Adaptive window width control for cyclic shifted pilot aided channel estimation suitable for SC-ANC bi-directional relay using joint Tx/Rx MMSE-FDE

In analog network coded (ANC) relay with conventional channel estimation, the feedback of the estimated channel state information (CSI) is required, and hence, the bandwidth efficiency decreases. A cyclic-shifted pilot aided channel estimation (CSPACE) is used to simultaneously estimate two equivalent channels which are required for joint transmit/receive frequency-domain equalization (FDE) and own transmitted signal removal and hence, it requires no CSI feedback. In CSPACE, the delay time-domain windowing is used to separate two equivalent channels and suppress the impact of noise. However, in single-carrier (SC) ANC multi-antenna bi-directional relay (SC-ANC-MBDR) with the joint transmit/receive FDE, the equivalent channel is a concatenation of the propagation channel and the transmit FDE, and hence, its impulse response spreads over the entire delay time-domain. Therefore, the optimal delay time-domain window varies according to changing instantaneous received signal-to-noise power ratio (SNR), and as a consequence, the channel estimation accuracy degrades if the window width for the delay time-domain windowing is not adapted to the instantaneous received SNR. In this paper, we propose an adaptive window width control (AWWC) for CSPACE. The proposed AWWC adaptively changes the window size so as to minimize the mean square error (MSE) between the channel estimate and the actual channel. It is confirmed by the computer simulation that CSPACE using our proposed AWWC can always achieve BER performance superior to when using fixed window width.