This paper addresses relay precoder designs for amplify-and-forward MIMO relay networks with imperfect channel state information (CSI). We first derive the capacity of a MIMO relay network with imperfect CSI. Two relay precoding schemes are then proposed -- Scheme I maximizes the upper bound of the capacity obtained by applying Jensen's equality, whilst scheme II simply ignores the error of CSI of the channel from the relay to the destination. Numerical results show that, the capacity increases with the correlation coefficients between the CSI known to the estimating nodes and the CSI known to other nodes. %With higher correlation, e.g. correlation coefficient $\rho_1=1, \rho_2=0.9$, the proposed scheme I and II approaches the capacity achieved with perfect CSI at all nodes. Furthermore, the correlation coefficient of the channel from the source to the relay has more impact on the capacity than the channel from the relay to the destination. Numerical results also show that, the proposed relay precoder Scheme I achieves better capacity than Scheme II and the existing scheme, while Scheme II in some cases performs better than the existing scheme.
['Ronghong Mo', 'Yong Huat Chew', 'Chau Yuen']
Relay Precoder Designs for Amplify-and-Forward MIMO Relay Networks with Imperfect Channel State Information