Presence Of Hidden Nodes Research Articles

Joint Network Topology Inference in the Presence of Hidden Nodes

Joint Network Topology Inference in the Presence of Hidden Nodes

Performance Modeling of an NR-U and WiFi Coexistence System Using the NR-U Category-4 LBT Procedure and WiFi DCF Mechanism in the Presence of Hidden Nodes

The hidden-node problem is an important problem that should be considered in the design of a wireless communication system. This paper studies the performance modeling of an NR-U and WiFi coexistence system using the NR-U category-4 LBT procedure and WiFi DCF mechanism in the presence of hidden nodes. 2-D Markov models are first developed to describe the NR-U category-4 LBT procedure of an NR-U gNB and the WiFi DCF procedure of a WiFi AP, respectively, taking into account the effects of hidden nodes. Based on the two Markov models, theoretical models are further derived for analyzing the throughput of a gNB/AP and the delay of an NR-U/WiFi packet. Finally, the derived theoretical models are validated through simulation results and based on the theoretical models, the impacts of major system parameters on the system performance in terms of the throughput and packet delay are investigated, including the data packet arrival rate, the density, the sensing distance, and the channel transmission rate of a gNB.

Performance Modeling of an NR-U and WiFi Coexistence System Using the NR-U Category-4 LBT Procedure and 802.11e EDCA Mechanism in the Presence of Hidden Nodes

This paper studies the performance modeling of an NR-U and WiFi coexistence system using the NR-U category-4 LBT procedure and 802.11e EDCA mechanism in the presence of hidden nodes. 3-D Markov models are first developed to describe the NR-U category-4 LBT procedure for a priority-p queue of an NR-U gNB and the 802.11e EDCA mechanism for an AC-q queue of a WiFi AP, taking into account the effects of hidden nodes and the transmission of different-priority data. Based on the Markov models, theoretical models are derived for analyzing the mean throughput of a priority-p queue in an NR-U gNB and that of an AC-q queue in a WiFi AP as well as the mean transmission delay of an NR-U priority-p data packet and that of a WiFi AC-q data packet. The derived theoretical performance models are validated through simulation results. Based on the performance models, the impacts of major system parameters on the system performance are investigated, including the density of NR-U gNBs, the sensing distance and channel transmission rate of an NR-U gNB, and the data packet arrival rate at an NR-U gNB.

Implementation of an Associative Memory using a Restricted Hopfield Network

A trainable analog restricted Hopfield Network is presented in this paper. It consists of two layers of nodes, visible and hidden nodes, connected by weighted directional paths forming a bipartite graph with no intralayer connection. An energy or Lyapunov function was derived to show that the proposed network will converge to stable states. The proposed network can be trained using either the modified SPSA or BPTT algorithms to ensure that all the weights are symmetric. Simulation results show that the presence of hidden nodes increases the network’s memory capacity. Using EXOR as an example, the network can be trained to be a dynamic classifier. Using A, U, T, S as training characters, the network was trained to be an associative memory. Simulation results show that the network can perform perfect re-creation of noisy images. Its recreation performance has higher noise tolerance than the standard Hopfield Network and the Restricted Boltzmann Machine. Simulation results also illustrate the importance of feedback iteration in implementing associative memory to re-create from noisy images.

Modeling and simulation of the IEEE 802.11e wireless protocol with hidden nodes using Colored Petri Nets

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.

SCSMA: A Smart CSMA/CA Using Blind Learning for Wireless Sensor Networks

A smart carrier sense multiple access (SCSMA) using control messages is proposed for low power and low bandwidth wireless sensor networks (WSNs). In traditional WSNs, the use of media access control (MAC) messages is not recommended since data are of small size. However, if data size is increased with data aggregation or multimedia data, the control messages can be used for reliable data transmission. Thus, an efficient mechanism is needed to avoid the collision of control messages and data. SCSMA employs a blind learning algorithm with low complexity to prevent collision during channel contention and data transmission, even in the presence of hidden nodes. It is shown by simulation and analysis that SCSMA improves throughput by 29.5% to 71.6%, and reduces energy consumption by 20.5% to 36.2%, compared to the recent best approach using MAC messages. Simulation data are also verified by experimental data.

