Reduce Collision Probability Research Articles

A Collision-Tolerant-Based Anti-Collision Algorithm for Large Scale RFID System

Tag identification is an important issue in an RFID system. Most existing anti-collision algorithms solely focus on reducing collision probability while suffering from vast idle slots. This letter proposes a collision-tolerant dynamic-framed slotted Aloha (CE-DFSA) algorithm, which attempts to identify multiple tags in a slot to reduce the total identification time in the process of identification. In CE-DFSA, tags are allocated with orthogonal Walsh sequence so that multiple tags can be identified in a time slot without spreading the spectrum. Simulation results show that the proposed algorithm considerably accelerates the tag identification process with improved efficiency compared with existing anti-collision algorithms.

Efficient Data Forwarding for Machine Type Communications in Internet of Things Networks

The MTC (Machine Type Communications) system is one of the most promising technologies to provide IoT (Internet of Things) applications. The MTC system suffers from congestion due to limited data transmission capacity and burst traffic. The congestion disturbs data delivery, results in an increase of energy consumption due to data retransmission, and finally poses a threat to the providers of IoT applications. In this paper, we focus on the congestion problem and present an efficient data forwarding mechanism to regulate the burst channel access from a large number of MTC devices. To regulate the communication channel access from the devices, we predict the number of devices by separating traffic load into the prediction of the number of devices that newly attempt to have access and the prediction of the number of devices that retry to access the channel. Through simulations, we show that our mechanism improves access success probability and reduces collision probability and access delay.

Improved Predictive Contention Window-Based Broadcast Optimization Strategy in Vehicular Cyber-Physical System

Vehicles in the vehicular cyber-physical system should avoid intense competition by adjusting contention windows of media access control (MAC) protocol. Accordingly, we propose an improved prediction contention window adjustment mechanism to optimise the broadcast performance. The set should be updated via a feedback mechanism, so as to solve the problem of changeable vehicular communication scenarios. After that, an improved Markov model is designed to analyse the backoff procedure and to obtain the window sizes related to the attribute set, for the purpose of creating the reference table by Bayesian personalised ranking algorithm. Besides, an estimation mechanism based on hidden Markov is provided to predict the following vehicle's state and to generate a mapping table that consists of the attribute set and size of the window. Comparing with traditional adjustment schemes, extensive simulations demonstrate that the proposed strategy could optimise the broadcast performance effectively in terms of reducing collision probability and transmission delay.

Minimizing contention collision probability and guaranteeing packet delay for cloud big data transmissions in 4G LTE-A packet random access

For transmitting Explosive Bursts Big Data of Mobile Cloud Computing applications, the 4G LTE/LTE-A standards are specified to provide extreme high data rate and low access delay for various real-time-demanded cloud services. In the uplink, data packet transmissions of different classes of traffic of various UEs need randomly contend for the limited number of preambles through the Uplink RACH channel time slots. Clearly, the extremely explosive data contentions certainly yield serious collisions, and then significantly increase access delay and packet dropping rate. That is, the quality of service (QoS) of the delay-sensitive-based real-time traffic and the loss-sensitive-based non-real-time traffic cannot be guaranteed satisfyingly. For overcoming the critical random access issue in cloud services over 4G LTE-A, 3GPP specifies the Uniform Distribution Backoff Procedure and Access Class Barring (ACB) as the random access mechanism. The Random Access CHannel (RACH) for random contentions in 3GPP LTE-A neglects some key factors: 1) different classes of traffic requiring different delay bounds, 2) how to reducing collision probability, 3) intensive congestion traffic and 4) differentiating the collision domains. This paper thus proposes an adaptive random contention approach (ARC) that consists of three phases: 1) Sigmoid-based Access Class Barring algorithm, 2) Dynamic Preamble Selection Range (DPSR) algorithm, and 3) Dynamic Initial Backoff (DIB) algorithm. The main contribution of ARC is based on the adaptive Sigmoid feature analysis of Cumulative Distribution Function of Normal Distribution according to the successful contention probability and the RACH congestion state. Numerical results demonstrate that the proposed approach outperforms the compared approaches in collision probability, goodput and access delay. Furthermore, the mathematical analytical model for the proposed approach is analyzed. The analysis result is very close the simulation result. It justifies the correctness and efficiency of the proposed approach.

