setup, AMBR, S1AP Cause, Source to Target transparent container, CSG ID, CSG Membership Indication, Handover Restriction List) message to the target eNodeB. This message creates the UE context in the target eNodeB, including information about the bearers, and the security context. For each EPS Bearer, the Bearers to Setup includes Serving GW address and uplink TEID for user plane, and EPS Bearer QoS. If the direct forwarding flag indicates unavailability of direct forwarding and the target MME knows that there is no indirect data forwarding connectivity between source and target, the Bearers to Setup shall include "Data forwarding not possible" indication for each EPS bearer. Handover Restriction List is sent if available in the Target MME. S1AP Cause indicates the RAN Cause as received from source MME. The Target MME shall include the CSG ID and CSG Membership Indication when provided by the source MME in the Forward Relocation Request message. The target eNodeB sends a Handover Request Acknowledge (EPS Bearer Setup list, EPS Bearers failed to setup list Target to Source transparent container) message to the target MME. The EPS Bearer Setup list includes a list of addresses and TEIDs allocated at the target eNodeB for downlink traffic on S1 U reference point (one TEID per bearer) and addresses and TEIDs for receiving forwarded data if necessary. If the UE AMBR is changed, e.g. all the EPS bearers which are associated to the same APN are rejected in the target eNodeB, the MME shall recalculate the new UE-AMBR and signal the modified UE AMBR value to the target eNodeB. If none of the default EPS bearers have been accepted by the target eNodeB, the target MME shall reject the handover. If the target cell is a CSG cell, the target eNodeB shall verify the CSG ID provided by the target MME, and reject the handover with an appropriate cause if it does not match the CSG ID for the target cell. If the target eNodeB is in hybrid mode, it may use the CSG Membership Indication to perform differentiated treatment for CSG and non-CSG members. Step 6. If indirect forwarding applies and the Serving GW is relocated, the target MME sets up forwarding parameters by sending Create Indirect Data Forwarding Tunnel Request (target eNodeB addresses and TEIDs for forwarding) to the Serving GW. The Serving GW sends a Create Indirect Data Forwarding Tunnel Response (target Serving GW addresses and TEIDs for forwarding) to the target MME. If the Serving GW is not relocated, indirect forwarding may be set up in step 8 below. Indirect forwarding may be performed via a Serving GW which is different from the Serving GW used as the anchor point for the UE.
  45. 45. LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW (S1) Step 7. If the MME has been relocated, the target MME sends a Forward Relocation Response (Cause, Target to Source transparent container, Serving GW change indication, EPS Bearer Setup List, Addresses and TEIDs) message to the source MME. For indirect forwarding, this message includes Serving GW Address and TEIDs for indirect forwarding (source or target). Serving GW change indication indicates a new Serving GW has been selected. Step 8. If indirect forwarding applies, the source MME sends Create Indirect Data Forwarding Tunnel Request (addresses and TEIDs for forwarding) to the Serving GW. If the Serving GW is relocated it includes the tunnel identifier to the target serving GW. The Serving GW responds with a Create Indirect Data Forwarding Tunnel Response (Serving GW addresses and TEIDs for forwarding) message to the source MME. Indirect forwarding may be performed via a Serving GW which is different from the Serving GW used as the anchor point for the UE. Step 9. The source MME sends a Handover Command (Target to Source transparent container, Bearers subject to forwarding, Bearers to Release) message to the source eNodeB. The Bearers subject to forwarding includes list of addresses and TEIDs allocated for forwarding. The Bearers to Release includes the list of bearers to be released. Step 9a. The Handover Command is constructed using the Target to Source transparent container and is sent to the UE. Upon reception of this message the UE will remove any EPS bearers for which it did not receive the corresponding EPS radio bearers in the target cell. Step 10. The source eNodeB sends the eNodeB Status Transfer message to the target eNodeB via the MME(s) to convey the PDCP and HFN status of the E-RABs for which PDCP status preservation applies. The source eNodeB may omit sending this message if none of the E-RABs of the UE shall be treated with PDCP status preservation. If there is an MME relocation the source MME sends this information to the target MME via the Forward Access Context Notification message which the target MME acknowledges. The source MME or, if the MME is relocated, the target MME, sends the information to the target eNodeB via the eNodeB Status Transfer message. Step 11. The source eNodeB should start forwarding of downlink data from the source eNodeB towards the target eNodeB for bearers subject to data forwarding. This may be either direct (step 11a) or indirect forwarding (step 11b). Step 12. After the UE has successfully synchronized to the target cell, it sends a Handover Confirm message to the target eNodeB. Downlink packets forwarded from the source eNodeB can be sent to the UE. Also, uplink packets can be sent from the UE, which are forwarded to the target Serving GW and on to the PDN GW. Step 13. The target eNodeB sends a Handover Notify (TAI+ECGI) message to the target MME.
