This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 IEEE SENSORS JOURNAL, VOL. XX, NO. XX, XXXX 2022 1 FCLR:Fuzzy Control-based Layering Routing Protocol for Underwater Acoustic Networks Duoliang Han, Xiujuan Du, Xiuxiu Liu, Xiaojing Tian Abstract— Because of its wide application in the underwater environment, underwater acoustic networks (UANs) have received high attention. However, the intrinsic attributions of low bandwidth, long propagation delay, high bit error rate, and restricted energy bring about great challenges to data transmission in UANs. In this paper, we propose a routing protocol for UANs called fuzzy controlbased layering routing protocol (FCLR). With the FCLR protocol, an underwater node may learn or update its layer and the information of its neighbors from packets overhead before selecting the best forwarding node. A fuzzy control system is used to select the best forwarding node based on input variables including residual energy and node density of neighbor nodes. Extensive experiments are conducted by the NS3 network simulator to evaluate the performance of the FCLR protocol. The results show that the FCLR protocol has superior performance in terms of packet delivery rate, end to end delay, and total energy consumption. Furthermore, the FCLR protocol is tested in Qinghai Lake, the largest saltwater lake in China, and its performance was evaluated in terms of packet delivery rate, throughput, and end-to-end delay. When nodes are moving, the packet delivery rate can reach 92.6 percent and the throughput can reach 350.64bps. Index Terms— UANs, Fuzzy Control, FCLR, Routing protocol, NS3, Performance evaluation I. I NTRODUCTION NDERWATER acoustic networks (UANs) have become a hot issue for researchers in the last decade or so due to their widespread applications in disaster detection, pollution detection, and military applications [1]–[4]. UANs are essentially ad-hoc networks, which are made up of surface base stations and underwater sensor nodes. In general, sensor nodes deployed in water are used to collect and transmit data [5], [6]. One or more sink nodes are deployed on the surface to receive data from sensor nodes in the water, and the sink nodes are also responsible for transmitting data to a data center [7]– [10]. The architecture of UANs appears simple, yet it faces substantial challenges. Because of the serious scattering of light signals and heavy attenuation of radio frenquency signal in water, neither light nor radio frequency signal is applied to UANs, UANs adopt acoustic waves to deliver data [11]– [13]. Meanwhile, UANs face the following challenges: (1) U This work was supported in part by the Innovation Team Foundation of Qinghai Office of Science and Technology under Grant No.2020-ZJ903, in part by the National Natural Science Foundation of China under Grant No.61962052. (Corresponding author:Xiujuan Du.) Duoliang Han and Xiaojing Tian are now with Department of Computer, Qinghai Normal University, Xining 810008, China.(e-mail: 2945219148 @qq.com, 1984159821@qq.com) Xiujuan Du and Xiuxiu Liu are now with Department of Computer, Qinghai Normal University, Qinghai Provincial Key Laboratory of IoT, The State Key Laboratory of Tibetan Intelligent Information Processing and Application, and Academy of Plateau Science and Sustainability, Xining 810008, China.(e-mail:dxj@qhnu.edu.cn, 1154894860@qq.com). the sensor nodes are powered by batteries, and it is hard to recharge and change the battery, thus the energy is limited; (2) the bandwidth of underwater channels is narrow; (3) the speed of the acoustic signal is slow, resulting in a long propagation delay; (4) the quality of the underwater acoustic channel is poor. Therefore, it is very challenging to design a routing protocol with excellent performance [14]–[19]. An effective routing protocol performs well in terms of energy efficiency, end-to-end delay (EED), and packet delivery rate (PDR). Therefore, it is essential to develop effective routing protocols to confront the challenges faced by UANs and improve UANs communication quality [20]. At present, some routing protocols designed for underwater acoustic networks assign weights to different parameters of candidate nodes, and the weights remain unchanged once assigned. However, with the forwarding of packets, different discriminant parameters of a candidate node interact and influence each other, and the interaction and influence are difficult to be described by given formula. So fuzzy control is introduced in this paper to deal with the uncertain interaction among different discriminant parameters of candidate nodes. Fuzzy control has been widely employed in terrestrial wireless sensor networks due to its ability to deal with uncertainties and optimize parameters in recent years [21], [22]. So to optimize the routing decision for UANs, a fuzzy control-based layering routing (FCLR) protocol is proposed. FCLR implements fuzzy routing decisions with two parameter inputs to improve the network performance. © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 2 IEEE SENSORS JOURNAL, VOL. XX, NO. XX, XXXX 2022 Before finding the best forwarding node(BFN) in routing deceison, an underwater node may learn or update its layer and the information of neighbors nodes from packets overhead, then an fuzzy control system(FCS) is used to select the best forwarding node based on input variables including residual energy and node density of neighbor nodes. With the FCLR protocol, each sensor node maintains a neighbor information table(NIT) based on the information from control or data packets overhead. The sink node broadcasts control packets periodically, which is updated and forwarded by the receiving nodes with higher layer. We employ the FCS to select the BFN, besides the layer, the residual energy ratio, and node density are also used as inputs of FCS. After the BFN is determined, data packets are forwarded to the BFN by the source node or the current forwarding node(CFN). The major contributions of this paper are as follows: (1) To deal with the uncertain interaction among different discriminant parameters of candidate nodes, a fuzzy control system is introduced into the routing decision of UANs in this paper, and a fuzzy control-based FCLR routing protocol is proposed. In addition, to solve the problem of void area, only those neighbor nodes with lower layers are eligible to be candidate forwarding nodes in our proposed routing protocol. Furthermore, considering the balance of node energy, residual energy and node density are used as the measure of candidate nodes. (2) The proposed protocol is realized by programming in the NS3 platform and Raspberry PI embedded development board. Extensive simulation experiments and field tests in Qinghai lake which