A Channel Bonding Based QoS-Aware OFDMA MAC Protocol for the Next Generation WLAN

The IEEE 802.11ax, which was approved by the IEEE Standards Association (IEEE-SA) in March, 2014 as the next generation Wireless Local Area Network (WLAN) standard, has rigorous requirements in terms of high throughput and Quality of Service (QoS) support in the dense user scenario. To achieve high throughput by utilizing the wide bandwidth while decreasing the collision probability among stations, a Channel Bonding based QoS-aware Orthogonal Frequency Division Multiple Access (OFDMA) MAC protocol (CBQO) is proposed in this paper. Based on the combination of channel bonding and OFDMA, the capability of reducing collision probability in the dense user scenario is enhanced compared to the traditional OFDMA based MAC protocol, since the amount of subchannels is improved several times by the introduction of the channel bonding, and the wide channel provided by channel bonding are efficiently allocated among stations according to their QoS requirements, as the OFDMA provides a flexible and fine-grained management of the channel resource. Simulation results show that the proposed protocol outperforms the IEEE 802.11ac MAC protocol in terms of both throughput and delay of video traffic.

SNR-based relay selection in cooperative wireless ad hoc networks

Cooperative communications aim to gain spatial diversity from stations cooperating during data transmission without requiring multiple transceiver antennas on the same station. However, performance from cooperative communications highly depends on the relay-selection method. This paper proposes and evaluates a distributed relay-selection method based on the signal-to-noise ratio of the communication links of candidate relay nodes. A node is selected as a relay node based on the signal-to-noise ratio of its communication link. Moreover, data might be delivered through a relay node that can support high transmission rate rather than through a direct link with a low transmission rate. This paper provides a detailed analysis of the collision probability in the proposed method as compared to a conventional random backoff method. Results demonstrate that the proposed relay-selection method reduces collision probability, and hence, enhances system throughput.

Load-aware channel hopping protocol design for mobile ad hoc networks

Using multiple channels in wireless networks improves spatial reuse and reduces collision probability and thus enhances network throughput. Designing a multi-channel MAC protocol is challenging because multi-channel-specific issues such as channel assignment, the multi-channel hidden terminal problem, and the missing receiver problem, must be solved. Most existing multi-channel MAC protocols suffer from either higher hardware cost or poor throughput. Some channel hopping multi-channel protocols achieve pretty good performance in certain situations but fail to adjust their channel hopping mechanisms according to varied traffic loads. In this paper, we propose a load-aware channel hopping MAC protocol (LACH) that solves all the multi-channel-specific problems mentioned above. LACH enables nodes to dynamically adjust their schedules based on their traffic loads. In addition to load awareness, LACH has several other attractive features: (1) Each node is equipped with a single half-duplex transceiver. (2) Each node's initial hopping sequence is generated by its ID. Knowing the neighbor nodes' IDs, a node can calculate its neighbors' initial channel hopping sequences without control packet exchanges. (3) Nodes can be evenly distributed among available channels. Through performance analysis, simulations, and real system implementation, we verify that LACH is a promising protocol suitable for a network with time-varied traffic loads.

