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The Linear Wireless Ad‐Hoc Network (Linear WANET), as a branch of the Ad‐Hoc network, refers to a self‐organizing multi‐hop wireless network in which nodes are arranged linearly. Frame aggregation and RTS/CTS schemes are introduced in IEEE 802.11 aims to improve network transmission performance. However, the traditional mechanisms may not have good adaptability in linear multi‐hop networks. Thus, we defined a Linear WANET simulation model based on the IEEE 802.11 protocol. We established this model on the NS‐3 network simulator to perform A‐MSDU, A‐MPDU, and two‐level frame aggregation simulation and analyzed the aggregation performance under different channel environments. Meanwhile, the RTS/CTS and TXOP mechanisms were also simulated in this article. We analyzed the performance of each mechanism in a Linear WANET under saturated and unsaturated environments. We found that the linear multi‐hop characteristic has a significant impact on the performance of the frame aggregation mechanism. In the Linear WANET, the A‐MSDU mechanism can improve system performance to a limited extent, but at the same time, it will increase the packet loss rate and delay. So, the two‐level aggregation can improve the maximum throughput of the system with better channel conditions. In the case of single A‐MPDU aggregation, there has a lowest data delivery interval that the Linear WANET system can withstand. The A‐MPDU mechanism is a better choice for the poor channel conditions with unsaturated system throughput. Meanwhile, we also found that the native TXOP mechanism cannot effectively improve the system efficiency of Linear WANET. The RTS/CTS mechanism can enhance system throughput performance in most cases, especially in a saturated throughput environment. [ABSTRACT FROM AUTHOR]

Abstract The Linear Wireless Ad‐Hoc Network (Linear WANET), as a branch of the Ad‐Hoc network, refers to a self‐organizing multi‐hop wireless network in which nodes are arranged linearly. Frame aggregation and RTS/CTS schemes are introduced in IEEE 802.11 aims to improve network transmission performance. However, the traditional mechanisms may not have good adaptability in linear multi‐hop networks. Thus, we defined a Linear WANET simulation model based on the IEEE 802.11 protocol. We established this model on the NS‐3 network simulator to perform A‐MSDU, A‐MPDU, and two‐level frame aggregation simulation and analyzed the aggregation performance under different channel environments. Meanwhile, the RTS/CTS and TXOP mechanisms were also simulated in this article. We analyzed the performance of each mechanism in a Linear WANET under saturated and unsaturated environments. We found that the linear multi‐hop characteristic has a significant impact on the performance of the frame aggregation mechanism. In the Linear WANET, the A‐MSDU mechanism can improve system performance to a limited extent, but at the same time, it will increase the packet loss rate and delay. So, the two‐level aggregation can improve the maximum throughput of the system with better channel conditions. In the case of single A‐MPDU aggregation, there has a lowest data delivery interval that the Linear WANET system can withstand. The A‐MPDU mechanism is a better choice for the poor channel conditions with unsaturated system throughput. Meanwhile, we also found that the native TXOP mechanism cannot effectively improve the system efficiency of Linear WANET. The RTS/CTS mechanism can enhance system throughput performance in most cases, especially in a saturated throughput environment.

Infrastructure-less (sometimes known as ad-hoc) networking paradigm is very appealing and potentially shaping its future into almost all emerging networks (i.e., IoT, wireless sensor networks, vehicular ad-hoc networks, emergency, and tactical radio networks, etc.). However, when conventional networking protocols are used, such networks often perform poorly, mainly because of interference within the network and limited network throughput. Recent advancements in wireless communications have enabled full-duplex (FD) operation by suppressing self-interference, which can theoretically double the network throughput. However, conventional medium access control (MAC) protocols like carrier-sense multiple access with collision avoidance (CSMA/CA) favor half-duplex (HD) operation and fail to benefit from FD transmission opportunities. This article proposes a novel hybrid MAC protocol for full-duplex ad-hoc networks. The proposed MAC combines time division multiple access (TDMA) and IEEE 802.11 distributed coordination function (DCF) strengths in chains of time-slotted contention-based control frames and collision-free data frames. The aim is to fully utilize FD transmission opportunities to increase network throughput. The proposed protocol modifies request-to-send (RTS) and clear-to-send (CTS) frames in IEEE 802.11 DCF MAC to form FD-RTS/CTS frames. These frames are used to enable collision-free FD communications among neighbors. The proposed scheme mitigates conventional MAC issues like hidden-node problem (HNP) and exposed-node problem (ENP). It also allows concurrent FD data transmissions in a collision-free manner. The model is generic and can be applied to any ad-hoc wireless network. In this article, the design is applied to a single channel ad-hoc network with FD transceivers. We compared the proposed design with IEEE 802.11 CSMA/CA protocol with both HD and FD transceivers. The simulation results show a 30% gain in throughput, reduced latency, and fairness among participating wireless nodes.