is the largest salt lake in China are conducted to evaluate the performance of the FCLR protocol. The results verify the superior performance of the proposed FCLR protocol in terms of PDR, EED, and total energy consumption (TEC). (3) The algorithms in the literature review need location information or depth information in routing decisions, while the FCLR protocol does not need any location or depth information. Therefore, the FCLR protocol reduces overhead and saves costs. The rest of this paper is organized as follows: the related work of the routing protocol for UANs is discussed in section II. The network model is described in Section III. Section IV presents the FCLR protocol and describes the specific algorithm. In section V, we conduct comprehensive simulations and analyze the results for the proposed protocol. In Section VI, we evaluate the performance of the FCLR protocol in field tests. In section VII, we summarize the paper and propose future research. II. R ELATED WORKS So far researchers have proposed and designed some routing protocols for UANs, among which some are more energysaving, and some have better delivery rates. Next, we will review some of the protocols in this section. The earlier protocols proposed for UANs were the vectorbased forwarding (VBF) and depth-based routing (DBR) protocols, and both of them are classic in UANs [23], [24]. The VBF protocol depends on location information to work. In the VBF protocol, a virtual routing pipe from the source node to the destination node is created based on the locations of the communication node-pair, and only the sensor nodes in the pipe have the opportunity to forward data packets. Nodes outside the pipeline will discard the packets after they receive the packets. Therefore, the VBF protocol outperforms simple flooding protocol in terms of energy-consuming. However, multiple nodes in the pipe involved in forwarding in one hop result in additional energy consumption. Furthermore, the nodes outside the pipe in the VBF protocol are unqualified to forward data packets, which may cause the void area problem in sparsely deployed UANs. The DBR protocol takes advantage of a greedy forwarding algorithm. Each node in the DBR protocol is equipped with a depth sensor, which is used to get the depth information of the node. One data packet is more likely to be forwarded by the node closest to the water surface (i.e.,the node with a smaller depth than the current forwarding node). In contrast to VBF, the DBR protocol does not require full position information of nodes and consumes less energy, but it may also cause the void area problem in sparsly deployed UANs. In [25], Coutinho R. W. et al. proposed a geographic and opportunistic routing (GEDAR) protocol with depth adjustment for mobile UANs. To transmit a data packet, the GEDAR protocol employs the location information of underwater nodes and surface sonobuoys. The GEDAR protocol develops a depth adjustment approach to address the problem of communication void area, which has a significant impact on the performance of geographic and opportunistic routing protocols. Li Z et al. proposed a forwarding protocol based on relative distance(RDBF) in [26]. The goal of RDBF is to achieve energy-saving, efficient transmission and low latency routing. The RDBF protocol uses a fitness factor to determine the suitability of a node to forward data packets, and there are only a few nodes forwarding data packets, so the energy consumption is reduced. However, because forwarding nodes are selected based on their closeness, there will be an imbalance in energy consumption, resulting in the energy hole problem. M. A. Rahman et al. proposed an energy-efficient cooperative opportunistic routing (EE-COR) protocol for UANs in [27]. EECOR selects forwarding nodes based on energy consumption and packet delivery rate and uses a holding timer to schedule data packet transmission, which improves the packet delivery rate, but the routing hole problem has not been addressed. Anwar et al. presented a routing protocol for UANs called localization-free interference and energy holes minimization (LF-IEHM) [28]. LF-IEHM solves the energy hole problem without the need for location information of nodes. In LFIEHM, the sensor nodes are capable of changing their transmission range during communication, so LF-IEHM has better throughput. However, it consumes more energy during packet delivery. In [29], Khan et al. proposed a cooperative energy efficient optimal relay selection protocol(Co-eeors). When selecting the forwarding node, Co-eeors take into account the information of the node such as depth and location. Co-eeors improves packet delivery rate compared with other © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 DUOLIANG HAN et al.: FCLR: FUZZY CONTROL-BASED LAYERING ROUTING PROTOCOL FOR UNDERWATER ACOUSTIC NETWORKS (XXXX 2022) 3 TABLE I T HE P ERFORMANCE C OMPARISON O F T HE A BOVE P ROTOCOLS Protocol Year Control Message Requirements VBF 2006 No Location Information Single entity Improving robust and energy efficiency DBR 2008 Yes Depth Information Single entity Handling dynamic networks with good energy efficiency GEDAR 2014 Yes Depth Information Single entity Addressing the problem of communication void area RDBF 2014 Yes Location Information Single entity Providing transmission efficient, energysaving, and low delay routing EECOR 2017 Yes Depth Information Single entity Improving energy efficiency LF-IEHM 2018 Yes Pressure Information Single entity Overcoming interference during data packet forwarding and mitigating energy hole Co-EEORS 2018 Yes Depth Information Single entity Ensuring reliable delivery of packets Co-EEERD 2019 Yes Location Information Single entity Improving energy efficiency and network reliability EDORQ 2020 No Depth Information Single entity Guaranteeing the energy-saving and reliable data transmission RLOR 2021 Yes Depth Information Single entity Improving the reliability and energy efficiency, avoid void area ELW-CFR 2021 Yes Layer Information Single entity Improving energy efficiency and address void hole problem protocols. However, the need for depth information increased the hardware complexity of nodes, and the acquisition of accurate distance is another challenging issue. When nodes are deployed sparsely and the distance between neighbor nodes is long, the performance of the Co-eeors protocol is poor. Ullah and Khan et al. proposed two energy-efficient and reliable delivery routing protocols, EERD and CO-EERD [30]. EERD is a single-path routing protocol, with which a packet is delivered to the sink only along the best path. EERD employs a weight function to select the best forwarding node and a reliable routing path. However, the unpredictability of subsea links decreases