Resource Allocation for Network MIMO Systems with HARQ and Partial Channel Knowledge

In this article, we consider a cellular system, where multiple base stations (BSs) cooperate to decode signals coming from mobile terminals (MTs), using a hybrid automatic repeat request error protection mechanism. We focus on the problem of weighted network sum rate maximization, by addressing the following three resource allocation problems: (a) the scheduling of MT transmissions, (b) the scheduling of cooperating BSs for each MT, and (c) the allocation of resources on the backhaul network. Both a star and a ring architecture for the backhaul network are considered. We propose two approaches, where resource allocation on the backhaul is performed either before or after reception of the packet on the wireless link, with a either partial (statistical) or full knowledge of instantaneous channels. Since both assignments are NP-hard, we also propose greedy algorithms. Based on the numerical results we compare the performance of the various approaches in a typical cellular scenario. The main results, among others, are that (a) the perfect channel knowledge allows a reduction of the backhaul usage by 2.5 to 3 times with respect to the case of partial channel knowledge, and (b) the ring architecture turns out to be more flexible than the star architecture. In particular, the most flexible architecture is given by the RING topology with decoding at the BS, where the backhaul throughput can be allocated to the BSs in any proportion, while at the same time the transfer of information from the serving BS to the RNC is avoided.