Collision Avoidance Mechanism Research Articles

An Energy Efficient Hybrid MAC Protocol With Dynamic Sleep-Based Scheduling for High Density IoT Networks

Advances in the development of low powered sensors has meant they can now provide solutions to Internet of Things (IoT) networks that suffer from restricted power supply and a lack of resource facilities. In this paper, a hybrid time division multiple access (TDMA)-carrier sense multiple access with a collision avoidance mechanism (CSMA/CA) medium access control (MAC) protocol has been proposed that efficiently utilizes the energy of the nodes and dynamically adapts the sleep/wake-up periods according to the variance in the network loads. This hybrid protocol first schedules the TDMA time slots (TDMA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">slots</sub> ), and then allocates each slot to a group of devices that compete for the medium using the CSMA/CA. This case is different from the traditional CSMA/CA-TDMA hybrid protocol, in which all the devices compete to access the channel, following which, each successful device is allocated an individual time slot. At the commencement of each superframe, the base station broadcasts a scheduler table, which includes network grouping information that is used by the IoT devices to categorize themselves into wake-up and sleep groups. To reduce the number of collisions or channel access failures, this information permits only one group to compete for each TDMA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">slot</sub> . A 3-D Markov model is used to develop a per user stochastic behavior for the proposed hybrid MAC protocol-based adaptable sleep mode. The simulation results demonstrate the effectiveness of the proposed protocol, which improves the network throughput and enhances energy conservation by 40%-60% more than the IEEE 802.15.4-based MAC protocol.

Formation Control and Distributed Goal Assignment for Multi-Agent Non-Holonomic Systems

This paper presents control algorithms for multiple non-holonomic mobile robots moving in formation. Trajectory tracking based on linear feedback control is combined with inter-agent collision avoidance. Artificial potential functions (APF) are used to generate a repulsive component of the control. Stability analysis is based on a Lyapunov-like function. Then the presented method is extended to include a goal exchange algorithm that makes the convergence of the formation much more rapid and, in addition, reduces the number of collision avoidance interactions. The extended method is theoretically justified using a Lyapunov-like function. The controller is discontinuous but the set of discontinuity points is of zero measure. The novelty of the proposed method lies in integration of the closed-loop control for non-holonomic mobile robots with the distributed goal assignment, which is usually regarded in the literature as part of trajectory planning problem. A Lyapunov-like function joins both trajectory tracking and goal assignment analyses. It is shown that distributed goal exchange supports stability of the closed-loop control system. Moreover, robots are equipped with a reactive collision avoidance mechanism, which often does not exist in the known algorithms. The effectiveness of the presented method is illustrated by numerical simulations carried out on the large formation of robots.

Deconfliction in High-Density Unmanned Aerial Vehicle Systems

Small unmanned aerial vehicles play increasingly important roles in many industries and organizations in the United States and around the globe. As usage becomes more widespread, airspace will become increasingly crowded. These high-density unmanned aerial vehicle (UAV) situations will pose many unique challenges, including in conflict resolution. Using agent-based models, conflict resolution and the well-clear and action-distance concepts for small multirotor UAVs in dense environments were explored. Specifically, the safety and efficiency of several collision-avoidance mechanisms under different possible densities, accelerations, and action distances were investigated. The results suggest that selecting appropriate action distances and collision-avoidance mechanisms will be vital to maintaining safety and efficiency. Interestingly, excessive action distances quickly degrade performance: using a simple method under high-density conditions (), well-clear distances above approximately 750 m have extremely low efficiency ( as many deliveries accomplished in 5000 simulation hours compared to lower distances). More advanced algorithms also suffer from low efficiency at higher () response distances. Different definitions for near-midair collisions and their effects on system safety and well-clear distance are discussed.

SPP 2.0: Simple Packet Protocol for ultra low cost wired networks

This article presents the Simple Packet Protocol version 2.0 (SPP 2.0). The protocol core is technology-independent and it is designed to provide communication for low data rate wired bus networks. The protocol is characterized by its low hardware requirements which allows for implementing it on embedded systems with limited hardware resources and achieving a very low price per node. An important feature of the SPP 2.0 is that its design addresses the multi-master asynchronous communication with flexible addressing model. Thanks to an effective collision avoidance and detection mechanism, the protocol is reliable under heavy network load conditions even without any additional feedback from a receiver. The presented SPP 2.0 is designed to provide wired communication for embedded systems connected with economical and maintenance-free wired network. SPP 2.0 systems can be easily integrated into larger networks, including IoT applications. The possible use cases for the protocol include: wired sensor and actuator networks, building automation systems, and modular embedded hardware platform prototyping.

