Link-adaptive medium access control protocols for high-speed wireless networks

Medium Access Control (MAC) protocols for wireless networks have been studied extensively to support broadband communication services with various Quality-of-Service (QoS) requirements. Our study aimed to improve the performance of MAC protocols using channel information in high-speed wireless networks such as wireless local area networks (WLANs) and wireless personal area networks (WPANs).; First, a rate-adaptive protocol with dynamic fragmentation was proposed to enhance the throughput based on fragment transmission bursts and channel information. Instead of using a fragmentation threshold as in the IEEE 802.11 standard, I introduced multiple thresholds for different data rates, so that more data could be transmitted at higher data rates when the channel is good. In the proposed scheme, the channel can be used more effectively to squeeze more bits into the medium.; Second, I proposed an efficient polling-based MAC protocol, referred to as Two-Step MultiPolling (TS-MP), with the goal of serving as a centralized polling-based channel access method that also supports time-bounded services. The TS-MP protocol uses two multi-polling frames for different purposes. The first polling frame is broadcast to collect information such as the numbers of pending frames and the physical layer transmission rates for the communication links among all stations, which help to implement rate adaptation over the time-varying wireless channel. The second polling frame contains a polling sequence for data transmissions that was designed based on the collected information.; Finally, I proposed a feedback-assisted and link-adaptable MAC protocol and an efficient channel-time allocation algorithm for delay-constrained real-time traffic in WPANs. Channel time for each node is initially allocated based on statistical packet inter-arrival time. Then, the initial allocation is dynamically adjusted by using feedback information coming from each DEV. Feedback information includes buffer status, packet transmission delay, and physical transmission rate. From the buffer status and rate information, the central DEV can allocate sufficient channel time for transmissions of pending packets at a DEV. In addition, the allocated channel times can be synchronized to the packet arrival time using the feedback information. This reduces the overall transmission delay. To cope with time-varying wireless channels, a dynamic rate-selection algorithm assisted by physical layer information is proposed.