Collision Resolution Mechanism Research Articles

Towards Fast and Reliable Multihop Routing in VANETs

In Vehicular Ad-hoc Networks (VANETs), fast and reliable dissemination of safety messages is a key step toward improving the overall road safety. In a highly dynamic VANET environment, safety message dissemination in a multi-hop manner is a challenging and complex problem that has gained significant attention recently. Many protocols and schemes have been proposed to efficiently share safety messages among vehicles. However, most existing techniques do not perform well under real-world traffic conditions, or perform adequately only under very limited scenarios and traffic conditions. This research proposes a highly efficient and reliable multi-hop broadcasting protocol, Intelligent Forwarding Protocol (IFP), that exploits handshake-less communication, ACK Decoupling, and an efficient collision resolution mechanism. In this research, IFP has been extensively studied and evaluated to establish its robustness and superiority over existing schemes. A key contribution of this paper is to present an in-depth analysis and optimization of IFP using theoretical modeling, thorough simulations, and extensive real-world experimentation. With IFP, the message propagation delay is significantly reduced and packet delivery ratio is drastically improved.

Collision-free scheduling of multi-bridge machining systems: a colored traveling salesman problem-based approach

Multi-bridge machining systems U+0028 MBMS U+0029 have gained wide applications in industry due to their high production capacity and efficiency. They contain multiple bridge machines working in parallel within their partially overlapping workspaces. Their scheduling problems can be abstracted into a serial-colored travelling salesman problem in which each salesman has some exclusive cities and some cities shared with its neighbor U+0028 s U+0029. To solve it, we develop a greedy algorithm that selects a neighboring city satisfying proximity. The algorithm allows a salesman to select randomly its shared cities and runs accordingly many times. It can thus be used to solve job scheduling problems for MBMS. Subsequently, a collision-free scheduling method is proposed to address both job scheduling and collision resolution issues of MBMS. It is an extension of the greedy algorithm by introducing time window constraints and a collision resolution mechanism. Thus, the augmented greedy algorithm can try its best to select stepwise a job for an individual machine such that no time overlaps exist between it and the job sequence of the neighboring machine dealt in the corresponding overlapping workspace; and remove such a time overlap only when it is inevitable. Finally, we conduct a case study of a large triplebridge waterjet cutting system by applying the proposed method.

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.

Receiver initiated fast sequential collision resolution in 802.11 WLAN

Future wireless local area networks (WLANs) have potential bit rates of the order of hundreds of Mbps. However, the current IEEE 802.11 medium access control (MAC) protocol does not scale well to high bit rate WLANs. By using collision detection in wireless networks, the time spent on collision can be reduced, thus improving system throughput. In this paper, we propose an enhancement that uses a tone transmitted on a small time slot (called contention slot) which enables receiver initiated collision detection to the transmitters. In this proposed protocol, the receiver detects the collision when multiple data packets are received and it transmits a jamming signal to all the transmitting stations so that they can immediately stop their ongoing transmissions. In addition to collision detection, we propose a sequential collision resolution mechanism where preferential access is given to all the colliding packets to reduce unfairness and to increase system throughput.

RM-MAC: a reservation based multi-channel MAC protocol for wireless sensor networks

Convergecast is a general communication pattern of wireless sensor networks (WSNs) in which sensed data is collected from outlying sensor nodes and is transmitted to a sink node. In this paper, we consider periodic convergecast, in which data packets are generated and transmitted repeatedly with a certain interval. To support the periodical packet delivery efficiently, we propose a reservation based multi-channel MAC protocol (RM-MAC) which employs a time reservation mechanism. Periodical packet delivery allows receiver nodes to recognize when the next packet is transmitted, which makes the nodes reserve the time for the next packet transmission. Consequently, our proposed mechanism can guarantee minimum delivery latency from source nodes to a sink node. Furthermore, RM-MAC provides a collision resolution mechanism which coordinates the reserved periodical transmissions among multiple sender nodes. It can prevent repeated collisions caused by the multiple-senders-single-receiver problem. We implement RM-MAC by using an ns-2 simulator to compare its performance with other protocols. The simulation results show that RM-MAC outperforms existing protocols in terms of energy efficiency and packet delivery latency.