Medium access control (MAC) protocol operations for in-band full duplex multi-hop networks play an important role in efficient data relaying and throughput enhancement. Knowledge of the relationship between essential operations in MAC protocol for full duplex MAC (FD MAC) networks and network performance is important and useful in terms of the protocol and network design. FD MAC protocols often require exchanging control frames, e.g., request to send/clear to send (RTS/CTS). However, the conventional model cannot analyze the performance of wireless multi-hop networks with RTS/CTS-based FD MAC. Thus, this paper proposes a throughput analysis model for wireless multi-hop networks with RTS/CTS-based FD MAC. The proposed model includes novel "airtime expressions", which allows us to handle RTS/CTS operations under FD MAC. The proposed model provides the end-to-end throughput of multi-hop networks with RTS/CTS-based FD MAC for any number of hops and any payload size. The validity of the analytical expressions is confirmed through comparisons with simulation results. [ABSTRACT FROM AUTHOR]

The scarcity of water resources throughout the world demands its optimum utilization in various sectors. Smart Sensing-enabled irrigation management systems are the ideal solutions to ensure the optimum utilization of water resources in the agriculture sector. This paper presents a wireless sensor network-enabled Decision Support System (DSS) for developing a need-based irrigation schedule for the orange orchard. For efficient monitoring of various in-field parameters, our proposed approach uses the latest smart sensing technology such as soil moisture, leaf-wetness, temperature and humidity. The proposed smart sensing-enabled test-bed was deployed in the orange orchard of our institute for approximately one year and successfully adjusted its irrigation schedule according to the needs and demands of the plants. Moreover, a modified Longest Common SubSequence (LCSS) mechanism is integrated with the proposed DSS for distinguishing multi-valued noise from the abrupt changing scenarios. To resolve the concurrent communication problem of two or more wasp-mote sensor boards with a common receiver, an enhanced RTS/CTS handshake mechanism is presented. Our proposed DSS compares the most recently refined data with pre-defined threshold values for efficient water management in the orchard. Irrigation activity is scheduled if water deficit criterion is met and the farmer is informed accordingly. Both the experimental and simulation results show that the proposed scheme performs better in comparison to the existing schemes. [ABSTRACT FROM AUTHOR]

In dense wireless local area networks (WLANs), the primary causes of interference and hindrance to spatial reuse are the well-known hidden node problem (HNP) and the exposed node problem (ENP). In this paper, we propose a joint solution to these problems. The proposed mechanism, referred to as Probe/PreAck (PR/PA), utilizes the concept of a two-way handshake for efficient channel reservation and spatial reuse by means of two control frames called PR and PA. The PR frame is designed for the semi-reservation of a channel initiated by a transmitting node, while the PA frame is used for the receiver-oriented permission of a channel reservation. Once a transmitting node advertises a PR frame, the channel is temporarily reserved, and the channel reservation is finally completed after the node receives the corresponding PA frame. Otherwise, the channel reservation is immediately released. Unlike the ready-tosend/clear-to-send mechanism, which is a well-known solution to HNP, the proposed mechanism does not unnecessarily prevent nodes from accessing the channel but selectively blocks transmitting and receiving nodes when they overhear the PA and PR frames transmitted by neighboring nodes, respectively. In this way, the proposed PR/PA mechanism effectively deals with both HNP and ENP in a unified framework. We further enhance the PR/PA mechanism by devising an immediate destination switching scheme, which is implemented in access points (APs) to improve the downlink throughput. If an AP fails to complete the exchange of PR and PA frames with a specific destination, it sends another PR frame to a different destination node without performing a new back-off procedure. Moreover, we adopt the transmission time control scheme to assure successful spatial reuse in multiple basic service set (BSS) WLANs. By adjusting the transmission time of the data frames simultaneously transmitted in different BSSs, severe interference between the data and acknowledgment frames can be avoided. The results of a simulation study confirmed that the proposed mechanism outperformed conventional mechanisms in dense multi-BSS WLANs; the downlink throughput was increased by more than 10 times while the overall network throughput was increased by approximately 50%.