the reliability of data transmission. Thus, the CO-EERD protocol introduces cooperative routing into EERD, which improves the delivery rate and the reliability of transmission. In [31], Yongjie Lu et al. proposed an energyefficient depth-based opportunistic routing algorithm with Qlearning (EDORQ) for UANs. Through Q-learning and void detection, EDORQ improves the network performance in terms of packet delivery ratio, average network overhead and energy consumption. However, to get the depth information, each node in EDORQ needs to be equipped with a depth sensor, which increases the hardware cost. Ying Zhang et.al proposed a reinforcement learning-based opportunistic routing protocol (RLOR) in [32]. The RLOR is a kind of distributed routing approach which employs a recovery mechanism to solve the routing problem of void areas. RLOR improves the delivery rate of data packets in sparse UANs while bringing about additional energy consumption and delay. Umar Draz proposed an energy-efficient proactive routing scheme (ELWCFR) for enabling reliable communication in the underwater internet of things [33]. In the ELW-CFR protocol, nodes are deployed layer-by-layer to avoid the void area problem. Cluster or Single Entity Main goal However, node movement leads to a rapid drop in the delivery rate of the ELW-CFR protocol. Table I lists the performance comparison of the above protocols. III. N ETWORK M ODEL The application environment of UANs is underwater, such as in oceans and lakes. Underwater acoustic communication faces many problems, such as noise interference, the Doppler effect and the propagation loss of acoustic signals in water, etc., which make the design and implementation of routing protocols for UANs extremely difficult. The signal loss and noise models of UANs are presented in this section. A. Path Loss Model Acoustic signal can be absorbed and reflected by water, which causes the signal a certain amount of attenuation and loss in the water. The loss of the sound signal in water mainly includes expansion loss and absorption loss [34]. The transmission path loss(TPL) is given by: T P L = k ∗ 10 ∗ log (d) + d ∗ a(f ) (1) where k is the spread coefficient, d is the distance between two nodes and f is the carrier frequency, a(f ) is the energy absorption coefficient which is given by: a(f ) = 0.11 ∗ f 2 44 ∗ f 2 + + 2.75 ∗ 0.0001 + 0.003 (2) 1 + f2 4100 + f 2 B. Channel Noise Model Underwater acoustic communication is greatly influenced by noise. Turbulence, shipping, waves, and thermal noise are the four major types of noise in the water, and they are represented © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 4 IEEE SENSORS JOURNAL, VOL. XX, NO. XX, XXXX 2022 TABLE II A BBREVIATIONS A ND S YMBOLS U SED I N T HIS PAPER Data center Sink node Abbreviations/Symbols Description UANs Underwater acoustic networks FCLR Fuzzy control-based layering routing FCS Fuzzy control system Forwarding node NIT Neighbor information table Transmission range BFN Best forwarding node Acoustic link CFN Current forwarding node Source node QFN Qualified forwarding node RER Residual energy ratio QND Qualified node density FP Forwarding probability Lcur Layer of current forwarding node Lsend Layer of sending node Er Residual energy of qualified forwarding node Ei Initial energy of qualified forwarding node NLq −1 Number of upper layer node of QFN Nall Number of all neighbor nodes of QFN Neighbor ID Layer Residual energy Node density PDR Packet delivery rate 3 0 Er 1 ND1 TEC Total energy consumption 28 1 Er 2 ND2 TP Throughput of the network 94 2 Er 3 ND3 EED End to end delay 188 3 Er 4 ND4 ... ... ... ... Radio link Sink node Source node Fig. 1. UANs structure. TABLE III T HE S TRUCTURE OF NIT by Ntu (f ), Nsh (f ), Nwa (f ), and Nth (f ) respectively [5]. The power spectral density of environmental noise N is given by: N = Ntu (f ) + Nsh (f ) + Nwa (f ) + Nth (f ) (3) where Ntu (f ), Nsh (f ), Nwa (f ), Nth (f ) are given by (4) ,(5), (6), (7) respectively: 10 log Ntu (f ) = 17 − 30 log(f ) (4) 10logNsh (f ) = 40 + 20(s − 0.5) +26log(f ) − 60log(f + 0.03) (5) √ 10 log Nwa (f ) = 50 + 7.5 w +20 log(f ) − 40 log(f + 0.4) (6) 10logN th(f ) = −15 + 20log(f ) (7) where f is the frequency in kHz, w is the speed of wind in m/s and s is the movement factor of shipping. IV. P ROPOSED P ROTOCOL The FCLR protocol employs an FCS to select the BFN, with the residual energy ratio and node density as inputs of the FCS. The FCLR protocol is described in detail in this section. The abbreviations and symbols used in this paper are listed in Table II. A. Network Structure We considered the network structure in Fig.1 for the FCLR protocol. A sink node is deployed on the surface of the water and is responsible for collecting data from the source node and forwarding data to the data center. A source node is deployed at the bottom of the water to collect information. Many sensor nodes are deployed in the water and are responsible for forwarding data collected by the source node to the sink node. The data packets are transmitted to the sink node hop by hop. When a data packet is received by the sink node successfully, the transmission is completed. B. Node Layer and Neighbor Information Table In the FCLR protocol, each node maintains dynamically a layer, which is used to indicate the number of hops from the node to the sink node. The layer of the sink node is set to 0. The layer of other nodes is initialized to 0xFF. Moreover, each node also maintains an NIT to record the IDs, layers, residual energy, and qualified node density (QND) of neighbor nodes in real-time. The structure of NIT is shown in Table III. The layering algorithm is shown in Algorithm 1. To facilitate the nodes in UANs to obtain or update their layers, the sink node broadcasts HELLO packets periodically. In a HELLO packet, the ID, layer, residual energy and other information of the sending node are included. The format of a HELLO packet is shown in Table IV, in which PHN denotes © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 DUOLIANG HAN et al.: FCLR: FUZZY CONTROL-BASED LAYERING ROUTING PROTOCOL FOR UNDERWATER ACOUSTIC NETWORKS (XXXX 2022) TABLE IV T HE FORMAT OF THE HELLO PACKET Bits 8 16 16 2 ... 16 16 ... Packet type 0:DATA Fields Layer S ID R ID ... Er ND ... 