MOB_SCN-RSP CDMA Code Scanning Interval (No Data Traffic) Anonymous RNG-RSP RNG-REQ RNG-RSP Scan BS No 2 MOB_SCN-REP MOB_MSHO-REQ MOB_BSHO-RSP MOB_MSHO-IND Network Re-entry with BS No 2 FIGURE 6-11 MS initiated hard handover call flow with association level O [1,9] advertised periodically by the serving BS through the broadcast MOB_NBR-ADV message. During the scanning period, user data is not exchanged between the MS and the serving BS; instead the MS receives the preambles from each neighbor BS and calculates the RSSI. An optional procedure called association can be used to help the handover process. The association enables the MS to acquire and record ranging parameters and service availability information during scanning. Three association levels are defined in the standard as follows [1]: a. In association level 0, the MS completes ranging during the scanning period with randomly chosen ranging Code Division Multiple Access (CDMA) code. A unique code from an initial ranging code set that is assigned to the MS and used for dedicated ranging [1]. Table 6-5 IEEE 802.16m Signaling Header Types, their Usage, and Parameters [2] Signaling Header Type Description Usage Parameters Bandwidth This header is transmitted when the MS Bandwidth Request Request with FID (4 bits) is the flow identifier whose value is set to requests bandwidth through a non- 0b0001. dedicated uplink resource. In this case, Type (5 bits) indicates the MAC signaling header the MS transmits this signaling header type. and includes its STID over the non- dedicated uplink resource. Length (3 bits) denotes the length of the signaling header in bytes. BR Size (19 bits) is the aggregated bandwidth request size in bytes. BR FID (4 bits) is the FID for which uplink bandwidth is requested. STID (12 bits) is the STID of the MS which requests the bandwidth. Bandwidth This header is used when the MS Bandwidth Request FID (4 bits) which is set to 0b0001. Request requests bandwidth (incrementally or without STID Type (5 bits) denotes the MAC signaling header 