Collision Resolution Research Articles

A Collision Resolution Protocol for Random Access in Massive MIMO

In 5G and beyond wireless scenarios, it is expected to support tremendous amount of communicating machines. With an exponential increase of machine-to-machine (M2M) system deployments, efficient approaches to massive access by a large number of devices are to be studied. In this paper, we propose a massive multiple-input multiple-output (MIMO) based grant-free random access (RA) with resolution of preamble collision for massive access. Based on the channel hardening and favorable propagation characteristics of massive MIMO, collided signals processed at the base station (BS) can be viewed as a variation of superposition modulation, and are to be recovered by successive interference cancellation (SIC) techniques. Besides, taking into consideration the effect of pass loss and fractional power control (FPC), analytic expressions of success probability of the proposed collision resolution with conjugate beamforming (CB) and zero-forcing beamforming (ZFB) are derived. With simulation results, we verify the analyses and show that the proposed protocol can resolve most preamble collisions.

A beamformer for multiple packet reception based on blank intervals. Part I: The flat-fading channel case

Multiple packet reception (MPR) has become a promising technique to considerably improve the throughput in a wireless network due to its provided collision resolution capability. In this paper we present a blind algorithm to separate several data packets, up to an ambiguity in the extracted signal phase, exploiting its asynchronous nature, which in general has been considered an undesirable effect in wireless networks. The separation algorithm consists on finding the minor subspace of each data packets in the received mixed signal. This leads to an equalizer which minimizes multiple access interference (MAI), on the desired data packet. It can be adapted in a simple form to perform in synchronous scenarios without the necessity of further processing compared to other techniques such as matrix decomposition for signal projection or the use of CMA or KMA or some of their derived algorithms for signal separation.

A Grant-Based Random Access Protocol in Extra-Large Massive MIMO System

Extra-large massive multiple-input multiple-output (XL-MIMO) systems is a new concept, where spatial non-stationarities allow activate a high number of user equipments (UEs). This letter focuses on a grant-based random access (RA) approach in the novel XL-MIMO channel scenarios. Modifications in the classical Strongest User Collision Resolution (SUCRe) protocol have been aggregated to explore the visibility regions (VRs) overlapping in XL-MIMO. The proposed grant-based RA protocol takes advantage of this new degree of freedom for improving the number of access attempts and accepted UEs. As a result, the proposed grant-based protocol for XL-MIMO systems is capable of reducing latency in the pilot allocation step.

The problem of resolution of legal collisions and conflict in the context of property rights protection

The article discusses the problems of resolving legal collisions and conflicts in the context of protecting property rights. The authors of the article examined the problems of the conceptualization of legal disputes, conflict resolution as a legal science, the specificity of legal conflicts expressed in a whole system of essential features. It is concluded that legal conflict is a relatively independent category of legal conflictology and constitutes a contradictory unity of legal dispute and opposition of legislative acts. The distinction is drawn between a legal dispute and a legislative conflict. The correlation of the concept and essence of legal disputes and legal conflict taking into account the diversity of approaches to their content. Consideration of the system-forming features of legal conflictology as a legal science allowed researchers to identify its specifics. Legal conflictology emphasizes the importance of legal components in social contradictions and the possibility of using legal norms to control the course of conflict and its resolution. The article analyzes in detail the main civil law methods of protecting property rights. The authors of the article determined the actualization of the problem of applying the legal methods of protecting property rights and other property rights, analyzed the signs of property law, civil law methods of protecting property rights and other property rights, highlighted the specificity of the species characteristics of civil lawsuits.