1:ACK 2:HELLO PHN NHN Position Head Load the previous hop node and NHN denotes the next hop node. S ID (R ID) is the ID of the sending node (receiving node). The HELLO packets are updated and forwarded by the receiving nodes with a higher layer. After receiving a HELLO packet, the receiving node extracts the ID, layer, residual energy and node density from the HELLO packet, and stores them into its NIT, then the node determines whether to update and forward the HELLO packet. To avoid collision and overmuch energy consumption, only the nodes whose layers are higher than that of the sender update and forward the HELLO packet. The fields of layer, sender ID, residual energy, and node density in the HELLO packet are updated hop by hop. The periodic broadcasting of HELLO packets and the timely updating of NIT help the CFN to select the BFN from its newly updated neighbor table. We employ the same layer updating mechanism in the FCLR protocol as in reference [35]. Algorithm 1 provides the layer updating procedure. As in Algorithm 1, Lcur represents the layer of the current node, Lsink denotes the layer of the sink node, and Lsend indicates the layer of the previous hop node(sending node). We set an aging timer for the layer of each node, and a node starts its aging timer when its layer is updated. The aging timer is introduced for the following purposes: (1) If a node receives a HELLO packet before the aging timer expires and the value of the layer field in the packet (Lsend ) is no less than the layer of the receiving node (Lcur ), the layer of the receiving node and its aging time remain unchanged; (2) If a node receives a HELLO packet before the aging timer expires and the value of layer field in the packet (Lsend ) is less than Lcur − 1 (the layer of the receiving node minus 1), the layer of the receiving node is changed to (Lsend +1) and its aging timer restarts;(3) If a node receives a HELLO packet after its aging timer has expired, it updates its layer to Lsend + 1 and restarts the aging timer. After a node obtains or updates its layer according to the HELLO or data packets received, it can forward the HELLO or data packets. With the proposed FCLR protocol, HELLO packets are transmitted always along the paths from nodes with low-layer to nodes with high-layer; and DATA packets are transmitted along the paths from nodes with high-layer to nodes with low-layer till to the sink node with layer 0, in this way the transmission efficiency and reliability are improved. C. BFN SELECTION To reduce collision, improve energy efficiency, and data PDR, the FCLR protocol implements single path routing. In other words, the BFN needs to be selected at each hop 5 Algorithm 1 Layer update procedure 1: 2: 3: 4: 5: 6: 7: 8: 9: 10: 11: 12: 13: 14: 15: Network initialization completed; Lcur = 255; Lsink = 0; when a node N receives a HELLO packet from node M; if Lcur ==255 then Lcur = Lsend + 1 //Lsend is the layer of the sending node; Node N updates the HELLO packet and continues to forward; else if agingtimer > 0 and Lcur < Lsend + 1 then Lcur remain unchanged, discard the HELLO packet; else Lcur = Lsend + 1 ; update HELLO packet and forward; end if end if before forwarding data packets. When a non-BFN node hears a data packet, it just updates its layer and NIT according to the information of the header fields from the packet without forwarding the packet. To balance the energy consumption among nodes and prolong the lifetime of the whole network, when determining the BFN, the residual energy and node density of candidate nodes are taken into account, and two weight coefficients are introduced for the two routing discriminant parameters of the candidate node. However, with the forwarding of packets, the two discriminant parameters of a candidate node interact and influence each other, and the interaction and influence are difficult to be described by given formula. So fuzzy control is introduced in this paper to deal with the uncertain interaction among different discriminant parameters of candidate nodes. FCS is an intelligent control system that uses fuzzy set theory, fuzzy language variables, and fuzzy logic reasoning for decision-making, so it is an intelligent decision-making system. FCS can imitate human inference and decision-making process and is widely used in various fields. Since FCS has many advantages such as low computational complexity and strong adaptability, to optimize the routing decision for UANs, an FCS-based layering routing (FCLR) protocol is proposed. In FCS, the structure of dual input and single output is the most common. In UANs, if a node has more residual energy and more upper layer neighbor nodes, it is more suitable to be the next hop forwarding node. So considering the energy limitation and the imbalance of energy consumption of nodes in UANs, the residual energy rate (RER) and QND of qualified forwarding node (QFN) are taken as the input variables, and the forwarding probability (FP) of QFN is taken as the output variable of FCS in the proposed FCLR protocol. The core of an FCS is a fuzzy controller, also known as an fuzzy language controller. The fuzzy controller is mainly composed of the fuzzy interface, fuzzy rule base, inference and defuzzy-interface. The fuzzy control takes five steps as follows: Step 1: Determine the input and output variables; Step 2: Define the linguistic values of the input and output; Step 3: Determine the membership functions of input and output variables; Step 4: Establish the rules of fuzzy control; Step 5: Output the result after rule matching, rule triggering, © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 6 IEEE SENSORS JOURNAL, VOL. XX, NO. XX, XXXX 2022 TABLE V L INGUISTIC VALUES FOR RER, QND A ND FP Fuzzification RER Fuzzy inference Defuzzification FP QND Fuzzy rule Input/output variables Membership RER Low Medium High QND Low Medium High FP Low Medium High Fig. 2. The flow chart of BFN selection. a l m c 0HPEHUVKLSGHJUHH n y z o b x /RZ 0HGLXP +LJK 5(5 Fig. 3. The network topology. Fig. 4. Membership functions of RER. defuzzification, etc.. Before selecting the BFN by the FCS, the node first finds out all the neighbor nodes with layers less than Lcur as the qualified forwarding node (QFN). Next, the residual energy rate (RER) of QFN and qualified node density are input into the FCS. The flow chart of BFN selection is shown in Fig.2. RER: the rate of the residual energy of a QFN to its initial energy, it is given by: node n. Thus, the QNDs of node y and node z are 1/2 and 3/5 respectively according to Eq.9. The RER and QND of the QFN node (node y, and node z successively) are used as input variables of the FCS, and the output value of FCS is the probability that the QFN node is selected as the BFN, which is defined as forwarding probability (FP). The larger the FP, the more probably the QFN node is selected as the BFN. In FCS, three triangle membership functions are used for fuzzification and three linguistic values for RER, QND and FP are specified as shown in Table V. The membership functions of Low, Medium and High are fL , fM and fH , respectively, which are given by equation (10) - (12) [36]. x60 0, 0.5−x , 0 6 x 6 0.5 fL (x) = (10) 0.5 0, x > 0.5 0, x60 x , 0 6 x 6 0.5 0.5 fM (x) = (11) , 0.5 6 x 6 