Exploiting the prefix information to enhance the performance of FSA-based RFID systems

For a radio frequency identification (RFID) system deployed in dense environment, the reader must quickly and reliably extract information from numerous tags. To harmonize the channel access among competing tags and reduce collision probability, conventionally, framed slotted ALOHA (FSA) scheme is employed to resolve the collisions occurring when numerous tags simultaneously respond to the query of the reader. Typically, FSA algorithm consists of two parts: (i) estimating the number of available tags in vicinity, and (ii) base on the estimated value, setting the frame length accordingly. However, in the FSA scheme, when collision happens, it is impossible to estimate how many colliding tags simultaneously reply in a single slot, which, in turn, can lead to inaccuracy of the estimated cardinality and unreasonable setting of the frame length. This will further result in under-utilization of channel resource and the degradation of the system performance. The problem can be aggravated when all slots in the frame are entirely collided under a dense environment, rendering the malfunction of the estimator.To address this problem, in this paper, a prefix assisted approach, namely, PA-FSA, is proposed to enhance the estimation accuracy of the traditional FSA. Specifically, in PA-FSA, each tag appends a prefix in front of RN16 short message. When replying RN16 to the reader, a tag randomly and independently selects one bit in the prefix and sets the bit as active. By synchronizing prefixes of multiple colliding replies and counting the number of active bits in the overlapping prefixes, the reader can more precisely estimate how many tags have collided in a single slot, thus significantly improving the estimation accuracy. Extensive simulation results indicate that, compared with the traditional schemes, PA-FSA can estimate the tag cardinality more accurately and efficiently. Additionally, with PA-FSA adopted, system can reduce the communication overhead for approximately 50% and shorten the tag identification time for about 15%.

Bandwidth Reservation as a Coexistence Strategy in Opportunistic Spectrum Access Environments

We consider a scenario in which a licensed wireless operator or primary network (PN) coexists with an ad-hoc, cognitive, secondary network. To minimize harmful interference on the primary users (PUs), secondary users (SUs) sense the PU activity on the licensed spectrum band before transmitting in spectrum opportunities. We study a bandwidth reservation (BR) scheme by which the PN keeps a set of adjacent channels free of PU transmissions. These reserved channels only accommodate PU traffic when all the non-reserved channels are used, and the SUs only occupy available channels within the reserved spectrum. Intuitively, this strategy reduces collision probability and simplifies the design of opportunistic spectrum access (OSA) mechanisms. However, from the point of view of the PN, BR entails a tradeoff between the benefits of an improved coexistence with SUs, and the capacity reduction associated to having fewer options for PU channel allocation. The main objective of this paper is to determine when BR improves the overall PN performance under SU activity. The SUs are characterized by a hardware limited radio, imperfect spectrum sensing, bayesian estimation of PU activity and multichannel access. Because PU capacity is the central issue, we assume a PN capable of exploiting all the available bandwidth at every moment. By means of a Markov-reward model, we compute the expected PU capacity with and without BR, considering propagation effects, interference and random locations. The results show that, in a non-congested PN with SU activity, the interference reduction capability of BR increases the overall capacity of the PN compared to not using BR.

Multiple-Rendezvous Multichannel MAC Protocol Design for Underwater Sensor Networks

Compared with traditional terrestrial radio transmissions in wireless sensor networks, the challenges of transmissions in underwater sensor networks (UWSNs) include lower transmission rate, longer delay time, and higher power consumption. In such a circumstance, the negative effects of transmission collisions deteriorate. Most of the existing UWSN medium access control (MAC) protocols handle the collision problem in a single-hop or light-loaded environment. They fail to function effectively in a multihop network consisting of more sensor nodes with heavier traffic loads. Using the concept of cyclic quorum systems, we propose a distributed multiple-rendezvous multichannel MAC protocol, MM-MAC, in this paper to reduce collision probability. The advantages of the proposed protocol are threefold: 1) Only one modem is needed for each node to solve the missing receiver problem which is often encountered in multichannel protocols; 2) multiple sensor node pairs can complete their channel negotiations on different channels simultaneously; and 3) data packets will not be collided by control packets and vice versa. Simulation results verify that our protocol can reduce collision probability significantly which enhances the network performance in a multihop UWSN.

