Collision Avoidance Mechanism Research Articles

Construction and Analysis of Shift-Invariant, Asynchronous-Symmetric Channel-Hopping Sequences for Cognitive Radio Networks

Besides designing channel-hopping (CH) sequences, finding good methods of communication rendezvous is important for improving spectral efficiency and alleviating traffic load of cognitive radio (CR) networks. In this paper, new asynchronous-symmetric CH sequences are constructed and their (channel overlap, even-channel-use, and pairwise shift invariance) properties are investigated. Their operations in three transmission scenarios involving different basic collision-avoidance mechanisms are analyzed and compared in terms of maximum time-to-rendezvous, rendezvous-success (RS) rate, and RS variance. This paper shows that the new sequences have shorter period, larger cardinality, and smaller RS variations than other CH sequences, thus supporting greater number of secondary users and more frequent and uniform rendezvous in the CR networks.

WBAN MAC Protocols— Non-Saturation Modeling and Performance Analysis

The current literature on discrete-time Markov chain (DTMC) based analysis of IEEE 802.15.6 MAC protocols for wireless body area networks (WBANs), do not consider the ACK timeout state, wherein the colliding nodes check the ill fate of their transmissions, while other contending nodes perform backoff check that slot as usual. In this paper, our DTMC model accurately captures the carrier sense multiple access with collision avoidance (CSMA/CA) mechanism of IEEE 802.15.6 medium access control (MAC) and allows the contending nodes performing backoff to utilize the ACK timeout slot during collisions. The compared rigorous results are obtained by considering a non-ideal channel in non-saturation conditions, and CSMA/CA parameters pertaining to UWB PHY of IEEE 802.15.6 MAC protocols.

Priority-based queuing and transmission rate management using a fuzzy logic controller in WSNs

Abstract Wireless sensor networks (WSNs) operate under challenging conditions, such as maintaining message latency and the reliability of data transmission and maximizing the battery life of sensor nodes. The aim of this study is to propose a fuzzy logic algorithm for solving these issues, which are difficult to address with traditional techniques. The idea, in this study, is to employ a fuzzy logic scheme to optimize energy consumption and minimize packet drops. We demonstrated how fuzzy logic can be used to tackle this specific communication problem with minimal computational complexity. In this context, the implementation of a fuzzy logic in the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism is achieved through filling the queue length and the traffic rate at each node. Through simulations, we show that our proposed technique has a better performance in terms of energy consumption compared to the basic implementation of CSMA/CA.

Broadcast transponders for low flying unmanned aerial vehicles

Abstract Present day unmanned aerial vehicle (UAV) technology in urban mobility applications is severely limited in use due to lack of reliable collision avoidance mechanisms. There are numerous applications for UAVs in urban environments, including information awareness, urban management, on-demand goods deliveries, and even parking assist, but present day legal regulations preclude their use over safety concerns, requiring presence of a pilot and restricting UAV use in urban areas. Indeed, possibility of midair collision is a significant concern in a densely populated urban area, and will only get worse as UAV use becomes widespread. Collision avoidance cannot be done effectively using onboard sensors. A transponder system like automatic dependent surveillance-broadcast (ADS-B) could be used to augment airspace awareness of UAVs, greatly reducing collision risks. SPH Engineering has successfully integrated such transponders with two of the most popular consumer class autopilots. In each case a device by Sagetech was used, the smallest commercially available transponder to date. This is a major step towards commercial UAV integration into regulated airspace. Unfortunately, ADS-B is ill suited for small low flying UAVs that are navigating unregulated airspace. While weight and power are the more obvious limitations, the use of ADS-B also requires International Civil Aviation Organization (ICAO) certification, which is both expensive and lengthy. Furthermore, at close range receiver was overwhelmed by transmit power. In a collision avoidance scenario for delivery drones short range is exactly where reliable reception is most needed. This article presents an approach, which is used to design a collision avoidance system in accordance with safety regulations of manned aviation that would be specific to small, commercial UAVs operating in unregulated airspace.

