cedures in IEEE 802.16m can be divided into four steps: Handover Initiation Handover procedure may be initiated either by the MS or the BS. When handover is initiated by the MS, the triggers and conditions are defined by the serving BS and a handover initiation message is sent by the MS to begin the handover procedure. In the case of BS-initiated handover, the handover preparation is performed before handover initiation, and the AAI_HO-CMD message is sent by the BS to initiate the handover procedure (see Figure 6-15). During handover initiation, the serving BS indicates whether the MS can maintain data communication with the serving BS while performing network re-entry with the target BS by setting the HO_Re-entry_Mode field in AAI_HO-CMD to 1; otherwise, the HO_Re-entry_Mode filed is set to 0. Handover Preparation During the handover preparation stage, the serving BS communicates with potential target base stations. The target BS may obtain MS context from the serving BS via core network for handover optimization. If ranging with the target BS is not performed prior to or during handover preparation, dedicated ranging resources such as ranging code or ranging opportunity with the target BS may be reserved for the MS to facilitate non-contention-based handover ranging. The information related to MS identity and security context may be updated during handover preparation. Any inconsistent system information between the MS and the target BS, if detected, may be provided to the MS by the serving BS during handover preparation. If only one target BS is included in the handover command, the handover preparation phase is completed when the serving BS informs the MS of its handover decision via a handover command. If multiple target base stations are included in the handover command, the handover preparation phase is completed when the MS informs the serving BS about its target selection through a handover indi- cation message. The handover command may include dedicated ranging resource allocation and resource pre-alloc