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Cognitive radio (CR) is an emergent communication platform that offers solutions for spectrum scarcity issues. Cognitive radio networks (CRNs) will offer increased bandwidth to mobile consumers through wireless heterogeneous architectures and dynamic spectrum acquisition mechanisms. However, CRNs enforce challenges because of the fluctuating behaviour of the spectrum available and the diverse requirements for a varied range of applications. The functions of spectrum management can resolve those challenges to realize a new paradigm of the network. Secondary users (SUs) can opportunistically explore and employ the blank spaces present in licensed channels. This makes the SU evacuate the licensed channel and then switch to a vacant channel, when an incumbent primary user (PU) interferes with the channel, it causes degradation of SUs because of the frequent switching of channels. Also, the deafness problem is commonly seen in a CRN, where the QoS is critically affected due to the hidden interferences. This research proposes a Genetic Algorithm Optimized Fuzzy decision system for performing channel selection, channel switching, and spectrum allocation in a multi-channel multi-hop CRN. The proposed scheme acts as a decision support system (DSS), focusing on reducing the channel switching rate, hidden node interferences, and efficient spectrum allocation. Meta-heuristic genetic algorithm (GA) optimizes the parameters of the fuzzy decision system (FDS), for obtaining optimized decisions. The proposed DSS in the CR environment is simulated in the MATLAB platform and the results show improved performance concerning throughput and channel utilization.

Connectivity provisioning in large-scale Internet-of-Things (IoT) networks raises several challenges, one of which is the high collision rate among the transmission attempts of IoT devices. Transmission collisions result in prolonged data delivery delay and increased energy consumption of IoT devices. Contention-based wireless communication technologies such as WiFi is particularly vulnerable to this issue. As a remedy, a new standard IEEE 802.11ah is designed and such methods as RAW (Restricted Access Window) grouping is incorporated in order to curb the high collision rate. Meanwhile, in IEEE 802.11ah the transmission range and the number of devices that can be accommodated are also drastically increased. As a result, the impact of the hidden terminal problem is significantly amplified, which causes transmission collisions. In this paper, we propose an approach to avoid the high collision rate at the phase of the AP(Access Point) selection for IEEE 802.11ah networks. The proposed scheme considers the traffic load balancing and the hidden terminal issue simultaneously, without incurring any burden to the IoT devices. No modification of the IEEE 802.11ah standard is needed. Via extensive NS-3 simulations, we have verified that the proposed AP selection scheme outperforms the existing schemes in terms of data delivery delay and energy consumption by reducing transmission collisions.

Wireless Multimedia Sensor Networks (WMSNs) have emerged as the new class of wireless sensor networks (WSNs) to meet the stringent Quality of Service (QoS) requirements of emerging applications. Multipath routing with cross-layer approach appears to be a potential solution for supporting the distinct characteristics of WMSNs. However, due to the broadcast nature of the underlying medium, multiple paths are exposed to inter-path interference. In addition, low-power wireless links are asymmetric, error-prone and unreliable in nature. Consequently, an accurate and stable link quality estimation is essential to guarantee the performance of routing protocol. This paper proposes Triangle link quality metric and minimum inter-path Interference based Geographic Multipath Routing (TIGMR) protocol which finds multiple node-disjoint paths in IEEE 802.15.4 compliant network. This cross-layer routing protocol selects forwarding node based on a triangle link quality metric, remaining energy, and distance while anticipating minimum adjacent path interference effect. In addition, TIGMR protocol avoids Hidden Node Problem (HNP) at the sink node without using Request-To-Send/Clear-To-Send (RTS/CTS) handshake mechanism. Simulation results indicate TIGMR protocol optimizes overall performance and improves network lifetime as compared with state-of-the-art Two-Phase Geographic Forwarding (TPGF) and Link Quality and Energy-Aware Routing (LQEAR) protocols.

Previous studies showed that the packet collision probability in the 802.11 Distributed Coordination Function (DCF) can approach zero by adopting Centralized Random Backoff (CRB), which improves the total throughput performance. Moreover, it was reported that wireless networks using CRB maintain a high level of compatibility to legacy wireless local area networks (WLANs) when they coexist. However, little attention has been paid to relations between the performance of CRB and the retransmission limit, although the number of retransmission limit is an essential parameter that must be carefully chosen when implementing CRB for efficient WLANs. This article presents more realistic Markov chain models, and studies the impact of retransmission limit on the performance of CRB. These relations are also investigated by Monte Carlo simulation in more practical scenarios. Results show the trade-off that the total throughput increases with the retransmission limit when the number of nodes is larger than 15; whereas, the channel access opportunities in the mixed network scenario are more unevenly distributed between nodes as the retransmission limit increases. It is also shown in the simulation results that the throughput degradation caused by the hidden node problem is alleviated as the retransmission limit increases.

Wireless technologies are continuously evolving, including features such as the extension to mid- and long-range communications and the support of an increasing number of devices. However, longer ranges increase the probability of suffering from hidden terminal issues. In the particular case of Wireless Local Area Networks (WLANs), the use of Quality of Service (QoS) mechanisms introduced in IEEE 802.11e compromises scalability, exacerbates the hidden node problem, and creates congestion as the number of users and the variety of services in the network grow. In this context, this paper presents a configurable Colored Petri Net (CPN) model for the IEEE 802.11e protocol with the aim of analyzing the QoS support in mid- and long-range WLANs The CPN model covers the behavior of the protocol in the presence of hidden nodes to examine the performance of the RTS/CTS exchange in scenarios where the QoS differentiation may involve massive collision chains and high delays. Our CPN model sets the basis for further exploring the performance of the various mechanisms defined by the IEEE 802.11 standard. We then use this CPN model to provide a comprehensive study of the effectiveness of this protocol by using the simulation and monitoring capabilities of CPN Tools.

