Cooperation strategies allow communication devices to work together to improve network capacity. Consider a network consisting of a k-user multiple access channel (MAC) and a node that is connected to all k encoders via rate-limited bidirectional links, referred to as the "cooperation facilitator" (CF). Define the cooperation benefit as the sum-capacity gain resulting from the communication between the encoders and the CF and the cooperation rate as the total rate the CF shares with the encoders. This work demonstrates the existence of a class of k-user MACs where the ratio of the cooperation benefit to cooperation rate tends to infinity as the cooperation rate tends to zero.Examples of channels in this class include the binary erasure MAC for k = 2 and the k-user Gaussian MAC for any k ≥ 2.

Cooperation strategies allow communication devices to work together to improve network capacity. Consider a network consisting of a k-user multiple access channel (MAC) and a node that is connected to all k encoders via rate-limited bidirectional links, referred to as the "cooperation facilitator" (CF). Define the cooperation benefit as the sum-capacity gain resulting from the communication between the encoders and the CF and the cooperation rate as the total rate the CF shares with the encoders. This work demonstrates the existence of a class of k-user MACs where the ratio of the cooperation benefit to cooperation rate tends to infinity as the cooperation rate tends to zero.Examples of channels in this class include the binary erasure MAC for k = 2 and the k-user Gaussian MAC for any k ≥ 2. Index TermsConferencing encoders, cooperation facilitator, cost constraints, edge removal problem, multiple access channel, multivariate covering lemma, network information theory.

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Abstract-In this paper, we propose a new cooperation model for discrete memoryless multiple access channels. Unlike in prior cooperation models (e.g., conferencing encoders), where the transmitters cooperate directly, in this model the transmitters cooperate through a larger network. We show that under this indirect cooperation model, there exist channels for which the increase in sum-capacity resulting from cooperation is significantly larger than the rate shared by the transmitters to establish the cooperation. This result contrasts both with results on the benefit of cooperation under prior models and results in the network coding literature, where attempts to find examples in which similar small network modifications yield large capacity benefits have to date been unsuccessful.