Optimization of Ship-borne Anti-collision Sounding System Based on Internet of Things and Full Convolution Neural Network

Shu, J.; Deng, M., and He, J., 2020. Optimization of ship-borne anti-collision sounding system based on Internet of Things and full convolution neural network. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 757–761. Coconut Creek (Florida), ISSN 0749-0208.The traditional ship-borne anti-collision sounding system has low resolution of detection image and collision of detection signals, which affects the accuracy of detection results. For this reason, this paper combines the Internet of Things and full convolution neural network method to optimize the ship-borne anti-collision sounding system. The resolution of detection image is improved by full convolution neural network method. On the basis of the above, the modular reconstruction of anti-collision sounding system is carried out. The system takes STM32F103 VET6 embedded chip as the control core of the system, uses CC2530 to implement ZigBee wireless network communication, and integrates ZigBee wireless communication technology and embedded technology. Now anti-collision and bathymetry function, aiming at the problem of signal collision of each node in wireless network, anti-collision algorithm is introduced to optimize the system, to prevent signal collision when receiving, and to ensure the synchronization and accuracy of the whole system. Experiments show that the system has the advantages of low energy consumption, fast response and high accuracy.

Collision decoding and reporting: A new collision resolution approach using full-duplex radio in WLANs

Full-duplex radio is a next-generation wireless communication technology, because it allows signals to be sent and received simultaneously within the same channel by cancelling self-interference signals. Thus, many full-duplex medium access control (MAC) protocols have been proposed to utilize the full-duplex radio. For backward compatibility with legacy stations (STAs), most of them operate based on the IEEE 802.11 distributed coordination function, which is a competition-based distributed method. Consequently, collisions among STAs are still an important problem in designing a full-duplex MAC protocol. Unlike traditional half-duplex radio, full-duplex radio can sense incoming signals during transmission. Therefore, a novel collision resolution method suitable for the full-duplex radio is required. In this paper, we propose a new collision resolution method called collision decoding and reporting (CDR). In this method, if a collision is detected, each transmitter STA tries to decode another transmitter STA’s frame by cancelling self-interference signals, and memorizes a decoded transmission information. Afterwards, it reports the decoded transmission information to access point (AP) by using its data frame. As a result, the AP knows that another transmitter STA has data to transmit, and offers a transmission opportunity to another transmitter STA without competition. Therefore, the throughput of wireless local area networks increases by reducing competition overheads such as idle back-off slots and collisions. To evaluate the performance of the CDR method, analytical evaluations and simulations have been performed. We observed that the proposed method achieves a throughput gain compared to existing collision resolution methods.

New Techniques for Pairwise Symmetry Breaking in Multi-Agent Path Finding

We consider two new classes of pairwise path symmetries which appear in the context of Multi-Agent Path Finding (MAPF). The first of them, corridor symmetry, arises when two agents attempt to pass through the same narrow passage in opposite directions. The second, target symmetry, arises when the shortest path of one agent passes through the target location of a second agent after the second agent has already arrived at it. These symmetries can produce an exponential explosion in the space of possible collision resolutions, leading to unacceptable runtimes even for state-of-the-art MAPF algorithms such as Conflict-Based Search (CBS). We propose to break these symmetries using new reasoning techniques that: (1) detect each class of symmetry and (2) resolve them by introducing specialized constraints. We experimentally show that our techniques can, in some cases, more than double the success rate of CBS and improve its runtime by one order of magnitude.

A scalable computational platform for particulate Stokes suspensions

We describe a computational framework for simulating suspensions of rigid particles in Newtonian Stokes flow. One central building block is a collision-resolution algorithm that overcomes the numerical constraints arising from particle collisions. This algorithm extends the well-known complementarity method for non-smooth multi-body dynamics to resolve collisions in dense rigid body suspensions. This approach formulates the collision resolution problem as a linear complementarity problem with geometric ‘non-overlapping’ constraints imposed at each time-step. It is then reformulated as a constrained quadratic programming problem and the Barzilai-Borwein projected gradient descent method is applied for its solution. This framework is designed to be applicable for any convex particle shape, e.g., spheres and spherocylinders, and applicable to any Stokes mobility solver, including the Rotne-Prager-Yamakawa approximation, Stokesian Dynamics, and PDE solvers (e.g., boundary integral and immersed boundary methods). In particular, this method imposes Newton's Third Law and records the entire contact network. Further, we describe a fast, parallel, and spectrally-accurate boundary integral method tailored for spherical particles, capable of resolving lubrication effects. We show weak and strong parallel scalings up to 8×104 particles with approximately 4×107 degrees of freedom on 1792 cores. We demonstrate the versatility of this framework with several examples, including sedimentation of particle clusters, and active matter systems composed of ensembles of particles driven to rotate.

