Providing Services for the High-Speed Train and Local Users in the Same OFDMA System: Resource Allocation in the Downlink

We consider providing broadband wireless services for passengers in a high-speed train and local users (low-mobility users) in the same OFDMA system. For the train, a two-hop architecture, under which, passengers communicate with base stations (BSs) via a mobile relay (MR) is employed. Then all passengers in the train can be treated as one large user represented by the MR. Since the channel conditions of the MR and local users are different in both large scale-fading and small-scale fading, we allocate the system resources over two time-scales for them. We formulate the resource allocation problem in the downlink OFDMA system as a capacity optimization problem for the MR subject to the sum capacity constraint of local users. We discuss the problem in two cases where perfect intercarrier interference (ICI) cancellation and no ICI cancellation are applied at the MR. The corresponding capacities and optimal power and subcarrier allocation (OPSA) policies are presented for each case. The capacities obtained in these two cases bound the achievable transmission rate of the MR and provide meaningful guidance for the application of ICI cancellation. Finally, the implementation issues of resource allocation policies are discussed to simplify application in practical scenarios.