  46. 46. LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW (S1) Step 14. If the MME has been relocated, the target MME sends a Forward Relocation Complete Notification () message to the source MME. The source MME in response sends a Forward Relocation Complete Acknowledge () message to the target MME. Regardless if MME has been relocated or not, a timer in source MME is started to supervise when resources in Source eNodeB and if the Serving GW is relocated, also resources in Source Serving GW shall be released. Upon receipt of the Forward Relocation Complete Acknowledge message the target MME starts a timer if the target MME allocated S GW resources for indirect forwarding. Step 15. The MME sends a Modify Bearer Request (eNodeB address and TEID allocated at the target eNodeB for downlink traffic on S1 U for the accepted EPS bearers, ISR Activated) message to the target Serving GW for each PDN connection, including the PDN connections that need to be released. If the PDN GW requested UE's location and/or User CSG information (determined from the UE context), the MME also includes the User Location Information IE and/or User CSG Information IE in this message. If the UE Time Zone has changed, the MME includes the UE Time Zone IE in this message. For the case that neither MME nor S-GW changed, if ISR was activated before this procedure MME should maintain ISR. The UE is informed about the ISR status in the Tracking Area Update procedure. The MME releases the non-accepted dedicated bearers by triggering the bearer release procedure. If the Serving GW receives a DL packet for a non-accepted bearer, the Serving GW drops the DL packet and does not send a Downlink Data Notification to the MME. If the default bearer of a PDN connection has not been accepted by the target eNodeB and there are other PDN connections active, the MME shall handle it in the same way as if all bearers of a PDN connection have not been accepted. The MME releases these PDN connections by triggering the MME requested PDN disconnection procedure. When the Modify Bearer Request does not indicate ISR Activated the Serving GW deletes any ISR resources by sending a Delete Bearer Request to the other CN node that has bearer resources on the Serving GW reserved. Step 16. If the Serving GW is relocated, the target Serving GW assigns addresses and TEIDs (one per bearer) for downlink traffic from the PDN GW. It sends a Modify Bearer Request (Serving GW addresses for user plane and TEID(s), Serving Network) message per PDN connection to the PDN GW(s). The S GW also includes User Location Information IE and/or UE Time Zone IE and/or User CSG Information IE if they are present in step 15. The Serving GW allocates DL TEIDs on S5/S8 even for non-accepted bearers. The PDN GW updates its context field and returns a Modify Bearer Response (Charging Id, MSISDN) message to the target Serving GW. The MSISDN is included if the PDN GW has it stored in its UE context. The PDN GW starts sending downlink packets to the target GW using the newly received address and TEIDs. These downlink packets will use the new downlink path via the target Serving GW to the target eNodeB.