Vehicular safety applications based on DSRC/802.11p have strict reliability requirement (greater than 0.99). However, it is difficult to achieve high reliability in wireless medium as the transmission is vulnerable to various wave propagation issues. To the best of our knowledge, none of the existing emergency message dissemination schemes in the literature, achieves a predefined reliability in lossy channel. In this paper, we propose a novel scheme, called reliable emergency message dissemination scheme (REMD), which achieves a predefined reliability for message dissemination while satisfying delay requirements, for various channel conditions. We aim to guarantee very high reliability (e.g., 99%) in each hop, with low control overhead while keeping low end-to-end latency for time-critical applications. We employ zero-correlated unipolar orthogonal codes to combat hidden terminal problem. We exploit periodic beacons, to accurately estimate reception quality of 802.11p wireless link in each cell; then, we use this information to determine the optimal number of broadcast repetitions in each hop. In addition, to ensure reliability in multi-hop, we utilize cooperative communication. The simulation results show that REMD outperforms the existing well-known schemes in the literature. Furthermore, REMD satisfies latency requirements for time-critical vehicular applications and has less network overhead than the existing schemes.

Neighbor discovery plays a major role in the wireless self-organizing network, which is the cornerstone for the autonomous coverage extension and performance enhancement such as cooperative transmission and multi-hop transmission. However, the hidden node problem is frequently encountered in neighbor discovery procedure based on the simple flooding due to the uncoordinated transmission, which gives rise to unnecessary energy waste. In this paper, the hidden node problem in the conventional neighbor discovery procedure is analyzed. A novel neighbor discovery procedure with the ability of node distance estimation and power allocation for the packet retransmission after collision is proposed, which utilizes fuzzy location information to properly configure the transmission power of the collided packets for better reception. The proposed algorithm improves the power efficiency of the neighbor discovery procedure by reducing the number of transmissions required for the successful reception with negligible induced complexity. Through the Monte-Carlo simulation, the proposed procedure with fuzzy location information and the power allocation method outperforms the conventional procedure in different node population scenarios, and the proposed procedure is insensitive to the distance estimation error, displaying strong robustness.

TCP communications on wireless multi-hop net-works are bi-directional communications using DATA packets and ACK packets. These properties increase the hidden node problem and the intra-flow interference. PiggyCode, which is an existing scheme focused on bi-directionality of DATA packets and ACK packets, reduces the number of transmissions by applying Network Coding to the DATA packets and ACK packets when relaying these packets. Although some studies have considered the improvement of PiggyCode by insertion of the wait time, they did not take the Delayed-ACK option into account. In this paper, we propose a novel queue management scheme to consider the Delayed-ACK option. Furthermore, we confirm the efficiency of the proposed method via experimental evaluations.

Light ad hoc network is a newly developing system structure in ad hoc network compared with radio frequency (RF) based ad hoc networks. Due to its unique characteristic in physical layer, LANET is a special plan that deploy networks in both sparse and dense situation. In ad hoc networks, most of the study focus on the medium access control (MAC) protocols and routing protocols. In this work, we pay attention to the physical layer, which use optical wireless communication to overcome the challenges in ad hoc network. Therefore, we offer LANET as a solution to hidden terminal problem.

Recently, 802.11ah network has been widely used to support up to 8,192 nodes to serve various Internet of Things (IoT) communication applications. Because of the large number of nodes, it introduces a group-based MAC protocol, which divides nodes into groups to alleviate the hidden node problem. However, hundreds or even thousands of nodes are assigned into a group to contend the shared wireless channel. As a result, the problem is still serious and it causes a serious decline in system efficiency. Therefore, hidden nodes must be considered when grouping nodes in 802.11ah network. In this paper, the problem of minimizing the number of hidden nodes in group-based 802.11ah networks is expressed as 0/1 integer linear programming (0/1 ILP). In addition, the two additional problems extended from the above problem are also expressed as two 0/1 ILPs. Then, three approximation algorithms are proposed for these three NP-hard problems. The approximation ratio of the obtained feasible solutions to those of the three problems is competitively bounded.

Device-to-device (D2D) communication is such a paradigm that anticipated to play a cabalistic role for the next-generation cellular networks especially for the 5G cellular network as it promises to extend the network coverage and offload some traffics from the cellular transceiver’s side to the user devices’ side and it may operate in both licensed and unlicensed spectra simultaneously. D2D communication in the unlicensed spectrum may facilitate the purpose of D2D communication as the licensed spectrum almost possessed. Interference is the main drawback of the unlicensed spectrum. In this paper, we propose the request-to-send/clear-to-send (RTS/CTS) mechanism with the free-to-receive (FTR)-MNAV technique to improve the performance of the D2D communication in the unlicensed spectrum. Deployment of the carrier sense multiple access with collision avoidance (CSMA/CA) protocol can alleviate interference, but collisions occur due to the hidden node problem. The integration of the RTS/CTS mechanism with the CSMA/CA protocol can minimize the hidden node problem, but the blocking and false blocking problems are introduced. The proposed scheme can reduce the blocking and false blocking problems, which improves the performance of the D2D communication in the unlicensed spectrum where neighbor nodes maintain Multiple Network Allocation Vector (MNAV) to resolve the blocking problem and broadcast the FTR control packet to the respective neighbor nodes if the transmission is completed prior to the expiration of the timer or actual communication does not take place due to any reason, thus solving the false blocking problem and improving the performance of the D2D communication in the unlicensed spectrum.

The IEEE 802.15.6 standard has the potential to provide cost-effective and unobtrusive medical services to individuals with chronic health conditions. It is a low-power standard developed for wireless body area networks and enables wireless communication inside or near a human body. This standard utilizes a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol to improve network performance under different channel access priorities. However, the CSMA/CA proposed in the IEEE 802.15.6 standard has poor throughput performance and link reliability when some of the nodes deployed on a human body are hidden from each other. We employ the RTS/CTS scheme to solve hidden node problems in IEEE 802.15.6 networks over a lossy channel. To improve performance of the RTS/CTS scheme, we adjust transmission power levels of the nodes according to transmission failures. We estimate throughput and energy consumption of the proposed model by differentiating several parameters, such as contention window size, values of bit error ratios, number of nodes in different priority classes. The performance results are obtained through analytical approximations and simulations. We observe that the proposed model significantly improves performance of the IEEE 802.15.6 CSMA/CA by resolving hidden node problems.