Energy efficient medium access scheme for visible light communication system based on IEEE 802.15.7 with unsaturated traffic

Visible light communication (VLC) networks can provide high-rate transmissions with advantages such as high security, low power consumption and so on. Multiple users get access to the VLC network according to the carrier sense multiple access with collision avoidance (CSMA/CA) mechanism defined by IEEE 802.15.7 media access control layer specifications. In this study, the authors propose an energy efficient medium access scheme to improve the performance of IEEE 802.15.7 CSMA/CA mechanism under unsaturated traffic conditions. Aiming at reducing the power consumed on unnecessary waiting and at improving the channel utilisation efficiency, they first apply a successive transmission scheme on the node, which has completed one successful transmission and gets the chance of transmitting the next packet without backoff delay period according to the network condition. Then, a dynamic contention window is exploited to mitigate the collisions, where they derive the optimal minimum contention window based on throughput analysis. The power consumption can be reduced with improved throughput, when both the traffic load and the number of nodes in the network are taken into account. Simulation results demonstrate that the authors’ proposed scheme outperforms the IEEE 802.15.7 CSMA/CA scheme with respect to the average power consumption, system throughput and packet dropping probability.

A performance study for the multicast collision prevention mechanism for IEEE 802.11

In IEEE 802.11 networks a data packet is delivered simultaneously to multiple receivers through the multicast paradigm. The standard defines a simple mechanism that does not implement any error-recovery mechanism, thus, the reliability of the service provided to the multicast users is penalized. This issue is more important as the number of collisions increases due to a large number of active stations and/or a high load network. In this paper we carry out a detailed optimization study of the multicast collision prevention (MCP) mechanism, a highly-efficient multicast collision avoidance mechanism for IEEE 802.11 previously introduced by the authors. Besides a more in deep explanation of MCP, this study includes a comparative performance evaluation of the optimized MCP with the IEEE 802.11 standard. Results shown that, through this optimization, the number of collisions in MCP can be made negligible for any network load.

On Optimal Device-to-Device Resource Allocation for Minimizing End-to-End Delay in VANETs

In vehicular ad hoc networks (VANETs), the IEEE 802.11p is a popular and standardized protocol for communications among vehicles and infrastructure (e.g., roadside units). However, because of a limited communication range and the randomly access nature of the carrier sense multiple access with collision avoidance (CSMA/CA) mechanism, the end-to-end delay could be high due to both store-and-catch-up (SAC) delay when the network is temporally disconnected and the channel access contention delay. In this paper, we propose a new method based on fifth-generation device-to-device (D2D) technology to improve the delay performance of VANETs. The basic idea is that direct D2D-based communications among vehicles remove the contention delay and can support longer distance. Specifically, we design a hybrid system with both D2D- and IEEE 802.11p-based communications, where the D2D links are controlled by the cellular base stations (BSs) in the overlay scheme. Each vehicle periodically checks its packet lifetime and requests the BSs to establish D2D links, if needed. The optimal resource allocation problem at the BSs is to select optimal receiver vehicles to establish D2D links and assign proper channels for them so that the total delay is minimized. The problem is equivalent to a maximum weighted independent set problem with dependent weights (MWIS-DW), which is NP-hard. To calculate the weights, an analytical approach is developed to model the expected end-to-end delay. Furthermore, we propose a greedy-based algorithm to solve this problem and develop a theoretical performance lower bound for the algorithm. The effectiveness of the algorithm under various scenarios is evaluated through simulations.

A successive transmission medium access scheme with dynamic contention window for VLC system with saturated traffic

The visible light communication (VLC) network is usually relatively small scale and can provide high-data-rate information transmission, where multiple users get access to the network according to the carrier sense multiple access with collision avoidance (CSMA/CA) mechanism specified by IEEE 802.15.7 standard. In this paper, we propose a novel dynamic contention window with successive transmission (DCW-ST) scheme to improve the performance of this channel access mechanism and to achieve better network throughput without delay performance degradation. Specifically, we propose to adjust the contention window dynamically to adapt to the time-changing network size. Further, we derive the contention window size to achieve trade-off of throughput and delay, and the minimum contention window size required for the throughput enhancement. In addition, in order to further improve the delay performance, we present a successive transmission scheme that allows the nodes which have completed one transmission successfully to get the chance of transmitting information successively according to the network condition. Simulations are performed for the VLC system in saturated traffic and compared with the theoretical performances, which demonstrate that our proposed scheme outperforms the legacy CSMA/CA of IEEE 802.15.7.

