Cooperative Strategies for Simultaneous and Broadcast Relay Channels

Consider the simultaneous relay channel (SRC) that consists of a set of relay channels where the source wishes to transmit common and private information to each of the destinations. This problem is recognized as being equivalent to that of sending common and private information to several destinations in presence of helper relays where each channel outcome becomes a branch of the broadcast relay channel (BRC). Cooperative schemes and capacity region for a set with two memoryless relay channels are investigated. The proposed coding schemes, based on decode-and-forward (DF) and compress-and-forward (CF), must be capable of transmitting information simultaneously to all destinations in such a set. Depending on the quality of source-to-relay and relay-to-destination channels, inner bounds on the capacity of the general BRC are derived. Three cases of particular interest are considered: 1) cooperation is based on DF strategy for both users, referred to as DF-DF region; 2) cooperation is based on CF strategy for both users, referred to as CF-CF region; and 3) cooperation is based on DF strategy for one destination and CF for the other, referred to as DF-CF region. These results can be seen as a generalization and hence unification of previous works. An outer bound on the capacity of the general BRC is also derived. Capacity results are obtained for the specific cases of semidegraded and degraded Gaussian SRCs. Rates are evaluated for Gaussian models where the source must guarantee a minimum amount of information to both users while additional information is sent to each of them.