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The proposed approach is designed to boost the IEEE 802.15.4 / ZigBee-based WSN streaming efficiency by introducing multipurpose routing. We investigate how those networks can be designed in order to achieve optimum throughput using computational models to explain intra-track and inter-track interference in multipath routing networks. One mode of action in particular – Spatial-TDMA (S-TDMA), Zig Bee dependent WSNs, will greatly reduce the amount of interference, both in one- and multi-track environments. It is also seen that two-way networks can be stronger than their one-way counterparts by means of deliberately selected implementation parameters. Finally, a greater degree of spatial isolation between the routes used indicates improved average efficiency in multi-path scenarios. The simulation is one of our results.

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.

Sensor network contains plenty of nodes for many applications like environmental monitoring, target identification and intrusion detection. So that, the life cycle of the network should be maximized as much as possible with less delay and high channel utilization. In this paper the proposed work presents a Self-organized Tree Hierarchy medium access control protocol (STH-MAC) for the data transfer from source to destination. Hidden terminal problem and load balancing are the common issues of the sensor network. Carrier Sense Multiple Access with collision avoidance is the normal scheme to avoid such kind of problem. MAC controls can have pipelining with priority base. Sleep interval is monitored based on the priority of nodes.

Innumerable complex industrial processes, such as blast furnace (BF) ironmaking process, greatly rely on some well-performing quality models to realize prediction and control of product quality. This paper proposes an improved orthogonal incremental random vector functional-link networks (I-OI-RVFLNs) algorithm with compact structure and high computational efficiency and applies it to quality modeling of BF ironmaking process. First, in order to improve the convergence speed of the basic I-RVFLNs, Schmidt orthogonalization method is introduced to orthogonalize the output vectors of the hidden layer nodes obtaining the least squares solution. Then, the proposed I-OI-RVFLNs algorithm further improves the network construction mode of the existing I-RVFLNs simplifying the network structure. To cut out the hidden nodes with smaller output weights, the number of hidden nodes of the proposed method is first fixed in advance and then the output weights of each hidden node are iteratively updated to approximate the network output. In this way, the problem of low computational efficiency caused by too many hidden nodes in basic I-RVFLNs can be avoided in the proposed algorithm. Lastly, data experiments using actual industrial data show that the proposed algorithm has much better performance in terms of convergence speed and computational efficiency than other compared algorithms.

The concept of SCN offers a fast framework with universal approximation guarantee for lifelong learning of non-stationary data streams. Its adaptive scope selection property enables for proper random generation of hidden unit parameters advancing conventional randomized approaches constrained with a fixed scope of random parameters. This paper proposes deep stacked stochastic configuration network (DSSCN) for continual learning of non-stationary data streams which contributes two major aspects: 1) DSSCN features a self-constructing methodology of deep stacked network structure where hidden unit and hidden layer are extracted automatically from continuously generated data streams; 2) the concept of SCN is developed to randomly assign inverse covariance matrix of multivariate Gaussian function in the hidden node addition step bypassing its computationally prohibitive tuning phase. Numerical evaluation and comparison with prominent data stream algorithms under two procedures: periodic hold-out and prequential test-then-train processes demonstrate the advantage of proposed methodology., This paper has been published in Information Sciences

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.

Shifting from the time domain to the frequency domain is an interesting recent direction that has been exploited to improve the performance of wireless networks. It is shown that the frequency-domain based proposals are of obvious benefits especially for higher rates and densities which are important attributes of the next-generation wireless networks. In this survey paper, we provide an overview of the concept of frequency-domain based contention and polling MAC protocols, and we show how these schemes could enhance the performance of wireless networks. We also attempt to provide a comprehensive survey of such schemes including related proposals for the next-generation IEEE 802.11ax wireless networks. In addition, we compare the surveyed protocols based on factors like the evaluation methods, the number of contention rounds, the conveyed signals, and the purpose of each protocol. We further address different challenges and issues of frequency-domain schemes including the hidden terminal problem, the number of subcarriers, TDMA-like transmissions, coexistence, the number of antennas, machine to machine networks, overlapping networks, and synchronization. Finally, we highlight different possible directions for future work.

Interference management through power control in wireless networks has both the hidden terminal problem which induces transmission collisions, and the exposed terminal problem which blocks concurrent transmissions. Both problems are caused by the varied interference range of different links. Through observing that the nodes adopt the power control mechanism induce collisions in one scenario and miss concurrent transmission opportunities in two scenarios, this paper presents IAPC (Interference-Aware Power Control), a novel protocol to improve the network throughput from the three aspects. IAPC makes the interference range of each link covered by its CTS (Clear-To-Send) transmission through utilizing a signature detection process, so as to avoid interference. Meanwhile, it makes the CTS frame carry the transmission and reception power information of this link, according to which the neighboring node can determine a limited transmission power, trying to make itself outside the interference range of the ongoing link, so as to exploit concurrent transmissions. The signature detection range has been investigated through both experiment results and theoretical analysis, and the performance improvement of IAPC comparing with the other protocols has been shown through simulation results based on ns2.

