Directional Access And Spatial Multiplexing Mechanism Design For Wireless Ad Hoc Networks

Due to its flexible and fast networking mode, wireless ad hoc networks have been widely used in military, agriculture and disaster relief environment. However, as the network information increased dramatically, ad hoc network with omni-directional antenna cannot meet the demand for network capacity and bandwidth. While the directional antenna has superiority on spatial reuse, antenna gain, transmission range and interference rejection, it can greatly improve the performance of wireless ad hoc networks. Thus, a directional access and spatial multiplexing mechanism for wireless ad hoc networks is proposed in this paper to take full advantage of directional antenna.Taking into consideration of the inevitable collisions in random access mechanism and the real-time demand of ad hoc networks, the proposed mechanism is based on TDMA, and slots are allocated in a distributed way through a location-information table kept by every node in the network. In order to achieve spatial multiplexing and improve the wireless channel utilization rate, two contention stages are added in each slot so that up to three nodes can send data in the same slot. The contention stage uses binary countdown mechanism instead of traditional CSMA for nodes to win the slot by sending unique busy tone sequence according to their MAC ID so that collision is completely avoided. Meanwhile, the binary countdown mechanism is improved to eliminate unfair competition and support priority. In addition, the proposed mechanism offers adaptive power control to reduce energy consumption, interference, and enhance the spatial reusing capability.The proposed directional access and spatial multiplexing mechanism is analyzed in both theoretical and emulational way. First, the expressions of network throughput and average delay in saturation networks are derived. Then MATLAB is used to verify the theoretical analysis, and simulate the proposed mechanism as well as three traditional access mechanisms, DMAC, IEEE802.11DCF and omni-TDMA. As can be seen from scene one, the simulation results are in line with the theoretical analysis. And the simulation results of scene two show that the performance of network throughput and average delay in wireless ad hoc networks is significantly improved using the proposed mechanism.