CSMA-Based Utility-Optimal Scheduling in the WLAN With a Full-Duplex Access Point

Full-duplex wireless communication has been recognized as an effective technique to improve the system throughput. This paper designs a CSMA-based utility-optimal scheduling scheme to fully explore the performance improvement brought by AP's full-duplex capability. In particular, to keep the backwards compatibility of the legacy users, we allow users to compete to access the channel using the CSMA protocol in their uplink transmissions while let the AP select its downlink user to communicate with for completing the full-duplex transmission upon each uplink access. Moreover, to achieve the optimal system utility, we then formulate an optimization problem of maximizing the downlink aggregate utility subject to the uplink users' data rate constraints. The formulated problem falls into a mixed integer nonlinear programming form, which is generally NP-hard to solve. To make the problem tractable, we divide it into user pairing and access-intensity adjustment subproblems. More specifically, we devise a user pairing criterion based on the signal-to-interference-plus-noise ratio to reduce the uplink-downlink interference, and adopt the Hungarian algorithm to find the best matching between uplink and downlink users. After that, we adjust the access-intensity of users (i.e., the ratio of the mean packet transmission time to the mean backoff time) to maximize the downlink aggregate utility based on the geometric programming. Simulation results are presented to evaluate the performance of our scheduling design and demonstrate the downlink aggregate utility improvement compared to other scheduling schemes in full-duplex WLANs.