A Broadcast Approach to Multiple Access with Partial CSIT

Abstract

A new broadcast strategy is designed for multiple access communication with partial channel state information at the transmitters. Specifically, a two-user multiple access channel is considered, in which the state of each channel is known only to its corresponding transmitter. In broadcast approaches, in principle, the transmitter sends multiple independent superimposed information layers, where the rate of each layer is adapted to a specific channel realization. The novel aspect of the proposed strategy is that it adapts the designed codebooks to the state of the whole network, which in contrast to the existing ones in which each transmitter adapts its transmission strategy only to the state of its direct channel to the receiver. Noting that the contribution of each user to a network-wide measure (e.g., capacity region) depends not only on the user's direct channel to the receiver, but also on the qualities of other channels, in the proposed strategy the transmitters adapt their transmissions to the combined states resulting from all users' channels. This leads to a larger achievable rate region, which is characterized and compared to two outer bounds. Furthermore, the proposed strategy is proved to achieve the sum-rate capacity asymptotically.