Proposal of a combined CFR estimation method for practical bidirectional ANC-OFDM system in higher time-varying fading channel

In bidirectional analogue network coding based on orthogonal frequency division multiplexing (ANC-OFDM) system, two users can transfer their data to each other via the Relay during two timeslots. Each user can demodulate the other user’s data after removing the self-data with equalizing by employing the combined channel frequency response (CFR) estimated at each user in the 2nd timeslot. From this reason, the accurate channel estimation method for the combined CFR acts on the bit-error-rate (BER) performance of the bidirectional ANC-OFDM system. To satisfy the requirement, a combined CFR estimation with Chu code and a combined CFR estimation with Walsh code methods were proposed for bidirectional ANC-OFDM system which can achieve the higher channel estimation accuracy. However, their accuracy of channel estimation would be degraded a lot at the non-Nyquist rate in the practical bidirectional ANC-OFDM system. To solve this problem, this paper proposes a combined CFR estimation method for practical bidirectional ANC-OFDM system which can improve much higher the accuracy of channel estimation and get better BER performance. The silent features of the proposed method are to estimate the combined CFR by applying the maximum likelihood technique with the proposed special pilot subcarrier arrangement which can provide the accurate channel estimation for the combined CFR in the practical bidirectional ANC-OFDM system and to estimate the combined CFR over one OFDM frame by applying the cubic spline interpolation technique which can achieve the higher channel estimation accuracy in higher time-varying fading channel. In the performance evaluations, the normalized mean square error (MSE) as the channel estimation accuracy and BER performances are evaluated by using the computer simulations in higher time-varying fading channel at the non-Nyquist rate. The excellent normalized MSE and BER performances of the proposed method have been verified by the computer simulations in this paper.