Relay selection and power allocation in parallel and non-parallel OFDM relay networks

This paper focuses on relay selection, subcarrier selection and power allocation (PA) in two-hop multi-relay networks in frequency-selective (FS) fading channel. The multiple relays adopt amplify-and-forward (AF) protocol and are subject to an aggregate power constraint. In order to maximize the instantaneous information rate of the system, both parallel mode (all the relays transmit signals simultaneously) and non-parallel mode (the relays transmit signals sequentially) are analyzed. In the parallel mode, compared with some other previous optimal PA work, our proposed optimal subcarrier selection (OSS) scheme and optimal relay selection (ORS) scheme both can get a better performance in terms of the instantaneous information rate and have a lower complexity. In the non-parallel mode, though our OSS scheme gets a little worse performance than the previous optimal scheme in terms of the rate, it has a much lower complexity. Thus, as for the non-parallel mode our OSS scheme is more suitable for some real-time transmissions. The simulations are also provided to validate the proposed schemes.