Secure multi-party collision resolution protocol for air traffic control

Secure multi-party collision resolution protocol for air traffic control

Achieving Fair Random Access Performance in Massive MIMO Crowded Machine-Type Networks

The use of massive multiple-input multiple-output (MIMO) to serve a crowd of user equipments (UEs) is challenged by the deficit of pilots. Assuming that the UEs are intermittently active, this problem can be addressed by a shared access to the pilots and a suitable random access (RA) protocol. The strongest-user collision resolution (SUCRe) is a previously proposed RA protocol that often privileges the UEs closer to the base station (BS). In contrast, we propose a novel RA protocol using a decentralized pilot power allocation method that aims at a fairer performance. The proposed access class barring with power control (ACBPC) protocol allows each UE to estimate, without additional overhead, how many UEs collided for the chosen pilot and calculate an ACB factor, which is then used to determine the pilot retransmission probability in the next protocol step. The results show that the proposed ACBPC protocol is superior to SUCRe in terms of providing a fair connectivity for very crowded networks, although still being distributed and uncoordinated as the original SUCRe protocol.

A Comment on Eq. (20a) in “Centralized Random Backoff for Collision Resolution in Wi-Fi Networks”

It was recently noted that the analytical expression (20a) in the paper titled “Centralized Random Backoff for Collision Resolution in Wi-Fi Networks” is incorrect, although the analytical results presented in the figures (e.g. Fig. 14b) are correct. The error looks significant. In order to correct equation (20a), it should be re-written as presented in this comment. This modification is essential in order to exactly produce the analytic results in the figures in the paper.

An energy efficient distributed queuing random access (EE-DQRA) MAC protocol for wireless body sensor networks

In wireless sensor networks, a significant amount of energy is consumed by the sensor nodes during data packet transmission and reception. An IEEE 802.15.4 MAC protocol is not able to completely satisfy all the requirements of wireless body sensor networks (BSNs) in a healthcare environment. Hence there is a demand for the design of a new scalable and energy saving MAC protocols. In this paper the challenging healthcare requirements are considered and based upon these requirements, an energy efficient distributed queuing random access (EE-DQRA) MAC protocol is proposed for BSN scenarios which utilizes the concept of distributed queuing for enhanced radio channel utilization. The theoretical analysis of energy efficient EE-DQRA MAC protocol is being carried out systematically considering the limitations of IEEE 802.15.4 and DQ-MAC protocol. Further, EE-DQRA performance is validated with IEEE 802.15.4 system parameters using computer simulations. The effect of relative traffic load and payload length on the energy consumption, delay and throughput are also analyzed. The simulation results shows that the proposed EE-DQRA MAC with M/M/K queuing has better energy performance than the existing DQ-MAC and IEEE 802.15.4 MAC in BSN scenarios due to collisionless transmission in the data transmission queuing (DTQ) module while keeping the control packet overhead smaller in collision resolution queuing (CRQ) module. It is also evident that EE-DQRA requires a minimum delay in comparison to IEEE802.15.4 and DQ-MAC, due to overhead minimization and M/M/K queuing utilization in DTQ system.

