Hard Handoff Scheme Exploiting Uplink and Downlink Signals in IEEE 802.16e Systems

We consider hard handoff scheme based on uplink and downlink signals in IEEE 802.16e systems. To exploit the channel reciprocity in TDD systems, the proposed scheme triggers handoff initiation process using uplink signal. A serving base station monitors uplink traffic signal and triggers handoff process when the uplink signal strength or SINR becomes less than the predetermined level. This process can prevent mobile stations from periodically monitoring and reporting downlink signals of neighbor base stations at the non handoff region. In the handoff decision process, the proposed scheme exploits not only uplink signal but also downlink signal as the handoff criteria to reduce ping-pong and outage probability. To efficiently combine uplink and downlink signal levels, the proposed scheme adopt an uplink and downlink joint hysteresis to determine a handoff direction. Using the joint hysteresis can reduce the outage probability compared with using uplink and downlink hysteresis independently. We evaluate the performance of the proposed scheme using computer simulation. The simulation results show that the proposed algorithm has better performance than the conventional mobile assisted handoff scheme of IEEE 802.16e in terms of the average number of handoff and the outage probability during handoff.