Limited-feedback-based adaptive power allocation and subcarrier pairing for OFDM DF relay networks with diversity

Abstract—A limited-feedback-based dynamic resource alloca-tion algorithm is proposed for a relay cooperative network with orthogonal frequency-division-multiplexing (OFDM) modulation. A communication model where one source node communicates with one destination node assisted by one half-duplex decode-and– forward (DF) relay is considered in this paper. We first consider the selective DF scheme, in which some relay subcarriers will keep idle if they do not have the advantage of forwarding the received symbols. Furthermore, we consider the enhanced DF scheme where the idle subcarriers are used to transmit new messages at the source. We aim to maximize the system’s instantaneous rate by jointly optimizing power allocation and subcarrier pairing on each subcarrier based on the Lloyd algorithm. Both sum and individual power constraints are considered. The joint optimization turns out to be a mixed integer programming problem. We then transform it into a convex optimization by continuous relaxation and achieve the solution in the dual domain. The performance of the proposed joint resource allocation algorithm is verified by simulations. We find that the proposed scheme outperforms the existing methods in various channel conditions. We also observe that only a few feedback bits can achieve most of the performance gain of the perfect channel-state-information (CSI)-based resource allocation algorithm at different levels of signal-to-noise ratio (SNR). Index Terms—Decode and forward (DF), limited feedback, Lloyd algorithm, orthogonal frequency-division multiplexing (OFDM), power allocation, subcarrier pairing. I