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Pre-Coordination Mechanism for Fast Handover in WiMAX Networks

Pre-Coordination Mechanism for Fast Handover in WiMAX Networks. Jenhui Chen, Chih-Chieh Wang and Jiann-Der Lee International Conference on Wireless Broadband and Ultra Wideband Communications, 2007 AusWireless, 2007. Outline. Introduction IEEE 802.16e handover Procedures

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Pre-Coordination Mechanism for Fast Handover in WiMAX Networks

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  1. Pre-Coordination Mechanism for Fast Handover in WiMAX Networks Jenhui Chen, Chih-Chieh Wang and Jiann-Der Lee International Conference on Wireless Broadband and Ultra Wideband Communications, 2007 AusWireless, 2007

  2. Outline • Introduction • IEEE 802.16e handover Procedures • Pre-Coordination Mechanism • Simulation Results • Conclusion

  3. Introduction • In 802.16e standard, a mobile subscriber station (MSS) can achieve a best disruption time (DT) of handover. • Under macro diversity handover(MDHO) and fast base station switching (FBSS). • Both methods require the base station (BS) to maintain the neighboring list. • It will waste a large amount of system resources. • There are three different hard handover levels of association. • These can’t achieve optimal DT.

  4. Introduction (cont’) • The feasible solution is reducing the number of forward-and-back turn around times. • Some research proposed location management and random mobility model, but non of them aim at speeding up the handover processing time. • Propose a pre-coordination mechanism (PCM) for BS initialized predicted handover scheme (PHS). • Speed • Location • Handover time (THO)

  5. MDHO and FBSS • The Macro Diversity Hand-Over (MDHO) or Fast BS Switching (FBSS) capability can be enabled or disabled in the REG-REQ/RSP message exchange. • Support of MDHO and FBSS is optional for both MS and BS.

  6. MDHO and FBSS (cont’) • Active BS • A BS which is informed of the MS capabilities, security parameters, service flows and full MAC context information. • Diversity Set • a list of active BSs to the MS. • managed by the MS and BS. • Anchor BS • a BS in the Diversity Set where the MS is registered, synchronized with, performs ranging with and monitors the DL for control information.

  7. In MDHO • MS communicates with all BSs in the Diversity Set for downlink and uplink unicast messages at the same time. • The BSs involving in MDHO • are synchronized based on a common time source. • have synchronized frame structure. • have the same frequency assignment. • shall use the same set of CIDs for the connections that are established with the MS. • are required to share or transfer MAC context. • Authentication state, registration information, etc. • The same MAC/PHY PDUs shall be sent by all the BSs involving in MDHO to the MS.

  8. In FBSS • the MS only communicates with the Anchor BS for UL and DL messages and traffic. • Transition from one Anchor BS to is performed without invocation of HO procedure • BSs involving in FBSS • are synchronized based on a common time source • have synchronized frames • operate at same frequency channel • are required to share or transfer MAC context.

  9. 802.16e Handover Procedures (1/3) Architecture of IEEE 802.16e (AE) standard.

  10. 802.16e Handover Procedures (2/3) • AE-I is exercised in one cell between Serving Base Station (SBS) and Mobile Subscriber Station (MSS). • Inbound： • Packet frames are sent from internet to SBS by mobile internet protocol. • SBS forwards the packet frames to the MSS. • Outbound： • MSS may sent packages to any user of internet by the way of SBS.

  11. 802.16e Handover Procedures (3/3) • AE-II is performed for frame synchronization when MS switches the wireless link from SBS to TBS. • In two cells. • AE-III is executed by a non-serving BS • The BS is neighbor BSs but will be a candidate of TBS. • Perform association of hard handover. • Association of hard handover is an optional initial ranging procedure. • Level 0, Level 1 and Level 2

  12. Association Level 0 (1/3) • Scan/Association without coordination • Contention-based ranging without coordination of handover. • SBS allocates periodic intervals to MSS. • MSS randomly choose a ranging code to perform the initial ranging. • The ranging code is based on random backoff mechanism. • Countdown interval CW=2n+5 n є [0,5]. • After TBS receives ranging code, it sends RNG-RSP and allocate adequate resource for MSS to transmit RNG-REQ.

  13. Association Level 0 (2/3)

  14. Association Level 0 (3/3) • The service disruption time (DT) is defined as starting from SBS or MSS sends a handover request until MSS complete frame synchronization with TBS. • Contention based ranging process + re-authorization + RNG-REQ + re-registration + synchronization with new downlink.

