Optimal asymmetric resource allocation for dual-hop multi-relay LTE-Advanced systems in the downlink

We propose an optimal asymmetric resource allocation (ARA) algorithm for the decode-and-forward (DF) dualhop multi-relay Long Term Evolution Advanced (LTE-Advanced) system in the downlink, with orthogonal frequency division multiplexing (OFDM) transmission. Our work is different in that the time slots for the two hops via each of the relays are designed to be asymmetric, i.e., with K relays in the cell, a total of 2K time slots may be of different durations, which enhances the degree of freedom over the previous work. Also, a destination may be served by multiple relays at the same time to enhance the transmission diversity. Moreover, closed-form results for optimal allocation are derived, which requires only limited feedback information. Simulation results show that, thanks to the multi-relay, multi-user and time diversities, the proposed ARA scheme can provide a much better performance than the scheme with symmetric time allocation, as well as the scheme with asymmetric time allocation for a system composed of independent single-relay sub-systems, especially when the relays are close to the source.