A pilot emitting amplify-and-forward relay and its application to hop-by-hop beamforming

A pilot emitting amplify-and-forward relay and hop-by-hop beamforming (HBF) scheme are proposed for two-hop relaying systems. The conventional beamforming (CBF) is performed with respect to an overall channel from a source node (SN) to a destination node (DN) through a relay node (RN) while the proposed HBF performs two independent beamformings, from the SN to the RN and from the RN to the DN. For beamforming, the SN and the DN require the channel state information (CSI) from the SN to the RN and from the RN to the DN, respectively. From our analytic and numerical results, it is shown that the bit-error-rate (BER) performance of the proposed HBF is identical to that of CBF with the perfect CSI. However, the proposed HBF can achieve a lower BER than the CBF method since the channel estimation performance of the HBF system is better than that of CBF, and this is verified by deriving and comparing the mean square errors of the channel estimations of HBF and CBF.