As full duplex wireless communication evolves into a practical technique, it will be built into communication nodes in many application scenarios. However, it is difficult to do so for legacy communication nodes. Thus, full duplex communication nodes will coexist with half duplex communication nodes in the same application environment. In this paper, a wireless local area network(LAN) with a full duplex access point (AP) and half duplex clients is studied, and a media access control(MAC) protocol called asymmetrical duplex (A-Duplex) is developed to support efficient coexistence between half duplex clients and the full duplex AP. A-Duplex explores packet-alignment based capture effect to establish dual links between the AP and two different clients. In this way, the capability of a full duplex AP can be utilized by half duplex clients, which leads to much improvednetwork throughput.
Moreover, to ensure fairness of the MAC protocol, a virtual deficit round robin algorithm is proposed for the AP to select appropriate half duplex clients for dual-link setup. A-Duplex does not require any change in the physical layer of half duplex clients; only an update of MAC driver is necessary. Thus, it is well suited for coexistence between half duplex clients and a full duplex AP. Both analysis and simulations are conducted to evaluate performance of A-Duplex. Results show that it improves the throughput by 48% and 188% and reduces the average packet delay by 26% and 22%, as compared to the IEEE 802.11 Distributed Coordination Function (DCF) with and without RTS/CTS, respectively. Moreover, the throughput remains steady as the number of clients grows. A-Duplex also maintains a high level of fairness.