A New Upper Bound on the Achievable Rate of Relay Channel With MIP-QF Strategy

Recently, a new mutual information preserving quantize-and-forward (MIP-QF) is proposed for the half-duplex relay channel, where the relay node does not need to decode the source signal correctly. In this paper, a new MIP-QF upper bound on the achievable rate of the half-duplex relay channel is proposed, which is shown to be lying between the compress-and-forward (CF) bound and the cut-set bound. For the half-duplex additive white Gaussian noise (AWGN) relay channel, the specific MIP-QF bound and the optimal duplex ratios of the MIP-QF upper bound and the MMSE-CF bound are also derived. In addition, we also show that the decode-and-forward (DF) bound can exceed the MIP-QF bound in some special cases that the relay is close to the source and far away from the destination. The validity and accuracy of the proposed theoretical results are verified by numerical results under the half-duplex AWGN relay channel.