Channel Access Scheme for MIMO-Enabled Ad Hoc Networks with Adaptive Diversity/Multiplexing Gains
Transmission power control (TPC) is used in wireless networks to improve channel reuse and/or reduce energy consumption. It has been often applied to single-input single-output (SISO) systems, where each node is equipped with a single antenna. Multi-input multi-output (MIMO) systems can improve the throughput or the signal-to-noise ratio (SNR) by providing multiplexing or diversity gains, respectively. In this paper, we incorporate a power-controlled MAC protocol for a wireless network with two antennas per node. Our protocol, coined CMAC, combines different types of MIMO gains, allowing for dynamic switching between diversity and multiplexing modes so as to maximize a utility function that depends on both energy consumption and throughput. CMAC adapts the antenna mode, the transmission power, and the modulation order on a per-packet basis. By antenna mode we mean one of five possible transmit/receive antenna configurations: 1  1 (SISO), 2  1 (MISO-D), 1  2 (SIMO-D), 2  2 (MIMO-D), and 2  2 (MIMO-M). The second, third, and fourth configurations offer a diversity gain, whereas the last configuration offers a multiplexing gain. By using control packets to bound the transmission power of potentially interfering terminals, CMAC allows for multiple interference-limited transmissions to take place in the vicinity of a receiving terminal. We study via simulations the performance of CMAC in ad hoc topologies. Our results indicate that relative to non-adaptive protocols, CMAC achieves a significant improvement in both the overall energy consumption and the throughput.
mimo ad hoc networks multiplexing gain power control diversity gain