Distributed Fair Channel Access in NOMA Random Access Systems

This paper considers non-orthogonal multiple access (NOMA) systems in which users randomly transmit packets in each slot while the transmit power is adjusted so that the receive power of each packet at the base station can be one of two predetermined values. While the NOMA random access system can support simultaneous transmissions from up to two users with different target receive powers, it complicates the access protocol design as each user not only has to optimize the transmission probability but also has to suitably choose the target receive power. By considering the fact that users may have different capability of choosing the target receive power due to their diverse locations in a cell, we propose an online distributed channel access algorithm which enables the users to adaptively choose the target receive power and control the transmission probability over time through observing channel outcomes such as idle, success and collision. Numerical results demonstrate that the proposed algorithm can optimize the system performance in terms of throughput and access fairness.