  47. 47. LTE MEASUREMENT HANDOVER HANDOVER INTRA MME/SGW (S1) If the Serving GW is not relocated, but has received the User Location Information IE and/or UE Time Zone IE and/or User CSG Information IE from the MME in step 15, the Serving GW shall inform the PDN GW(s) about these information that e.g. can be used for charging, by sending the message Modify Bearer Request (User Location Information IE, UE Time Zone IE, User CSG Information IE) to the PDN GW(s) concerned. A Modify Bearer Response message is sent back to the Serving GW. If the Serving GW is not relocated and it has not received User Location Information IE nor UE Time Zone IE nor User CSG Information IE from the MME in step 15, no message is sent in this step and downlink packets from the Serving GW are immediately sent on to the target eNodeB. Step 17. The target Serving GW sends a Modify Bearer Response message to the target MME. The message is a response to a message sent at step 15. If the Serving GW does not change, the Serving GW shall send one or more "end marker" packets on the old path immediately after switching the path in order to assist the reordering function in the target eNodeB. Step 18. The UE initiates a Tracking Area Update procedure when one of the conditions listed in clause "Triggers for tracking area update" applies. The target MME knows that it is a Handover procedure that has been performed for this UE as it received the bearer context(s) by handover messages and therefore the target MME performs only a subset of the TA update procedure, specifically it excludes the context transfer procedures between source MME and target MME. Step 19. When the timer started in step 14 expires the source MME sends a UE Context Release Command () message to the source eNodeB. The source eNodeB releases its resources related to the UE and responds with a UE Context Release Complete () message. When the timer started in step 14 expires and if the source MME received the Serving GW change indication in the Forward Relocation Response message, it deletes the EPS bearer resources by sending Delete Session Request (Cause, LBI) messages to the Source Serving GW. Cause indicates to the Source Serving GW that the Serving GW changes and the Source Serving GW shall not initiate a delete procedure towards the PDN GW. The Source Serving GW acknowledges with Delete Session Response () messages. If ISR has been activated before this procedure, the cause also indicates to the Source S GW that the Source S GW shall delete the bearer resources on the other old CN node by sending Delete Bearer Request message(s) to that CN node. Step 20. If indirect forwarding was used then the expiry of the timer at source MME started at step 14triggers the source MME to send a Delete Indirect Data Forwarding Tunnel Request message to the S GW to release the temporary resources used for indirect forwarding that were allocated at step 8. Step 21. If indirect forwarding was used and the Serving GW is relocated, then the expiry of the timer at target MME started at step 14 triggers the target MME to send a Delete Indirect Data Forwarding Tunnel Request message to the target S GW to release temporary resources used for indirect forwarding that were allocated at step 6.
  48. 48. 47 LTE MEASUREMENT HANDOVER HANDOVER IRAT TO 2G/3G
  49. 49. 48 LTE MEASUREMENT HANDOVER HANDOVER IRAT TO CDMA2000 1XRTT and HRPD (High Rate Packet Data)
  50. 50. 49 LTE MEASUREMENT HANDOVER HANDOVER EVENTS If we can see the algorithm, it looks like 3G HO event concept: “hysteresis” – “time to trigger” – “cell individual offset” Event Type Description Event A1 Serving becomes better than threshold Event A2 Serving becomes worse than threshold Event A3 Neighbour becomes offset better than serving Event A4 Neighbour becomes better than threshold Event A5 Serving becomes worse than threshold1 and neighbour becomes better than threshold2 Event B1 Inter RAT neighbour becomes better than threshold Event B2 Serving becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2
  51. 51. 50 LTE MEASUREMENT HANDOVER HANDOVER EVENTS A1
  52. 52. 51 LTE MEASUREMENT HANDOVER HANDOVER EVENTS A2
  53. 53. 52 LTE MEASUREMENT HANDOVER HANDOVER EVENTS A3
  54. 54. 53 LTE MEASUREMENT HANDOVER HANDOVER EVENTS A4
  55. 55. 54 LTE MEASUREMENT HANDOVER HANDOVER EVENTS A5
  56. 56. 55 LTE MEASUREMENT HANDOVER HANDOVER EVENTS B1
  57. 57. 56 LTE MEASUREMENT HANDOVER HANDOVER EVENTS B2
  58. 58. 57 LTE MEASUREMENT HANDOVER Speed dependent scaling of measurement parameters
  59. 59. 58 LTE MEASUREMENT HANDOVER
  60. 60. END Please contact me if there is something wrong in the slide

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