Adaptive Token Circulation to Avoid Malicious UEs Hoarding Tokens and Assure D2D Relay Efficiency

Device-to-device (D2D) relay can be used to expand the service coverage of a base station (BS) and improve network throughput. In D2D relay, when a user equipment (UE) has bad channel quality, it solicits a neighbor to relay its data from the BS. In view that UEs are usually owned by self-interested users, token-based incentive methods adopt tokens as virtual currencies to let UEs sell and buy relay services, which encourages UEs to help relay data for other UEs. However, malicious UEs may keep gathering tokens from others but never spend tokens, which we call hoarders. Hence, negotiable tokens would reduce gradually, and many UEs cannot afford relay services due to lack of tokens. In this case, these token-based incentive methods will incur bad performance or even collapse. To this end, we propose an adaptive token circulation (ATC) scheme to tax the UEs that have ample tokens and subsidize the UEs in need of tokens. ATC works well in a multi-cell environment and does not cause the inflation of tokens. Simulation results reveal that the ATC scheme keeps high D2D throughput when there exist hoarders, thereby assuring the efficiency of D2D relay.