Adaptive-opportunistic Aloha: A media access control protocol for unmanned aerial vehicle–wireless sensor network systems

Recognizing that data collection in a unmanned aerial vehicle–wireless sensor network system is significantly different from that in a conventional wireless sensor network system, we propose a media access control protocol called adaptive-opportunistic Aloha for unmanned aerial vehicle–wireless sensor network systems. Based on a cross-layered design, this proposed adaptive-opportunistic Aloha protocol takes several important factors into consideration, including distribution of sensors, energy consumption, and transmission efficiency. In order for unmanned aerial vehicle to uniformly collect data from the ground sensors that are distributed in a random fashion, adaptive-opportunistic Aloha adopts a priority-based mechanism for channel assignment and collision avoidance, and importantly, the priority could be adaptively changed according to locations and distribution of the sensors. To improve energy efficiency, the adaptive-opportunistic Aloha can effectively put the sensors into the sleep mode when they do not need to send data, and they will be woken up by a beacon signal from the unmanned aerial vehicle for data transmission. Unlike opportunistic Aloha protocol, a well-known unmanned aerial vehicle–wireless sensor network media access control protocol, the adaptive-opportunistic Aloha adds a handshake into every time interval of transmission to help enhance the throughput with an acceptable level of system bit error rate. Experiment results have shown that the proposed media access control protocol can improve the overall throughput of unmanned aerial vehicle–wireless sensor network systems by more than 30% over opportunistic Aloha.

Guidance of Multi-Agent Fixed-Wing Aircraft Using a Moving Mesh Method

This paper presents a novel guidance logic for multi-agent fixed-wing unmanned aerial systems using a moving mesh method. The moving mesh method is originally designed for use in the adaptive numerical solution of partial differential equations, where a high proportion of mesh points are placed in the regions of large solution variations and few points in the rest of the domain. In this work, the positions of the aircraft are considered as mesh nodes connected to form a triangular mesh in two spatial dimensions. The outer aircraft positions are planned with the reference point algorithm. This logic provides the outer agents moving point positions that are relative to a virtual point position with the desired heading angle and velocity. The inner agents, or interior mesh nodes, are moved with a moving mesh technique to keep the whole mesh as uniform as possible. The moving mesh technique has built-in mechanisms to keep the mesh as uniform as possible and prevent nodes from crossing over or tangling. This property can be seen as an automatic internal collision avoidance mechanism. It also has explicit formulas for nodal velocities, making the technique easy to implement on computer. The mesh nodes are replaced by unmanned aerial systems with nonlinear six degrees of freedom dynamics. The centralized moving mesh guidance is complimented by a decentralized nonlinear predictive controller to control each aircraft. To validate flexibility and coherency of agents and formation, the moving point concept is used in the simulation to follow an arbitrary, linear, sinewave-like, or curvature shaped flight segments. Robustness of the algorithm is also verified where agents were affected by external wind.

Fault-Tolerant Formation Control of Unmanned Aerial Vehicles in the Presence of Actuator Faults and Obstacles

This paper presents a leader-follower type of fault-tolerant formation control (FTFC) methodology with application to multiple unmanned aerial vehicles (UAVs) in the presence of actuator failures and potential collisions. The proposed FTFC scheme consists of both outer-loop and inner-loop controllers. First, a leader-follower control scheme with integration of a collision avoidance mechanism is designed as the outer-loop controller for guaranteeing UAVs to keep the desired formation while avoiding the approaching obstacles. Then, an active fault-tolerant control (FTC) strategy for counteracting the actuator failures and also for preventing the healthy actuators from saturation is synthesized as the inner-loop controller. Finally, a group of numerical simulations are carried out to verify the effectiveness of the proposed approach.

A bandwidth-efficient and fair CSMA/TDMA based multichannel MAC scheme for V2V communications

