Down-link OFDRMA communications

Orthogonal frequency-division multiplexing with random multiple access (OFDRMA) is discussed for down-link communications, whereby a single base-station transmits information towards several active users. Current methods for down-link communication partition the frequency resources among the active users in an orthogonal fashion, i.e. a central unit (typically the base-station itself) dynamically allocates the resources such that each user is allocated a fixed and exclusive set of sub-bands (a.k.a. bins, or subcarriers). The task and overhead required for orchestrating the frequency sub-bands allocations among the users in an optimal fashion can be quite cumbersome, and typically involves increased computational complexity, latency and bandwidth resources. The main purpose we address in this paper is to avoid the task and overhead required in the state-of-the-art OFDM systems in both the base-station and the users, while sacrificing as little as possible in terms of users side error rate performance. This is of particular importance in multi-user multiple-input multiple-output systems, which become increasingly popular these recent years. In OFDRMA a user is assumed to be allocated with a predetermined, randomly selected frequency bins. A multi-antenna multi-user delivery approach is presented based on pre-coding and multi-cast transmission. It is shown to provide robustness against the forced randomness of the scheme. Simulation results are provided for demonstrating the performance attainable with OFDRMA and the proposed transmission scheme.