  Effective capacity, which provides the maximum constant arrival rate that a
given service process can support while satisfying statistical delay
constraints, is analyzed in a multiuser scenario. In particular, we study the
achievable effective capacity region of the users in multiaccess fading
channels (MAC) in the presence of quality of service (QoS) constraints. We
assume that channel side information (CSI) is available at both the
transmitters and the receiver, and superposition coding technique with
successive decoding is used. When the power is fixed at the transmitters, we
show that varying the decoding order with respect to the channel state can
significantly increase the achievable throughput region. For a two-user case,
we obtain the optimal decoding strategy when the users have the same QoS
constraints. Meanwhile, it is shown that time-division multiple-access (TDMA)
can achieve better performance than superposition coding with fixed successive
decoding order at the receiver side for certain QoS constraints. For power and
rate adaptation, we determine the optimal power allocation policy with fixed
decoding order at the receiver side. Numerical results are provided to
demonstrate our results.
