Energy Efficient Cooperative MIMO Systems

In this paper we propose an energy efficient cooperative MIMO system. Space-time block codes (STBC) and code combining techniques are applied to utilize the inherent spatial diversity in wireless cooperative MIMO systems. We form a group of senders and receivers to provide higher order MIMO diversity and implement our STBC scheme in a distributed manner. In the receiving group, code combining is used with error control coding techniques to utilize receiver diversity. With the distributed implementation of STBC and code combining, MIMO diversity can be obtained in cooperative MIMO systems. We present analysis and simulation results for reliability (BER vs SNR curves) and energy efficiency. Our reliability curves are significantly better than SISO achieving MIMO-like diversity gains. Additionally, we examine energy consumption and show that the data transmission power can be low as 0.7 mW for 4-node send/receive group size in our cooperative MIMO system, compared to a point-to-point SISO system that consumes 30 mW. However, the cooperative MIMO introduces overhead and sacrifices system capacity. With the same number of sending nodes/antennas, the system capacity of 4×4 cooperative MIMO system is less than conventional 4×4 MIMO system due to cooperation overheads [1]. Thus there is tradeoff between energy consumption and system capacity in proposed system. In summary, our proposed system provides reliable and energy-efficient transmission by leveraging MIMO diversity gains through cooperation between nodes.