The IEEE 802.11 standard defines the specifications of the media access control (MAC) and physical (PHY) layers for vehicular ad hoc networks (VANETs). In IEEE 802.11, distributed coordination function (DCF) is the fundamental access technique, which employs a carrier sense multiple access with collision avoidance (CSMA/CA) mechanism to access the medium. In addition, request to send (RTS)/ clear to send (CTS) mechanism is used to overcome hidden vehicular nodes problem. In this paper, an analytical model is developed to evaluate the performance of the IEEE 802.11 MAC for VANETs. The algorithm of CSMA/CA and RTS/CTS mechanism are presented. Markov chain model based analytical analysis is presented to investigate the performance. Parameters that can influence the performance such as vehicles velocity, vehicle density, contention window size, maximum retransmission limit etc. are considered. The relationship between the performance metrics and parameters are derived. Throughput, packet dropping rate (PDR) and delay expressions are obtained. Moreover, numerical results are demonstrated to verify the analysis. The comparison between CSMA/CA and RTS/CTS access mechanisms is presented. [ABSTRACT FROM AUTHOR]

Location Based Services are providing one of the fastest growing market segments today. While the most common technique for location determination is GPS, several alternative approaches have been proposed for Wi-Fi environments, based on time of flight, signal strength, etc. Time based techniques not only require accurate timestamping mechanisms, but also precise and synchronized clocks, which is quite difficult and expensive in industry. On the other hand, signal strength based methods need a lot of ground truth data. These method also require time consuming work and efforts before the system comes into use. In considerations of costs and time consumption, we present in this paper an approach for determining the location of a general Wi-Fi device combining RTS/CTS and TDoA techniques. The proposed model is deployable in various environments and contains two different methods, with clock mapping functions and asynchronized clocks. We also explain limitations of current round trip time (RTT) based RTS/CTS systems. Extensive experiments have been conducted and demonstrated how an accuracy of about one foot can be obtained and also the assumption of RTT measurements have been verified.

The traditional IEEE802.11 Request-to-Send/Clear-to-Send (RTS/CTS) handshaking in medium access control layer has been widely adopted in wireless ad hoc networks to reduce the hidden node problem. However, it induces the false blocking problem, which occurs when nodes are prevented from replying to any incoming RTS packets when they are in deferring state after overhearing the RTS and/or CTS packets. Worse still, these unreplied RTS packets will then cause other neighbouring nodes to defer blindly which propagates the false blocking problem, resulting in exhaustion of scarce energy resource and throughput degradation. In this paper, we propose an adaptive Ready-to-Send and blocking notification (RSBN) scheme to mitigate the false blocking problem. The adaptive RSBN scheme not only validates the overheard RTS packets to avoid blind deferment but also informs neighbouring nodes of the nodes' deferring status to block unnecessary RTS packets. We validate the proposed scheme by simulations and the results have shown that the adaptive RSBN scheme can achieve higher performance. [ABSTRACT FROM AUTHOR]

