Joint MIMO-OFDM and MAC Design for Broadband Multihop Ad Hoc Networks

Multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) are very promising techniques to exploit spatial diversity and frequency diversity in the physical layer of broadband wireless communications. However, the application of these techniques to broadband multihop ad hoc networks is subject to inefficiencies since existing medium access control (MAC) schemes are designed to allow only one node to transmit in a neighborhood. Therefore, adding more relays to increase the transmission range decreases the throughput. With MIMO-OFDM, multiple transmissions can coexist in the same neighborhood. A new transceiver architecture with MIMO-OFDM and MAC scheme is proposed in this paper. The new MAC scheme multiple-antennas receiver-initiated busy-tone medium access (MARI-BTMA) is based on receiver-initiated busy-tone medium access (RI-BTMA) and uses multiple out of band busy tones to avoid the collision of nodes on the same channel. With the proposed MAC scheme, multiple users can transmit simultaneously in the same neighborhood. Although basic MARI-BTMA shows good performance at high traffic load, to improve the performance at low traffic loads, 1-persistent MARI-BTMA is proposed so that users can choose different MAC scheme according to the statistical traffic load in the system. In this paper, both theoretical and numerical analysis of the throughput and delay are presented. Analysis and simulation results show the improved performance of MARI-BTMA compared with RI-BTMA and carrier sensing medium access/collision avoidance (CSMA/CA).