In device-to-device (D2D) environments where a number of wireless nodes are connected in ad hoc mode, the most popular mechanism for multiple access control is CSMA/CA as in IEEE 802.11 networks. Consequently, a considerable number of hidden terminals can be found in large-scale and dense D2D networks, and usually they may cause severe performance problems. Previous studies to improve the hidden terminal problem in dense wireless networks have suggested various solutions: e.g., channel assignment, transmit power control, and grouping schemes. In this paper, we adopt a different approach—a hidden terminal aware clustering mechanism, which detects the hidden terminals and enables the nodes to form clusters based on the detected information. A simple polling-based channel access scheme is also proposed such that all nodes belonging to a same cluster can access channel through their neighbors’ polling, which eliminates the hidden terminal problem. Mathematical analysis and simulations show that our proposed scheme significantly improves the performance of large-scale D2D networks.

Nowadays “Internet of Things” or IoT becomes the most popular technology in the Internet system. Types of devices and sensors have been connected as a network of devices and sensors. While a wireless sensor network is a traditional network of sensors that can be considered as a beginning point of IoT systems. Currently, these sensor data are not only exchanged within a local network but also are delivered to other devices in the Internet. Consequently, well-known organizations such as IEEE, IETF, ITU-T and ISO/IET are trying to set standards for wireless sensor devices in IoT systems. The recommended standard utilizes many of internet stack standards such as CoAP, UDP and IP. However, the traditional design of WSNs is to avoid using internet protocol in the system to reduce transmission overhead and power consumption due to resource limitation. Fortunately, the current technology in both hardware and software allow the internet standard to sufficiently operate in a small sensor. In this paper, we propose a MAC protocol named CU-MAC to efficiently support IoT standard that need request-respond communication or bi-direction communication. CU-MAC uses multi-channel communication to perform continuous and bi-directional data transfer at low duty-cycle. It also has a mechanism to overcome the hidden terminal problem. We evaluated the performance of CU-MAC on both simulation and real testbed based on Contiki OS. The result shows that CU-MAC outperforms other existing MAC protocols in term of packet delivery ratio at 98.7% and requires lower duty-cycle than others to operate in the high traffic environment.

IEEE 802.11ad defines a new physical and medium access control layer for IEEE 802.11 networks to operate in the unlicensed 60 GHz millimeter wave spectrum for multi-gigabit wireless communications. Higher frequency waves have higher propagation loss but smaller antenna size. Hence, for millimeter wave networks, higher number of antennas can be packed together, enabling beamforming with very large gains. In this paper, we propose a novel Directional MAC protocol for Basic Stations (DMBS) with the goal of fully leveraging spatial reusability, and limiting deafness and hidden terminal problems with minimal overhead, and without using any complicated hardware for localization. The distinguishing features of DMBS are threefold. First, DMBS extends the association beamforming training time (A-BFT) of IEEE 802.11ad, during which the stations perform initial beamforming training with the access point (AP), by an intelligent listening mechanism. This mechanism allows the stations to passively learn about the best direction of the neighboring stations, decreasing the associated beamforming training overhead. Second, DMBS determines the best transmission direction by using multi-directional sequential (circular) RTS/CTS (Request To Send/ Clear To Send) (CRTS/CCTS) packets, and tracks the best direction by updating its beamforming table upon reception of every RTS/CTS packet, without requiring any additional hardware for localization. If the location information of the destination is up-to-date, the source station only transmits directional RTS/CTS (DRTS/DCTS) in the known direction. Third, DMBS uses two network allocation vectors (NAVs). The first NAV, denoted by NAV1, is used to reduce deafness by determining the busy nodes upon the reception of every RTS/CTS packet. The second NAV, called NAV2, is used to limit hidden terminal problem while maximizing spatial reusability by determining whether a transmission can interfere with active communication links. If NAV2 is set, then the node defers its multi-directional communication but still communicates directionally. We provide a novel Markov chain based analytical model to calculate the aggregate network throughput of DMBS. We demonstrate via extensive simulations that DMBS performs better than existing directional communication protocols in terms of throughput for different network sizes, mobilities and number of receivers.

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-to-send/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%.

In researches and applications on maritime transportation, the information is collected by maritime vessels and Underwater Wireless Sensor Networks (UWSNs). The reliable wireless links among maritime vessels are needed to keep the communications efficiency and security. The movements of maritime vessels bring challenges to the reliable and real-time information transmissions, which require proper MAC layer supports of Ship Ad-hoc NETwork (SANET). An improved multi-channel VeMAC protocol based on TDMA, named I-VeMAC, is proposed to meet the transmission requirement on MAC layer. I-VeMAC reduces the time cost of the transmission of service information. In the control channel, time slots are occupied by relay nodes and conflict nodes. In order to solve the merge conflicts in service channels and optimize the transmissions in the control channel, I-VeMAC analyzes the relative positions of time slots. Meanwhile, the service providers provide slot information of nodes within 2 hops to conflict nodes, and recalculate the time slot allocation. It is proved that the hidden terminal problem will be solved without the nearby nodes announcing the time slot information within 2 hops. The simulation results show that the improved method reduces the time cost of solving merge conflict in VeMAC and the transmission delay. I-VeMAC improves the throughput, and it can be used in real-time transmission in SANET for UWSNs data harvesting.

Wireless Network-on-Chip (WiNoC) has been recently introduced for addressing the scalability limitations of conventional multi-hop NoC architectures. Existing WiNoC architectures generally use millimeter-wave antennas without significant directional gains, along with token passing protocol to access the shared wireless medium. This limits the achievable performance benefits since only one wireless pair can communicate at a time. It is also not practical in the immediate future to arbitrarily scale up the number of non-overlapping channels by designing transceivers operating in disjoint frequency bands in the millimeter-wave spectrum commonly adopted for on-chip wireless interconnects. Consequently, we explore the use of directional antennas whereby multiple wireless interconnect pairs can communicate simultaneously. However, concurrent wireless communications can result in interference. This can be minimized in NoC by optimal placement of wireless interfaces (WIs) to maximize performance while minimizing interference. To address this, we propose an interference-aware WIs placement algorithm with routing strategy for WiNoC architecture by incorporating directional planar log-periodic antennas (PLPAs). This directional wireless network-on-chip (DWiNoC) architecture enables point-to-point links between transceivers and hence multiple wireless links can operate at the same time without interference.

