Energy Saving MAC for MIMO Systems

Over the last decade multiple-input and multiple-output (MIMO) systems have been actively researched and started to be deployed in wireless communications owing to the significant increase in channel capacity. In this paper, we propose an energy saving MAC protocol in MIMO (ESMACM) systems by focusing on energy efficiency instead of capacity maximization. ESMACM considers the energy consumption together with the tradeoff between reliability (i.e., diversity) and throughput (i.e., multiplexing gain), and dynamically chooses an appropriate number of antennas for transmission. In computing the total energy consumption, ESMACM counts circuit energy as well as transmission energy. Naturally the circuit energy consumption is directly proportional to the number of active antennas. Through numerical analysis, we confirm that our ESMACM considerably saves energy consumption compared to conventional capacity maximization schemes that use a fixed number of MIMO channels, for a given outage constraint. Our finding is that the capacity maximizing communication which possibly can be regarded best in terms of energy efficiency gives a different solution from the energy minimizing communication.