Adaptive coding strategies for beamforming ad hoc networks

The application of beamforming to mobile ad hoc networks has been studied extensively. It has been shown that a simple transmit beamforming protocol may yield better performance than a traditional four-way handshake protocol. However, for a data packet of moderate size (around 10⁴ bits), obtaining a reasonable packet error rate in fast fading requires an average uncoded bit error rate of 10^-5. This is impractical in most radio networks and especially in the ad hoc case. Therefore the use of error correcting codes is required. Furthermore, to fully take advantage of the channel capacity, an adaptation coding scheme with variable code rate is usually required. The choice of the variable rate coding scheme and MAC protocol has been addressed recently as a cross-layer design problem. However, most variable rate coding methods choose the rate in a heuristic manner. In this paper we introduce a procedure to calculate an appropriate code rate for an ad hoc network employing both transmit and receive beamforming under a basic access (CSMA/CA) protocol. Though the method can be applied to CSMA networks with or without beamforming, due to the limited space of the space, in this paper we only present the detail calculation for the beamforming case. Simulation results show that the new combination of variable-rate coding and beamforming improves network throughput significantly.