Pilot-assisted channel estimation without feedback for bi-directional broadband ANC

Broadband analog network coding (ANC) has been recently introduced to increase the network capacity by exploiting the broadcasting nature of the wireless channel. However, channel state information (CSI) knowledge is required for self-information removal and signal detection. Recently, a pilot-assisted channel estimation (PACE) scheme has been presented for broadband ANC, where feedback of the channel estimates from the relay to the users is required. In this work, we introduce a PACE scheme without feedback from the relay for broadband ANC using orthogonal frequency-division multiplexing (OFDM). In the first time slot the users transmit their respective pilots to the relay and in the second time slot the relay simply amplifies and forwards the received pilot signals to both users. Each user can then estimate all the CSI it needs for self-information removal and coherent signal detection, without requiring any feedback from the relay. The bit error rate (BER) performance of broadband ANC using the proposed PACE is evaluated by computer simulation. It was shown that the proposed PACE scheme causes only a slight BER performance degradation compared to the conventional PACE scheme while eliminating the feedback channel requirement.