A Low-Cost Monocular Vision-Based Obstacle Avoidance Using SVM and Optical Flow

Development of low-cost robots with the capability to detect and avoid obstacles along their path is essential for autonomous navigation. These robots have limited computational resources and payload capacity. Further, existing direct range-finding methods have the trade-off of complexity against range. In this paper, we propose a vision-based system for obstacle detection which is lightweight and useful for low-cost robots. Currently, monocular vision approaches used in the literature suffer from various environmental constraints such as texture and color. To mitigate these limitations, a novel algorithm is proposed, termed as Pyramid Histogram of Oriented Optical Flow ([Formula: see text]-HOOF), which distinctly captures motion vectors from local image patches and provides a robust descriptor capable of discriminating obstacles from nonobstacles. A support vector machine (SVM) classifier that uses [Formula: see text]-HOOF for real-time obstacle classification is utilized. To avoid obstacles, a behavior-based collision avoidance mechanism is designed that updates the probability of encountering an obstacle while navigating. The proposed approach depends only on the relative motion of the robot with respect to its surroundings, and therefore is suitable for both indoor and outdoor applications and has been validated through simulated and hardware experiments.

EIMAC: a multi‐channel MAC protocol towards energy efficiency and low interference for WBANs

Wireless body area networks (WBANs) can be widely used in wireless medical, motion detection etc. However, the existence of interference results in the increase in energy consumption and delay. To mitigate interference, nodes are prevented from using the same or similar spectrum resources by adopting multi-channel media access control (MAC) protocols. Here, the authors propose a multi-channel MAC protocol towards energy efficiency and low interference (EIMAC). Firstly, the states of each channel are clarified by the channel mapping mechanism. A novel channel selection strategy, considering the unfairness between high or low priorities, then is carried out. After that, considering the characteristics of node including residual energy, user priority, and data volume, the authors propose a low energy consumption enabled transmission mechanism. Lastly, the authors utilise a novel collision avoidance mechanism to reduce the collision probability of packets. Numerical results show that EIMAC significantly enhance the performance of WBANs in terms of delay, throughput, and energy consumption.

Collision Avoidance and Path Following Control of Unmanned Aerial Vehicle in Hazardous Environment

Recent years have seen a rapidly increasing number of applications using unmanned aerial vehicles (UAVs). In order to greatly enhance the capabilities of UAVs working along with other manned aerial vehicles in more cluttered, hazardous, and sophisticated environments without violating the aviation traffic regulations, this paper proposes a new hybrid collision avoidance method along with a modified path following approach. The proposed hybrid collision avoidance scheme consists of a global path planner and a local collision avoidance mechanism for the purpose of greatly reducing computational efforts raised by global method, while ensuring the safe and satisfactory performance of collision avoidance. The global path planner is designed using rapidly exploring random tree (RRT), and the dynamics of UAV are also taken into consideration to generate a feasible and optimal path. The light-computational local collision avoidance mechanism, which can partially modify the globally planned path in dynamic environment when any hazardous obstacles blocking the desired path, is developed based on an intelligent fuzzy logic approach by integrating a set of decision making strategies and several aviation traffic regulations. Regarding the presented path following methodology, an improvement to the previous cross-track error calculation mechanism is made by employing the extended Kalman filter (EKF) to estimate the cross-track error. Finally, design of height and attitude control system of UAV is also addressed. Extensive simulation and experimental studies on a series of scenarios with both static and dynamic objects are conducted to demonstrate the effectiveness of the proposed hybrid collision avoidance approach and cross-track error prediction based path following method.