For Massive Access With Sporadic Traffic in M2M Communication: Collision Avoidance or Collision Resolution

To meet the increased requirement of machine-to-machine (M2M) communication, the potential to support massive access with sporadic traffic in uplink of two typical methods, one is the collision avoidance (CA) method at the user side, and the other is the collision resolution (CR) method at the base station (BS) side, is explored under grant-free protocol in this paper. A comprehensive study from MAC layer is conducted under the proposed distributed queue model, which describes the queue behavior of each device and the interaction between devices under grant-free protocol. The upper bounds of the throughput and the success probability of CA method are derived and the closed forms of the throughput and the success probability of a typical CR method, known as power domain multiple access (PDMA), are derived. The performance is further analyzed besides delay and stability. Through simulations, we validate that there is a hopeful upper bound for CA method, and the performance of PDMA can be flexibly improved with variable power level, which has a similar effect with channel extension. On the other hand, we note that grant-free protocol is suitable for access when the input traffic is below a critical threshold, otherwise packets would be blocked at the queue and the delay would increase infinitely.

Dynamic Backoff Collision Resolution for Massive M2M Random Access in Cellular IoT Networks

The deployment of machine-to-machine (M2M) communications on cellular networks provides ubiquitous services to Internet-of-Things (IoT) systems. Cellular networks have been chosen as the best infrastructure for M2M communications due to the wide coverage and spectral efficiency. However, with the increased number of devices connecting to the network, massive number of devices are expected to simultaneously access the network resources. This massive access results in excessive congestion and collisions in the random access channel (RACH) which causes major degradation in systems performance. This article focuses on resolving the RACH collisions during the massive access scenarios for cellular M2M communications. We propose a collision resolution scheme using the backoff procedure which dynamically adjusts the backoff indicator (BI) based on the number of backlog devices and the available resources. The proposed scheme is integrated with three well-known random access schemes; standard random access (SRA), static access class barring (ACB) and dynamic access class barring (DAB). Furthermore, the paper presents an analysis for access success probability based on the dynamic backoff procedure. The optimal value of BI that achieves the highest access success probability is derived for the three different schemes. The analysis and simulation results indicate that the dynamic value of BI achieves approximately 99.9% access success rate with a slight increase in access delay of around 10%, which is considered a reasonable increment for delay-tolerant applications during the massive arrivals scenarios.

ІННОВАЦІЙНЕ РІШЕННЯ ДЛЯ LEO-СИСТЕМИ З АРХІТЕКТУРОЮ «РОЗПОДІЛЕНОГО СУПУТНИКА»

An innovative solution for practical implementation in a LEO system with a "distributed satellite" architecture that can be used to provide low-orbital spacecraft communications with ground stations and users of 5G / IoT satellite services is proposed. The essence of the proposed development in the system of low-orbital satellite communication with FC-architecture is that to reduce the delay in signaling to consumers and the probability of overloading the network into a prospective system of low-orbital satellite communication, which contains artificial Earth satellites, each of which functions in Earth orbit and equipped with onboard repeaters, inter-satellite communications, a network of ground-based communication and control systems for artificial satellites of the Earth, a grouping of low-orbiting space their devices (LEO-system), which includes the grouping of root (leading) satellites and satellites-repeaters (slave), around each root satellite is formed micro-grouping of satellites-repeaters, and functions of the root satellite in the selected orbital phase of the orbital -or micro-satellites that are connected to the annular network by communication lines between satellites, and - functions of satellites-repeaters - kubsat, new is the introduction of a multilevel boundary cloud system, which is a heterogeneity well distributed computing cloud structure. At the same time, the boundary clouds of the multilevel system are connected by ultra-high-speed wireless terahertz radio lines and wireless optical communication systems. The technique of estimation of access time in the proposed structure of "fog computing" on the basis of the model of access in "fog computing" with the resolution of collisions of data sources implementing the survey mode is presented

Asynchronous Blind Network-Assisted Diversity Multiple Access

We present a blind collision resolution algorithm in slow fading channels based on retransmission diversity. The algorithm neither assumes packet nor symbol synchronization of the different users and it does not demand estimates of the arrival times of the collided signals. The proposed scheme works independently of the relative alignment of the packets, so it can also resolve synchronous collisions. The decoding complexity does not scale with the packet size and thus does not burden the receiver. In the blocking mode, the algorithm achieves high throughput and low queuing delay similar to synchronous network division multiple access (NDMA) protocols. In the non-blocking mode, there is longer queuing delay of the packets before transmission, but the throughput is still high due to faster accumulation of the buffered packets at the transmitters.