This paper proposes a Triggered CCHI Multichannel MAC protocol for efficient safety message dissemination in Vehicular Ad Hoc Networks. The proposed protocol allows a vehicle to start control channel interval (CCHI) by terminating service channel interval (SCHI) whenever a safety message arrives during SCHI. It enhances the performance of VANET by reducing resource wastage and unwanted delay caused by fixed interval of CCHI and SCHI. Further, CCHI keeps on increasing until all safety messages are not transmitted. A virtual TDMA beaconing process is also proposed in this paper to ensure delivery of periodic status messages. Multichannel hidden terminal problem is also addressed using cluster member request and cluster head request. An analytical model is developed to evaluate the proposed protocol with respect to packet delivery ratio, throughput, safety message delay and packet loss ratio. Extensive simulation is carried out to validate the analytical model and to demonstrate the improvement in comparison to existing similar MAC protocols and IEEE802.11p.

Rendezvous in cognitive radio ad-hoc networks is an essential step for a pair of unknown cognitive radio (CR) users to initiate a communication. Most of the existing studies address rendezvous problems as a design of a search strategy to meet on the same channel at the same time. However, in a multi-user environment, a rendezvous cannot guarantee even if two users are on the same channel at the same time due to channel contention and the multi-channel hidden node problem. To overcome problems, we propose a novel cognitive radio rendezvous (CR-RDV) protocol by integrating the rendezvous and medium access control (MAC) issues. We modify the traditional backoff strategy based on remaining transmission time and packet length to avoid the concurrent transmission with the primary users (PUs). Moreover, an additional sensing period is introduced immediately after the RTS packet to solve the blocking problem in the multi-user environment. The proposed CR-RDV protocol is analysed based on the modified Bianchi model and an absorbing Markov chain model to capture the multi-user and rendezvous channel contention. Through extensive simulations, we show that the proposed CR-RDV protocol outperforms the existing methods with respect to throughput, delay, and packet dropping.

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 vehicular ad hoc networks (VANETs), data propagation is quite challenging due to the high mobility of vehicles, the instability of communication links, and the inherent topology changes. This paper presents FWDP, a fuzzy logic-based vehicle weighting model (VWM) for scheduling prioritized data in VANETs. FWDP employs roadside units (RSUs) to dominate the frequent topology changes and manage the data propagation. A Fuzzy C-Mean clustering (FCMC) is used for handling clustered vehicles that compete to utilize the shared channel. RSUs receive prioritized data from cluster heads (CHs) in the proposed model wherein CHs allocate scheduled service channels to weighted vehicles during an interval. FWDP is equipped with a fuzzy inference system (FIS) for vehicle weighting according to the velocity and inter-vehicle distance metrics. In addition, RSUs compute the signal-to-noise and the interference ratio (SINR) to solve the hidden terminal problem to prevent radio interference. The OMNET++ simulator is used to show the performance improvement of FWDP in terms of the packet delivery ratio, interference ratio, suspend data ratio, Throughput, end-to-end delay, channel utilization, and packet loss ratio metrics intended for low, intermediate, and high vehicle densities.

The system that we propose in this paper aims to help robots to rescue immobilized victims by providing first aid (e.g.: oxygen masks). Such first aid can increase the chances of saved lives, by maintaining the status of victims until the arrive of rescue team for the take over. The proposed system takes advantage from a grid-based architecture for sites monitoring that has been presented in a previous work. It is composed of a mobile robot and a wireless sensor network (WSN). The robot has the mission of rescuing victims, and the WSN has three main missions: (1) detecting the existence of victims or any anomaly in the area, (2) disseminating reliably information and alerts and finally (3) providing the robot with efficient route guidance. To disseminate information with low cost (i.e avoids collisions caused mainly by the hidden node problem), we propose a distributed algorithm that insures the no collisions in the broadcast scheme using a grid, we called it No-Collision Grid Based (NCCB). Using NCGB allows to create all possible paths from any cell to the victim. This helps in guiding the robot through the safest and shortest route in a distributed manner. In order to increase the number of rescued victims, we used Ant Colony System with Victim Lifetime Window (ACS-VLM) to schedule the sequence of victims to rescue. The proposed solution has been validated through intensive simulations which show an important improvement in terms of overall network overhead, success ratio and the number of rescued victims.