E-LBT: an Enhanced Listen Before Talk Mechanism for Collision Avoidance in an LTE-U and WiFi Coexistence System

This paper considers the hidden-node problem in downlink transmission of an LTE-U and WiFi coexistence system operating in unlicensed bands. An enhanced LTE-U node structure is first presented, in which a WiFi module is introduced in an LTE-U eNB, and the RRC and MAC functional blocks in both LTE-U eNB and LTE-U UE are redefined. The purpose is to enable information exchange between an LTE-U node and a WiFi node in order to handle the hidden-node problem. Based on the enhanced LTE-U node structure, an enhanced listen-before-talk (e-LBT) mechanism is further presented, which incorporates an RTS/CTS handshaking procedure in the basic LBT mechanism. To support RTS/CTS handshaking, the relevant information that needs to be exchanged between e-MACWiFi in the WiFi module and e-RRC in the LTE-U module of an LTE-U node is identified, and the message format to be exchanged between e-MACWiFi and e-RRC is defined. Simulation results show that the proposed e-LBT mechanism can significantly improve the performance of the coexistence system in terms of the LTE-U system throughput and WiFi system throughput as compared with the basic LBT mechanism.

A Network Equivalent-Based Algorithm for Adaptive Parameter Tuning in 802.15.4 WSNs.

Previous studies have shown that in many wireless sensor network applications the IEEE 802.15.4 carrier sense multiple access with collision avoidance (CSMA/CA) mechanism with default parameters cannot guarantee the constraints of reliability, time efficiency, or energy efficiency. Although many adaptive parameter tuning algorithms have been proposed, many of them cannot correctly identify the changes of the network condition and are unable to effectively perform the parameter tuning operation. Considering the randomness that CSMA/CA brings about, for most of the proposed algorithms, it is a challenge to distinguish significant violations that were caused by actual changes of the network from the general fluctuations that were due to CSMA/CA. In this paper, we propose a lightweight algorithm called the network equivalent adaptive parameter tuning (NEAPT) algorithm. It is fully distributed and can work without any predefined information or acknowledgement. NEAPT not only takes reliability as an evaluation of a network condition, but it proposes a synthetic value, called the equivalent node number, and takes it as another reference for a network condition. Simulation results show that by taking both reliability and the equivalent node number into consideration, NEAPT can effectively identify the network changes and provide adequate and steady performances for wireless sensor networks (WSNs) in both stationary and dynamic conditions.

Asymmetric Propagation Delay-Aware TDMA MAC Protocol for Mobile Underwater Acoustic Sensor Networks

The propagation delay in mobile underwater acoustic sensor network (MUASN) is asymmetric because of its low sound propagation speed, and this asymmetry grows with the increase in packet travel time, which damages the collision avoidance mechanism of the spatial reuse medium access control (MAC) protocols for MUASN. We propose an asymmetric propagation delay-aware time division multiple access (APD-TDMA) for a MUASN in which periodic data packet transmission is required for a sink node (SN). Collisions at the SN are avoided by deferring data packet transmission after reception of a beacon packet from the SN, and data packets are arrived at the SN in a packet-train manner. The time-offset, which is the time for a node to wait before the transmission of a data packet after reception of a beacon packet, is determined by estimating the propagation delay over two consecutive cycles such that the idle interval at the SN is minimized, and this time-offset is announced by the beacon packet. Simulation results demonstrate that the APD-TDMA improves the channel access delay and the channel utilization by approximately 20% and 30%, respectively, compared with those of the block time bounded TDMA under the given network conditions.

Collision Avoidance Mechanism for Symmetric Circular Formations of Unitary Mass Autonomous Vehicles at Constant Speed

Collective motion is a promising field that studies how local interactions lead groups of individuals to global behaviors. Biologists try to understand how those subjects interplay in nature, and engineers are concerned with the application of interaction strategies to mobile vehicles, satellites, robots, etc. There are several models in literature that employ strategies observed in groups of beings in nature. The aim is not to literally mimic them but to extract suitable strategies for the chosen application. These models, constituted of multiple mobile agents, can be used in tasks such as data collection, surveillance and monitoring. One approach is to use phase-coupled oscillators to design the mobile agents, in which each member is an oscillator and they are coupled according to an interconnection network. This design usually does not keep track and handle the possible collisions within the group, and real applications obviously must manage these situations to prevent the equipment from crashing. This paper introduces a collision avoidance mechanism to a model of particles with phase-coupled oscillators dynamics for symmetric circular formations.