Collision-Tolerant Media Access Control with On-Off Accumulative Transmission

In this paper, a cross-layer collision-tolerant (CT) media access control (MAC) scheme is proposed for wireless networks. Unlike conventional MAC schemes that discard and retransmit signals colliding at a receiver, the CT-MAC extracts the salient information from the colliding signals with a new on-off accumulative transmission (OOAT) scheme in the physical layer. Users employing OOAT deliver information to the base station (BS) through uncoordinated on-off transmissions of multiple identical sub-symbols (accumulative transmission). Silence periods are inserted between sub-symbols inside a frame to reduce collision probability and render a special signal structure for physical layer detection. Algebraic properties of the on-off transmission patterns, which are represented as cyclic-shifted binary vectors, are analyzed, and the results provide guidelines on the design of OOAT systems and other systems that rely on cyclic-shifted binary vectors. Then, we demonstrate that the structure of the on-off transmission patterns enables a sub-optimum iterative detection method, which improves performance by iteratively exchanging extrinsic soft information between a forward and a backward soft interference cancellation (SIC). Both analytical and simulation results show that the new CT-MAC with OOAT scheme significantly outperforms many existing cross-layer MAC schemes in terms of the number of users supported and the normalized throughput.

4세대 이동통신시스템을 위한 우선순위 기반 지능적 상향링크 랜덤 접속 방법 및 표준화

4세대 이동통신시스템에서는 사용자가 이용하는 서비스 종류 및 가입한 요금제, 서비스 이용 형태 등에 따라서 각 사용자에게 서로 다른 품질의 서비스를 제공하는 것이 매우 중요하다. 본 논문에서는 단말이 상향링크 자원 요청을 위해서 수행하는 random access 과정을 개선하여 각 사용자 별 서비스 품질 차별화를 도모하였다. 구체적으로 bandwidth request 채널의 구조를 primary 영역과 secondary 영역으로 구분하였고 각 영역을 이용하여 random access를 수행할 수 있는 사용자의 등급을 영역 별로 제한하였다. 이러한 제안 기술을 이용하면 서로 다른 등급의 사용자 사이에 발생하는 불필요한 random access 경쟁을 방지할 수 있기 때문에 전체적인 사용자의 random access 성공 확률을 유지하면서 primary 영역을 이용하여 random access를 시도하는 사용자의 성공 확률을 증가시킬 수 있다. 제안 기술은 2010년 3월 IEEE 802.16 Session #66 회의에서 발표되었고 제안 기술의 개념 및 필요한 메시지가 802. 16m 표준에 채택되는 성과를 거두었다. Fourth-generation (4G) cellular communication systems must provide different quality-of-service (QoS) to users according to the service type, membership class, and usage case of each user. For the purpose of user's QoS differentiation, we propose an enhanced uplink random access scheme for bandwidth request. More specifically, we divide a bandwidth request channel into two parts: One is a primary region and the other is a secondary region. Then, each region has a unique minimum access class that allows only specific users to perform random access through that region. By doing so, we can reduce collision probability and increase the success probability of bandwidth request. From the perspective of standardization, we presented this scheme in the IEEE 802.16m Session #66 held on March 2010. As a result, the concept of the proposed scheme and required messages were defined in the 802.16m standard.

High-throughput time group access MCR-SS-CSMA/CA for wireless ad hoc networks with layered-tree topology

Multi-hop packet transmission error due to packet collision is a serious issue for realizing large-scale wireless ad hoc networks. In order to solve the issues, a multicode-reception spread-spectrum (MCR-SS)-CSMA/CA scheme is proposed as multiple access scheme for layered-tree networks. This scheme is further improved by adding a time group access (TGA) technique to gain higher interference reduction between nodes. The proposed TGA scheme divides the layered-tree network into upper subnets group and lower subnets group, thus reducing collision probability among subnets. Network throughput and data delivery ratio for the proposed scheme are analyzed by simulations based on the IEEE 802.15.4/ZigBee specification. Simulation results show that the proposed schemes can improve packet delivery ratio and network throughput remarkably.