Two Variants of Secure Routing Algorithms in Mobile Ad Hoc Network

Background and Objective: Two different variants of secure routing algorithms are proposed in the present work. In both the variants a stable route is established between source and destination. Methods: The selected route is associated with the nodes having sufficient energy to establish the route and to transmit the data packets, minimum velocity to reduce the frequency of link failure, maximum distance from the source node to reduce the number of hops in the selected route, minimum number of neighbors to reduce the routing overhead. Each variant has two phases. In the first phase it is assumed that the selected route has no attackers. The first phase is made more realistic in the second phase by considering the presence of attacker in the selected route. In the first variant a node associated with the selected route overhears the transmission of the next forwarder node to detect an attacker node in the routing path. But a node may fail to overhear its next hop in presence of hidden node, due to limited overhear range etc. Such problem is eliminated in the second variant. In the second variant each node associated with the selected route searches its data packet buffer for the reception of the next data packet from its predecessor node associated with the same route and suspects the predecessor node as an attacker in case the next data packet is not found in the buffer. The performance of both the variants is compared on the basis of packet delivery ratio, throughput and average end-to-end delay. Results: The throughput and packet delivery ratio are higher in the second variant than the first variant whereas the average end-to-end delay is less in the second variant than the first variant. Conclusion: Moreover both the variants outperform the existing schemes in terms of packet delivery ratio, throughput and average end-to-end delay.

Blind Learning of Tree Network Topologies in the Presence of Hidden Nodes

This paper considers the problem of learning the unknown structure of a network with the underlying topology given by a polyforest (a collection of directed trees with potentially multiple roots). The main result is an algorithm that consistently learns the network structure using only second-order statistics of the data. The methodology is robust with respect to the presence of unmeasured (latent) nodes: the algorithm detects the exact number and location of the latent nodes, when they satisfy specific degree conditions in the actual network graph. It is shown that the same degree conditions are also necessary for a consistent reconstruction. Thus, the proposed reconstruction algorithm achieves the fundamental limitations in learning the structure of a polyforest network of linear dynamic systems in the presence of latent nodes. This paper overcomes the limitations of previous results that only addressed single-rooted trees, tackling the problem in an efficient way since the computational complexity of the derived algorithm is proven to be polynomial in the number of observed nodes.

THE RESEARCH OF PROBLEMS OF THE INFORMATION ALGORITHM FUNCTIONING IN THE PRESENCE OF PRESERVED NODES IN WIRELESS SENSOR NETWORKS

Sensor networks are one of the most relevant and promising technologies for wide application in various spheres of human life. Relatively inexpensive components, namely, sensor nodes are combined into one network. Due to the use of a significant number of nodes, in addition to the overall impact on functionality, this also leads to a decrease in the reliability of the network. Wireless connectivity has a number of limitations when it comes to the direct connection to the public communications network or the next-generation networks with optical components. For example, the relatively small distance to send information between constituent components. It follows next idea -sooner or later there will be the denial of nodes, which will lead to the isolation of other sensors. To avoid this, or at least to ensure the network connectivity during a failover, more nodes on a separate site need to be used. Also, due to the presence of connectivity between touch nodes, there are a number of general features that should be taken into account when designing such a network and deploying it in real-world conditions. One of these tasks is to ensure the accuracy of packets of information’s transfer between the sensor nodes, as violations of its integrity, quality, reliability and safety can lead to serious consequences. Due to insignificant volumes of memory, sensor nodes are not able to capture data about all nodes, their physical addresses, metrics for the fastest transmission of information packets. In view of this, the number of requests for the same node may exceed the critical rate at a certain time. However, there may also be a situation where a node that has not been earlier tested can be connected to the network. In this case, the question of the authenticity of the data that will circulate in the network from a similar, hidden node to others is sharply raised. Therefore, it is necessary to study the existing and the introduction of new algorithms for the transmission of information in the presence of hidden nodes in wireless sensory networks at the present stage of development.

Time slotted channel hopping with collision avoidance

Time slotted channel hopping (TSCH) mode proposed by the IEEE 802.15.4e-2015 standard enhances the reliability of low-power networks. TSCH supports the critical applications embedded in harsh environments with high-efficiency. Multi-channel hopping and time slotted access nature of this mode provides deterministic latency for applications and achieves a greater throughput capacity. The shared links nature of this mode risks the packets transmission to fail when the participating nodes are colliding nodes. Retransmitting the packets randomly risks it to fail several times, influencing the sensor energy and packet latency. To ensure collision avoidance in the presence of hidden nodes, we provide: time slotted channel hopping with correct collision avoidance backoff algorithm (TSCH-CCA) and Enhanced priority channel access backoff algorithm (E-PCA)) applied respectively to both normal packets and critical events packets. Our solution shows significant improvements in terms of latency, network congestion, network lifetime, critical event packets lifetime, and collision avoidance.