The IEEE 802.15.4 standard is the most widely used for the realization of Wireless Sensor Networks (WSN) and Internet of Things (IoT) applications. The effects of various disturbances on IEEE 802.15.4 wireless transmissions in the 2.4 GHz band have been studied previously for background noise, multipath fading, wideband and narrowband interference caused by WiFi and Bluetooth networks. The influence of co-channel interference, which originates from collisions between IEEE 802.15.4 devices which perform simultaneous radio transmission, has not been investigated previously. The IEEE 802.15.4 standard uses the Carrier Sense Medium Access with Collision Avoidance (CSMA/CA) channel access mechanism to prevent collisions between devices, but this mechanism does not provide protection from a hidden node problem, which is the primary source of co-channel interference. Hidden node collision in the CSMA/CA channel access mechanism occurs because of the time-spatial relation between nodes located inside the radio range of the recipient device. In our paper, we determined the spatial probability for k -tuple of mutually hidden nodes using the Monte Carlo simulation method. Furthermore, we analyzed the influence of co-channel interference on the error probability of IEEE 802.15.4 communication, and derived accurate analytical models by considering the non-ideal features of the used spreading sequences. The accuracy of the derived mathematical models was tested by numerical Monte Carlo simulation of the IEEE 802.15.4 communication and in a real-world experiment using IEEE 802.15.4 compliant wireless transceivers for creating co-channel interference. The presented simulation and real world experiment results show consistency with the proposed analytical error probability models.

In recent years, wireless sensor networks (WSNs) have been widely used for controlling remote devices and also for gathering sensor data of distributed WSN devices. The WSNs support current Internet of Things (IoT) technologies in the background. However, it is becoming a salient issue that frequent packet delivery losses occur during data gathering on WSNs along with the increasing number of nodes. Two fundamental difficulties exist for MAC and upper layers on IEEE 802.15.4 standard: transmission collisions among two-hop away nodes, known as the “Hidden node problem,” and traffic congestion during data transfer that engenders buffer overflow at nodes. To resolve these difficulties, we propose a self-organizing network coordination framework for WSNs that realizes an adaptive time-division transmission by nodes and also traffic congestion handling in a decentralized manner. Specifically, the framework is based on a decentralized time division technique using a simplified pulse-coupled oscillator model. By coordinating the transmission timing adaptively, each node sends messages without collisions. “Hidden node problems” as well as “Exposed node problems” will be prevented, in principle, when using our method. Additionally, to reduce traffic congestion in a decentralized manner, time slots in the transmission cycle on each node are used efficiently by additional algorithms: an “empty time slots utilization algorithm” and a “takeover algorithm of neighboring nodes’ transmission slots”. These are introduced for efficient large data gathering applications. We simulated a 60-node data gathering application and evaluated its superiority to a conventional WSN method using CSMA/CA on IEEE 802.15.4 standard. We also conducted hardware experiments using nine developed WSN nodes and confirmed our framework’s feasibility in real situations targeted at real-time landslide detection with distributed WSN nodes.

The co-channel deployment of femtocells can lead to severe cross-tier interference to macrocell users which is resolved through the use of cognitive radio technology in which the femtocells, acting as unlicensed users, opportunistically access the spectrum of the primary macrocell in a cognitive way. This research proposes a cooperative scheme to improve the spectrum access opportunity for unlicensed femtocell in a two-tier heterogeneous network by exploiting the hybrid-automatic repeat request (HARQ) feedback information of macrocell transmission assuming the macrocell spectrum is considerably underutilized. This HARQ based scheme is very useful to get rid of the ‘hidden node problem’ and ‘exposed node problem’ encountered in conventional ‘listen-before-talk’ strategy used by the cognitive users. The outage performance of macrocell user is also improved due to cooperation from the femtocell. Performance analysis of the scheme is presented in Nakagami fading environment for a single femtocell scenario and compared with the conventional non-cooperative spectrum access via numerical examples. Appreciable improvements in terms of macrocell outage, macrocell and femtocell throughput over the conventional non-cooperative spectrum access have been found by considering a fixed macrocell traffic arrival rate. Moreover the dependence of femtocell location on the performance of the proposed scheme is further explored.

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.

Visible light communication (VLC) is an emerging technology that uses light rays in the range of 380–740 nm for signal propagation at a high data rate compared to radio frequency (RF). Nevertheless, it is not realistic to achieve full-duplex communication in VLC because of challenges such as glare, line-of-sight transmission requirement, interference, and energy constraint. Infrared or RF can complement VLC in order to achieve full-duplex communication. However, aggregated VLC–RF networks cannot be realized without addressing challenges such as network addressing and medium access control (MAC). In this study, we present the self-adaptive medium access control (SA-MAC) protocol for aggregated VLC–RF wireless networks. The aim of our study is to minimize network delay, energy consumption, and collision while increasing throughput. By leveraging the CSMA/CA and sub-carrier orthogonality we model the SA-MAC protocol for aggregated VLC–RF wireless networks and we demonstrate the discrete Markov chain model that shows the states of a node in SA-MAC. Finally, we simulate our protocol in NS3 simulator then we compare simulation results with the Markov chain results and other existing protocols in the literature such as the carrier sense multiple access with collision detection hidden node avoidance (CSMA/CD-HA) and dynamic contention window-based successive transmission (DCW-ST). Numerical results from simulation and Markov chain model converge, especially when the number of node increases. Furthermore, the results from our study show that the proposed protocol increases network performance significantly.

