Performance analysis of water-filling for outdated CSI multiple hops MIMO relay systems

Water-filling methods is one of techniques to improve a performance of multiple input multiple output (MIMO) system. However, the application of water-filling method to multiple hops MIMO relay system hasn´t been discussed, especially in amplify and forward scheme. In this paper, the water-filling method for multiple hops MIMO relay system with amplify and forward scheme is proposed and evaluated in both perfect channel state information (CSI) and imperfect CSI. The effect of imperfect CSI on water-filling and on co-channel interference is taken into account. Compared to average transmit power, the end-to-end channel capacity of proposed water-filling method is higher in perfect CSI, however, it is subject to the effect of imperfect CSI. Additionally, a half duplex and a full duplex transmission method are also discussed in this paper. The end-to-end channel capacity of full duplex is higher and more robust than that of half duplex due to a double of allocation time and a half of delay time.