V2I communications are characterized by the presence of network nodes in vehicles and in the infrastructures that these vehicles use, as well as by the wireless interactions among them. Safety-related applications demand stringent requirements in terms of latency and packet delivery probability, especially when safety messages have to be delivered to vehicles by the infrastructure. Interference issues stem from the typical characteristics of wireless communications, i.e., the noise of the wireless medium, the limited communication range of the wireless entities, and the receiver passivity of all the conventional wireless transceivers during transmissions. This paper presents a synchronization mechanism to artificially replicate at a host premises destructive interference due to hidden terminals, together with an application-level technique to minimize that interference by shifting the packet transmission time, similarly to the MAC TDMA channel access method. As both have been field-tested, the paper also analyzes the results of these tests, all performed with real hardware on IEEE 802.11p over different frequencies and transmission powers, and with repeatability in mind. The resulting figures attest that interference effects due to hidden terminals may indeed take place on real IEEE 802.11p networks, and that carefully designed time-shifting mechanisms can actively mitigate them.

Television white space (TVWS) spectrum consists of bands that are reserved for terrestrial television which is licensed TV broadcasting, and it is open to unlicensed secondary users under regulatory conditions. TVWS spectrum sharing approaches focus on protecting the TV bands from the interference caused by the secondary users. To access this TVWS spectrum by secondary users several wireless technologies came into picture ie., IEEE 802.22 (Wireless Regional Area Network) which has a TDM based MAC protocol and IEEE 802.11af (Super WiFi) which has a CSMA based MAC protocol. Different wireless technologies with different PHY/MAC design leads to coexist in the TVWS which faces a hidden terminal problem and exposed terminal problem. In this research work, first analyzed the throughput of 802.22 under the hidden 802.11af and the probability of accessing the channel by 802.11af under exposed 802.22 CPE transmitters. Secondly, proposed a Dynamic Reservation Period (DRP) algorithm which shows that, under exposed terminal of 802.22 CPE transmitters also a fair channel accessing exists to 802.11af and throughput of 802.22 doesn't affect by DRP. Extensive simulation work was carried out in a realistic scenario based on the available TVWS channels in a certain geographical area.

Wireless Sensor Networks (WSNs) are often used for gathering data collected by sensor nodes spread over large monitored areas. Star topologies, having a sink node at their center, are becoming a clear trend when the size of the monitored area allows it. The range of the radio links used, increases due to the decision to use a sub-GHz frequency and/or a particular signal coding that ensures a significant processing gain in the radio link budget. Even though such long-range radio links are beneficial in specific applications, in spite of the low data rate limit, often remains a weakness for application in many domains. Our overall objective is to consider combining the use of a switched-beam antenna only for the sink node of a star topology and omnidirectional antennas for wireless sensor nodes, in order to achieve a better balance between Range and Data Rate. When switched- beam antennas are used to equip some nodes, usual medium access methods have to be revised as does the discovery of the neighborhood of the sink. In this paper, we propose a scheme that allows the sink node to discover all its neighboring nodes within a limited timeframe, despite the hidden terminal problem effects worsen by antennas directivity. Index Terms-Star topology, wireless Sensor Networks, neigh- borhood discovery, MAC protocols, switched beam antenna

To facilitate introduction of IoT devices to the environments such as factories and hospitals, it is desirable that the network administrators can accurately monitor the conditions of wireless networks. In the existing schemes or products, physical layer information and MAC layer information are often acquired and analysed individually. In this paper, we propose a sensing system that allows synchronized time series analysis between physical and MAC layers for detailed quality assessment of wireless links. By synchronizing the data from physical and MAC layers, we show that it is possible to identify the cause of frame losses, which occurred due to a hidden terminal problem. We implemented a prototype sensor node using an FPGA and conducted an experiment to acquire the data from both layers. From the experiment, we confirmed that the prototype sensor node has enough performance on time synchronization and resolution between cross layered data.

Wireless local area networks (WLANs) based on IEEE 802.11 Distributed Coordination Function (DCF) have been widely used in many industry. This paper mainly analyzes the system performance of IEEE 802.11 DCF under different channel conditions. Firstly, the performance of the system with hidden nodes and without hidden nodes are compared. Then we analyze the performance of system with saturated and unsaturated. Finally, the research methods of IEEE 802.11 DCF are analyzed.

Providing cost-effective and high throughput WiFi access for vehicle drivers and passengers is a promising solution to support the increasing demand for in-vehicle Internet applications. Prior to accessing Internet services via an on-road WiFi access point (AP), a vehicle user has to wait for a certain duration, referred to as access delay, until the user is authenticated and assigned proper network layer parameters, such as an Internet protocol address. Investigation of the access delay in a vehicular environment is critical, since a large access delay can significantly reduce the duration that a vehicle actually benefits from Internet connectivity during its temporary existence within the coverage area of an on-road WiFi AP, especially with high vehicle moving speeds. In this paper, we propose an analytical model based on a Markov chain to study the dependency of the access delay on different factors, including the wireless channel conditions, the number of vehicles accessing the AP service, and the employed authentication mechanism, such as the WiFi protected access II (WPA2)-pre-shared key and the WPA2–802.1X modes. The accuracy of the analytical model is studied via computer simulations and experimental testing using commercial off-the-shelf WiFi products together with a channel emulator that emulates the wireless channel conditions in a vehicular environment. Simulation and experiment results highlight the accuracy of the proposed analytical model. Results in this paper provide useful guidelines for future selection/development of suitable WiFi network access schemes in a vehicular environment.

