Energy-Efficient Protocols for Wireless Networks with Adaptive MIMO Capabilities Mohammad Z. Siam*, Marwan Krunz*, Shuguang Cui**, and Alaa Muqattash* * Department of Electrical and Computer Engineering ** Department of Electrical and Computer Engineering The University of Arizona Texas A&M University Tucson, AZ 85721 College Station, TX 77843 {siam, krunz, alaa}@ece.arizona.edu cui@ece.tamu.edu Abstract Transmission power control has been used in wireless networks to improve the channel reuse and/or reduce energy consumption. It has been mainly applied to single-input single-output (SISO) systems, where each node is equipped with a single antenna. In this paper, we propose a power-controlled channel access protocol for MIMO-capable wireless LANs with two antennas per node. Our protocol, called E-BASIC, extends the classic CSMA/CA access scheme by allowing for dynamic adjustment of the transmission mode and the transmission power on a per-packet basis so as to minimize the total energy consumption. By transmission mode we mean one of the four possible transmit/receive antenna configurations: 1 × 1 (SISO), 2 × 1 (MISO), 1 × 2 (SIMO), and 2 × 2 (MIMO). Depending on the transmitter-receiver distance, any of the four modes can be the optimal one in terms of minimizing the total energy consumption. We study the performance of E-BASIC in both ad hoc and access point topologies. We also incorporate E-BASIC in the design of a power-aware routing (PAR) scheme that selects minimum-energy end-to-end paths. Our adaptive designs are first conducted assuming fixed-rate transmission, but later extended to multi-rate systems. To account for the energy-throughput tradeoff in our designs, we impose a constraint on the average packet delivery time. Simulations indicate that the proposed adaptations achieve a significant reduction in the overall energy consumption relative to non-adaptive MIMO systems. Index Terms This research was supported in part by NSF (under grants CNS-0721935, CNS-0627118, CNS-0325979, and CNS-0313234), Raytheon, and Connection One (an I/UCRC NSF/industry/university consortium). Any opinions, findings, conclusions, or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the National Science Foundation. An abridged version of this paper was presented at the IWCMC 2006 Conference, Vancouver, Canada, July 3-6, 2006.