1 1−x 0.5 0, x>1 x 6 0.5 0, x−0.5 , 0.5 6x61 fH (x) = (12) 0.5 0, x>1 RER = Er , RER ∈ (0, 1) Ei (8) where Ei and Er are the initial energy and residual energy of the QFN respectively. QND: the rate of the number of neighbors whose layer is smaller than that of QFN to the number of neighbors of QFN, it is given by: QN D = NLq −1 , QN D ∈ (0, 1) Naq (9) where NLq −1 is the number of neighbor nodes whose layer is 1 smaller than that of QFN and Naq is the number of all neighbor nodes of the QFN. Lq is the layer of QFN. The network topology is shown in Fig.3. In Fig.3, the node x is the current node, Ni ={y, z} composes the set of QFN, that is, Ni is the set of neighbor nodes in the upper layer of CFN x. The nodes in Ni are nodes with the layer Lcur − 1. Nj ={a, b, c, x} is the set of neighbor nodes of QFN y and Nk ={l, m, n, o, x} is the set of neighbor nodes of QFN z. As shown in Fig.3, the neighbor nodes of the QFN y with a smaller layer are node a and node c, the neighbor nodes of the QFN z with an smaller layer are node l, node m, and We plotted the membership function curves of RER, QND and FP as Fig.4, Fig.5 and Fig.6 respectively. Fuzzy rules adopt if-then rules in FCS. For example, if RER is Medium and QND is High, then FP is High. Consequently, the total fuzzy rules employed by the control engine are shown in Table VI. © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 0HPEHUVKLSGHJUHH 0HPEHUVKLSGHJUHH DUOLIANG HAN et al.: FCLR: FUZZY CONTROL-BASED LAYERING ROUTING PROTOCOL FOR UNDERWATER ACOUSTIC NETWORKS (XXXX 2022) /RZ 0HGLXP +LJK /RZ 0HGLXP +LJK 7 41' )RUZDUGLQJSUREDELOLW\ Fig. 6. The Membership function and FP for node y. Fig. 5. Membership functions of QND. TABLE VI TOTAL F UZZY RULE U SED B Y T HE C ONTROL E NGINE RER QND Forwarding probability 1 Low Low Low 2 Low Medium Low 3 Medium Low Low 4 Medium Medium Medium 5 Low High Medium 6 High Low Medium 7 Medium High High 8 High Medium High 9 High High High 0HPEHUVKLSGHJUHH Rule /RZ 0HGLXP +LJK )RUZDUGLQJSUREDELOLW\ Fig. 7. The Membership function and FP for node z. Since the method of gravity center has smoother output control than the method of maximum membership, the method of gravity center is used in the process of defuzzification, in which the x-axis value of the center point of the area enclosed by the membership function curve and the x-axis is the final output value of the FCS. The calculation formula of the output value FP on a discrete domain with j output quantized number is given in equation (10). j P FP = (Xi µ(Xi )) i=1 j P (13) µ(Xi ) i=1 where j is the number of quantized values on the discrete domain of the x-axis, Xi is the ith fuzzy value in the x-axis and µ(Xi ) is the membership degree of Xi . Now we present the BFN selection in detail, which is divided into the following steps. Step 1: Before a source node (or a CFN) forwards data, it first selects the nodes whose layers are 1 lower than its layer from the neighbor table as the QFN nodes. Step 2: The current node calculates the RER and QND of QFN nodes according to equations (8) and (9). Step 3: The RER and QND of QFN nodes are input into the FCS successfully and the FPs of QFN nodes are output. Step 4: The node ID of the BFN is returned. Step 5: The BFN forwards the data packet. Assume the RER and QND of node y are 0.85 and 0.5 respectively, and the RER and QND of node z are 0.92 and 0.6 respectively. The FP and membership functions for node y and node z are shown in Fig.6 and Fig.7 respectively. According to Table VI, the following rules take effect: Rule 1: IF RER is Medium and QND is Medium, then FP is Medium; Rule 2: IF RER is Medium and QND is High, then FP is High; Rule 3: IF RER is High and QND is Medium, then FP is High; Rule 4: IF RER is High and QND is High, then FP is High. After fuzzy inference and defuzzification, the output values of FCS for node y and node z are 0.62 and 0.69 respectively. Therefore, the probability that node z is selected as the BFN is higher than that of node B, and the QFN with the maximum forwarding probability is selected as the BFN. D. Data Forwarding © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 8 IEEE SENSORS JOURNAL, VOL. XX, NO. XX, XXXX 2022 Source node or CFN have data to send Yes Source node or CFN will select BFN Neighbor nodes hear the data packet Neighbor_ID == sink_ID ? Update NIT No Select QFN m_ID == BFN_ID ? Calculating RER and QND of QFN Sink_ID == BFN_ID ? Yes Input RER and QND No Discard the data packet float Fuzzy_controller::trimf(float x, float a, float b, float c) { float u; if (x >= a && x <= b) u = (x - a) / (b - a); else if (x > b && x <= c) u = (c - x) / (c - b); else u = 0.0; return u; } RER =it->second.ap /DEFAULT_INIT_AP ; QND=(it->second.up_layer_neighbor_number)/(it->second.all_neighbor_number) ; desired_tmp = Fuzzy_controller::calculate_FP(RER,QND); No Yes Reveiving the data packet Fig. 9. Example codes of the FCLR protocol. (0,250,0) FCS Determine the maximum value of the output result Sink node Communication completed successfully (250,0,0) return the BFN_ID Ordinary node Forwarding data packet End Fig. 8. The main workflow chart of the FCLR protocol. After the BFN is determined, the data packets can be sent (or forwarded). Usually, all the neighbor nodes within the communication range of the sender can hear the data packets, and one of the following three cases may occur: Case 1: If the receiving node is the sink node, the sink node will receive the data packet, update its NIT and forward the data packet to the data center by a radio frequency signal. Case 2: If the receiving node is the BFN, the BFN will receive the data packet, update its NIT, then select the next BFN at the next hop, and forward the data packet to the next BFN; Case3: If a node other than the BFN hears a data packet, it will update its NIT and discard the packet. When the sink node receives the data packet, it is considered that the communication has been completed successfully. The main workflow of the FCLR protocol is shown in Fig.8. Fig.8 shows the overall process to select the best forwarding node and perform routing forwarding. V. P ERFORMANCE E VALUATION In this section, we evaluate the performance of the proposed FCLR protocol. The FCLR protocol is compared with DBR, QELAR, VBF, RLOR, and ELW-CFR protocols in terms of packet delivery rate (PDR), end-to-end delay (EED), and total energy consumption (TEC). The performance of the proposed FCLR protocol is evaluated by simulation experiments with the NS3 simulator, which is a new network simulator written in C++. Compared with NS2, the architecture of NS3 is clearer and more convenient for the researcher to develop their routing protocol. Fig.9 gives some codes of triangle membership functions and the calculation of input and output variables