Collision Avoidance Effects on the Mobility of a UAV Swarm Using Chaotic Ant Colony with Model Predictive Control

The recent development of compact and economic small Unmanned Aerial Vehicles (UAVs) permits the development of new UAV swarm applications. In order to enhance the area coverage of such UAV swarms, a novel mobility model has been presented in previous work, combining an Ant Colony algorithm with chaotic dynamics (CACOC). This work is extending CACOC by a Collision Avoidance (CA) mechanism and testing its efficiency in terms of area coverage by the UAV swarm. For this purpose, CACOC is used to compute UAV target waypoints which are tracked by model predictively controlled UAVs. The UAVs are represented by realistic motion models within the virtual robot experimentation platform (V-Rep). This environment is used to evaluate the performance of the proposed CACOC with CA algorithm in an area exploration scenario with 3 UAVs. Finally, its performance is analyzed using metrics.

Throughput Optimization in WLAN/Cellular Integrated Network Using Partially Overlapped Channels

The wireless network that integrates a heterogeneous cellular network and a WLAN is referred to as a WLAN/cellular integrated network (WCIN). In a fourth generation WCIN, in order to achieve collision-avoidance between the LTE-A and IEEE 802.11 family, some interference-free mechanisms, such as carrier sense adaptive transmission and listen-before-talk, are proposed. However, the interference-free medium access mechanisms leave some unexploited partially overlapped 802.11ac channels, which result in a waste of spectrum. In this paper, we propose an interference-tolerant medium access method to optimize the WCIN throughput by utilizing those partially overlapped channels (POCs). First, we show the feasibility of enhancing WLAN throughput by utilizing 802.11ac POCs in a WCIN. Second, we mathematically model the partial overlap when an 802.11ac channel is partially overlapping with an LTE-A component carrier. Third, we propose an interference-tolerant medium access mechanism to optimize the WCIN throughput. The interference-tolerant one ensures that the interference to LTE-A users is tolerable in a given WCIN. Finally, we construct a hardware-in-the-loop testbed to evaluate and compare our proposed mechanism with three other state-of-the-art mechanisms. The experimental results show that our approach achieves at most 39% more throughput than one of the state-of-the-art collision-avoidance mechanisms regarding the entire WCIN.

Adapted Speed Mechanism for Collision Avoidance in Vehicular Ad hoc Networks Environment

The disrespect of the safety distance between vehicles is the cause of several road accidents. This distance cannot certainly be estimated at random because of some physical rules to be calculated. The more speed gets higher, the more stopping distance increases, mainly in danger case. Thus, the difference between two vehicles must be calculated accordingly. In this paper, we present a mechanism called Adapted Speed Mechanism (ASM) allowing the adaptation of speed to keep the necessary safety distance between vehicles. This mechanism is based on VANET network operation and Multi Agent System integration to ensure communication and collaboration between vehicles. So, it is necessary to perform real-time calculations to make adequate and relevant decisions.

Efficient and Agile Carrier Sense Multiple Access in Capillary Machine-to-Machine Communication Networks

This paper presents an intelligent collision avoidance mechanism within a carrier sense multiple access framework to instill efficiency and agility in random access performance in capillary machine-to-machine communication networks. Under a hierarchical infrastructure-based setting, a resourceful gateway/coordinator node serves as the conduit between the resource-limited end-nodes and the application/service level network nodes. The coordinator periodically executes the dynamic algorithm, which determines the appropriate backoff window size for the present estimated load, and the end-nodes are opportunistically updated with this window size. Based on key analytic properties derived from a stochastic model of the associated protocol, the intelligent collision avoidance mechanism is shown to be efficient in aggregate throughput, equitable among the nodes regarding packet service times and energy efficiency, and agile in responding to intermittent node activity and traffic elasticity/burstiness. Numerical results show that the intelligent collision avoidance mechanism significantly outperforms the usually deployed binary exponential backoff in most of the settings, while matching a normative protocol fair closely.

Kinetic description of collision avoidance in pedestrian crowds by sidestepping

In this paper we study a kinetic model for pedestrians, who are assumed to adapt their motion towards a desired direction while avoiding collisions with others by stepping aside. These minimal microscopic interaction rules lead to complex emergent macroscopic phenomena, such as velocity alignment in unidirectional flows and lane or stripe formation in bidirectional flows. We start by discussing collision avoidance mechanisms at the microscopic scale, then we study the corresponding Boltzmann-type kinetic description and its hydrodynamic mean-field approximation in the grazing collision limit. In the spatially homogeneous case we prove directional alignment under specific conditions on the sidestepping rules for both the collisional and the mean-field model. In the spatially inhomogeneous case we illustrate, by means of various numerical experiments, the rich dynamics that the proposed model is able to reproduce.

