TANG AND WANG:MAC FOR EFFICIENT COEXISTENCE BETWEEN FULL AND HALF-DUPLEX COMMUNICATIONS 588 07 0.6 n=2 02 e, Number of clien Maximum move speed (m/sec Fig.14.Packet loss. DCF with RTS/CTS as benchmark.The ratios of throughput roughpu significant. VIII.DISCUSSION A.Accommodating Full-Duplex Clients 6-full duriex wo SIR MAP A-Duplex supports coexistence between afull duplex AP and legacy half duplex nodes.However,it can be easily extended to that for the network with only half duplex clients.Second.when the AP selects aclient for downlink transmissions during dual ink setup,it trea uplex c nand half duplex mum Fig.15.Packet delay according to a rate adaptation algorithm.In other words,the x with SIR MAP(1)and full eftect nee if the lowest amons all scenarios shown in Fis.15.802.11 DCE with two different clients the SIR needed to determine RTS/CTS has the highest delay.As for full duplex without the rate for downlink transmission. 802w and MAC pro er the AP establi ay of A-Dupl duced by about 2 an ins th lowing co 26%.respectivel establish asymmetrical dual links:2)If a full duples cli wins the channel,then the AP can establish either symmetrical option th cal dual li similar delay.Moreover.the results show that the movement or a single link with a half duplex client.In all three cases two strategies can be followed by the AP to select a client pertormance:The packet as the mov downl ion.In the first strategy.the AP way dual lin P为au5小p highest downlink transmission rate in case 1).Thus.throughput nent is mainly attributed to capture effec ond strategy. the on the path onent of the nt according whTepetiodierenpahloseponenik.Wechose802.i TANG AND WANG: MAC FOR EFFICIENT COEXISTENCE BETWEEN FULL- AND HALF-DUPLEX COMMUNICATIONS 5883 Fig. 14. Packet loss. Fig. 15. Packet delay. The packet delays of full duplex with SIR MAP(1) and full duplex with SIR MAP(2) are almost the same and are the lowest among all scenarios shown in Fig. 15. 802.11 DCF with RTS/CTS has the highest delay. As for full duplex without SIR MAP, its delay is between 802.11 DCF and MAC pro￾tocol. Compared to 802.11 DCF without RTS/CTS and with RTS/CTS, the delay of A-Duplex is reduced by about 22% and 26%, respectively. From the above results we can conclude that the full duplex with SIR MAP(1) is a better option than full duplex with SIR MAP(2), since it leads to lower packet loss and achieves similar delay. Moreover, the results show that the movement of the clients almost does not obviously impact the network performance; The packet loss remains stable as the moving speed varies, which means that the MAP can be dynamically updated in time. 4) The Effect of Path Loss Exponent: In A-Duplex the throughput improvement is mainly attributed to capture effect. However, the SIR depends on the path loss exponent of the environment. Thus, the performance of A-Duplex is evaluated with respect to different path loss exponents. We choose 802.11 Fig. 16. The ratio of throughput improvement of A-Duplex under different pass loss exponents; 802.11 DCF with RTS/CTS is chosen as the benchmark. DCF with RTS/CTS as benchmark. The ratios of throughput improvement are shown in Fig. 16. As the path loss expo￾nent increases, the throughput improvement becomes more significant. VIII. DISCUSSION A. Accommodating Full-Duplex Clients A-Duplex supports coexistence between a full duplex AP and legacy half duplex nodes. However, it can be easily extended to support a network including both full duplex and half duplex clients. First, the SIR MAP is established in the same way as that for the network with only half duplex clients. Second, when the AP selects a client for downlink transmissions during dual￾link setup, it treats full duplex clients and half duplex clients similarly. If the AP establishes dual links with a full duplex client, the transmission rate in the downlink is determined according to a rate adaptation algorithm. In other words, the downlink rate does not rely on the SIR MAP, since no capture effect needs to be utilized in symmetrical full duplex dual links. However, if the AP establishes asymmetrical dual links with two different clients, the SIR MAP is still needed to determine the rate for downlink transmission. Whether the AP establishes symmetrical or asymmetrical dual links depends on the following conditions: 1) If a half duplex client wins the channel access, then the AP can only establish asymmetrical dual links; 2) If a full duplex client wins the channel, then the AP can establish either symmetrical or asymmetrical dual links; 3) If the AP wins the channel, it can establish symmetrical dual links with a full duplex client or a single link with a half duplex client. In all three cases, two strategies can be followed by the AP to select a client for downlink transmission. In the first strategy, the AP always selects a full duplex client to set up symmetrical dual links in cases 2) and 3), and selects a half duplex client that supports the highest downlink transmission rate in case 1). Thus, throughput of the network is much improved. In the second strategy, the AP selects a client according to the virtual deficit round robin algorithm in all three cases. In this strategy, even if a full duplex client wins the channel, the AP may still select another client