The Sentech Chair in Broadband Wireless Multimedia Communications at the University of Pretoria, South Africa, the National Research Foundation (NRF) and the Independent Communications Authority of South Africa (ICASA).

The major challenge pertaining to single-hop wireless networks is to design a medium access control (MAC) scheme to efficiently utilize the scarce wireless bandwidth; whereas the most popular solution, IEEE 802.11 distributed coordination function, achieves only limited performance because of the considerable idle time and the high rate of transmission collisions caused by the backoff procedure at high loads. In this paper, we propose a novel contention/reservation MAC scheme, which aims at ensuring low control overheads and collision-free data transmission to maximize system performance. Our scheme provides an efficient control contention resolution algorithm which resolve one or at least one successful reservation in a time frame, thus only a few numbers of control minislots are necessary for a number of active mobile stations contending for reservations. Moreover, with the help of the broadcast messages from the Access Point, all mobile stations determine a nearly-round-robin and collision-free data transmission schedule in a distributed manner, and also implicitly resolves the well-known hidden terminal problem. Extensive simulation results demonstrate that the proposed MAC scheme achieves exceptional system performance under a wide range of traffic loads and various system parameters, and also shown to be robust even when under attack by malicious mobile stations.

A binary countdown-based mechanism for resolving contentions in cluster-based wireless sensor networks is proposed.Energy-efficiency is improved by spreading the contention over all available elimination rounds.An analytical model for dimensioning main protocol parameters is provided. This paper presents an energy-efficient technique for resolving intra-cluster contentions in cluster-based wireless sensor networks. The proposed technique, bit map - binary countdown (BM-BCD), provides collision-free medium access by exchanging short signal tones between the head node and member nodes of the cluster. The BM-BCD improves existing tone-based contention resolution schemes in the following two aspects. Firstly, BM-BCD overcomes the hidden terminal problem by actively involving head node into the contention resolution process. Secondly, BM-BCD introduces a novel group-splitting algorithm which improves energy efficiency of member nodes by spreading the contention resolution over all available elimination rounds. The paper also introduces a simple intra-cluster MAC protocol, named STAR-TONE, which incorporates the proposed BM-BCD, and provides an analytical model for dimensioning main protocol parameters. Our analysis, verified by simulations, demonstrates that BM-BCD reduces the power consumption during contention for up to 44.5% compared to the baseline countdown protocol under bursty traffic conditions. Display Omitted

A new IEEE standard for large-scale wireless connectivity in IoT and M2M applications, called IEEE 802.11ah, has recently been introduced. A single access point (AP) of 802.11ah can provide connectivity to a large number of devices (up to 8192) with the communication range of up to 1źkm. Due to such a large coverage area with a large number of connected devices, however, the hidden node problem of 802.11ah networks is severer than typical Wi-Fi networks. Especially, we observe that frequent occurrences of a collision chain results in significant deterioration of network performance even with the group-based access restriction mechanism of 802.11ah. To solve this problem, we propose a collision chain mitigation scheme that detects and interrupts a collision chain, lets a smaller number of devices contend thereafter and also provide the information from which a carrier-sensitivity table is constructed by AP. Although the proposed scheme mitigates performance deterioration due to a collision chain when occurred, collision chains still occur. So, we propose a grouping algorithm which can perform both initial grouping and regrouping from existing groups based on the carrier-sensitivity table constructed by the mitigation scheme so that only a negligible number of hidden devices remain in each group and the root cause of collision chain is obviated. Our simulation study shows that the mitigation scheme alone makes network throughput comparable to the case of no hidden devices and its combination with the grouping algorithm improves throughput performance over the 8-group case of the conventional mechanism by up to 146%.

An IEEE 802.11ah network has been designed to service a wide range of sensor network applications where a single access point (AP) covers a transmission range of up to 1źkm and needs to support more than 8000 nodes. As a result, it has much more hidden node pairs compared to conventional 802.11a/b/g/n/ac networks. In addition, since nodes in power saving mode wake up simultaneously to send frames after receiving a beacon frame from the AP, the hidden node problem can become worse, resulting in frequent packet collisions and performance degradation. The 802.11ah standard proposes a group-based contention scheme to resolve the performance degradation problem, but it cannot resolve it appropriately.In this paper, we analyze the harmful impact of the hidden node problem on network performance and propose a new grouping algorithm to alleviate the performance degradation. Our proposed hidden matrix based regrouping (HMR) algorithm first finds hidden node pairs, and generates a hidden node matrix accordingly. Then it regroups hidden nodes to alleviate the hidden node problem using the hidden node matrix. Through extensive simulations, we show that our HMR algorithm eliminates most of hidden node pairs, thereby improving the performance of the 802.11ah network significantly in terms of the number of hidden node pairs and power-save poll (PS-Poll) transmission end time.