As more user applications emerge for wireless devices, the corresponding amount of traffic is rapidly expanding, with the corollary that ever-greater spectrum capacity is required. Service providers are experiencing deployment blockages due to insufficient bandwidth being available to accommodate such devices. TV White Space (TVWS) represents an opportunity to supplement existing licensed spectrum by exploiting unlicensed resources. TVWS spectrum has materialised from the unused TV channels in the switchover from analogue to digital platforms. The main obstacles to TVWS adoption are reliable detection of primary users (PU) i.e., TV operators and consumers, allied with specifically, the hidden node problem. This paper presents a new Generalised Enhanced Detection Algorithm (GEDA) that exploits the unique way Digital Terrestrial TV (DTT) channels are deployed in different geographical areas. GEDA effectively transforms an energy detector into a feature sensor to achieve significant improvements in detection probability of a DTT PU. Furthermore, by framing a novel margin strategy utilising a keep out contour, the hidden node issue is resolved and a viable secondary user sensing solution formulated. Experimental results for a cognitive radio TVWS model have formalised both the bandwidth and throughput gains secured by TVWS users with this new paradigm.

The wireless mesh network (WMN) has attracted significant interests as a broadband wireless network to provide ubiquitous wireless access for broadband services. Especially with incorporating multiple orthogonal channels and multiple directional antennas into the WMN, each node can communicate with its neighbor nodes simultaneously without interference between them. However, as we allow more freedom, we need a more sophisticated algorithm to fully utilize it and developing such an algorithm is not easy in general. In this paper, we study a joint channel assignment, link scheduling, routing, and rate control problem for the WMN with multiple orthogonal channels and multiple directional antennas. This problem is inherently hard to solve, since the problem is formulated as a mixed integer nonlinear problem (MINLP). However, despite of its inherent difficulty, we develop an algorithm to solve the problem by using the generalized Benders decomposition approach [2]. The simulation results show the proposed algorithm provides the optimal solution to maximize the network utility, which is defined as the sum of utilities of all sessions.

From the perspective of a single user, concurrent utilization of all available radio access technologies (RATs) is always beneficial for increasing individual data rate. However, given the interactions among users, occupying multiple RATs at each user might not be optimal from a network-wide viewpoint. In this paper, we explore the answer to the posed question what is the optimal access strategy in multi-RAT cellular networks, solving a distributed RAT access control problem for maximizing network throughput. With stochastic geometry, we analytically evaluate network throughputs for two different access modes: 1) single RAT access (altruistic access) and 2) simultaneous multiple RATs access (selfish access). Comparing the network throughputs for the two modes, we first show that the network throughput can be maximized by properly mixing the two access modes and then derive the optimal portions of each mode in a network, which motivates a distributed RAT access control in a probabilistic sense. The optimal mixture of the two modes controls scheduling contention and interference among users to maximize the network throughput. We also analyze the effects of various system parameters, such as the number of frequency sub-bands for each RAT, user density, and access point density, on the optimal portions of the two access modes.

IEEE 802.11 MAC is designed for single channel and based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). The throughput of network is limited by the bandwidth of the single channel and the CSMA-based MAC protocol with omnidirectional antennas can cause the serious unfairness or flow starvation. By exploiting the multiple channels and using the directional antennas, nodes located in each other's vicinity may communicate simultaneously. This helps to increase the spatial reuse of the wireless channel and thus increase the network performance. In this paper, we propose a Multi-channel MAC protocol with Directional Antennas (MMAC-DA) that adopts IEEE 802.11 Power Saving Mechanism (PSM) and exploits multiple channel resources and directional antennas. Nodes have to exchange control packets during the Announcement Traffic Indication Message (ATIM) window to select data channels and determine the beam directions which are used to exchange data packets during the data window. The simulation results show that MMAC-DA can improve the network performance in terms of aggregate throughput, packet delivery ratio, energy efficiency and fairness index.

Spectrum Sensing is one of the important tasks for wireless devices. By sensing the spectrum, wireless devices sense their radio environment and perform spectrum access accordingly to reduce collisions. Due to radio propagation effects and inherent noise in the measurements, performance of todays wireless technologies with individual spectrum sensing cannot solve the hidden node problem. Cooperative sensing is seen as a way to improve the performance of wireless devices improving the radio bandwidth utilization and minimizing interference among wireless devices. To the best of our knowledge, this is the first work which provides protocols for cooperative sensing and presents experimental results with IEEEź802.15.4 devices. We present and implement protocols and applications for primary, secondary and cooperative users with a dedicated control channel. Thereby, the secondary user receiver serves as a first cooperative node in the system which reduces collisions between primary and secondary users. We evaluate the system performance with receiver sensing and additional cooperative nodes. We also propose a mechanism to extend the protocol for multiple secondary users sharing the same control channel. Based on the evaluations, we also provide recommendations for usage of cooperative sensing with focus on IEEEź802.15.4.

Due to a poor understanding of the interactions among transmitters, wireless networks using carrier sense multiple access with collision avoidance (CSMA/CA) have been commonly stigmatized as unpredictable in nature. Even elementary questions regarding the throughput limitations of these networks cannot be answered in general. In this paper, we investigate the behavior of wireless CSMA/CA networks to understand how the transmissions of a particular node affect the medium access, and ultimately the throughput, of other nodes in the network. We introduce a theory which accurately models the behavior of these networks and show that, contrary to popular belief, their performance is predictable and can be described by a system of equations. Using the proposed theory, we provide the analytical expressions necessary to fully characterize the capacity region of any wireless CSMA/CA network. We show that this region is nonconvex in general and agnostic to the probability distributions of all network parameters, depending only on their expected values. Our theory is also shown to extend naturally to time division multiple access (TDMA) networks and to predict how the network responds to infeasible input rates.