Unlike radio communication in terrestrial wireless sensor networks, acoustic channel in underwater wireless sensor network (UWSN) is challenged by long propagation delay and swarm mobility. The long propagation delay causes the deterioration of network throughput and unfairness. Moreover, the swarm mobility causes unreliable access and the failure of channel reservation. In this paper, we propose a novel delay tolerant MAC protocol (DTMAC) inspired by the coupon collector’s problem. It proposes a distributed coupon collection algorithm in UWSNs. If a node needs to send a packet, the packet will be repeatedly transmitted $m$ times, with a transmission probability to be $p$ . Under the traditional protocol interference model, we first set up a probability model for throughput of DTMAC, and then give the throughput-optimal value for $m$ and $p$ with the successful transmission probability as tuning parameter. Because no any acknowledge or channel reservation is used, the throughput of DTMAC is not influenced by propagation delay. In addition, space unfairness problem also no longer exists since DTMAC is not concerned with transmission distance. The simulation results show that the throughput of DTMAC greatly outperforms that of MAC protocol with RTS/CTS scheme in most underwater scenarios. [ABSTRACT FROM PUBLISHER]

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During the past few years the widespread use of the wireless local area networks (WLANs) communication technique is one of the most popular technologies in data telecommunications and networking. The IEEE 802.11 protocol has achieved worldwide acceptance with WLANs with minimum management and maintenance costs. The theoretical performance and numerical results in terms of saturation throughput and delay of distributed coordination function (DCF) were finished by Ziouva and Antonakopoulous. It took into account of the busy medium conditions and how they affected the use of the backoff mechanism. However, the definition of their proposed channel busy probability is not suitable for the operating system architecture. In this paper, the channel busy conditions is modified and the Ziouva and Antonakopoulous's (ZA's) model is improved, and the more accurate analyses of the DCF are presented. Our analysis is also extended to the computation of the delay performance of both the request-to-send/clear-to-send (RTS/CTS) and basic access mechanisms. The numerical results show that the modified model has better performance than the ZA's model under ideal channel scenario. [ABSTRACT FROM AUTHOR]

In this paper, we present a new discrete time Markov chain model to estimate the packet transmission probability τ, in order to develop mathematical models to derive the saturation throughput and the average packet delay of a 802.11 wireless LAN based on the RTS/CTS access method in the presence of noise, which distorts transmitted frames. Besides the standard backoff rule of the 802.11, Distributed Coordination Function assumes that each loss in the network is caused only by collision and acts to treat this situation by delaying the retransmission of the lost packet. We propose an enhancement of the IEEE 802.11 RTS/CTS scheme to recognize the reason of a transmission failure (collision or noise errors). Thus, the data packet is immediately retransmitted with zero-waiting time if a failure happens due to distortion by noise. This retransmission continues until the data packet is successfully transmitted or it is dropped when the number of packet transmission retries attains its limit. After that, we model the enhanced RTS/CTS scheme using a four-dimensional Markov model and we compare its performance with the actual RTS/CTS scheme. [ABSTRACT FROM AUTHOR]

M2 M communication is information exchange between machines and machines without any human interaction. M2 M communication based on cellular network suffers from the extremely large number of devices in service coverage. In cellular network case, the large number of devices lead to communication problem caused by collisions between the senders. In this work we study the collision probability, saturation throughput and packet error rate for the carrier sense multiple access collision avoidance (CSMA/CA) protocol with request to send and clear to send (RTS/CTS) mechanism in the case of frequency band division. We propose in this paper a modified version of CSMA/CA-RTS/CTS to be compatible with the band repartition technique and we prove that an important gain is introduced in terms of system performance especially for loaded networks. Different backoff stage numbers with different finite retransmission limit values are investigated. Simulations highlight that dividing the RTS band into independent channels reduces drastically the RTS collision probability and in particular the packet error rate. A gain in terms of saturation throughput is also demonstrated especially in charged networks mode. [ABSTRACT FROM AUTHOR]

Hidden node collision in a contention-based medium access control protocol contributes to poor wireless network performance. This paper extended the Bianchi's study and introduces a mathematical model that can be used to calculate throughput and delay for the IEEE 802.11 distributed coordination function of a multihop wireless network infrastructure assuming the presence of hidden node collision. This research investigates three essential parameters of multi-hop wireless networks. More specifically, this paper aims to analyze the effect of hidden nodes, network size, and maximum backoff stage on the overall system throughput and packet delay. Results clearly reveal the effect of large wireless network size, maximum backoff stage, and collision probability on throughput and packet delay. On one hand, throughput does not depend on the maximum backoff stage ( m) for a small network size (e.g., n $$=$$ 10). On the other hand, throughput does not strongly depend on the number of nodes when the backoff stage values are high. Comparing our proposed model in case single-hop with the Bianchi model, the analysis results indicate that the throughput values in our model when the numbers of nodes are 10, 50, and 100 are 0.6031, 0.4172 and 0.3433 respectively; whereas the throughput values are respectively 0.8370, 0.8317 and 0.8255 at the same number of nodes for the Bianchi model. The difference can be attributed to several assumptions made in our proposed model that were not considered in the Bianchi model. [ABSTRACT FROM AUTHOR]