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.

LTE operation in the unlicensed spectrum based on Licensed-Assisted Access (LAA) is being considered as an option to increase the capacity of 4G/5G wireless networks. This solution allows the eNodeB to contend with other nodes by accessing the shared medium and, through carrier aggregation (CA), to use both licensed and unlicensed bands to deliver best effort services. Nevertheless, the hidden node problem over shared medium access networks is an obstacle that must be addressed in order to reduce or avoid performance degradation problems. The metrics associated to LAA reflect the behavior of a node facing collisions. A better understanding of these metrics can help to identify nodes affected by hidden terminals, making it possible to take smart decisions about the continuity of a node on the unlicensed band, resulting in an improved network performance. In this paper, we first study the Channel Quality Indicator (CQI), Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ) metrics on the context of LAA for a User Equipment (UE) that is facing different levels of interference. Then, a combination of the above metrics is used in order to develop an algorithm for collision detection. Finally, the performance of the algorithm is evaluated using a simulation tool under realistic channel conditions. The results show that is feasible to detect, with an adequate accuracy level, if a node is affected by collisions and subsequently if this node is located in hidden area. This is demonstrated with different levels of interference, realistic channel conditions and users in movement inside the hidden area.

In this paper, we propose a novel spectrum sensing scheme for multiuser multiple-input–multiple-output cooperative cognitive radio networks and a decision confidence algorithm for the antenna selection in FC to reduce its computational burden. Here first, a log-likelihood-ratio test (LRT) based energy detection of primary user link is performed by each secondary user employing multiple receive antennas and with imperfect channel state information. Next, the local decision is sent to the fusion center (FC) via multiple transmit antennas to combat the hidden node problem. Finally, the global decision is made at FC, equipped with multiple receive antennas using maximal ratio combining algorithm considering correlated fading channel between FC and SUs. Closed form expressions are obtained for probability of detection ( P d ) and probability of false alarm. The performance evaluations show that the P d ≥ 0 . 95 with N t = 2 , N r f = 8 , S N R = − 5 d B at P f a = 0 . 1 is achieved with the proposed scheme even in the presence of antenna interference between the MIMO channel. Further, the proposed scheme reduces the overall computational complexity and time complexity of MIMO cooperative sensing technique.

In this paper, an analytic model is built to study the medium access control (MAC) performance and reliability of general two-dimensional (2-D) IEEE 802.11 based wireless networks for one-hop broadcast communications. First, a semi-Markov process (SMP) model is introduced to capture the medium contention and backoff behavior and the impact of hidden terminal problem in IEEE 802.11 broadcast wireless networks in a more precise way. An M/G/1/K queue is used to model arrival and service of messages in an individual mobile terminal. To the contention for the shared medium, the SMP model interacts with the M/G/1/K queue through fixed-point iteration. Furthermore, based on the fixed-point solution, performance metrics including packet delivery probability (PDP), MAC-level and Application-level transmission delay, and MAC-level and Application-level packet reception ratio (PRR) are derived. The 2-D PDPs are derived through a coverage area computation for the impact of hidden terminal problem and concurrent transmissions to evaluate point-to-point reception probability, and then through integration of the reception probabilities over the circular intended range of the sending node. The analytical model takes into account IEEE 802.11 backoff counter process, hidden terminal problem, message inter-arrival interval, distinct transmission range, carrier sensing and interference ranges, and Nakagami fading channel with distance dependent path loss. Finally, as an example, the proposed analytic model is applied to a 2-D ad hoc network. The new model is validated through extensive simulations and new observations about the effects of network parameters on the performance and reliability are obtained.

This work seeks to develop an analytical model for the per-node throughput analysis of IEEE 802.11 WLAN networks with hidden nodes by extending Bianchi's model. With the analytic model we derive the per-node throughput of each node and quantify the impact of hidden nodes on per-node throughput. Through our analysis, we find that nodes having more hidden nodes are likely to have worse throughput performance than nodes having less hidden nodes, so resulting in unfairness in per-node throughput.We next propose a new algorithm, called the fake collision algorithm, to solve the unfairness due to hidden nodes. The proposed fake collision algorithm allows nodes with poor throughput to acquire more transmission opportunities by slightly modifying the Binary Exponential Backoff algorithm of the IEEE 802.11 Distributed Coordination Function. To this end, the fake collision algorithm uses a new control parameter called the fake collision probability which can be obtained from a computation algorithm that we develop based on our analytic model. We show that the fairness in per-node throughput can be achieved with the fake collision probability for each node through simulation.

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.