Design and performance analysis of a full-duplex MAC protocol for wireless local area networks

In this paper, Synchronized Contention Window Full-Duplex (S-CW FD) protocol is presented as a medium access control (MAC) protocol that enables full-duplex (FD) in wireless local area networks (WLANs), while seamlessly operating together with legacy nodes. For performance analysis, a Markov chain model of S-CW FD is devised, using this model, the saturated throughput of S-CW FD is derived and the results are validated by comparisons with OPNET simulations. Later, through detailed simulations, S-CW FD is evaluated against standard half-duplex IEEE 802.11, considering realistic self-interference and channel models and the effect of hidden nodes. It is shown that S-CW FD MAC protocol can double the throughput of standard half duplex IEEE 802.11 without hidden nodes in the network, and its improvement can get as high as ten fold in the presence of hidden nodes. In this work, S-CW FD is also compared to two similar contention based FD MAC protocols from the literature, and it is shown that, under typical network loads, S-CW FD outperforms those protocols by up to 30%, despite much lower complexity. Overall, S-CW FD stands out as a promising candidate for implementing FD in WLANs due to significant performance improvements, simplicity and flexibility for application in different FD modes to support bidirectional, relaying and cellular scenarios.

Research on an uplink carrier sense multiple access algorithm of large indoor visible light communication networks based on an optical hard core point process.

The IEEE 802.15.7 protocol suggests that it could coordinate the channel access process based on the competitive method of carrier sensing. However, the directionality of light and randomness of diffuse reflection would give rise to a serious imperfect carrier sense (ICS) problem [e.g., hidden node (HN) problem and exposed node (EN) problem], which brings great challenges in realizing the optical carrier sense multiple access (CSMA) mechanism. In this paper, the carrier sense process implemented by diffuse reflection light is modeled as the choice of independent sets. We establish an ICS model with the presence of ENs and HNs for the multi-point to multi-point visible light communication (VLC) uplink communications system. Considering the severe optical ICS problem, an optical hard core point process (OHCPP) is developed, which characterizes the optical CSMA for the indoor VLC uplink communications system. Due to the limited coverage of the transmitted optical signal, in our OHCPP, the ENs within the transmitters' carrier sense region could be retained provided that they could not corrupt the ongoing communications. Moreover, because of the directionality of both light emitting diode (LED) transmitters and receivers, theoretical analysis of the HN problem becomes difficult. In this paper, we derive the closed-form expression for approximating the outage probability and transmission capacity of VLC networks with the presence of HNs and ENs. Simulation results validate the analysis and also show the existence of an optimal physical carrier-sensing threshold that maximizes the transmission capacity for a given emission angle of LED.

Modelling of IEEE 802.11 DCF in the presence of hidden nodes

Today, the most commonly used technology for wireless networks is IEEE 802.11. The performance of the Medium Access Control MAC layer, which consists of Distributed Coordination Function DCF and Point Coordination Function PCF, has been examined over a long time period. The DCF is the random access scheme that uses CSMA/CA in IEEE 802.11 MAC layer protocol. There are various issues related to the performance evaluation of IEEE 802.11 DCF and one of the important issues is the problem of hidden terminals which exists in practice in any wireless network. In this paper, a two-dimensional analytical model is proposed for the analysis of IEEE 802.11 DCF in the presence of hidden terminals for both basic access and RTS/CTS modes by making use of the Markov chain.

Throughput and Delay Analysis of IEEE 802.11 DCF in the Presence of Hidden Nodes for Multi-hop Wireless Networks