of FCS. A. Simulation Parameter Setting (0,0,500) Source node Fig. 10. The network topology in simulation experiments. We consider the network model described previously. The sensor nodes are randomly deployed in a 3D area of 500m*500m*500m, and the sink node is deployed on the water surface, which is shown in Fig.10. A movement model is applied to the sensor nodes, and each node moves at 1-3m/s in the horizontal direction and the movement in the vertical direction can be negligible. The main simulation parameters are listed in Table VII. B. Performance Metrics To better evaluate the performance of the protocol, the following evaluation indicators are selected: 1) Packet Delivery Rate: PDR: The rate of the number of packets successfully received by the sink node to the number of packets sent by source nodes. PDR is given by: Ntrans P P DR = i=1 Nrece Nsend Ntrans (14) where Ntrans is the experiment times. Nrece is the number of data packets successfully received by the sink node. Nsend is the number of data packets sent by source nodes. © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 DUOLIANG HAN et al.: FCLR: FUZZY CONTROL-BASED LAYERING ROUTING PROTOCOL FOR UNDERWATER ACOUSTIC NETWORKS (XXXX 2022) 9 1 .0 TABLE VII S IMULATION PARAMETER 0 .8 Value Unit Simulation scene range 500*500*500 m Simulation time 800 S Number of nodes 300-800 Data packet size 64 Bytes Hello packet size 33 Bytes Transmitting power 2.0 w Receiving power 0.1 w Idle power 0.01 w Topology Random Initial energy 1000 Number of experiments 20 0 .6 F C L R Q E L A R D B R V B F P D R Simulation parameter 0 .4 0 .2 0 .0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 N u m b e r o f N o d e Fig. 11. The effect of the number of nodes on PDR. J 5 4 EED: The time taken to deliver a data packet from a source node to the sink node. EED is given by: E E D (s ) Ntrans P (Tsink − Tsource ) i=1 F C L Q E L D B R V B F R L O E L W 3 (15) 2 where Ntrans is the experiment times. Tsink is the time when the sink node receives a data packet, and Tsource is the time when the source node sends the packet. TEC: The sum of the energy consumed by all nodes for transmitting, receiving, and hearing packets during the simulation time. TEC is calculated according to the equation(16): 1 EED = Ntrans P T EC = Ntrans (Esend + Erece + Eidle + Esleep ) i=1 Ntrans (16) where Ntrans is the experiment times. Esend , Erece , Eidle and Esleep are the energy consumed by nodes in sending, receiving, idle and sleep states respectively. C. Simulation Results Analysis In this section, we analyze the effects of node number and node movement speed on PDR, EED, and TEC. Furthermore, we analyze the effect of the initial energy of nodes on PDR. 1) The effect of the number of nodes on protocol performance: The effects of node number on PDR, EED, and TEC are shown in Fig.11, Fig.12, and Fig.13 respectively. To fully evaluate the performance of the FCLR protocol, in Fig.11, Fig.12, and Fig.13, the PDR, EED, and TEC of the FCLR protocol are compared with the QELAR, DBR, VBF, RLOR, and ELW-CFR protocols respectively. As shown in Fig.11, the PDRs of the six protocols all show an increasing trend as the number of nodes increases, which is because, a better node would be selected as the BFNs with the number of (candidate) forwarding nodes increases, and the better BFN can deliver data packets to the sink more R A R R -C F R 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 N u m b e r o f n o d e s Fig. 12. The effect of the number of nodes on EED. successfully. From Fig.11, it can be seen that when the number of nodes reaches 600 (800, 800, 800, 700, or 700), the PDR of the FCLR (QELAR, DBR, VBF, RLOR, or ELW-CFR) protocol reaches its maximum value. The PDR of the FCLR protocol is always higher than any of the QELAR, DBR, VBF, and ELW-CFR protocols but lower than that of the RLOR protocol. From Fig.12 we can see that the EEDs of the six protocols all show a decreasing trend as the number of nodes increases. When the number of nodes reaches 800, the EEDs of all the protocols reach their minimum values. When the number of nodes is smaller than 700, the EED of the FCLR protocol is less than any of the QELAR, DBR, VBF, RLOR, and ELWCFR protocols. However, when the number of nodes is more than 700, the EED of the FCLR protocol is higher than that of the QELAR and ELW-CFR protocols. From Fig.13 we can see that the TECs consumed by FCLR, QELAR, DBR, and VBF protocols increase as the number of nodes increases since more nodes are involved in receiving or hearing, or forwarding packets. It is also seen that the TEC of the FCLR protocol is the least compared with QELAR, DBR, and VBF protocols. This is because in the FCLR protocol only one node (the BFN) forwards the packet at this hop. Redundant forwarding is unavoidable in other protocols due to the nature of broadcasting. The number of redundant packets forwarded © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 10 IEEE SENSORS JOURNAL, VOL. XX, NO. XX, XXXX 2022 1 .0 0 .8 1 0 0 0 0 8 0 0 0 F C L R Q E L A R D B R V B F 6 0 0 0 4 0 0 0 2 0 0 0 0 .6 P D R T o ta l E n e r g y C o n s u m p tio n (J ) 1 2 0 0 0 0 .4 0 .2 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 0 .0 N u m b e r o f N o d e 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 I n itia l e n e r g y (J ) Fig. 13. The effect of the number of nodes on TEC. Fig. 15. The effect of the initial energy on PDR. 1 .0 0 .8 0 .6 P D R 1 -3 m /s 3 -5 m /s 0 .4 0 .2 0 .0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 N o d e o f N u m b e r Fig. 14. The Effect of node movement speed on PDR. increases with the number of nodes, resulting in an increasing in TEC. From Fig.11 to Fig.13, we can see that the FCLR protocol outperforms the DBR and VBF protocols in terms of PDR, EED, and TEC. Although the PDR of the RLOR protocol is better than that of the FCLR protocol, the FCLR protocol outperforms the RLOR protocol in terms of EED. In addition, the FCLR protocol outperforms the QELAR protocol in terms of TEC. In general, the FCLR protocol has superior performance in terms of PDR, EED, and TEC. 2) The effect of movement speed on protocol performance: To further evaluate the effect of node movement on the performance of the FCLR protocol, we set the nodes to be moveable. The movement speed is set to 1-3m/s and 35m/s successively in simulation experiments. We analyze the effect of node movement on the network performance. The simulation experimental results are shown in Fig.14. From Fig.14 it can be seen that the speed of node movement has a significant effect on the PDR. The PDR with nodes moving at 3-5m/s is significantly lower than that with nodes moving at 1-3m/s. This is because when the movement speed of the node is high, the neighbor nodes of the sending node may move out of the senders transmission range. If the NIT of the current node is not updated timely, the wrong BFN may fail to receive and forward data packets, which leads to lower PDR. It is also seen that, when nodes move at 3-5m/s, the PDR can still reach 75.8%. Meanwhile, we can see that when the number of nodes is 600, the PDR reaches its peak value for both movement speeds. 