High Throughput MAC Protocol Using Sequential Collision Resolution and Outband Signalling

Abstract Since the release of the IEEE 802.11 standard, several efforts have been made to improve its performance. By using collision resolution together with collision detection in wireless networks, the time spent on collision can be reduced, thus improving system throughput. In this paper, collision detection is initiated by the receiver and a Sequential Collision Resolution mechanism is proposed where preferential access is given to all the colliding packets. Extensive simulations are carried out to evaluate the performance of this collision resolution protocol and a higher system throughput and lower delay is obtained.

On elastic traffic via contention resolution diversity slotted aloha satellite access

SummaryThis paper presents a performance study relative to the coupling of the Transmission Control Protocol (TCP) with the Contention Resolution Diversity slotted aloha (CRDSA) protocol, in the case of greedy TCP connections (also called elephants) on Digital Video Broadcasting‐Return Channel via a geostationary satellite. CRDSA, which takes advantage of interference cancellation algorithms for collision/contention resolution, has already exhibited interesting performance when the power levels of all received bursts are perfectly balanced. In this paper, we extend the study to a more realistic case, where a certain spreading of the bursts' power levels is taken into account. The consequent capture effect even facilitates the collision resolution mechanism and yields an improvement in the overall TCP performance with respect to the balanced case. Furthermore, in certain conditions, the adoption of packet level forward error correction allows achieving even higher peaks of throughput than the expected ones. Copyright © 2014 John Wiley & Sons, Ltd.

Resolving Collision in EPCglobal Class-1 Gen-2 System by Utilizing the Preamble

The collision resolution mechanism is a key factor for successful communication in dense Radio-Frequency Identification (RFID) systems. One of such collision resolution mechanisms is the ALOHA protocol used in the EPCglobal Class-1 Gen-2 standard (EPCglobal). The success of the ALOHA-based protocols in RFID systems depends on the estimation of the number of tags in the electromagnetic field of an interrogator. The majority of the proposed optimization methods of the ALOHA-based protocols focus mainly on the estimation of the number of tags based on past slot results. Only few of the proposed methods try to determine the exact number of tags that involve an analysis of the received signal. One such method is the Radar Cross Section (RCS) method. We will show that RCS is not appropriate for RFID systems that include channel filtering as in the case of the EPCglobal standard. As a replacement for the RCS method, we propose a new anti-collision method to improve the anti-collision mechanism based on the utilization of the frequency analysis of the preamble. We will demonstrate that the method improves the existing anti-collision algorithm used in the EPCglobal and enhances the capture effect capability.

Modified Binary Exponential Backoff Algorithm to Minimize Mobiles Communication Time

the field of Wireless Local Area Networks (LANs) is expanding rapidly as a result of advances in digital communications, portable computers, and semiconductor technology. The early adopters of this technology have primarily been vertical application that places a premium on the mobility offered by such systems. Binary Exponential Backoff (BEB) refers to a collision resolution mechanism used in random access MAC protocols. This algorithm is used in Ethernet (IEEE 802.3) wired LANs. In Ethernet networks, this algorithm is commonly used to schedule retransmissions after collisions. The paper's goal is to minimize the time transmission cycle of the information between mobiles moving in a Wi-Fi by changing the BEB algorithm. The Protocol CSMA / CA manage access to the radio channel by performing an arbitration based on time. This causes many problems in relation to time transmission between mobiles moving in a cell 802.11. what we have done show that the protocol using CSMA / CA access time believed rapidly when the number of stations and / or the network load increases or other circumstances affects the network.