Graphical abstractDisplay Omitted An SDMA-based MAC protocol (S-MAC) for wireless ad hoc networks is proposed.Exploiting the creation of spatial channels to enhance network capacity.Providing collision-free access to the communication medium based on the location of a node.Improving the performance of throughput and spatial channel reuse. A wireless ad hoc network consists of a set of wireless devices. The wireless devices are capable of communicating with each other without the assistance of base stations. Space Division Multiple Access (SDMA) is a new technology designed to optimize the performance of current and future mobile communication systems. In this paper, an SDMA-based MAC protocol (S-MAC) for wireless ad hoc networks with smart antennas is proposed. The proposed protocol exploits the SDMA system to allow reception of more than one packet from spatially separated transmitters. Using SDMA technology provides collision-free access to the communication medium based on the location of a node. The proposed protocol solves the hidden terminal problem, the exposed terminal problem, and the deafness problem. Simulation results demonstrate the effectiveness of the proposed S-MAC in improving throughput and increasing spatial channel reuse.

We evaluate the practical network coding (NC) gain in a wireless ad hoc networks. First, we introduce how network coding can be applied to IEEE 802.11 ad hoc networks. Next, we find obstructive factors by which the NC gain may decrease as compared with the theoretical NC gain. Finally, through the performance evaluation, we analyze why a performance difference occurs between practical and theoretical NC gains owing to the suggested obstructive factors. According to the simulated results, even though there is some overhead caused by the characteristics of the media access control (MAC) protocol and control signals to apply NC to wireless ad hoc networks, the practical NC gain is almost the same as the theoretical gain in an ideal environment for NC. However, in the NC system with the hidden node problem, the NC gain decreases because of packet collision. In the NC system using a promiscuous mode where packet overhearing is possible, nodes consume more power than the conventional system because of overhearing packets. For instance, when the number of overhearing nodes not related to NC is set to 15, the power reduction rate is -38.04%. Furthermore, under the network conditions inappropriate for NC, such as asymmetric flows and scarce coding structures, the NC gain can be considerably reduced. For example, in 5x5 and 7x7 grid topology networks, the load reduction rate by NC are only 4.12% and 7.01%, respectively. Therefore, research to solve the suggested obstructive factors is necessary to achieve sufficient NC gain in a practical wireless network such as an IEEE 802.11 ad hoc networks.

A novel wireless resource partition method is proposed to theoretically solve the hidden terminal problem (HTP) for wireless networks with uniform transmission ranges, and known, stationary node locations. A hidden terminal graph (HTG) representation is used to capture the potential hidden terminal interference among wireless nodes. The wireless resource partitioning solution of the HTP problem is cast as a graph-coloring problem on the HTG. Under a unit-disk wireless transmission range model, a novel, efficient, constructive solution to the HTG graph-coloring problem is proposed. Specifically, by spatially grouping wireless nodes into a hexagonal grid coordinate system, it is shown that the supremum of chromatic number of a HTG can be bounded by [6,12], regardless of the number of nodes or how the nodes are distributed spatially. Moreover, 12 is also the maximum number of wireless resource partitions needed to resolve the corresponding HTP problem. Extensive simulation results reveal that the performance of this hex-coloring method is comparable to existing heuristic graph-coloring methods such as DSATUR for problems with moderate size (a few hundreds of nodes). When the problem size scales up to a few thousands of nodes, the hex-coloring solution consistently achieves superior solutions (fewer wireless resources required) while consuming 3 orders of magnitude less computing time.

Access control is one of the major security concerns for wireless sensor networks. However, applying conventional access control models that rely on the central Certificate Authority and sophisticated cryptographic algorithms to wireless sensor networks poses new challenges as wireless sensor networks are highly distributed and resource-constrained. In this paper, a distributed and fine-grained access control model based on the trust and centrality degree is proposed (TC-BAC). Our design uses the combination of trust and risk to grant access control. To meet the security requirements of an access control system with the absence of Certificate Authority, a distributed trust mechanism is developed to allow access of a trusted node to a network. Then, centrality degree is used to assess the risk factor of a node and award the access, which can reduce the risk ratio of the access control scheme and provide a certain protection level. Finally, our design also takes multi-domain access control into account and solves this problem by utilizing a mapping mechanism and group access policies. We show with simulation that TC-BAC can achieve both the intended level of security and high efficiency suitable for wireless sensor networks.

We investigate a principled extension of the π -calculus for formal modeling of mobile communicating systems with stateful channels. In our proposed extension, called π Z, a channel is associated with a stateful abstract type in the Z specification language. We develop both reduction as well as labeled transition semantics for π Z. We show that the important properties of the π -calculus are preserved in π Z: (1) τ -transitions match reductions; and (2) bisimilarity induced by the labeled transitions is closed under parallel composition, name restriction, and a restricted recursion. The paper illustrates the use of stateful channels by modeling the ‘hidden node problem’ in a wireless network.

