Hierarchical Multiple Access (HiMA) for Fog-RAN: Protocol Design and Resource Allocation

We introduce a set of multiple access protocols, called hierarchical multiple access (HiMA), which are based on non-orthogonal multiple access (NOMA) and time-division multiple access (TDMA), optimized for the hierarchical network scenario. The proposed protocols can be efficiently utilized in various network configurations with an hierarchical form, such as relay networks, cloud-radio access networks (C-RANs), and fog-radio access networks (F-RANs). In particular, C-RANs and, more recently, F-RANs are regarded as promising paradigms to fully utilize the edge of the networks. Therefore, the implementation of novel multiple access protocols to properly exploit these configurations is critical for the fifth generation and beyond of wireless access. Furthermore, the resource allocation problem is formulated for each protocol with respect to the timeslot duration and power. As a result two fairness metrics are optimized, namely max-min rate fairness and proportional fairness. Finally, numerical results reveal the effectiveness of the joint design in the hierarchical network and an interesting trade-off is identified between fairness and achievable rate. Interestingly, despite NOMA being a very promising alternative to conventional multiple access schemes, the protocol that is solely based on NOMA does not always outperform the rest.