The effect of frequency offset on the multiple antennas receiver initiated busy tone medium access (MARI-BTMA) protocol

Multi-hop ad hoc networks suffer from hidden nodes and exposed nodes. The multiple antennas receiver initiated busy tone medium access (MARI-BTMA) with the MIMO-OFDM transceiver architecture is a promising technique to exploit diversity in the physical layer of broadband wireless communications to achieve better performance in the ad-hoc network. If the channel is asynchronous then this scheme suffers from frequency offset, which results in unfairness and lowers throughput. In this paper, the power leakage from multiple carriers due to the frequency offset is calculated. Varying the carrier sensing threshold level on the busy tone channels is proposed as a way to overcome this problem. The carrier sensing threshold level chosen is a trade-off between the exposed area and the hidden area. The optimal threshold level is derived which minimizes the sum of the exposed node area and the hidden node area. Numerical results show how the total area changes with respect to the frequency offset. The effect of frequency offset, path loss exponent and distance between the transmitter and the receiver on the optimal threshold level and the carrier sensing range are also analyzed