Individual Outage Rate Regions for Fading Multiple Access Channels

In this paper, outage regions are computed for the quasi-static fading multiple access channel (MAC) with constraints on the individual user outage probabilities and no channel state information at the transmitters (CSIT). An outage rate region is defined as the set of rate vectors for which the user outage probability constraints are satisfied simultaneously. Outage probability is typically defined in terms of a common outage event, defined as the event that a target user rate vector lies outside the achievable region of the MAC, conditioned on the fading state. In contrast, rate regions without CSIT are computed in this paper based on individual outage events and individual probability constraints that are satisfied simultaneously. An individual outage event for a given user occurs if the user´s message is not correctly decoded, irrespective of the decoding success of the messages for other users. Individual outage rate regions are useful for the MAC with heterogeneous user channels and quality-of-service (QoS) requirements. Explicit outage rate regions and total throughputs are computed for the two-user fading MAC. It is shown that rate regions and throughputs are significantly larger using individual outage probabilities than using the common outage probability.