By combining the features of CSMA and TDMA, fully decentralised WLAN MAC schemes have recently been proposed that converge to collision-free schedules. In this paper we describe a MAC with optimal long-run throughput that is almost decentralised. We then design two schemes that are practically realisable, decentralised approximations of this optimal scheme and operate with different amounts of sensing information. We achieve this by (1) introducing learning algorithms that can substantially speed up convergence to collision free operation; (2) developing a decentralised schedule length adaptation scheme that provides long-run fair (uniform) access to the medium while maintaining collision-free access for arbitrary numbers of stations.
A collision-free MAC is introduced in @cite_10 for wireless mesh backbones. It guarantees priority access for real-time traffic, but it is restricted to a fixed wireless network and requires extra control overhead for every transmission. Ordered CSMA @cite_16 uses a centralised controller to allocate packet transmission slots. It ensures that each station transmits immediately after the data frame transmission of the previous station. It has the drawback of requiring a centralised controller with its associated coordination overhead.
@cite_16 @cite_10
2107116407 2068118042
Since underwater acoustic (UWA) networks have the nature of long propagation delay, low bit rates and error-prone acoustic communication, protocols designed for underwater acoustic networks are significantly different from that of terrestrial radio networks. Limited by these nature of UWA channels, conventional medium access control (MAC) protocols of radio packet network ether have low efficiency or are not able to apply to underwater acoustic networks. It is necessary to develop an efficient MAC protocol for underwater acoustic networks. In this paper, a collision-free MAC protocol for UWA networks called Ordered Carrier Sense Multiple Access (Ordered CSMA) is proposed and analyzed. Ordered CSMA combines the concepts of round-robin scheduling and CSMA. In Ordered CSMA, each station transmits data frame in a fixed order. More specifically, each station transmits immediately after the data frame transmission of last station in the order, instead of waiting for a period of maximum propagation delay. To achieve this, each station is constantly sensing the carrier and listens to all received frames. Due to the characteristics of collision free and high channel utilization, Ordered CSMA shows a great MAC efficiency improvement in our simulations, compared to previous works. In this paper, a novel collision-free MAC scheme supporting multimedia applications is proposed for wireless mesh backbone. The proposed scheme is distributed, simple, and scalable. Benefiting from the fixed locations of wireless routers, the proposed MAC scheme reduces the control overhead greatly as compared with the conventional contention-based MAC protocols (e.g., IEEE 802.11). In addition, the proposed scheme can provide guaranteed priority access to real-time traffic and, at the same time, ensure fair channel access from the routers with data traffic. Unlike most of the existing works which focus on single-hop transmissions, the proposed MAC scheme takes the intra-flow correlations between up-stream and down-stream hops of a multi-hop flow into consideration. To avoid buffer overflow at bottleneck routers, a simple but effective congestion control mechanism is proposed. Simulation results demonstrate that the proposed scheme significantly improves the delay performance of real-time traffic, the fairness of data traffic, and the end-to-end data throughput, as compared with IEEE 802.11.