A reliable one-hop broadcast is a fundamental communication primitive in mobile ad hoc networks in which a message from the source node is guaranteed to be delivered to all nodes within the source node's transmission range. Despite the importance of it, reliable one-hop broadcast is not easy to accomplish due to collisions in wireless networks known as Hidden Terminal Problem. This paper presents a MAC protocol that not only guarantees reliable one-hop broadcast but also achieves it efficiently by exploring as many simultaneous executions of the communication as possible. In addition to the data packets, the proposed algorithm utilizes the control packets that prevent packet collisions, and at the same time, make the simultaneous communications possible to improve the network throughput. Simulation results show the effectiveness of the proposed algorithm.

Mobile multimedia applications have recently generated much interest in mobile ad hoc networks (MANETs) supporting quality-of-service (QoS) communications. Due to the limited bandwidth of a wireless node, a QoS multicast routing is often blocked if there is not a single multicast tree with the requested bandwidth, even when there is sufficient bandwidth in the network to support the call. In this paper, a multi-path QoS multicast routing (MQMR) protocol for MANETs is proposed. The scheme offers dynamic time slot control using a multi-path tree (or a uni-path tree) to meet the bandwidth requirements of a call. The final multi-path QoS multicast tree meets the QoS requirements, and the aggregate bandwidth of the paths meets the bandwidth requirements of a call. To avoid the hidden terminal problem or insufficient bandwidth in the bandwidth reservation process, each destination uses a decision rule. Moreover, a bandwidth reservation scheme is used for selecting the reserved time slots on each node in the multi-path QoS multicast tree. Simulation results demonstrate the effectiveness of MQMR in reducing network blocking and improving the call success ratio.

We use a single-hidden layer feedforward neural network (SLFN) to interpret the model of optimized geometric ensembles (OGE). Based on the SLFN, we simplify OGE into random optimized geometric ensembles (ROGE), which may contain much less hidden nodes than that of OGE. Furthermore, on 12 UCI data sets we verify that ROGE can achieve the same level of classification performance as OGE in less consumption of space and time.

It is well-known that the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)-based wireless networks suffer seriously from the hidden terminal problem and the exposed terminal problem. So far, no satisfactory solutions that can resolve both problems simultaneously have been found. In this paper, we present a joint solution to the two problems. Our approach avoids the drawback of lessening one problem but aggregating the other. It is compatible with the IEEE 802.11 MAC and requires no protocol change. Analysis and simulations show that the proposed scheme can significantly reduce the hidden and exposed terminal problems. Not only it can significantly improve the throughput of the network and the fairness among different flows, it can also provide a much more stable link layer. In simulated scenarios under heavy traffic conditions, compared to the conventional IEEE 802.11 MAC, the new method can achieve up to 1.8 times gain in network throughput for single-hop flows and up to 2.6 times gain for multihop flows.

Ad-hoc networks suffer from the problem of hidden nodes (terminals), which leads to severe degradation of network throughput. This survey gives a comprehensive overview of Medium Access Control (MAC) protocols which directly or indirectly address this problem. The presented protocols are grouped in several categories and are described in the order of their publication date. To give the reader a deep understanding of the progress made in the area of alleviating the hidden node problem a brief summary of the key ideas as well as a detailed comparison of different protocols are presented. Open research directions are also discussed to serve as a starting point for future protocol design and evaluation.

A packet scheduler and a medium access control (MAC) protocol are presented for a direct-sequence spread-spectrum, wireless ad hoc network that contains a mix of nodes with directional antennas and nodes with omnidirectional antennas. The scheduler and MAC protocol are designed to prevent the co-site interference problem that arises in some types of nodes employing directional antennas. It is shown that the presence of nodes with directional antennas exacerbates the vulnerability of the network to the receiver blocking problem. A modification of the MAC protocol is presented that mitigates the receiver blocking problem, and it is shown to improve the performance of a network that includes nodes with directional antennas.

Currently multi-channel multi-interface ad hoc networks (multi-channel ad hoc networks) have received amount of interest, especially under the context of real-time traffics, such as video applications. Channel assignment is one of the key challenges in multi-channel ad hoc networks. In this paper, based on a representative hybrid channel assignment strategy named as HMCP, a statistic link load based hybrid channel assignment strategy, SLL-HCA, is presented to obtain a better channel assignment metric than that in HMCP. SLL-HCA is based on the HMCP protocol and adopts the statistic link load metric to ensure load balancing in a two-hop neighborhood, and to prevent both the hidden node problem and the exposed node problem. In addition, an enhanced strategy, VE-SLL-HCA, by setting harsher channel assignment conditions and reserving lower interference of routing path for video-streaming traffic than other non-video traffic, is proposed to improve the QoS support of video-streaming over multi-channel ad hoc networks. Simulation results show that SLL-HCA achieves better throughput performance than HMCP in the presence of background traffic including CBR traffic or VBR traffic; and, the PSNR QoS metric for video-streaming is enhanced when using VE-SLL-HCA compared with SLL-HCA and HMCP, which confirms the validity of the proposed strategy for video-streaming traffics. Moreover, the simulation results also indicate that non-video traffic unlikely suffers an unacceptable performance in terms of throughput.

