Abstract
A water-filling (WF) method is one of the techniques to improve a performance of multiple-input multiple-output (MIMO) systems. However, the application of the WF method to multiple-hop MIMO relay systems (MMRSs) has not been discussed, especially in amplify-and-forward (AF) schemes. In this paper, the WF method for MMRSs with AF scheme is proposed and evaluated in both perfect and imperfect channel state information (CSI). The effect of imperfect CSI on optimization of transmit power at all transmitters and on co-channel interference is taken into account. Compared to the average transmit power, the end-to-end channel capacity of the WF method is higher in the perfect CSI; however, it is subject to the effect of imperfect CSI. Additionally, half-duplex and full-duplex transmission methods are also discussed in this paper. The end-to-end channel capacity of full duplex is higher and more robust than that of the half duplex due to a double of allocation time and a half of delay time.
Highlights
Multiple-input multiple-output (MIMO) relay systems have been discussed in several literatures [1,2,3,4]
The allocation of transmit power for each antenna based on channel model, meaning water-filling (WF), has been applied to improve the channel capacity of MIMO systems [5,6,7,8]
Scheme 1: the WF method is applied to each hop in MIMO relay systems (MMRSs)
Summary
Multiple-input multiple-output (MIMO) relay systems have been discussed in several literatures [1,2,3,4]. The allocation of transmit power for each antenna based on channel model, meaning water-filling (WF), has been applied to improve the channel capacity of MIMO systems [5,6,7,8]. There are some works on the beamforming design for the special type of half-duplex AF scheme MIMO relay system [18] In these literatures, the WF method was not applied. The WF method can be directly applied to DF scheme MMRSs. the perfect channel state information (CSI) and the half duplex were assumed. The WF method for AF scheme MMRSs is proposed and compared to the original WF of MIMO system. The half-duplex as well as the full-duplex transmission schemes are analyzed based on the end-to-end channel capacity.
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