1. Jenhui Chen, Chih-Chieh Wang and Jiann-Der Lee International Conference on Wireless Broadband and Ultra Wideband Communications, 2007 AusWireless, 2007 1

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

3. 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. 3

4. 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 (T HO ) 4

5. 5 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. 6 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. 7 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. 8 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. Architecture of IEEE 802.16e (AE) standard. 9

10. 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. 10

11. 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 11

12. 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=2 n+5 n є [0,5]. After TBS receives ranging code, it sends RNG-RSP and allocate adequate resource for MSS to transmit RNG- REQ. 12

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14. 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. 14

15. 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 T RA, T RR, the time of TL1 is 15

16. MMS and SBS transmission + SBS and nBS transmission + rendezvous time + re-authorization + re-registration + internet delay + synchronization with new downlink. 16

17. 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. 17

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

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21. 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. 21

22. 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 T HO. First, we can get velocity by 22

23. 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 C 00 : Number of channels 23

24. Pt: transmitted power. G t and G r : Transmitter and receiver antenna gain. PL(d): path loss with distance d. L: system loss. X σ : zero-mean Gaussian distributed random variable. F H : highest frequency of system. σ: path loss exponent C f and C H : frequency correction factor and receiver antenna height correction factor. H: receiver antenna height. 24

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

26. The number of channels in C 0 is represent as | C 0 | and we have According to the division of sections, we have The number of channels in A ij denoted as |C ij | will be 26

27. 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. 27

28. Step 8: Request Handover. SBS will prepare pre-coordination handover message of boundary MSS for each 10 sec. When MSS approaches T HO -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. 28

29. 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. 29

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34. 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. 34