Multiple Access Computation Offloading for the K-User Case

When multiple users seek to offload computational tasks to their access point, the nature of the multiple access scheme, and the optimization of its parameters, play a critical role in the system performance. For a system with heterogeneous tasks, we adopt a time-slotted signaling structure in which different numbers of users transmit in each slot, subject to individual power constraints. We consider the problem of optimizing the rates and powers of the users transmitting in each time slot, and the time slot lengths, so as to minimize the energy expended by the users. For time-division multiple access (TDMA) and "rate optimal" multiple access, we obtain reduced-dimension convex formulations, while for (suboptimal) non-orthogonal multiple access (NOMA) with independent decoding (ID) or fixed-order sequential decoding (FOSD), we develop a successive convex approximation algorithm with feasible point pursuit. These formulations are then embedded in a customized tree search algorithm for the set of offloading users. Our results demonstrate how the NOMA-FOSD schemes bridge the performance gap between TDMA and the rate-optimal schemes.