3) The effect of initial energy on protocol performance: The effect of the initial energy of nodes on PDR is shown in Fig.15, in which the initial energy is set to 10J, 20J, 30J, 40J, 50, 60J, 70J, and 80J. As shown in Fig.15, it can be seen that the initial energy has a significant effect on the PDR. When the initial energy of the node is between 10-60J, with the increase of the initial energy, the PDR increases obviously. When the initial energy of the nodes is 60J, the PDR of the FCLR protocol reaches the maximum value. As the initial energy of nodes increases gradually, the number of nodes that fail to participate in data forwarding due to insufficient energy gradually decreases. Therefore, the PDR of the FCLR protocol gradually increases. When the initial energy of the nodes exceeds 60J, the PDR remains at about 92%. This is because the nodes in the network hardly run out of their energy during the simulation time when the initial energy of the nodes exceeds 60J. There are some limitations to our work. The broadcasting interval of HELLO packets is not easy to determine. When the interval is large, the layer or NIT may not be updated in time, resulting in a node that has moved away being selected as the BFN and a drop in PDR. When the interval is small, there will be too many HELLO packets in the network, which leads to a collision between HELLO packets and data packets, also a drop in PDR. VI. P ERFORMANCE E VALUATION I N F IELD E XPERIMENTS To better verify the performance of the FCLR protocol and apply FCLR to the real environment, we developed and implemented the FCLR protocol in August 2021 and conducted tests in the real environment at Qinghai Lake, the largest saltwater lake in China, from September 19 to September 21, 2021, and the test scene is shown in Fig.16. We deployed five modems in the Qinghai lake. The five © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 DUOLIANG HAN et al.: FCLR: FUZZY CONTROL-BASED LAYERING ROUTING PROTOCOL FOR UNDERWATER ACOUSTIC NETWORKS (XXXX 2022) 11 TABLE VIII S IMULATION PARAMETER Fig. 16. Lake test scene. Raspberry Pi Cable Test parameter Value Modem model AMN-OFDM-13A Modem modulation mode OFDM Unit Number of modem 5 Modem ID 1,5,8,36,65 Distance of node 200-1200 m Transmitting power 20 w Transmission gain 20 Data type Picture Picture size 11.2/4.4 KB Data packet size 200 Bytes Hello packet size 33 Bytes Data packet interval 163 s Hello packet interval 47 s Data server Node_ID:1 Node_Type:Sink_node GPS:36.58494949340820,100.4923858642578 Depth:5 Node_ID:36 Node_Type:Forwarding node GPS:36.58472442626953,100.4927215576172 Depth:5 Node_ID:8 Node_Type:Forwarding node GPS:36.58496093750,"lon":100.4923095703125 Depth:5 Node_ID:5 Node_Type:Forwarding node GPS:36.57589340209961,100.5027389526367 Depth:5.0 Node_ID:65 Node_Type:Source_node GPS:36.58438873291016,100.5003356933594 Depth:6.0 Fig. 17. Node deployment in the Qinghai lake. modems formed firstly a one-hop network, then formed a twohop network, which is shown in. Fig.17. The IDs of the five nodes are 1, 5, 8, 36 and 65 respectively. In Fig.17, each node is powered by a battery and controlled by a raspberry pi microcomputer. The sink node is fixed at the dock in the test which has a diving depth of roughly 5m. The ID of the sink node is 1. The sink node is responsible for transmitting the data forwarded by other nodes to a server through 4G and the Internet. Node 5, Node 8 and Node 36 are responsible for relaying the data packets from the source node. The source node is responsible for collecting and transmitting data. The ID of the source node is 65. We carried out both one-hop experiments and two-hop experiments, in which the source node is stationary first and then mobile, the parameters used in the field test are shown in Table VIII. In the field test, the RCHF protocol proposed by our team was used as the MAC protocol. The RCHF MAC protocol has a re-transmission mechanism for data packets. However, it should be emphasized that: (1) when calculating PDR, the number of data packets received successfully by the sink node does not include the re-transmitted packets; (2) When calculating the throughput of the network, the number of data packets received successfully includes the re-transmitted data packets. In the field experiments, all the information such as the receiving time, sending time or re-transmission time of each packet at each node is recorded in a log file in each node, which is analyzed and counted. Based on the data in log files, the performance of the FCLR protocol is evaluated in terms of PDR, throughput, and end to end delay(EED). The PDR is defined as in equation (14) and the throughput is defined as follows. Throughput: the number of packets successfully received by the sink node multiplied by the length of a packet, divide by the time it takes to receive the packet, which is given by: N umrece ∗ Lenpack (17) T ime where N umrece is the number of packets successfully received by the sink node. Lenpack is the length of a data packet. T ime is the time interval from the time the sink node receives the first data packet to the time it receives the last data packet. TP = A. One-hop test with node stationary and move In all the field experiments, the sink node is deployed under a wharf and other nodes are deployed in water with a depth of about 5m. The nodes are either stationary or move with the water flow or a boat. The distance between two neighbor nodes is within a range of 200m-1000m. The data delivered © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 12 IEEE SENSORS JOURNAL, VOL. XX, NO. XX, XXXX 2022 TABLE IX T HE P ERFORMANCE OF O NE H OP N ETWORK WITH A S TATIONARY S OURCE N ODE Metrics Group PDR TP(bps) 1 2 3 4 Average 0.982 0.965 0.947 0.965 0.965 512 517.61 507.28 255 250 255.75 518.69 480.77 EED(s) 249 269 TABLE XI T HE P ERFORMANCE OF O NE H OP N ETWORK WITH A M OVING S OURCE N ODE Metrics Group PDR TP(bps) 1 2 3 4 Average 0.407 0.778 0.926 0.741 0.713 471.23 235.82 333.96 350.64 347.91 4 5 0 4 0 0 TABLE X T HE P ERFORMANCE OF O NE H OP N ETWORK WITH A M OVING S OURCE N ODE Group PDR TP(bps) EED(s) 1 2 3 4 Average 1 1 0.964 0.964 0.982 486.77 516.57 433.42 517.62 237 241 312 251 3 0 0 E E D (S ) Metrics 3 5 0 2 5 0 O n e h o p T w o -h o p 2 0 0 488.6 1 5 0 260.25 1 0 0 5 0 0 underwater is a digital picture of a fish with a size of 11.2KB. Table