The hidden terminal problem is a well-known problem in wireless networks that degrades the network performance due to collisions between nodes unable to sense each other. Preamble sampling WSNs are more sensitive to that problem than wireless local area networks due to the high vulnerability time caused by the long preamble transmission. This is specially important when the traffic load is high, for instance due to event detection and query dissemination or in regions closer to the sink. Typical mechanisms to reduce the negative effects of hidden terminals, like the use of RTS/CTS messages, cannot alleviate the problem in preamble sampling WSNs as the long preamble is still needed, thus not reducing the high vulnerability time. To alleviate the hidden terminal problem in this kind of networks the LWT-MAC, a new preamble sampling MAC protocol, is presented. The LWT-MAC protocol adapts to the sporadic increases in the network load by waking up sensor nodes at the end of a transmission. At the same time, it reduces the channel contention by implementing a non-aggressive retransmission procedure. In this work, the ability of the LWT-MAC protocol to reduce hidden terminal problems is evaluated and compared to the basic preamble sampling technique. Results show that the LWT-MAC protocol is able to significantly lighten the hidden terminal problem, thus improving the overall system performance.

Collisions in preamble sampling WSNs cause a high waste of resources due to the mandatory transmission of a long preamble before every message. Moreover, when hidden terminals are present, collisions are even more noticeable since the vulnerability time is proportional to the long preamble duration. This effect reduces considerably the network performance as both the number of collisions and the resources spent in them are significant. The effects of hidden nodes in preamble sampling WSNs, in different case scenarios and under variable offered loads, are analyzed in this work. Results show that the impact of hidden terminals in the network performance is non-negligible, specially at medium to high loads. These results should be considered by MAC protocol designers in order to devise mechanisms to mitigate the hidden terminal problem.

The number of hidden nodes is a critical factor for the generalization of ELM. Generally, it is heavy for time consumption to obtain the optimal number of hidden nodes with trial-and-error. A novel algorithm is proposed to optimize the hidden node number to guarantee good generalization, which employs the PSO in the optimization process with structural risk minimization principle. The simulation results indicate our algorithm for the optimal number of hidden nodes is reasonable and feasible with 6 datasets on benchmark problems by the accuracy comparisons.

The setting of the physical carrier sense is critical in wireless networks, since it often has to account for contrasting objectives like limiting the overall interference while ensuring high concurrency among wireless transmissions. This paper proposes an analytical approach for evaluating the impact of carrier sense setting on the throughput efficiency of wireless access networks. A time continuous Markov chain is used to describe the system, and to further gathering performance measures in terms of throughput and collision probability. Numerical results obtained through the model and further validated against simulations are used to derive qualitative dimensioning criteria for the carrier sense under different network conditions.

It is well known that a wireless local area network (WLAN) based on the IEEE 802.11 standard suffers from interference and scalability problems due to the limited number of non-overlapping channels. In order to mitigate the interference problem, channel assignment algorithms has been a popular research topic in recent years. It has been shown that such algorithms can greatly reduce the interference among wireless access points. However, in this paper, we show that previously proposed channel assignment algorithms may lead to an increased number of hidden nodes in dense network deployments. We also show that this can significantly decrease the performance of the network. Furthermore, we present results from experiments showing that the Request to send (RTS)/Clear to send (CTS) mechanism is unable to solve the hidden node problem in infrastructure WLANs, and therefore careful consideration needs to be taken when choosing channel assignment strategies in densely deployed wireless networks. To this end, we propose both a centralized channel assignment algorithm and a distributed channel assignment algorithm. Using a simulation study, we show that the proposed algorithms can outperform traditional channel assignment in densely deployed scenarios, in terms of QoS sensitive VoIP support without compromising the aggregate throughput, and that they are therefore a better performing alternative in such settings.

Motivated by observations from real world wireless local area network (WLAN) deployments, we develop in this paper a novel analytical model to characterize the saturation throughput of an IEEE 802.11-based access point (AP) and stations under the influence of hidden terminals. Unlike existing models, our model can accommodate different numbers of hidden nodes without increasing the model complexity. Given any number of hidden nodes, only four constraints are needed to describe the interaction between stations and the AP with the consideration of both uplink and downlink traffic. Simulation evaluation shows that our model predicts network performance accurately over a wide range of network sizes and indicates the existence of a throughput starvation problem. To address this problem, based on our model, we formulate a bandwidth allocation problem to optimize the network throughput and fairness under some predefined requirements by systematically tuning the AP and stations contention windows. Simulation results show that the starvation problem is resolved with our approach, and the target throughput is met.