Wimax standards and Security The Wimax

UL-MAP
(Dedicated ranging region)


Ranging code RNG-RSP

Association process (level 1)

RNG-REQ
(Serving BSID, MS MAC address)


FIGURE 6.7
Operation of scanning with association of level 1.

BS provides the association parameters (ranging region, unique code num- ber, and dedicated transmission opportunity) at a predefined rendezvous time. The serving BS informs the MS of these parameters by sending an MOB_SCN-RSP message. The rendezvous time specifies the frame in which the neighboring BS will transmit a UL-MAP containing the definition of the dedicated ranging region where the MS uses the assigned ranging code. The rendezvous time is defined as units of frames, which begins at the frame where the MOB_SCN-RSP message is transmitted. In the scanning inter- val, the MS synchronizes with the neighboring BS first, reads the UL-MAP transmitted at the rendezvous time, and extracts the description of the dedi- cated ranging region from this UL-MAP. Then, the MS determines the specific region where it should transmit the dedicated ranging code at the dedicated transmission opportunity. Neighboring BSs will assign a different code or a different transmission opportunity for the association, so there is no potential for transmissions from different MSs to collide. Hence, association will be fast. Association level 2 is similar to association level 1. The difference is that an MS does not have to wait to receive the RNG-RSP from a neighboring BS after it transmits the ranging code to it. Instead, the RNG-RSP information is sent from each neighboring BS to the serving BS over the backbone. The serving BS aggregates all ranging information into a single MOB_ASC-REP message and transmits it to the MS. When receiving this report message, the MS updates its association database (physical offsets, time offsets, and channel identities (CIDs)) for each associated BS. Association level 2 supports fast association without access collision and the efficient reception of aggregating association information, but it requires more signaling overhead between the serving BS
and target BSs.

2.