  15. Association Level 1 • It provides the MSS’s association with coordination. • Neighbor BS provide • rendezvous time • A unique code number (from the initial ranging code set) • A transmission opportunity within the allocated region • SBS • Provides these association parameters to the MS • Coordinate association between MMS and nBS • Then, handover process will spend TRA, TRR , the time of TL1 is

  16. Association Level 1 (cont’) • MMS and SBS transmission + SBS and nBS transmission + rendezvous time + re-authorization + re-registration + internet delay + synchronization with new downlink.

  17. Association Level 2 • Network Assisted Association Reporting. • Almost same with Level 1 • the MS DOSE NOT have to wait for RNG-RSP from the neighbor BS • the RNG-RSP information will be sent by each neighbor BS to the Serving BS (over the backbone). • The Serving BS may aggregate all ranging related information into a single MOB_ASC_REPORT message. • MSS and SBS transmission + SBS and TBS transmission + internet delay + synchronization with new downlink.

  18. Comparison 280ms 230ms 60ms PCM: pre-coordination mechanism

  19. Four-Level GCA Framework

  20. Pre-Coordination Mechanism

  21. The step of Mechanism • Step 1: Measure MSS Location. • BS periodically (10sec) broadcast report request (REP-REQ) message to check MSS is still in the service set. • By the response, BS can get SNR value and estimate the distance between SBS and MSS. • The distance is determine as • Step 2: Calculate MSS Movement.

  22. The step of Mechanism • Step 3: Calculate TBS. • As we know the direction of MSS, SBS can decide a unique TBS for MSS. • Using SNR and distances versus frequencies to decide the TBS. • Step 4: Predict THO. • First, we can get velocity by

  23. The step of Mechanism • Average time of Velocity MSS will be • According to GCA framework, we can calculated h leads to • Nc: Number of channels for usage in a macrocell • C00: Number of channels

  24. Pt: transmitted power. • Gt and Gr: Transmitter and receiver antenna gain. • PL(d): path loss with distance d. • L: system loss. • Xσ: zero-mean Gaussian distributed random variable. • FH: highest frequency of system. • σ: path loss exponent • Cf and CH: frequency correction factor and receiver antenna height correction factor. • H: receiver antenna height.

  25. The step of Mechanism • The movement distance between time ta and tb of MSS denote as • We can get • According to above equation, the MSS THO can predicted by

  26. The number of channels in C0 is represent as | C0 | and we have • According to the division of sections, we have • The number of channels in Aij denoted as |Cij| will be

  27. The step of Mechanism • Step 5: Pre-corrdination with TBS. • When MSSi at approaches , SBS will request pre-coordination to TBS for handover • Step 6 and Step 7: TBS Respond. • If the resource of TBS is available, TBS will allocate a non-contention-bas initial ranging opportunity to MSS. • In order to synchronously transfer fast HO. • TBS put fast_ranging_IE in UL-MAP and reply to SBS by MOB_BSHO-RSP. • TBS will only hold this request service for 10 sec.

  28. The step of Mechanism • Step 8: Request Handover. • SBS will prepare pre-coordination handover message of boundary MSS for each 10 sec. • When MSS approaches THO-10s, MSS requests for handover. • SBS broadcasts responded agreement message from TBS to MSS. • Step 9: Fast Handover. • When MSS receives the TBS message, MSS will immediately sends MOB_HO-IND message for handover.

  29. Simulation • Simulator: QualNet. • Simulator Model • Seven BSs and each have six hexagons around them. • The diameter of each hexagon is 1000m. • The range of operating spectrum is 2.40~2.46 GHz. • Simulation model is operating in TDD mode. • Simulator Environment • One serving BS with 40MSSs and 6 nBSs. • MSSs are randomly developed around the BS. • Using QPSK ½ encoding rate.

  30. Disruption time of HO call vs. Number of MSSs

  31. Parameters Used in Handover Failure Probabilities

  32. Handover Failure Probabilities vs. Speeds

  33. Conclusion • Proposed a pre-coordination mechanism (PCM) for BS. • Monitors moving MSS and prepares ranging code for handover. • PCM decreases the disruption time and handover failure probability. • The simulation result show that PCM can improve the lower DT by close to 11ms without changing standard.

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