A Channel Switching Scheme for Layered Video Using Relay Transmissions

Abstract

The advantage of multicast in wireless medium is that all stations can receive the data through a single transmission. The multicast is utilized by the application delivering video contents such as IPTV and internet streaming for efficient transmission. Although multicasting is efficient, legacy multicast has two critical problems as follows: bottleneck in multicast group and unfairness between unicast and multicast. The bottleneck problem is incurred since legacy multicast uses the lowest data rate to cover a single weak station. The lowest data rate is especially critical on the stations connected to an access point (AP) with higher data rate. It is not possible for the multicast stations adjacent AP to receive high-quality video. Rate adaptation of multicast was proposed to solve the bottleneck problem. The approach has a critical limitation that multicast rate fall back to basic rate when a single weak station is in the network. Another approach is relay multicast which utilizes relays having a strong link with destination. In these schemes, the candidates of relay are stations powered by battery. It is not feasible for the existing schemes to apply to real networks since energy-constraint devices do not serve as the relay to cause additional energy consumption. The alternative is proxy-based relay network using fixed proxy. The approach also has the limitation, insignificant improvement of throughput. The multicast The advantage of multicast in wireless medium is that all stations can receive the data through a single transmission. The multicast is utilized by the application delivering video contents such as IPTV and internet streaming for efficient transmission. Although multicasting is efficient, legacy multicast has two critical problems as follows: bottleneck in multicast group and unfairness between unicast and multicast. The bottleneck problem is incurred since legacy multicast uses the lowest data rate to cover a single weak station. The lowest data rate is especially critical on the stations connected to an access point (AP) with higher data rate. It is not possible for the multicast stations adjacent AP to receive high-quality video. Rate adaptation of multicast was proposed to solve the bottleneck problem. The approach has a critical limitation that multicast rate fall back to basic rate when a single weak station is in the network. Another approach is relay multicast which utilizes relays having a strong link with destination. In these schemes, the candidates of relay are stations powered by battery. It is not feasible for the existing schemes to apply to real networks since energy-constraint devices do not serve as the relay to cause additional energy consumption. The alternative is proxy-based relay network using fixed proxy. The approach also has the limitation, insignificant improvement of throughput. The multicast throughput lowers as the number of proxy relay increases. In addition to bottleneck problem, unfairness between uncast and multicast is caused by operation of legacy multicast and the property of video traffic. In this thesis, we propose SwitchingAP, switching mechanism for unicast-fair multicast of layered video exploiting relay transmission. SwitchingAP utilizes the idle time for AP to wait for end of relay transmission. Additional enhancement layers are transmitted to the stations adjacent to AP by moving to secondary channel during idle time. It is possible to improve the quality of layered video on the stations close to AP. The delay on unicast packets can be also eased by exploiting remaining time after transmission of enhancement layers, which improves fairness between unicast and multicast. Our simulation shows that the proposed scheme enhanced quality of layered video and alleviated delay and throughput unfairness between unicast and multicast.