Backoff-Based Coded Random Access for Intelligent Connected Vehicles

The rapid growth in the scale of the intelligent connected vehicles (ICVs) brings about the need for novel random access schemes that realize collision avoidance and reliable communication. The coded random access (CRA) scheme utilizes successive interference cancellation (SIC) across slots to enable the extraction of multiple users' packets from the collision slots and proves to be an efficient solution to collision resolution. In this paper, we propose a random backoff-based CRA scheme to achieve a tradeoff between the access success probability and access delay for CRA. Specifically, we partition the traditional CRA frame into subframes, so that the user access delay is reduced to the same scale of the subframe length. In addition, the backoff operation among subframes is introduced so that access failures originated from the subframe length limit can be reduced with the retransmission in subsequent subframes. In particular, we consider practical Nakagami-m fading channel in the CRA performance analysis and take into account the capture effect in the iterative interference cancellation process. Simulation results show that backoff-based CRA can significantly reduce the average access delay without severe negative effect on the access success probability for moderate system load compared with traditional CRA. Comparisons with the state-of-the-art non-orthogonal random access (NORA) scheme proposed for 5G indicates that backoff-based CRA provides a feasible solution for random access of large-scale ICVs.

Hybrid Zigbee RFID model for tag detection and energy tradeoff

Active RFID systems are utilised widely in extensive applications and have limited radio communication. Collisions subsist during the tag detection process of the reader which cause lassitude of tag's battery life. Surmounting these collisions and incrementing tag identification rate with remarkable high throughput remains as a key challenge in RFID based applications. Zigbee network provides multi hop data transmission and covers long distances. In this paper we propose a hybrid Zigbee RFID system model implemented with dynamic frame slotted grouping collision resolution protocol. During every iteration of tag estimation the frame size is adjusted predicated on the comparison of total number of singleton and idle slots against the number of collision slots without eliminating idle slots. Simulations were performed utilising Opnet simulator which showed decreased collision rate, execution time, system overhead and amended performance in the metrics of tag identification rate, energy efficiency with a maximum throughput of 0.63.

Multiple Delay Estimation for Collision Resolution in Non-Orthogonal Random Access

In machine-type communications (MTC), contention-based random access is employed to support a number of MTC devices with a limited number of resource blocks (RBs). Since multiple active devices may transmit signals in the same RB or channel, the collision caused by the presence of multiple signals is inevitable and the detection of collision becomes important. Furthermore, if the arrival time and the number of multiple signals can be estimated, successive interference cancellation (SIC) can be employed in time domain to improve the throughput. In this paper, we focus on the estimation of round-trip delays (RTD) of multiple signals in non-orthogonal random access (NORA) based on the maximum likelihood (ML) criterion. Since the computational complexity of the ML approach is high, we propose a low-complexity approach based on variational inference, which is widely used in machine learning. We also show that the number of signals can be reliably estimated from the estimated RTDs.

Steady-State Analysis of the Distributed Queueing Algorithm in a Single-Channel M2M Network

The Distributed Queuing (DQ) algorithm is predicted as one of the solutions to the issues currently found in IoT networks over the use of Aloha based algorithms. Since recently, the algorithm has been of interest to many IoT researchers as a replacement of those Aloha variants for channel access. However, previous works analyzed and evaluated the DQ algorithm without any consideration of the stability of its queues, assuming it is stable for any given number of nodes in the network. In this paper, we define the DQ stability condition in a single-channel M2M environment considering a traffic model of periodic and urgent frames from each node in the network. Besides, a steady-state evaluation of the algorithm’s performance metrics is also presented. In general, the DQ algorithm, when it is stable, was observed not to efficiently use the contention slots for the collision resolution. In a single-channel environment, the DQ algorithm is found to outperform the Aloha based algorithms only in an idle-to-saturation scenario.