IX and Table X list the test results in the one-hop test when the source node is stationary and moving respectively. As can be seen in Table IX, the maximum values of PDR and TP for the one-hop test when the source node is stationary can reach 98.2% and 518.69 bps respectively. The minimum EED delay is 249s. Among the four groups of experiments, the results of the first group are the most perfect in terms of PDR, TP and EED. In the results from the first group, the throughput is the highest since the sink node takes the least time to receive successfully all the data packets in the picture file. In contrast, in the results of the second group, the opposite was true, the increase in EED leads to a decreasing of TP. From Table X it can be seen that the maximum values of PDR and TP for the one-hop test when the source node is moving can reach 100% and 517.62 bps respectively. The minimum EED is 237s. Among the four groups of experiments, the results of the second group are the most perfect in terms of PDR, TP and EED. The results of the fourth group achieve the highest TP the lowest PDR, and the longest EED, in which more data packet are re-transmitted. According to Table IX and Table X, there is little differences in the performance of the proposed protocols in different experimental scenarios. The average of the test results shows that the performance of the network with a fixed source node outperforms that with a moving source node in terms of TP and EED. The PDR when the source node is moving is greater than the PDR when the source node is stationary, which is different from the simulation results. 1 2 3 4 A v e r a g e D iffe r e n t te s t g r o u p s Fig. 18. EED of one-hop test and two-hop test. B. Two-Hop test with nodes moving XI shows the PDRs and TPs of the two-hop test in which the three nodes with IDs of 5, 36 and 65 moved. Fig.18 shows the EED results of the one-hop and two-hop tests. From Table XI it can be seen that the maximum values of PDR and TP for the two-hop test can reach 92.6% and 471.23 bps respectively when Node 5, Node 36, and Node 65 are moving. The first test achieves the lowest PDR and the highest TP. The second test achieves the lowest TP. This is because a large number of collisions and re-transmission result in a long EED and small TP, which can be seen also in Fig.18. Fig.18 shows the EEDs of the one-hop and the two-hop tests. From Fig.18 it can be seen that the EED in the twohop test is significantly greater than that in one-hop test. The maximum delay in two-hop is 401s, in which some of the data packets to Node 1 forwarded by Node 5 are re-transmitted twice according to the log file, leading to the long delay at the second hop. The minimum EED in the two-hop test is 287s. According to Table X and Table XI, the overall performance in the one-hop network outperforms that in the two-hop network in terms of PDR, TP and EED. After analyzing the log files in each node we draw an important conclusion, that the multi-hop transmission in UANs decreases the overall performance of the network. The more hops, the worse the network performance. In the two-hop test, No.1 and No.36 are deployed under the dock, No.5, No.8, and No.65 are deployed in water using yachts. The depths of No.1 and No.36 are approximately 5m, and the depth of No.5, No.8, and No.65 are approximately 6m. The distances between The distance between two neighbor nodes is within a range of 200m-1200m. The data transmitted in the test is a digital photo of fish with a size of 4.4KB. Table In this paper, we propose a fuzzy control-based layering routing protocol FCLR. Extensive simulation experiments and real field tests are conducted based on the proposed FCLR protocol. We compare and analyze the proposed protocol with the QELAR, DBR, VBF, RLOR, and ELW-CFR protocols. VII. C ONCLUSION © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 DUOLIANG HAN et al.: FCLR: FUZZY CONTROL-BASED LAYERING ROUTING PROTOCOL FOR UNDERWATER ACOUSTIC NETWORKS (XXXX 2022) When the moving speed of nodes is 1-3m/s, the PDR of the FCLR protocol can reach 91.67%, which is higher than that of QELAR, DBR, VBF, and ELW-CFR protocols. The EED of the FCLR protocol is always less than any of the QELAR, DBR, VBF, RLOR and ELW-CFR protocols when the number of nodes is smaller than 700. With the increase in number of nodes, the TEC of the FCLR protocol increases, but it is smaller than that of QELAR, DBR, and VBF protocols. Moreover, when the initial energy of the nodes is 60J, the PDR of the FCLR protocol reaches the maximum value. When the initial energy of the nodes exceeds 60J, the PDR remains at about 92%. Meanwhile, the lake test results show that the FCLR protocol exhibits stable and acceptable performance in a real environment. When nodes are moving, the packet delivery rate can reach 92.6 percent and the throughput can reach 350.64bps. In future research, we will optimize the HELLO packet broadcast interval to alleviate the drop in PDR caused by a collision between HELLO packets and data packets. Furthermore, we will combine the FCLR protocol with reinforcement learning and other technologies to improve the FCLR protocol and further improve the performance of the network. R EFERENCES [1] Akyildiz IF, Pompili D, Melodia T. 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Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply. This article has been accepted for publication in IEEE Sensors Journal. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2022.3218136 14 IEEE SENSORS JOURNAL, VOL. XX, NO. XX, XXXX 2022 Duoliang Han received his master’s degree from Qinghai Normal University, in 2020. He is now a doctoral student in Qinghai Normal University, Qinghai, China. His research interests include protocol design and optimization. Xiujuan Du received her Ph. D degree from Tianjin University,Tianjin, China in 2010. She is currently a professor in Qinghai Normal University, Qinghai,China. Her research interests include underwater acoustic networks, wireless network and security and Internet of things. She has received the New Century Excellent Talent from Education Ministry, China, in 2011. Xiuxiu Liu received her master’s degree from Qinghai Normal University, in 2016. She is now a doctoral student and a lecturer in Qinghai Normal University, Qinghai, China. Her research interests include underwater acoustic networks. Xiaojing Tian received her master’s degree from Qinghai Normal University, in 2021. She is now a doctoral student in Qinghai Normal University, Qinghai, China. Her research interests include protocol design and optimization. © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: BEIJING INSTITUTE OF TECHNOLOGY. Downloaded on November 09,2022 at 07:15:09 UTC from IEEE Xplore. Restrictions apply.