A software approach to channel-state dependent scheduling for wireless LANs

This paper proposes a new practical packet scheduling scheme for wireless LANs called SoCPS and also explores extensively the effectiveness of wireless packet scheduling under a variety of conditions over an actual wireless LAN. One well-known aspect in packet scheduling at the base station is consideration of channel state dependency. In conventional studies, the channel state is expressed in microscopic two states in the Markovian sense. To eliminate a large overhead associated with acquiring such a fine-grain channel state and to establish a software-based enhancement, we introduce the notion of Strength of Connection (SoC) which can be expressed as the long-term strength of the connectivity between the base station and an end host. We examine schemes for identifying the channel state and examine the applicability to packet scheduling. We also design a packet scheduling scheme based on SoC called SoCPS. Finally, we investigate the performance under various conditions of traffic and wireless channel states. We have designed and implemented SoCPS on FreeBSD computers. Our evaluation results obtained with up to eight wireless-LAN nodes have determined the applicability of SoCPS and limitation in wireless packet scheduling for wireless LANs. In particular, while FIFO is sufficient in many cases where TCP traffic is dominant, scheduling with SoC consideration is effective for real-time UDP traffic.