An OFDM-aware Reservation Random Access Protocol for Interference Mitigation in OFDMA Femtocells

An efficient random access protocol utilizing the frequency diversity of OFDMA is proposed for mitigating femtocell interference in a decentralized cellular network. The proposed OFDM reservation random access (OFDM-RR) protocol builds upon a generalized version of the frequency-domain backoff scheme, which was originally proposed for WiFi networks. In this protocol, each node chooses one of K subchannels randomly and transmits a short reservation request on the corresponding subchannel. At the end of the slot, the node whose subchannel index is the highest wins the contention and immediately transmits on the full channel. A tie on the highest index is treated as a collision and is resolved by repeating the process with only those nodes involved in the collision. The throughput of this protocol is derived and compared with that of the classic reservation Aloha (R-Aloha) with the same total channel bandwidth. Although channelization increases the transmission time of the reservation packet in OFDM-RR (due to the smaller subchannel bandwidth), the collision resolution mechanism, which reduces the collision rate sharply, helps improve the throughput, particularly in the high-load region. For example, while R-Aloha almost collapses (near zero throughput) at an average load of ten requests/slot, the proposed protocol can provide a throughput of more than 55% at the same load using only two subchannels.

Minimizing Mobiles Communication Time Using Modified Binary Exponential Backoff Algorithm

The domain of wireless Local Area Networks (WLANs) is growing speedily as a consequence of developments in digital communications technology. The early adopters of this technology have mainly been vertical application that places a premium on the mobility offered by such systems. Examples of these types of applications consist of stocking control in depot environments, point of sale terminals, and rental car check-in. Furthermore to the mobility that becomes possible with wireless LANs; these systems have also been used in environments where cable installation is expensive or impractical. Such environments include manufacturing floors, trading floors on stock exchanges, conventions and trade shows, and historic buildings. With the increasing propagation of wireless LANs comes the need for standardization so as to allow interoperability for an increasingly mobile workforce. Despite all the advantages and facilities that Wi-FI offers, there is still the delay problem that is due to many reasons that are introduced in details in our case study which also presents the solutions and simulation that can reduce this delay for better performance of the wireless networks. Binary Exponential Backoff (BEB) refers to a collision resolution mechanism used in random access MAC protocols. This algorithm is used in Ethernet (IEEE 802.3) wired LANs. In Ethernet networks, this algorithm is commonly used to schedule retransmissions after collisions. The paper’s goal is to minimize the time transmission cycle of the information between mobiles moving in a Wi-Fi by changing the BEB algorithm. The Protocol CSMA / CA manage access to the radio channel by performing an arbitration based on time. This causes many problems in relation to time transmission between mobiles moving in a cell 802.11. what we have done show that the protocol using CSMA / CA access time believed rapidly when the number of stations and / or the network load increases or other circumstances affects the network.

The Cost of Mitigating Power Law Delay in Random Access Networks

Exponential backoff (EB) is a widely adopted collision resolution mechanism in many popular random-access networks including Ethernet and wireless LAN (WLAN). The prominence of EB is primarily attributed to its asymptotic throughput stability, which ensures a non-zero throughput even when the number of users in the network goes to infinity. Recent studies, however, show that EB is fundamentally unsuitable for applications that are sensitive to large delay and delay jitters, as it induces divergent second- and higher-order moments of medium access delay. Essentially, the medium access delay follows a power law distribution, a subclass of heavy-tailed distribution. To understand and alleviate the issue, this paper systematically analyzes the tail delay distribution of general backoff functions, with EB being a special case. In particular, we establish a tradeoff between the tail decaying rate of medium access delay distribution and the stability of throughput. To be more specific, convergent delay moments are attainable only when the backoff functions g(k) grow slower than exponential functions, i.e., when g(k) ∈ o(rk) for all r > 1. On the other hand, non-zero asymptotic throughput is attainable only when backoff functions grow at least as fast as an exponential function, i.e., g(k) ∈ Ω (rk) for some r > 1. This implies that bounded delay moments and stable throughput cannot be achieved at the same time. For practical implementation, we show that polynomial backoff (PB), where g(k) is a polynomial that grows slower than exponential functions, obtains finite delay moments and good throughput performance at the same time within a practical range of user population. This makes PB a better alternative than EB for multimedia applications with stringent delay requirements.

