Mobile WiMAX system operation and state diagrams - Part 4: State transitions in relay stations

[Part 1 begins with an introduction and a look at IEEE 802.16M mobile station (MS) state diagrams. Part 2 continues with a look at the mobile station Access State, Connected State, and Idle State, and their respective operating modes. Part 3 describes network entry/re-entry procedures and the handover process.]

4.4 STATE TRANSITIONS IN RELAY STATIONS
Optional multi-hop relay architecture may be used to provide extended coverage or performance improvement in a radio access network [10–12]. In multi-hop relay networks, the BS may be replaced by a relay-enabled 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 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.