This paper proposes an opportunistic approach to mitigating the hidden and exposed node problem in a high-throughput mesh network, by exploiting the frame aggregation and block acknowledgment (BACK) capabilities of IEEE 802.11n/ac wireless networking standard. Hidden nodes significantly drop down the throughput of a wireless mesh network by increasing data loss due to collision, whereas exposed nodes cause under-utilization of the achievable network capacity. The problem becomes worse in IEEE 802.11n/ac supported high-throughput mesh networks, due to the large physical layer frame size and prolonged channel reservation from frame aggregation. The proposed approach uses the standard carrier sense multiple access (CSMA) technology along with an opportunistic collision avoidance (OCA) method that blocks the communication for hidden nodes and opportunistically allows exposed nodes to communicate with the peers. The performance of the proposed CSMA/OCA mechanism for high throughput mesh networks is studied using the results from an IEEE 802.11n+s wireless mesh networking testbed, and the scalability of the scheme has been analyzed using simulation results.

Wireless laser communication exploits optical path to transmit and receive data. It is one of the most promising paradigms for wireless communication, with extremely high transmission rate and channel bandwidth. However, there exist remarkable challenges in constructing a wireless laser network due to the nature of point-to-point communication. In order to address this drawback, we develop a practical laser node model and network model based on the receiver antenna multiplexing, where the receiver is shared by more than one transmitter antennas at a node. Taking the antennas at a node as the constraints, we first propose the mechanism of transmitter antennas pointing independent of the receiver antenna status. Then, we introduce the concepts of virtual and actual link as well as virtual and actual topology transition. During network establishment, we formulate the slot allocation into an optimization problem to minimize the time slots for setting up multiple transmission paths in the case of simultaneous transmissions and, thus, reduce the frequency of link establishment and scheduling time. The simulation results verify the availability of scanning with multiple transmitter antennas while sharing one receiver antenna, the fast networking process and the efficiency of the proposed antenna scheduling scheme.

In recent years, wireless mesh networks (WMNs) have become popular because of their wide coverage areas and high fault tolerance. Although unlicensed-band off-the-shelf wireless devices based on IEEE 802.11 are widely deployed, WMNs based on IEEE 802.11 suffer from degradation of throughput owing to the hidden node problem. To mitigate this problem, in this study, we developed a new routing metric called the “Asymmetric Hidden node problem Aware routing Metric (AHAM).” AHAM enables a new flow to establish a source-destination path that largely avoids not only interference with hidden nodes of existing flows but also making hidden nodes on that path interfere with existing flows. This is because the hidden node problem can asymmetrically impact throughput between flows when new flows are established. As a response, AHAM aims to estimate the influence of hidden nodes accurately and compensate for how both the new and existing flows influence each other. Simulation results showed that AHAM realizes high throughput while maintaining network fairness compared with other metrics.

The explosive usage of IEEE 802.11 Wireless Local Area Network (WLAN) has resulted in its dense deployments and excessive interference between Basic Service Sets (BSSs) in urban area such as an apartment building and an airport. Serious problems of hidden/exposed terminal in high-density condition negatively impact system throughput. To improve the system efficiency, IEEE 802.11ax TG has been assembled. TG aims at realizing High-Efficiency- WLAN (HEW) by utilizing special reuse technologies including Dynamic Sensitivity Control (DSC), Transmit Power Control (TPC), and BSS Color Filtering (BCF). In this paper, we propose a DSC based on two-hop farthest terminal for dense WLAN. This scheme with minimum transmission power resolves the hidden terminal problem. Propagation loss of received signal from associated communication pair is used for the proper values of transmission power and carrier sense level. Furthermore, adjusting these parameters destination by destination can reduce exposed terminals effectively. We evaluate the performance of the proposed scheme in residential building scenario with three criteria, aggregate throughput, fairness and frame error rate. Simulation results show that the proposed scheme can improve aggregate downlink throughput and fairness compared to previously proposed method that carrier sense level is set based on expected RSSI level of received packet from communicating pair. Furthermore, improvement of frame loss rate implies that the hidden terminal problem can be solved by the proposed scheme.

We know that there is an issue for spectrum resources being unavailable because of increasing wireless services. To solve this a newer intelligent technology have been developed called as Cognitive Radio (CR). This technology inculcates the use of spectrum holes that occur due to the underutilization of the licensed spectrum. The identification of the spectrum holes can be done by using a method known as spectrum sensing. There are a variety of issues faced by individual CRs in precise spectrum sensing such as hidden terminal problem, shadowing and multipath fading. In order to facilitate the eradication of these issues a newer design of cooperative spectrum sensing have been developed called as Cooperative Spectrum Sensing (CSS). In this a particular weight have been designated to each CR participating in the process to classify according to reliability. Instead of using the conventional threshold equation an adaptive threshold equation have been devised for the initial energy detection algorithm and utilizing the adaptive threshold equation we have designed our algorithm

Cooperative Intelligent Transport Systems (C-ITS) are based on the exchange of messages between vehicles and with the road infrastructure in order to improve road safety, traffic efficiency, and travel comfort. Although the lower layers of the European C-ITS protocol stack support different wireless communication technologies, ITS-G5 is currently the preferred option for direct communication between traffic participants (i.e. without relaying the information through network infrastructure, such as a base station). In particular, the ITS-G5 specification is based on the IEEE 802.11-2012 standard, and therefore, implements decentralized radio resource management. As a result, the performance of ITS-G5 might be limited by congestion and hidden node problems. These issues can be overcome with an approach that centrally manages the radio resources, as in current LTE networks and proposed for the future 5G mobile communication standard. Both management approaches — centralized and decentralized — are compared in this paper with the focus on their ability to support cooperative awareness. Results show that the centralized approach is able to increase the number of vehicles experiencing high quality of service compared to the decentralized approach.

