IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS.VOL.14.NO.10.OCTOBER 2015 5871 A-Duplex:Medium Access Control for Efficient Coexistence Between Full-Duplex and Half-Duplex Communications Aimin Tang and Xudong Wang,Senior Member.IEEE As full-dupl cation are used.With the help of path loss attenuation and digital ar Ho s ad fin odes wil the full-duplex ccess poin is design,a pa e sive circuit is used tocancel the remaining self-interfer nce.In [5].a balanced cancellation 0c t is des igned for ont-end esign of the d for the AP to se in d with t in [4l to self-interference cancellation.Full duplex can nearly double propria the ph the capacity of a point-to-point communication link and thus dia ntrol (MAC)protocol plays a critical role and 225 far a few MAC protocols ebeen proposed to suppom ith full duplex radio ro duplex communications reasons First depiccoexis i the samedeo u I.INTRODUCTION d出 nce bet n antenna to but imple icated.Thes factors make it difficult for a smart phone or personal digital assistant (PDA)to adopt a full duplex radio.Second,many cancellation within 5 MHz bandwidth for IEEE 802.15.4.In egacy de AP all lesacy devices by full duple ones is neither economica only two antennas nor acceptable.Thus.coexistence between full duplex and half 2 duplex communication with a AP l for the and Wifi networks In this paper.we study a full duplex wireless LAN where but of the figures in this paper are available Digital Object Identifier 10.110/TWC.2015.2443792 perfect self-interference cancellation [4.Since all clients have 1536.127602015IFFE.P se is pen tted.bu IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 14, NO. 10, OCTOBER 2015 5871 A-Duplex: Medium Access Control for Efficient Coexistence Between Full-Duplex and Half-Duplex Communications Aimin Tang and Xudong Wang, Senior Member, IEEE Abstract—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 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 ef- ficient 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 improved network throughput. Moreover, to ensure fairness of the MAC protocol, a virtual deficit round-robin algorithm is proposed for the AP to se￾lect 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 per￾formance of A-Duplex. Results show that it improves the through￾put by 48% and 188% and reduces the average packet delay by 26% and 22%, as compared to the IEEE 802.11 Distributed Coordination Function 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. Index Terms—Medium access control, full-duplex communi￾cation, wireless LAN, coexistence between full-duplex and half￾duplex communications. I. INTRODUCTION F ULL duplex wireless communication is evolving into a more practical technique [1]–[5]. In [1], three antennas are used to achieve about 30 dB antenna cancellation. Combined with path loss attenuation, analog cancellation and digital can￾cellation, this design can achieve about 100 dB self-interference cancellation within 5 MHz bandwidth for IEEE 802.15.4. In [2], Balun cancellation is leveraged for an improved design of self-interference cancellation, in which only two antennas Manuscript received October 21, 2014; revised February 25, 2015 and June 6, 2015; accepted June 7, 2015. Date of publication June 12, 2015; date of current version October 8, 2015. The associate editor coordinating the review of this paper and approving it for publication was C.-F. Chiasserini. (Corresponding author: Xudong Wang.) The authors are with the UM–SJTU Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China (e-mail: wxudong@ieee.org). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TWC.2015.2443792 are used. With the help of path loss attenuation and digital cancellation, about 110 dB cancellation can be achieved within 20 MHz. In [3], an additional transmitting chain is added to generate an invert analog signal to cancel the self-interference. So far the best design is given in [4], where only one antenna is used to achieve almost perfect self-interference cancellation for full duplex WiFi radio. In this design, a passive circuit is first used to achieve 60 dB self-interference cancellation and then both linear and nonlinear digital cancellation are used to cancel the remaining self-interference. In [5], a balanced cancellation circuit is designed for RF front-end. This design can achieve 60 dB cancellation at the RF front-end. On the other hand, it can be integrated with the design in [4] to further improve the self-interference cancellation. Full duplex can nearly double the capacity of a point-to-point communication link and thus significantly improves the spectrum efficiency. However, to fully leverage the capability of full duplex communications in a network, an efficient media access control (MAC) protocol plays a critical role. So far a few MAC protocols have been proposed to support full duplex communications [6]–[9], but they assume that all nodes in the network are equipped with full duplex radios. However, in many application scenarios full duplex and half duplex radios have to coexist in the same network for two main reasons. First, despite fast progress in the development of full duplex radios, challenges still remain when applying full duplex radios to nodes such as smart phones or laptops. For example, in [1]–[3], [5], all radios need more than one antennas to achieve full duplex communications, and the distance between antennas are more than 20 cm. In [4], only one antenna is needed, but implementation of the circuit is rather complicated. These factors make it difficult for a smart phone or personal digital assistant (PDA) to adopt a full duplex radio. Second, many legacy devices only support half duplex communications. It is fine to replace a legacy AP by a full duplex AP, but replacing all legacy devices by full duplex ones is neither economical nor acceptable. Thus, coexistence between full duplex and half duplex communications becomes indispensable. For example, supporting a wireless LAN with a full duplex AP and half duplex clients is extremely meaningful for the next generation WiFi networks. In this paper, we study a full duplex wireless LAN where the AP supports full duplex communications but all clients are half duplex nodes. The full duplex AP is assumed to have perfect self-interference cancellation [4]. Since all clients have 1536-1276 © 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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