Efficient Anonymous Communication in SDN-Based Data Center Networks

With the rapid growth of application migration, the anonymity in data center networks becomes important in breaking attack chains and guaranteeing user privacy. However, existing anonymity systems are designed for the Internet environment, which suffer from high computational and network resource consumption and deliver low performance, thus failing to be directly deployed in data centers. In order to address this problem, this paper proposes an efficient and easily deployed anonymity scheme for software defined networking-based data centers, called mimic channel (MIC). The main idea behind MIC is to conceal the communication participants by modifying the source/destination addresses, such as media access control (MAC) and Internet protocol (IP) address at switch nodes, so as to achieve anonymity. Compared with the traditional overlay-based approaches, our in-network scheme has shorter transmission paths and less intermediate operations, thus achieving higher performance with less overhead. We also propose a collision avoidance mechanism to ensure the correctness of routing, and three mechanisms to enhance the traffic-analysis resistance. To enhance the practicality, we further propose solutions to enable MIC co-existing with some MIC-incompatible systems, such as packet analysis systems, intrusion detection systems, and firewall systems. Our security analysis demonstrates that MIC ensures unlinkability and improves traffic-analysis resistance. Our experiments show that MIC has extremely low overhead compared with the base-line transmission control protocol (TCP) (or secure sockets layer (SSL)), e.g., less than 1% overhead in terms of throughput. Experiments on MIC-based distributed file system show the applicability and efficiency of MIC.

Smart Collision Avoidance and Hazard Routing Mechanism for Intelligent Transport Network

The smart vehicular ad-hoc network is the network that consists of vehicles for smooth movement and better management of the vehicular connectivity across the given network. This research paper aims to propose a set of solution for the VANETs consisting of the automatic driven vehicles, also called as the autonomous car. Such vehicular networks are always prone to collision due to the natural or un-natural reasons which must be solved before the large-scale deployment of the autonomous transport systems. The newly designed intelligent transport movement control mechanism is based upon the intelligent data propagation along with the vehicle collision and traffic jam prevention schema [8], which may help the future designs of smart cities to become more robust and less error-prone. In the proposed model, the focus is on designing a new dynamic and robust hazard routing protocol for intelligent vehicular networks for improvement of the overall performance in various aspects. It is expected to improve the overall transmission delay as well as the number of collisions or adversaries across the vehicular network zone.

Hybrid Collision Avoidance-Tree Resolution for M2M Random Access

Wireless machine-to-machine (M2M) communication with synchronized traffic patterns plays an important role in many aircraft systems. Recent research has separately examined collision avoidance mechanisms, such as presmoothing and access barring, as well as collision resolution mechanisms, such as tree resolution, for M2M random access. In contrast, we examine the combination of collision avoidance and tree collision resolution into hybrid M2M random access protocols in the context of the popular Long-Term Evolution wireless system.

A CSMA-based MAC protocol for WLANs with automatic synchronization capability to provide hard quality of service guarantees

The carrier sensing multiple access with collision avoidance (CSMA/CA) protocol is a widely-adopted MAC protocol in the current wireless networks, but the quality of service (QoS) cannot be guaranteed due to random access. Investigations reveal that the collision avoidance mechanism which relies on the binary exponential backoff scheme is the root cause of QoS issue. Therefore, this paper first proposes a CSMA with automatic synchronization (CSMA/AS) MAC protocol to mitigate the collision problem caused by random access. By CSMA/AS, all the stations can be synchronized and then served in a round-robin fashion without contention collisions. Even if a new station joins, the wireless network can also quickly converge and go back to the synchronized state. The simulation results show that the proposed CSMA/AS protocol can fully mitigate the issues caused by random access, such as the severe contention collisions and large delay variation. In addition, this paper demonstrates how to provide hard QoS guarantees, such as fairness, rate guarantee, and delay guarantee, which cannot be achieved by the existing CSMA-based protocols. Because CSMA/CA does not rely on any additional control message, the implementation complexity of CSMA/AS is similar to that of legacy CSMA/CA protocols.