Wireless local area networks (WLANs) are the most popular kind of wireless Internet connection because of their simplicity of deployment and operation. As a result, the number of devices accessing the Internet through WLANs such as laptops, smartphones, or wearables, is increasing drastically at the same time that applications' throughput requirements do. To cope with these challenges, channel bonding (CB) techniques are used for enabling higher data rates by transmitting in wider channels, thus increasing spectrum efficiency. However, important issues like higher potential co-channel and adjacent channel interference arise when bonding channels. This may harm the performance of the carrier sense multiple access (CSMA) protocol because of recurrent backoff freezing while making nodes more sensitive to hidden node effects. In this paper, we address the following point at issue: is it convenient for high-density (HD) WLANs to use wider channels and potentially overlap in the spectrum? First, we highlight key aspects of DCB in toy scenarios through a continuous time Markov network (CTMN) model. Then, by means of extensive simulations covering a wide range of traffic loads and access point (AP) densities, we show that dynamic channel bonding (DCB) - which adapts the channel bandwidth on a per-packet transmission - significantly outperforms traditional single-channel on average. Nevertheless, results also corroborate that DCB is more prone to generate unfair situations where WLANs may starve. Contrary to most of the current thoughts pushing towards non-overlapping channels in HD deployments, we highlight the benefits of allocating channels as wider as possible to WLANs altogether with implementing adaptive access policies to cope with the unfairness situations that may appear., arXiv admin note: text overlap with arXiv:1801.00594

The authors consider a multihop wireless linear network where multiple nodes are evenly spaced over a straight line. Two scenarios are addressed: a network where only one source generates traffic to be transmitted via multiple hops to the destination and the case of linear sensor networks where all nodes in the line generate data. A novel contention-based medium access control (MAC) protocol, called L-CSMA, specifically devised for linear topologies, is proposed. Carrier-sensing multiple access (CSMA) suffers from the well-known hidden/exposed-node problems: The scope of L-CSMA is to reduce their impact, while minimizing the protocol overhead. L-CSMA assigns different levels of priority to nodes, depending on their positions in the line: Nodes closer to the destination have higher priority when accessing the channel. The priority is managed by assigning to nodes different durations of the carrier-sensing phase. This mechanism speeds up the transmission of packets that are already in the path, making the transmission flow more efficient. Results show that L-CSMA outperforms existing contention-based MAC protocols. A mathematical model to derive the performance in terms of packet success probability and throughput is provided. The key idea of the model is the definition of the generic state at the network level, instead of the node level, and its representation through a set of bits indicating the status (activity or not) of the corresponding link. The model is validated through comparison with simulations.

Wireless Body Area Networks (WBANs) can provide real-time and reliable health monitoring, attributing to the human-centered and sensor interoperability properties. WBANs have become a key component of the ubiquitous eHealth (electronic health) revolution that prospers on the basis of information and communication technologies. The prime consideration in WBAN is how to maximize the network lifetime with battery-powered sensor nodes in energy constraint. Novel solutions in Medium Access Control (MAC) protocols are imperative to satisfy the particular BAN scenario and the need of excellent energy efficiency in healthcare applications. In this paper, we propose a hybrid Lifetime Extended Directional Approach (LEDA) MAC protocol based on IEEE 802.15.6 to reduce energy consumption and prolong network lifetime. The LEDA MAC protocol takes full advantages of directional superiority in energy saving that employs multi-beam directional mode in Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) and single-beam directional mode in Time Division Multiple Access (TDMA) for alternative in data reservation and transmission according to the traffic varieties. Moreover, the impacts of some inherent problems of directional antennas such as deafness and hidden terminal problem can be decreased owing to that all nodes generate individual beam according to user priorities designated. Furthermore, LEDA MAC employs a Dynamic Polled Allocation Period (DPAP) for burst data transmissions to increase the network reliability and adaptability. Extensive analysis and simulation results show that the proposed LEDA MAC protocol achieves extended network lifetime with improved performance compared with IEEE 802.15.6.

A favorable technique is using directional antennas for high – speed wireless personal area networks and local.A new MAC protocol for wireless ad hoc networks which is referred to as New deafness-aware MAC(NDA-MAC) is proposed in this paper. There are many directional MAC protocols which have been proposed, but have not broadly solved the problem of deafness. We are proposing NDA-MAC protocol which can differentiate the deafness problem from collisions by using control channels and logical data.so we are providing a discrete-time Markov chain model for analyzing the deafness impact for both DA-MAC and the current technique. By wide simulations we are showing our NDA-MAC protocol can expressively perform the other current techniques with respect to the duration of deafness , throughput , transmission fairness and energy consumption. Mainly Ad-hoc networks are suffering from hidden nodes(terminals) problem ,leading to the problem of the nodes which are hidden (terminals), which indicates to Spartan degradation in network throughput. A survey of this which will give a basic idea of MAC protocols which will directly or indirectly indicate this problem .The mentioned protocols are set in various for giving the reader a detail understanding for the growth made in types and are discussed in detail. To provide the reader a bottomless understanding for the progress done in enhancing the hidden node problem as well as a detailed comparison of various protocols are shown. General Terms Switched Beam Antenna, Ad-hoc networks, Throughput

The IEEE 802.15.4 standard, which supports low-cost communications, has been applied in a variety of wireless networks. Developing accurate analytical models for the IEEE 802.15.4 medium access control (MAC) protocol is critical for the design and performance evaluation of such networks. Periodic traffic is a common traffic pattern generated in many practical application scenarios, for which most existing analytical models assuming either saturated or random network traffic patterns become inapplicable. In this paper, we develop an accurate and scalable analytical model to analyze the IEEE 802.15.4 MAC protocol with the periodic traffic. Our model can accurately capture the protocol stochastic behavior in each period in scenarios such as with or without retransmissions and with single clear channel assessment (CCA) or double CCAs. Extensive simulations are conducted to validate the proposed model by both transient and aggregate performance evaluations, and the results show that the model captures MAC behavior with periodic traffic accurately. We also discuss about extending the proposed model to account for heterogeneous scenarios and the hidden node problem.

There have been increases in the elderly population worldwide, and this has been accompanied by rapid growth in the health-care market, as there is an ongoing need to monitor the health of individuals. Wireless body area networks (WBANs) consist of wireless sensors attached on or inside the human body to monitor vital health-related problems, e.g., electrocardiograms (ECGs), electroencephalograms (EEGs), and electronystagmograms (ENGs). With WBANs, patients' vital signs are recorded by each sensor and sent to a coordinator. However, because of obstructions bythe human body, sensors cannot always send the data to the coordinator, requiring them to transmit at higher power. Therefore, we need to consider the lifetime of the sensors given their required transmit power. In the IEEE 802.15.6 standard, the transmission topology functions as a one-hop star plus one topology. In order to obtain a high throughput, we reduce the transmit power of the sensors and maintain equity for all sensors. We propose the multiple-hop transmission for WBANs based on the IEEE 802.15.6 carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol. We calculate the throughput and variance of the transmit power by performing simulations, and we discuss the results obtained using the proposed theorems.

