An Enhanced Full-Duplex MAC Protocol for an Underwater Acoustic Network Liu Songzou 1 , Basit Iqbal 1 , Imran Ullah Khan 1 , Hui Li 2 , Gang Qiao 1 1 College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001 China 2 College of Intelligent Systems Science and Engineering, Harbin Engineering University, Harbin, China { 1 liusongzuo@hotmail.com, 1 basit@hrbeu.edu.cn, 1 khan@hrbeu.edu.cn, 2 lihuiheu@hrbeu.edu.cn, 1 qiaogang@hrbeu.edu.cn} Abstract— The existing half-duplex medium access control protocols take longer time to transmit and receive successful data packets, due to longer propagation delays. Therefore, we proposed an Enhanced Full-Duplex Medium Access Control protocol for the underwater acoustic network. The proposed protocol increases throughputs by decreasing the time for successful data transmission. The proposed protocol sets a back- off timer to access the transmission opportunity by transmitting the ID based RTS control packet to the target destination node. The target destination sends back the CTS control packet containing the data transmission and ID information, then both immediately exchange the data with each other, consuming less transmission time while performing FD communication. We evaluate the performance of the proposed protocol with respect to increase in number of underwater sensor nodes and payload size. Simulation results proved that the proposed protocol significantly increased the throughputs, compared to the existing convention medium access control protocols. Keywords—Medium Access Control (MAC); Request-to-send (RTS); Clear-to-send (CTS); Underwater acoustic communication network (UWACN); Full-Duplex (FD) I. INTRODUCTION Lots of Underwater Acoustic Communication Medium Access Control (UWAC-MAC) protocols and systems have been proposed, showing extensive development in the field of underwater communication [1-10]. However, most of these protocols are half duplex in nature, where the sender and receiver cannot share their data simultaneously, resulting in large propagation delays and interference. The underwater acoustic networks (UWANs) protocols are applicable to various applications such as natural disaster detection and marine monitoring systems etc.. But, due to long underwater propagation delay, narrow bandwidth, and multipath fading, it is difficult for these protocols to use an underwater channel efficiently [11-13]. For instance, the proposed half-duplex (HD) bidirectional medium access control (MAC) protocols are less efficient and have poor channel utilizations, and their hand-shake procedures are time consuming and unable to efficiently solve the long underwater (UW) propagation delays[14-16]. Distributed Coordination Function (DCF) technique is used to prevent collisions in the Underwater handshaking mechanisms by monitoring the channel before transmission, and transmits a frame if the channel is ideal for the transmission of new packets [17]. To enhance the performance of the IEEE802.11e model an enhanced distributed channel access with virtual collision handler, has been implemented to avoid the multiple collisions, utilizing the DCF and the binary back-off timer characteristics [18]. Further, an analytical IEEE802.11 model implements the back- off freezing mechanism with DCF collision avoidances characteristics, to enhance the throughputs of the overall system [19]. To reduce long underwater propagation delays in aquatic environments, the authors in [20] proposed slotted floor acquisition multiple access protocol, which uses different time slots for transmission and reception. The UWAC protocol in [2] has the ability to transmit a sequence of packets to multiple neighboring nodes. This protocol is based on multiple access collision avoidance algorithm, which reduces the time required during the control packet hand shaking process and improved the channel utilization [2]. The proposed reverse opportunistic packet appending protocol analyzed the system throughputs and transmission delay in an underwater acoustic environment [21], and reduces the propagation delay of data receiving from neighboring nodes [21]. In [14] a single-hop network based time-slotted BiC-MAC is proposed, which enhances the throughputs and minimizes the inter nodal delay. In [22], the author modeled a ring-based underwater network while considering the underwater propagation delay, and theoretically analyzed the network throughputs using MAC multiple RTS control and data packets. All of the above mentioned protocols utilize back-off timer technique to avoid collisions and to improve the throughputs in harsh UW environment but these do not increase the overall efficiency of the system. Further, their hand-shaking procedures are time consuming and unable to solve long propagation delays issue. To address these issues we propose an Enhanced full-duplex medium access control (FD-MAC) protocol, utilizing full-duplex characteristics in an underwater acoustic network consisting of multiple underwater sensor nodes. In our proposed protocol, the source node that acquires the transmission opportunity broadcasts an RTS packet including an ID of the target node, and to the neighboring nodes, in order to transmit information to the target destination node. The destination node that receives the RTS sends a clear-to-send (CTS) packet to the source node, informing it to perform FD communication. When the source node receives the CTS packet, the source and the destination nodes transmit the sensed information to each other according to the transmission order. The existing MAC protocols in the underwater environment take a lot of time to transmit information successfully, due to long propagation delays. Alternatively, the proposed FD-MAC protocol improves the throughputs of the Proceedings of 2021 18th International Bhurban Conference on Applied Sciences & Technology (IBCAST) Islamabad, Pakistan, 12 – 16 January, 2021 894 978-0-7381-0535-2/21/$31.00 ©2021 IEEE 2021 International Bhurban Conference on Applied Sciences and Technologies (IBCAST) | 978-1-6654-0516-4/21/$31.00 ©2021 IEEE | DOI: 10.1109/IBCAST51254.2021.9393236 Authorized licensed use limited to: Harbin Engineering Univ Library. 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