LEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS,VOL 14.NO.10.OCTOBER 2015 APAA” THE OVERALL SATURATION THROUGHPUT FOR MULTILE AP A G95Ap国 others idle for other LANs.As a result,A-Duplex can properly adapt alldle cien (Cicnea to the situation of multiple APs in the same area.We alsc ucts1 nulat山 s to evaluate A-Duplex with multiple AP exist a much lar number of contending nodes.Thus,as shown in Table V,the ul aples chent be st duplex client win s the overall throughput drops but slightly,thanks to the mechanisms e throughput for each cell covere tric dual links if it has a packet to the full duplex client.If the AP wins the channel. our protocol can still work well when multiple APs running the A-Duplex protocol are in the range of each other. A ne to the fu C.A-Duplex in the Case of Imperfect Self-Interference address (DA)for itself,it repliesa CTS frame.Moreover,if it has a packet to the AP.the packet is sent after the CTS frame. In this paper,we assume that the AP can achieve perfec After the AP receives the CTSframe. self-interference cancellation.A-Duplex can also be modified finish.the Ap and ACK AP canno sly In this 1,up earlier,it needs to send a busytone(BT)signal to make sure the the uplink rate properly so that the AP can decode the packet uppose Cl correctly.To achieve this goal,the following procedure is taker APsends a data packet to Client in a half duplex mode. During self-calbrat ion of the full duplex io on the arameter.This parameter is by the CIS B.The Effect of Multiple AP the AP to a client,so an additional byte is added in the CTS evaluated by frame.In case the AP sets up dual links,the value of this con ver,it works well under an en- oyte repr nts the rem ning sen-in erference:o e remaining self-interference.it can adjust the transmission rate er can hear of the next frame by checking the modulation and coding table or example.given client contains the associated AP's address.Thus.when other determined by checking Table I. clients overhear such an RTS fra the same of A-Duplerre IX.CONCLUSION compute the SIR.but the clients from other APs just ignore the eloped in thi A-nents considered in A-Duplex to establish dual links to fully leverage case.For example.when AP I has established dual links and full duplex capability of the AP.To this end,a map of network then the client of the AP 2 sends an RTS frame to AP2.In this y and relatv frame.because t has updated The ab To improve fairness of A-Duplex.a virtual deficit round robin the channel alternately following the random access protocol. Thus,considering one particular wireless LAN with an AP t Io at A-Dons ed th tha performance of throughput,packet loss,and delay,as compared des.Duple can be5884 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 14, NO. 10, OCTOBER 2015 Fig. 17. Symmetric dual links for full duplex clients (Client A finishes data packet transmission earlier). (either half duplex or full duplex). Thus, the second strategy is more focused on fairness performance instead of throughput. Similar to the asymmetrical case, symmetrical dual links can be established in two ways. If a full duplex client wins the channel after sending an RTS frame, the AP knows that this is a full duplex client.2 It then establishes symmetric dual links if it has a packet to the full duplex client. If the AP wins the channel, it sets up symmetrical dual links as depicted in Fig. 17. First, the AP sends an RTS frame to the full duplex client A. When Client A receives the RTS frame and finds that the destination address (DA) for itself, it replies a CTS frame. Moreover, if it has a packet to the AP, the packet is sent after the CTS frame. After the AP receives the CTS frame, it waits an SIFS and then sends the data packet to Client A. When both transmissions finish, the AP and Client A reply ACK simultaneously. In this case, if either the AP or Client A finishes its data transmission earlier, it needs to send a busytone (BT) signal to make sure the two data packets finish at the same time. Suppose Client A has no packet to the AP, it only replies a CTS frame, and then the AP sends a data packet to Client A in a half duplex mode. B. The Effect of Multiple APs In this paper, A-Duplex is designed and evaluated by con￾sidering only one AP. However, it works well under an en￾vironment with multiple APs in the nearby area. We assume all APs that can potentially impact each other can hear each other. In this network, multiple APs and their associated clients contend the same channel. We know that an RTS frame from a client contains the associated AP’s address. Thus, when other clients overhear such an RTS frame, they can find out if the transmitting client is associated with the same AP or not. The clients with the same AP follows the procedure of A-Duplex to compute the SIR, but the clients from other APs just ignore the received RTS frame. It is possible that two clients associated with different APs cannot hear each other. A-Duplex still works properly in this case. For example, when AP 1 has established dual links and then the client of the AP 2 sends an RTS frame to AP 2. In this case, AP 2 will not return a CTS frame, because it has updated its NAV when it receives the CTS frame from AP 1. The above analysis shows that the clients of different APs get the channel alternately following the random access protocol. Thus, considering one particular wireless LAN with an AP and its associated clients, it works as if there exists no other wireless LANs except that a certain amount of time is left 2We assume the AP has classified the client type (either full duplex or half duplex) during the association process. TABLE V THE OVERALL SATURATION THROUGHPUT FOR MULTIPLE APs idle for other LANs. As a result, A-Duplex can properly adapt to the situation of multiple APs in the same area. We also conduct simulations to evaluate A-Duplex with multiple APs in the range of each other. Since multiple APs within the range of each other use the same channel, there exist a much larger number of contending nodes. Thus, as shown in Table V, the overall throughput drops but slightly, thanks to the mechanisms of RTS/CTS. However, the throughput for each cell covered by one AP is simply diluted. These simulation results confirm that our protocol can still work well when multiple APs running the A-Duplex protocol are in the range of each other. C. A-Duplex in the Case of Imperfect Self-Interference Cancellation In this paper, we assume that the AP can achieve perfect self-interference cancellation. A-Duplex can also be modified to adapt the case of imperfect cancellation. If the AP cannot achieve perfect self-interference cancellation, uplink reception in dual links is impacted. Thus, the client needs to reduce the uplink rate properly so that the AP can decode the packet correctly. To achieve this goal, the following procedure is taken. During self-calibration of the full duplex radio on the AP, the remaining self-interference can be quantified as a system parameter. This parameter is carried by the CTS frame from the AP to a client, so an additional byte is added in the CTS frame. In case the AP sets up dual links, the value of this byte represents the remaining self-interference; otherwise, the value is just zero. Finally, when a client receives the value of remaining self-interference, it can adjust the transmission rate of the next frame by checking the modulation and coding table. For example, given the SNR of the current transmission rate and the remaining self-interference, the adjusted rate can be determined by checking Table II. IX. CONCLUSION A MAC protocol called A-Duplex was developed in this paper to support a wireless LAN with a full duplex AP and half duplex clients. Packet-alignment based capture effect was considered in A-Duplex to establish dual links to fully leverage full duplex capability of the AP. To this end, a map of network topology and relative signal strength of different links was set up via a dynamic SIR update scheme. Such a map helps the AP form dual links while exploring the advantage of capture effect. To improve fairness of A-Duplex, a virtual deficit round robin algorithm was designed for the AP to select an appropriate client for downlink transmissions. Both analytical and simu￾lation results showed that A-Duplex effectively improved the performance of throughput, packet loss, and delay, as compared to existing MAC protocols. Besides, it maintained a high level of fairness. A-Duplex can be easily applied to legacy half duplex nodes, because it makes no change to the physical layer