MAC Protocols Design For Wireless Mesh Networks With Directional Antennas

Wireless mesh networks are new meshing topology with characteristics of ad hoc networks.Using directional antennas can increase spatial reuse and network throughput. It also achieves longer transmission distance and decreases transmissions hops and end-to-end delay. Therefore, using directional antennas can significantly improve the whole performance of wireless mesh networks.However, some new challenges are generated with using directional antennas, e.g. deafness and new hidden terminal. How to design an efficient and reliable MAC protocol becomes the key to achieve high performance of wireless mesh networks. In the paper, considering the typical characteristics of wireless mesh networks, we propose two different directional MAC schemes for single-hop and multi-hop environment. The main contributions of the paper are as follows:1. We propose a novel time-division MAC protocol based on link-scheduling for directional single-hop mesh networks. In the protocol, time is divided into frames of constant length, and each frame is divided into a scheduling and a transmission subframe. Nodes perform channel sensing during the scheduling subframe and transmit packets in parallel during the transmission subframe.Based on the directional transmissions, the LSCT(link-scheduling for concurrent transmissions)algorithm uses least slots to allocate more non-conflict links, which maximizes the network capacity.In addition, to provide per-link fairness in the protocol, LSCT is rotated in the beginning of each periodic frame. Extensive simulations have been done in EXata and the simulation results show that,compared with other typical DMAC protocol, our proposed protocol effectively takes advantages of spatial reuse, which achieves significant improvement in network throughput and decreases the end-to-end delay of packets transmission.2. We propose a directional MAC protocol with concurrent transmission of neighbor nodes for multi-hop mesh networks. In the protocol, based on the temporary synchronization in part of the networks, time is divided into three periods: master node generating, channel reservation and concurrent transmission. During the first period, node which completes backoff strategy first transmits an ORTS(Omni-directional RTS) frame to its intended destination. Target node which receives the ORTS then replies an OCTS(Omni-directional CTS) frame, which contains the information of receiving beam index. Once receiving the OCTS, source node sends a DRTS(Directional RTS) to its destination, which contains the information of transmitting beam index. Therefore, transceivers complete medium access and beam indication through the ORTS/OCTS/DRTS three-way handshake.As a result, they become the master pairs in the local area. During the second period, master node sets appropriate waiting time for channel reservation before its data transmission, allowing its neighbor nodes are able to access the channel in the same time(we call them slave nodes). During the last period, nodes which successfully reserve the channel transmit their packets concurrently without collisions. Simulation results show that frequent concurrent transmissions in local areas make great contributions to improve network throughput and bandwidth utilization.