Channel Estimations Using Extended Orthogonal Codes for AF Multiple-Relay Networks Over Frequency-Selective Fading Channels

In this paper, we present the efficient channel estimation scheme for amplify-and-forward (AF) multiple-relay networks in frequency-selective fading channels. It is first addressed that a known sequence transmitted from a source must have a perfect correlation property to achieve a minimum channel estimation error, particularly in the least squares (LS) sense. The known sequences retransmitted from the multiple relay must have to be decoupled at the destination to completely estimate the channel impulse responses (CIRs) between multiple links. To satisfy such requirements, we then propose a repeated known sequence consisting of Chu sequences at a source and a signed identity precoding using extended orthogonal codes, i.e., Hadamard codes, at relays. Moreover, we investigate various properties of the proposed channel estimations through the analysis of mean square error (MSE).