For management purposes, it is very important to estimate the available bandwidth for each link in a MANET, in an accurate, timely and efficient way. In this paper we show analytical results on the probability distribution function of the bandwidth of a link in a MANET based on IEEE 802.11, that take into account transmission errors. We also show some analytical results on the fraction of time the channel is available for a given virtual link, so the effects of other transmitting nodes can also be taken into account. Together, these results can be usefully exploited in an efficient, accurate and distributed available bandwidth estimation mechanism.

In this paper, we analytically study a random access network that uses the request-to-send and clear-to-send (RTS/CTS) handshake for reservation of transmission time. In the network, nodes initiate data transmission to a common base station (BS) by sending an RTS packet according to a transmission probability. The RTS packet of a node specifies the length of the node's requested data transmission interval, and will be successfully received by the BS if its signal to interference plus noise ratio (SINR) is higher than the capture ratio. The BS will then reply with a CTS packet to grant this node the requested data transmission interval and inform the other nodes not to interrupt. The transmission probabilities of RTS packets of all nodes will determine the average throughput and power consumption of each node. The set of all possible throughputs that can be achieved by the network is called the throughput region. We characterize the throughput region and provide an upper bound on the total transmission power consumption over the throughput region at the optimal operating point. Specifically, the upper bound corresponds to one of three points in the throughput region depending on the fraction of time occupied by the RTS packets. [ABSTRACT FROM PUBLISHER]

This paper used OPNET IT Guru academic edition to simulate four scenarios of ad ho based mobile local area networks in the existence of active high traffic applications: FTP and Database. In order to study the effect of hidden node problem due to mobility, the first and the third scenarios did not use the request to send (RTS) / clear to send (CTS) mechanism and the second and the fourth scenarios used the mechanism. The effect of mobility on TCP and applications performance is also shown. The paper showed how mobility affected the congestion window size, WLAN load, Throughput, Media Access Delay, received traffic for FTP and Database, response time for database and the retransmission parameters in case of using and not using RTS/CTS mechanism in the existence of FTP and Database traffic. The results revealed that with respect to the mobile client and the FTP application, when the RTS/CTS mechanism is used, the congestion window size is reduced, and the mobile servers have higher data load than fixed ones although stopped transmission earlier. With respect to the fixed client, however, the mobile servers have lower load and congestion window size. As for the database application and the mobile client, using the RTS/CTS mechanism and having the servers stayed mobile causes the congestion window size be low, with the fixed client, however, there was no difference whether the servers are mobile or fixed. The WLAN and throughput for the fixed servers are lower than the mobile ones and higher with the RTS/CTS scenarios. Also, there was no effect on the status of the server (mobile or fixed) on the media access delay but employing the RTS/CTS mechanism reduced the value. The highest received client traffic with respect to the mobile client is reported in the server is fixed and the RTS/CTS mechanism is employed with database application and in the mobile server with no RTS/CTS for FTP application. The minimum DB Query response time as a global value was reported when the RTS/CTS mechanism was used while the server was fixed and had a highly noticeable value when the server was fixed and no RTS/CTS mechanism was used. [ABSTRACT FROM AUTHOR]

Abstract: A new cross-layer routing protocol, named Dynamic Packet Guidance (DPG), is introduced for Mobile Ad hoc Networks (MANETs). Simulation results show that DPG is quite useful for usage in dense networks of mobile nodes, with medium-to-high speeds, and low-to-medium load. In these scenarios, DPG provides a superior performance compared to several well-known ad hoc routing protocols. The low end-to-end delay and smaller overhead that DPG achieves in such scenarios positively impacts the scalability of MANETs and reduces the energy requirements of nodes in such networks. DPG also shows immunity to failing nodes, as it operates consistently almost independently of failing nodes up to a certain ratio. [Copyright &y& Elsevier]