Wireless Mesh Sensor Networks (WMSNs) have recently received a great deal of attention in the scientific and developers communities due to the significant advances of this technology in the wireless communication field. The main reason was that competing WMSN approaches that emerged in the last few years provide mesh capabilities ( e . g ., robustness, scalability, multi-hop mesh routing, or energy efficiency, among others) to conventional WSN-based applications, encouraging researchers and end users to adopt new perspectives and solutions. Unfortunately, each one of these approaches lacks some (or many) of the aforementioned mesh capabilities, not assuring, a priori, the feasibility and, especially, the long-term stability of WMSN applications. The IEEE 802.15.5 standard and, in particular, its Asynchronous Energy Saving (ASES) mode was conceived to fill this gap since it integrates, in a single solution, most of these capabilities, guaranteeing, among other benefits, a long network lifetime. However, the ASES mode has no built-in mechanisms to mitigate the negative effects of hidden terminals, which sharply degrades the network performance. This fact leads us to conclude that any current WMSN approach is non-exempt of some problem, which prevents the definitive boost of this technology in the consumer market. Under these circumstances, our contribution to the WMSN field in this paper is a twofold proposal addressed to alleviating the hidden terminal problems in a scenario running under the most relevant design premises of ASES mode. Therefore, we first formulate a multi-objective optimization and then solve it by using Goal Programming. Both mathematical techniques are applied to obtain the best solution that simultaneously minimizes the aggregate message collision time due to hidden terminals and maximizes the network lifetime. Secondly, we propose the design of a MULti-channel TIme-scheduled algorithm for the HIdden Terminal problem avoidance (MULTI-HIT) which appropriately exploits the available bandwidth and accomplishes a straightforward coordination between any sender-receiver pair. Finally, the analysis and simulation experiments are presented and their results carefully discussed, demonstrating the effectiveness of both proposals in the WMSN arena. WMSN approaches offer new perspectives to conventional WSN-based applications.Among WMSN proposals, the ASES mode guarantees the most relevant mesh capabilities.ASES has no mechanisms to mitigate the negative effects of hidden terminals (HT).Under ASES rules, we propose an optimization model and a multi-channel time-slotted algorithm to alleviate the HT problem.An intensive performance evaluation study is discussed to validate our proposals.

From version 2.6.22, the mac80211 framework has been incorporated as part of the stock kernel in Linux. This means millions of Linux based devices depend on this framework to provide wireless networking. The framework provides functionalities and interfaces for wireless device drivers (e.g., ath5k) to delegate common tasks to the kernel and to exchange information between physical and upper layers. One of these tasks is rate control at the MAC layer, which uses a metric to evaluate the channel conditions and an algorithm to select a transmission rate that achieves the best performance objective (e.g., max throughput) for the given conditions. To the best of our knowledge, a comprehensive analysis of this framework and its rate control mechanisms does not exist. This paper is the first comprehensive study on rate control mechanisms supported by the mac80211 framework, including overview, evaluation and potential improvements of these mechanisms. In addition to proposing a way to solve the oscillation problem in one of the mechanisms, we propose and evaluate an adaptive and low-cost solution to address collisions due to the hidden terminal problem that has not been considered by both mechanisms. The results show more than 40% improvement if the proposed solution is used when hidden terminals are present.

Wireless sensor network is an emerging technology which consists of activities like sensing, computing, instrumenting and observing low power sensor nodes. In wireless sensor networks, maintaining the higher throughput is the main concern. Throughput of the network which is obtained from the wireless sensor network is vital issue which must be high which is measured in data packets per second in this context. The network of wireless sensors which is to be considered in this research mainly based on zigbee protocol and IEEE 802.15.4 standard and treated with cluster tree topology which is considered as a most suitable zigbee topology. The problem that sensors usually face in wireless sensor network is that when data packets are transferred from one node to another node, the throughput of the wireless sensor network decreases because of packet collisions and high network traffic. So we have proposed improved ABE mechanism which uses IEEE 802.15.4 slotted CSMA/CA to obtain the better throughput of zigbee based wireless sensor network.

Reduction in radio interference & improvement in communication throughput we can achieve by the use of directional antennas in wireless Adhoc network..Deafness & new hidden terminal problem causes a degradation in performance, which is introduced by directional antennas in wireless media access control. To solve these problems we can propose some protocols like circular RTR directional mac protocol to solve the above problems. We can evaluate the results of these protocols by simulation.

Virtual access point (VAP) is one of the most useful wireless virtualisation technologies because of its concurrent operation to compose multiple wireless networks via generating service set identifier. A single physical wireless NIC could access multiple networks in a single channel and thus establish a variety of wireless access point without additional wireless network interface. However, as the number of VAP increases, available bandwidth is reduced due to the fact that the number of management frame is increased dramatically in a single channel. Since the management frames should be sent as a basic data rate, channel utilisation and overall network performance would be degraded. To address this problem, system virtualisation is employed to augment wireless NIC hardware. Augmented wireless NICs are exposed to the guest OS and thus can access different wireless channel physically. The results obtained mitigate the bandwidth utilisation of management frame composed to the legacy VAP scheme, increasing round-trip time latency slightly.

In wireless multihop bidirectional communication environment, there is a possibility that packet collision and retransmission owing to the hidden node problem decrease efficiency of throughput. The aim of this article is to achieve efficient and reliable packet transmissions in such environments. To do so, we propose a packet transmission scheme named inter-flow network coding with passive acknowledgment. In inter-flow network coding with passive acknowledgment, it is necessary to optimize the encoding latency and to avoid passive acknowledgment packet collision, so we address these issues in this article. Finally, we also confirm that the inter-flow network coding with passive acknowledgment scheme is effective in terms of the collection ratio and delay through simulations.