The Unbounded Benefit of Encoder Cooperation for the k-User MAC

Cooperation strategies allow communication devices to work together to improve network capacity. Consider a network consisting of k encoders, a multiple access channel (MAC), a decoder, and a node, referred to as a “cooperation facilitator” (CF), that is connected to each encoder via a pair of rate-limited links, with one link going from the encoder to the CF and the other link going back. Let the “cooperation rate” be the total outgoing rate of the CF. This paper demonstrates the existence of a class of MACs where the ratio of the sum-capacity gain to cooperation rate tends to infinity as the cooperation rate tends to zero. For any k ≥ 2, examples of channels in this class include the k-user binary adder MAC and the k-user Gaussian MAC.