The Study on Energy Optimization in MAC Protocol Design for Wireless Networks

While the benefits of cooperation of the diversity of research have been in the literature, cooperation MAC protocol design also led to a lot of attention. In a single-relay repeated request (C-ARQ cooperation agreement, had better be to choose a relay node in a distributed attitude, use different time relay bag. However, back to forward this relay selection plan does not work efficiently in a dense network case; with high collision probability in the struggle of relays may different. In this paper, we put forward an optimal choice of, in order to maximize transmission system energy efficiency reduce collision probability. Energy efficiency performance the optimal transitive the established the simulation results verify the options.

Reducing collision probability on a shared medium using a variational method

We consider a network with N nodes competing for access to the channel using un-slotted ALOHA. When a request is sent, each node may answer after a certain backoff time. Only the first answer is of importance, that is why we want to minimize the loss rate of the first message. We derive the optimal backoff probability distribution which minimizes the collision probability on the first message answering toa request. Unlike previous works, we extract the collisionprobability in continuous time domain. To this goal, weuse a variational method. This problem had only be solvedbefore in a slotted context (i.e. discrete time domain), butwe want to be able to manage later situations where the nodes are not perfectly synchronized, which requires to know how to solve it in the continuous time context.

Study of bottleneck effect at an emergency evacuation exit using cellular automata model, mean field approximation analysis, and game theory

An improved cellular automaton model for pedestrian dynamics was established, where both static floor field and collision effect derived from game theory were considered. Several model parameters were carefully determined by previous studies. Results obtained through model-based simulation and analytical approach (derived from mean field approximation) proved that outflow rate from an evacuation exit, which is usually estimated using outflow coefficient in building codes in Japan, can be improved by placing an appropriate obstacle in front of the exit. This can reduce collision probability at the exit by increasing collisions around the obstacles ahead of the exit.

A Cross-Layer Routing Scheme Using Adaptive Retransmission Strategy for Wireless Mesh Networks

In this paper, we develop a link quality-based adaptive adjustment mechanism of the MAC maximum retransmission count to reduce collision probability of wireless Mesh networks. Based on statistics acquired in the link layer and the retransmission strategy, a multi-metric cross-layer on-demand routing scheme is proposed for wireless Mesh networks. The proposed scheme uses information such as available link bandwidth, node residual load rate and transmission efficiency of a path adequately to cross-layer routing. The network layer can adaptively select an optimal path to deliver packets based on the acquired statistics of the MAC layer. Extensive simulation results demonstrate that the proposed scheme can reduce link failure probability, improve network throughput, and decrease the end-to-end delay effectively.

A new multi-channel MAC protocol based on CDMA for ad hoc networks

This paper proposes a novel multichannel medium access control (MAC) protocol based on CDMA that improves network performance and reduces collision probability in wireless ad hoc networks. In the scheme, the code channel is divided into common channel, broadcast channel and several data channels. Simulation results show that the proposed protocol can achieve significantly better performance than the IEEE 802.11 standard.

A distributed collision resolution scheme for improving the performance in wireless LANs

The IEEE 802.11 distributed coordination function (DCF) provides a contention-based distribution channel access mechanism for stations to share the wireless medium. However, performance of the DCF drops dramatically due to high collision probability as the number of active stations becomes larger. In this paper, we propose a simple and effective collision resolution scheme for improving the performance of the DCF mechanism. Our idea is based on the estimation of the channel’s contention level, by measuring duration of busy and idle periods observed on the channel at each station. In order to reduce collision probability, the proposed scheme limits the number of contending stations at the same time according to the channel contention level. Performance of the proposed scheme is investigated by numerical analysis and simulation. Our results show that the proposed scheme is very effective and improves the performance under a wide range of contention levels.