Gaussian Broadcast Channels With Cooperating Receivers: The Single Common Message Case

The main purpose of this paper is to evaluate the benefits of receive cooperation in a broadcast situation where two receivers want to decode the same message. Additionally the cooperation channel is assumed to be orthogonal to the downlink channels. In the case where the cooperation channel is unidirectional, the channel capacity is determined and the performance loss induced by orthogonalizing the cooperation channel is evaluated. In the bidirectional and orthogonal case lower and upper bounds for the capacity are provided. More specifically two decoding schemes are compared. Coding scheme 1: the two receivers use estimate-and-forward. Coding scheme 2: each receiver uses, in a complementary manner, estimate-and-forward a certain fraction of the time and decode-and-forward for the rest of the time. For realistic levels of the cooperation powers the performance of the second scheme is shown to be close to the considered upper bound