Designing QoS-aware medium access control (MAC) scheme is a challenging issue in vehicular ad hoc networks. Proportional fairness and bandwidth utilization are among the significant requirements that should be taken into account by a MAC scheme. In this paper, a bandwidth-efficient and fair multichannel MAC protocol is proposed to address these two requirements, specifically in vehicle-to-vehicle communications. The proposed scheme is based on clustering of vehicles and exploits time division multiple access (TDMA) method alongside the carrier sense multiple access with collision avoidance mechanism to allocate DSRC-based resources in a different manner from IEEE 802.11p/IEEE 1609.4 protocols. It divides each channel into aligned dynamic-sized time frames. In each time frame, in a fully TDMA-based period, transmission opportunities are assigned to vehicles letting them have dedicated transmissions on the service and control channels. The maximum number of transmission opportunities per each frame is determined by the cluster head (CH) based on a defined optimization problem which aims at maximizing both proportional fairness and bandwidth utilization. Furthermore, the bandwidth utilization is assumed to be enhanced more through reallocation of unused transmission opportunities in each time frame, using a proposed reallocation algorithm. The proposed MAC protocol is treated as a lightweight scheme such that various types of unicast, multicast and broadcast communications are possible within the cluster without involving the CH. Evaluation results show that the proposed scheme has more than 90 % achievement in terms of proportional fairness and bandwidth utilization simultaneously, and in this case, has a considerable superiority over TC-MAC. In addition, using the proposed scheme, the satisfaction level of vehicles is preserved appropriately.

E-MAC: An evolutionary solution for collision avoidance in wireless ad hoc networks

Transmission collision is a main cause of throughput degradation and non-deterministic latency in wireless networks. Existing collision-avoidance mechanisms for distributed wireless networks are mostly based on the random backoff strategy, which cannot guarantee collision-free accesses. In this paper, we design a simple collision-avoidance MAC (E-MAC) for distributed wireless networks that can iteratively achieve collision-free access. In E-MAC, each transmitter will adjust its next transmission time according to which part of its packets suffering from the collision. And the iteration of this adjustment will quickly lead group of nodes converging to a collision-free network. E-MAC does not require any central coordination or global time synchronization. It is scalable to new entrants to the network and variable packet lengths. And it is also robust to system errors, such as inaccurate timing.

D2D: Delay-Aware Distributed Dynamic Adaptation of Contention Window in Wireless Networks

The IEEE 802.11e enhanced distributed channel access (EDCA) protocol follows class-based service differentiation for providing differentiated quality-of-service (QoS). However, its collision avoidance mechanism using backoff algorithm can be inefficient for providing improved performance with respect to throughput and channel access delay, especially in a high network configuration (i.e. number of stations) with imperfect wireless channel. The existing and emerging works have devoted considerable attention on tuning the backoff parameters for achieving optimal throughput only. The prior works do not consider the channel access delay and throughput metrics altogether for performance improvement. Additionally, in most of the cases, the optimal configuration of backoff parameters are performed by a centralized controller. In this paper, we propose a delay-aware distributed dynamic adaptation of contention window scheme, namely D2D , for the cumulative improvement of both the throughput and the channel access delay at runtime. The D2D scheme requires two ad-hoc, distributed, and easy-to-obtain estimates— delay deviation ratio and channel busyness ratio —of the present delay level and channel congestion status of the network, respectively. A key advantage of the D2D scheme is that it is compliant with the IEEE 802.11 standard, and, thus, can be seamlessly integrable with the existing wireless card. We show the integrated model of the medium access control protocol, namely D2D Channel Access ( D2DCA ), for the IEEE 802.11e networks. We further propose a two-dimensional Markov chain model of the D2DCA protocol for analyzing its theoretical performance in saturated networks with imperfect wireless channel. Theoretical comparison with the benchmark protocols establishes the effectiveness of the D2DCA protocol.

Explicit Model Following Distributed Control Scheme for Formation Flying of Mini UAVs

A centralized heterogeneous formation flight position control scheme has been formulated using an explicit model following design, based on a Linear Quadratic Regulator Proportional Integral (LQR PI) controller. The leader quadcopter is a stable reference model with desired dynamics whose output is perfectly tracked by the two wingmen quadcopters. The leader itself is controlled through the pole placement control method with desired stability characteristics, while the two followers are controlled through a robust and adaptive LQR PI control method. Selected 3-D formation geometry and static stability are maintained under a number of possible perturbations. With this control scheme, formation geometry may also be switched to any arbitrary shape during flight, provided a suitable collision avoidance mechanism is incorporated. In case of communication loss between the leader and any of the followers, the other follower provides the data, received from the leader, to the affected follower. The stability of the closed-loop system has been analyzed using singular values. The proposed approach for the tightly coupled formation flight of mini unmanned aerial vehicles has been validated with the help of extensive simulations using MATLAB/Simulink, which provided promising results.

