Multiple Access Channel with Unreliable Cribbing

It is by now well-known that cooperation between users can lead to significant performance gains. A common assumption in past works is that all the users are aware of the resources available for cooperation, and know exactly to what extent these resources can be used. In this work, we consider the multiple access channel (MAC) with (strictly causal, causal, and non-causal) cribbing that may be absent. The derived achievable regions are based on universal coding scheme which exploit the cribbing link if it is present, and can still operate (although at reduced rates) if cribbing is absent. We derive also an outer bound, which for some special case is tight.