Delay Analysis of OFDMA-Aloha

OFDMA is the basis of future broadband access, due to its many inherent advantages such as scalability and fine granularity for multi-user access. OFDMA-Aloha combines the flexibility of OFDMA with basic Aloha's collision resolution mechanism over sub-carriers, in an attempt to reduce packet collisions and achieve faster retransmission. However, this comes at the expense of a larger slot size, due to lower channel rates per subcarrier. The above gives rise to a fundamental question: whether to use a single wide-band Aloha channel and retransmit via random back-off in next K time slots, or to retransmit immediately in one of K narrow-band sub-channels which are each 1/K slower (OFDMA-Aloha)? We answer this question, by analyzing the two protocols: Aloha and OFDMA-Aloha under the same total bandwidth and load conditions. We first derive the exact distribution of the packet access delay of OFDMA-Aloha in the saturated case. Then, we extend the analysis to the unsaturated case and derive the mean queue length and packet delay by decomposing the system of interfering queues into multiple independent queues utilizing the symmetry in our system. Our results show that if the network is already saturated, channelization does not bring substantial reduction in the collision rate to the point where it outweighs the effect of expanded slot size. In this case the single channel Aloha performs better than OFDMA-Aloha especially when the gap between the number of channels and the number users is large. On other hand, when the network is lightly loaded, OFDMA-Aloha enjoys smaller packet delays, but not for long as it saturates faster than the single channel Aloha.

Delay-Optimal Broadcast for Multihop Wireless Networks Using Self-Interference Cancellation

Conventional wireless broadcast protocols rely heavily on the 802.11-based CSMA/CA model, which avoids interference and collision by conservative scheduling of transmissions. While CSMA/CA is amenable to multiple concurrent unicasts, it tends to degrade broadcast performance significantly, especially in lossy and large-scale networks. In this paper, we propose a new protocol called Chorus that improves the efficiency and scalability of broadcast service with a MAC/PHY layer that allows packet collisions. Chorus is built upon the observation that packets carrying the same data can be effectively detected and decoded, even when they overlap with each other and have comparable signal strengths. It resolves collision using symbol-level interference cancellation, and then combines the resolved symbols to restore the packet. Such a collision-tolerant mechanism significantly improves the transmission diversity and spatial reuse in wireless broadcast. Chorus' MAC-layer cognitive sensing and scheduling scheme further facilitates the realization of such an advantage, resulting in an asymptotic broadcast delay that is proportional to the network radius. We evaluate Chorus' PHY-layer collision resolution mechanism with symbol-level simulation, and validate its network-level performance via ns-2, in comparison with a typical CSMA/CA-based broadcast protocol. Our evaluation validates Chorus's superior performance with respect to scalability, reliability, delay, etc., under a broad range of network scenarios (e.g., single/multiple broadcast sessions, static/mobile topologies).

Scalable Network Synchronization with Pulse-Coupled Oscillators

The Pulse-Coupled Oscillator (PCO) is a novel protocol inspired by models used in mathematical biology to justify the emergence of synchrony in the natural world. Our paper introduces and demonstrates the efficacy of a new PCO protocol implementation that, by disabling all collision resolution mechanisms for a suitable portion of the node operations, lets the rapid establishment of a common clock and its maintenance. The key idea is to allow signals to be superimposed in time, a feature that is absent in previous implementations, because it is prevented by traditional medium access schemes. We map the PCO protocol into an event-driven asynchronous coloring algorithm, based on the local exchange of information to explain its convergence properties. The event-based description of the PCO protocol sets the stage for our experimental comparison with a competing decentralized network synchronization approach, namely, the Reference Broadcast Protocol (RBS). For comparison, we combined RBS with an asynchronous average consensus protocol, running exactly on the same MicaZ platforms. The experimental results showcase the better scalability of the PCO scheme compared to the competing method based on RBS, proving that the PCO primitive is a reasonable option to consider for wireless sensor network applications.

An optical router with multistage management functions for asynchronous optical packet switching network

An optical router with multistage distributed management features for the asynchronous optical packet switching (OPS) network is presented, which can improve switching capacity and all-optical scalability. A compact recycling-fiber-delay-line (Rec-FDL) based collision resolution mechanism is proposed to resolve the contentions for asynchronous and variable length optical packets. The analysis models of stabilities, packet loss rates (PLR) and average packet waiting latencies (PWL) for the router are developed based on the timer based optical packet assembly algorithm. The simulation shows that PLR and PWL for a 400-byte optical packet transmitted in the 32 wavelengths dense wavelength division multiplexing (DWDM) system equal to 3.48 × 10?4 and 0.072 ns, respectively. The non-blocking switching can be realized for the packets with lengths less than the buffer granularity of the Rec-FDL, and the optimized performance for the proposed router can be obtained through properly selecting of the system parameters.

