Energy-Optimal Multiple Access Computation Offloading: Signalling Structure and Efficient Communication Resource Allocation

Computation offloading enables energy-limited devices to expand the scope of the computational tasks that they can complete within specified latency requirements. However, when multiple devices seek to offload, effective allocation of resources becomes crucial. In this paper, we develop an energy-optimal signalling structure for a $K$-user offloading system, and an efficient algorithm for allocating the communication resources provided by that structure. The signalling structure is designed to exploit the differences between the users latencies and the reduction in interference that arises when a device completes its offloading. That results in a time-slotted signalling structure, which is then optimized for a multiple access scheme that exploits the full capabilities of the channel (FullMA). The optimized signalling structure enables us to substantially reduce the dimension of the resource allocation problem, and to develop efficient algorithms to tackle that problem for both the binary and partial offloading cases. Our numerical experiments illustrate that the proposed time-slotted FullMA signalling structure significantly reduces the energy consumption of the devices compared to some existing methods that employ orthogonal multiple access schemes, such as TDMA, and to those with FullMA, but sub-optimal single-time-slot signalling structures.