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

A New Interference-Aware Dynamic Safety Interval Protocol for Vehicular Networks

In IEEE 802.11p/1609-based vehicular networks, vehicles are allowed to exchange safety and control messages only within time periods, called control channel (CCH) interval, which are scheduled periodically. Currently, the length of the CCH interval is set to the fixed value (i.e. 50ms). However, the fixed-length intervals cannot be effective for dynamically changing traffic load. Hence, some protocols have been recently proposed to support variable-length CCH intervals in order to improve channel utilization. In existing protocols, the CCH interval is subdivided into safety and non-safety intervals, and the length of each interval is dynamically adjusted to accommodate the estimated traffic load. However, they do not consider the presence of hidden nodes. Consequently, messages transmitted in each interval are likely to overlap with simultaneous transmissions (i.e. interference) from hidden nodes. Particularly, life-critical safety messages which are exchanged within the safety interval can be unreliably delivered due to such interference, which deteriorates QoS of safety applications such as cooperative collision warning. In this paper, we therefore propose a new interference-aware Dynamic Safety Interval (DSI) protocol. DSI calculates the number of vehicles sharing the channel with the consideration of hidden nodes. The safety interval is derived based on the measured number of vehicles. From simulation study using the ns-2, we verified that DSI outperforms the existing protocols in terms of various metrics such as broadcast delivery ration, collision probability and safety message delay.

Throughput analysis of IEEE 802.15.4 beacon-enabled MAC protocol in the presence of hidden nodes

The presence of hidden nodes degrades the performance of wireless networks due to an excessive amount of data frame collisions. The IEEE 802.15.4 medium access control (MAC) protocol, which is widely used in current wireless sensor networks, does not provide any hidden node avoidance mechanisms and consequently could lead to severe performance degradation in networks with hidden nodes. This paper presents a simple technique based on discrete-time Markov chain analysis to approximate the throughput of IEEE 802.15.4 MAC protocol in the presence of hidden nodes. Using different network configurations, we validate the applicability of the proposed analysis for generic star-topology networks. Based on the analysis, the effects of network size, topology, frame length and frame arrival rate on the throughput of the system are investigated.

Towards the design of efficient nonbeacon-enabled ZigBee networks

This paper presents experimental results of the communication performance evaluation of a prototype ZigBee-based patient monitoring system commissioned in an in-patient floor of a Portuguese hospital (HPG –Hospital Privado de Guimara˜es). Besides, it revisits relevant problems that affect the performance of nonbeacon-enabled ZigBee networks. Initially, the presence of hidden-nodes and the impact of sensor node mobility are discussed. It was observed, for instance, that the message delivery ratio in a star network consisting of six wireless electrocardiogram sensor devices may decrease from 100% when no hidden-nodes are present to 83.96% when half of the sensor devices are unable to detect the transmissions made by the other half. An additional aspect which affects the communication reliability is a deadlock condition that can occur if routers are unable to process incoming packets during the backoff part of the CSMA-CA mechanism. A simple approach to increase the message delivery ratio in this case is proposed and its effectiveness is verified. The discussion and results presented in this paper aim to contribute to the design of efficient networks, and are valid to other scenarios and environments rather than hospitals.

ZigBee-based remote patient monitoring.

This paper describes a developed continuous patient monitoring system based on the ZigBee protocol. The system was tested in the hospital environment using six sensor devices in two different modes. For electrocardiogram transmission and in the absence of hidden-nodes, the system achieved a mean delivery ratio of 100% and 98.56%, respectively for star and 2-hop tree network topologies. When sensor devices were arranged in a way that three of them were unable to hear the transmissions made by the other three, the mean delivery ratio dropped to 83.96%. However, when sensor devices were reprogrammed to transmit only heart rate values, the mean delivery ratio increased to 99.90%, despite the presence of hidden-nodes.

A Markov-Blanket-Based Model for Gene Regulatory Network Inference

An efficient two-step Markov blanket method for modeling and inferring complex regulatory networks from large-scale microarray data sets is presented. The inferred gene regulatory network (GRN) is based on the time series gene expression data capturing the underlying gene interactions. For constructing a highly accurate GRN, the proposed method performs: 1) discovery of a gene's Markov Blanket (MB), 2) formulation of a flexible measure to determine the network's quality, 3) efficient searching with the aid of a guided genetic algorithm, and 4) pruning to obtain a minimal set of correct interactions. Investigations are carried out using both synthetic as well as yeast cell cycle gene expression data sets. The realistic synthetic data sets validate the robustness of the method by varying topology, sample size, time delay, noise, vertex in-degree, and the presence of hidden nodes. It is shown that the proposed approach has excellent inferential capabilities and high accuracy even in the presence of noise. The gene network inferred from yeast cell cycle data is investigated for its biological relevance using well-known interactions, sequence analysis, motif patterns, and GO data. Further, novel interactions are predicted for the unknown genes of the network and their influence on other genes is also discussed.

An SRN Model of the IEEE 802.11 DCF MAC Protocol in Multi-Hop Ad Hoc Networks with Hidden Nodes

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