Contention resolution mechanisms for asynchronous optical packet switching based high performance computing system

We propose an asynchronous optical packet switching (AOPS) based multistage interconnection network employing the distributed control and banyan-like routing scheme, which can construct the high performance computing system (HPCS). A flexible, low latency, and high capacity recycling-fiber-delay-line (Rec-FDL) based collision resolution mechanism is proposed with higher switching efficiency for burst services than that by the conventional packet retransmission algorithm (C-PRA). The system performances, including stability, blocking rate (BR), and longest packets waiting latency (LPWL) are analyzed. The simulation shows that the system stability condition for the Rec-FDL mechanism is the new packet arriving rate ? less than 30×106 packets/s. In addition, the BR and Rec-FDL induced LPWL are 0.1235---0.1413 and 6.305 ns---7.651 ns, respectively, with increasing the number of CPUs connected to the system from 4 to 16,384, while the increment for LPWL induced by the conventional algorithm is 3.9 ns at the same conditions as above. Therefore, the mechanism presented here is more beneficial for the system scalability and has higher latency reducing abilities than the C-PRA.

An Enhanced CSMA-CA Algorithm for IEEE 802.15.4 LR-WPANs

Two mechanisms are proposed to enhance throughput and energy efficiency of IEEE 802.15.4 CSMA-CA. The first one is an enhanced collision resolution (ECR) mechanism that adjusts the backoff exponent (BE) based on both consecutive clear channel assessment (CCA) busy results and a packet transmission. The second one is an enhanced backoff (EB) mechanism that shifts the range of backoff counters by utilizing the CCA outcome. The simulation results demonstrate that the proposed mechanisms significantly enhance both throughput and energy efficiency of IEEE 802.15.4

Performance Evaluation of an Enhanced GDCF for IEEE 802.11

In this letter, we propose an enhanced gentle distributed coordination function (GDCF), which is a simple and effective collision resolution mechanism, to improve the performance of IEEE 802.11 DCF. We compare performance of the enhanced GDCF with that of the legacy DCF and the conventional GDCF via analysis and simulations. The enhanced GDCF introduces a new counter to check the number of consecutively successful transmissions, and the maximum permitted values of the counter differ for different backoff stages. The proposed GDCF is shown to have performance superior to that of the conventional GDCF for various combinations of contending stations and frame length.

Enhancements of the modified PCF in IEEE 802.11 WLANs

The success of the IEEE 802.11 standard has prompted research into efficiency of the different medium access methods and their support for different traffic types. A modified version of the point coordination function (PCF) called modified PCF has been introduced as a way to improve the efficiency over the standard method. It has been shown through a simulation study and a mathematical analysis that channel utilization can be much improved compared to the standard, in case there is no so-called hidden station problem. However, under the hidden station problem, the efficiency of the modified PCF would obviously decrease. In this paper, some enhancements of the modified PCF are introduced. Firstly, we propose a retransmission process to allow frames involved in collisions to be retransmitted. Then, we propose a collision resolution mechanism to reduce the frame collision probability due to the hidden station problem. In addition, we propose a priority scheme to support prioritization for different traffic types such as interactive voice and video, and real-time data traffic in the modified PCF. To prevent the starvation of one low priority traffic, minimum transmission period is also guaranteed to each traffic type via an admission control algorithm. We study the performance of the modified PCF under the hidden station problem and the performance of the modified PCF with priority scheme through simulations. To illustrate the efficiency of the priority scheme, we therefore compare its simulation results with those of some standardized protocols: The distributed coordination function (DCF), the enhanced distributed channel access (EDCA), the PCF, and our previously proposed protocol: The modified PCF without priority scheme. The simulation results show that the increment of delay in the network due to the hidden station problem can be reduced using the proposed collision resolution mechanism. In addition, in a given scenario the modified PCF with priority scheme can provide better quality of service (QoS) support to different traffic types and also support a higher number of data stations than the previous proposals.