A Capacity Improvement Method for MIMO Systems at Low Signal-to-Noise Ratio Levels

In MIMO systems, antenna selection can increase channel capacity and reduce complexity and costs of RF circuits effectively. After the derivation of an approximate expression of MIMO system capacity at low signal-to-noise ratio levels, a novel method for further increasing MIMO system capacity was proposed. The transmit or receive antennas were selected out at the receiver side according to the Frobenius norm of the channel matrix and the results were fed back to the transmitter side by which the transmitter using water-filling power allocation to transmit signals. This method not only has lower computational complexity but also needs less feed back information than the antenna selection at the transmitter side. Simulation results indicate that applying this method on transmit and receive antennas respectively can significantly improve system capacity, while using this method simultaneously on transmit and receive antennas, the effect on capacity improvement is less obvious than the former.