Abstract: Emerging wireless mesh networks (WMNs) are known for their fast and low cost deployment. Conventional mesh deployment focuses on the outdoor environment, which regards the WMNs as backbone networks. This study deploys and measures indoor IEEE 802.11s mesh networks to extend WLAN capabilities with extensive experiment configurations. The testbed is constructed in a laboratory and a field crossing three floors of a building. Disagreeing with previous research, the results of this study indicate that RTS/CTS can improve throughput by up to 87.5%. Moreover, compared with the IEEE 802.11b/g, 802.11n achieves better fairness for multi-stream or multi-hop communications. Experimental results also suggest that a longer beacon interval, e.g. 500ms, can improve channel efficiency for a denser deployment. On the other hand, sparser deployments should use a shorter beacon interval, e.g. 100ms, to enhance link stability. [Copyright &y& Elsevier]

Since its development for wireless local area networks, the IEEE 802.11 standard has been widely used for various wireless networks due to its low cost and effectiveness in reducing collisions with simple and decentralized mechanisms. There are numerous analytical studies that have evaluated the performance of the IEEE 802.11 distributed coordination function (DCF) media access control (MAC) protocol in infrastructure and ad hoc networks. Most of these studies are confined to saturated traffic analysis, infrastructure networks or single hop ad hoc networks. In addition, most of them adopt simplified assumptions to reduce the complexity of the proposed models, which deviate from the IEEE 802.11 standards. In this paper, we present a novel analytical stochastic reward net model for performance evaluation of the IEEE 802.11 DCF MAC protocol in multi-hop ad hoc networks in the presence of hidden nodes, taking into account the characteristics of the physical layer, different traffic loads, packet size and carrier sense range. The proposed model captures most features of the protocol. Performance measures such as goodput and packet service time for various network configurations are computed. The proposed model is validated through extensive simulations. [ABSTRACT FROM AUTHOR]

In this paper, a new three-dimensional Markov model is proposed for the estimation of saturation throughput of RTS/CTS (request to send/clear to send) scheme in an error-prone wireless local area network (WLAN) channel. The model takes account of the effect of bit error on all the frames, and station short and long retry limits. Saturation throughput was re-analyzed using the new Markov model and numerical results closely matched those from simulation, confirming the accuracy of the new model. Evaluation of the influence of different parameters on throughput showed that the saturation throughput is sensitive to channel bit error rates and packet length, especially in high bit error conditions. [ABSTRACT FROM AUTHOR]

IEEE 802.11 MAC mainly relies on two techniques to combat interference: physical carrier sensing and RTS/CTS handshake (also known as “virtual carrier sensing”). Ideally, the RTS/CTS handshake can eliminate most interference. However, the effectiveness of RTS/CTS handshake is based on the assumption that hidden nodes are within transmission range of receivers. In this paper, we prove using analytic models that in ad hoc networks, such an assumption cannot hold due to the fact that power needed for interrupting a packet reception is much lower than that of delivering a packet successfully. Thus, the “virtual carrier sensing” implemented by RTS/CTS handshake cannot prevent all interference as we expect in theory. Physical carrier sensing can complement this in some degree. However, since interference happens at receivers, while physical carrier sensing is detecting transmitters (the same problem causing the hidden terminal situation), physical carrier sensing cannot help much, unless a very large carrier sensing range is adopted, which is limited by the antenna sensitivity. In this paper, we investigate how effective is the RTS/CTS handshake in terms of reducing interference. We show that in some situations, the interference range is much larger than transmission range, where RTS/CTS cannot function well. Two independent solutions are proposed in this paper. One is a simple enhancement to the IEEE 802.11 MAC protocol. The other is to utilize directional antennas. Simulation results verify that the proposed schemes indeed can help IEEE 802.11 resolve most interference caused by large interference range. [Copyright &y& Elsevier]