d BS (i.e., a BS with relay functionalities) and one or more Relay Stations (RS). Traffic and signaling between the MS and the BS can be relayed by the RS, thereby extending the coverage and improving the performance of the system in areas where relay stations are deployed. Each RS is under the supervision of a relay-enabled BS. In a multi-hop system, traffic and signaling 126 CHAPTER 4 IEEE 802. 16m System Operation and State Diagrams Serving Target HO Initiation HO Request HO Response HO Command HO Indication Network Re-entry MS-BS Communication during Network Re-entry HO COMPLETE Data Plane Established FIGURE 4-16 The IEEE 802. 16m handover process (mobile-initiated handover) [2] between an access RS and the BS may also be relayed through intermediate relay stations. The RS may be fixed in location or mobile. The MS may also communicate directly with the BS. Figure 4-17 illustrates the state transition diagram of an IEEE 802.16m relay station. The relay station state diagram consists of three states: (1) Initialization State; (2) Access State; and (3) Operational State. Note that the IEEE 802. 16m standard currently supports two-hop relaying only; therefore, some of the procedures concerning multi-hop relaying may not apply. 4.4.1 Initialization State In the Initialization State, the relay station performs cell selection by scanning and synchronizing to a base station (in the case of two-hop relay network topology) or another relay station (in the case of multi-hop relay network topology) to acquire the system timing and configuration information prior to entering the Access State. If the relay station successfully acquires system timing, decodes the configuration information, and selects a target access station, it transitions to the Access State; otherwise, it repeats the scanning and synchronization procedures (see Figure 4-18). The RS follows the same scanning and synchronization procedures as described for an MS. In addition, the RS may store preamble indices and corresponding received RF signal strength 