Intelligent Internal Stealthy Attack and its Countermeasure for Multicast Routing Protocol in MANET

Multicast communication of mobile ad hoc networks is vulnerable to internal attacks due to its routing structure and high scalability of its participants. Though existing intrusion detection systems (IDSs) act smartly to defend against attack strategies, adversaries also accordingly update their attacking plans intelligently so as to intervene in successful defending schemes. In our work, we present a novel indirect internal attack on a tree-based multicast routing protocol. Such an indirect attack intelligently makes neighbor nodes drop their routing-layer unicast control packets instead of processing or forwarding them. The adversary targets the collision avoidance mechanism of the Medium Access Control (MAC) protocol to indirectly affect the routing layer process. Simulation results show the success of this attacking strategy over the existing stealthy attack in wireless ad hoc networks: detection and countermeasure (SADEC) detection system. We design a cross-layer automata-based attack on multicast routing protocols (SAMRP) attacker detection system to identify and isolate the proposed attacker. NS-2 simulation and analytical results show the efficient performance, against an indirect internal attack, of SAMRP over the existing SADEC and BLM attacker detection systems.

Distributed Random Access Scheme for Collision Avoidance in Cellular Device-to-Device Communication

In this paper, we propose a fully-distributed random access protocol for the device-to-device (D2D) communication in a cellular network. The D2D communication can provide a significant capacity gain by enabling a cellular network to offload data traffic to direct communication links between devices (i.e., D2D link). However, a D2D link can generate serious interference to other D2D links as well as cellular devices without any proper interference control mechanism. Compared to centralized resource allocation and power control schemes for the D2D communication, a distributed scheme is advantageous in that it has smaller control overhead and is more responsive to traffic demands. To protect a D2D receiver, the proposed scheme employs a collision avoidance mechanism that creates an exclusion region around the D2D receiver, where interferers are prohibited from transmitting a signal. We analyze the proposed scheme by assuming that the locations of devices follow a Poisson point process. By simulation, we show that the analysis results accurately match the simulation results and that the proposed scheme outperforms a distributed D2D scheme without collision avoidance by a very wide margin.

Comprehensive Performance Analysis of IEEE 802157 CSMA/CA Mechanism for Saturated Traffic

IEEE 802.15.7 is a physical and MAC layer standard for visible-light communication. This paper thoroughly analyzes the carrier sensing multiple access with collision avoidance (CSMA/CA) mechanism of the MAC protocol of this standard. The nodal behavior of the CSMA/CA mechanism is modeled using a Markov chain. Performance parameters are derived for saturated traffic in a star topology network. The derived performance metrics of the network include throughput, transmission probability, collision probability, packet discard probability, delay, and power consumption. Furthermore in order to improve the obtained analytic results, a semi-analytic approach is developed. To verify the obtained results, CSMA/CA is completely simulated in a MATLAB environment, and network parameters are derived and compared with analytic models. Simulation results match the analytic ones very closely, which proves the validity of the proposed model.

Enhancing the selection of backoff interval using fuzzy logic over wireless Ad Hoc networks.

IEEE 802.11 is the de facto standard for medium access over wireless ad hoc network. The collision avoidance mechanism (i.e., random binary exponential backoff—BEB) of IEEE 802.11 DCF (distributed coordination function) is inefficient and unfair especially under heavy load. In the literature, many algorithms have been proposed to tune the contention window (CW) size. However, these algorithms make every node select its backoff interval between [0, CW] in a random and uniform manner. This randomness is incorporated to avoid collisions among the nodes. But this random backoff interval can change the optimal order and frequency of channel access among competing nodes which results in unfairness and increased delay. In this paper, we propose an algorithm that schedules the medium access in a fair and effective manner. This algorithm enhances IEEE 802.11 DCF with additional level of contention resolution that prioritizes the contending nodes according to its queue length and waiting time. Each node computes its unique backoff interval using fuzzy logic based on the input parameters collected from contending nodes through overhearing. We evaluate our algorithm against IEEE 802.11, GDCF (gentle distributed coordination function) protocols using ns-2.35 simulator and show that our algorithm achieves good performance.

Research on Double Collision Avoidance Mechanism of Ships at Sea

When power driven vessels encounter at sea, they need to avoid collision. The definition of right vessel may mislead ships officers think his or her direct navigating has absolute power with this special ship. This paper will define DCPA symbols; give the cause and the method of double collision avoidance mechanism of ships at sea.