Future Evolution of CSMA Protocols for the IEEE 802.11 Standard

In this paper a candidate protocol to replace the prevalent CSMA/CA medium access control in Wireless Local Area Networks is presented. The proposed protocol can achieve higher throughput than CSMA/CA, while maintaining fairness, and without additional implementation complexity. Under certain circumstances, it is able to reach and maintain collision-free operation, even when the number of contenders is variable and potentially large. It is backward compatible, allowing for new and legacy stations to coexist without degrading one another's performance, a property that can make the adoption process by future versions of the standard smooth and inexpensive.Comment: This paper has been accepted in the Second IEEE ICC Workshop 2013 on Telecommunication Standards: From Research to Standard

Enhanced Collision Resolution for the IEEE 802.11 Distributed Coordination Function

The IEEE 802.11 standard relies on the Distributed Coordination Function (DCF) as the fundamental medium access control method. DCF uses the Binary Exponential Backoff (BEB) algorithm to regulate channel access. The backoff period determined by BEB depends on a contention window (CW) whose size is doubled if a station suffers a collision and reset to its minimum value after a successful transmission. BEB doubles the CW size upon collision to reduce the collision probability in retransmission. However, this CW increase reduces channel access time because stations will spend more time sensing the channel rather than accessing it. Although resetting the CW to its minimum value increases channel access, it negatively affects fairness because it favours successfully transmitting stations over stations suffering from collisions. Moreover, resetting CW leads to increasing the collision probability and therefore increases the number of collisions. % Quality control editor: Please ensure that the intended meaning has been maintained in the edits of the previous sentence. Since increasing channel access time and reducing the probability of collisions are important factors to improve the DCF performance, and they conflict with each other, improving one will have an adverse effect on the other and consequently will harm the DCF performance. We propose an algorithm, \gls{ECRA}, that solves collisions once they occur without instantly increasing the CW size. Our algorithm reduces the collision probability without affecting channel access time. We also propose an accurate analytical model that allows comparing the theoretical saturation and maximum throughputs of our algorithm with those of benchmark algorithms. Our model uses a collision probability that is dependent on the station transmission history and thus provides a precise estimation of the probability that a station transmits in a random timeslot, which results in a more accurate throughput analysis. We present extensive simulations for fixed and mobile scenarios. The results show that on average, our algorithm outperformed BEB in terms of throughput and fairness. Compared to other benchmark algorithms, our algorithm improved, on average, throughput and delay performance

Random Access Scheduling without Message Passing: A Collision-based AIMD Approach

Department of Computer EngineeringWireless scheduling has been extensively studied in the literature. Since Maximum Weighted Scheduling has been developed and shown to achieve the optimal performance, there have been many efforts to overcome its complexity issue. Random access has attracted much attention due to its potential for low complexity and distributed control, which are desirable for scheduling in multi-hop wireless networks. Although several interesting random access scheduling schemes have been shown to be provably efficient, they suffer in practice from high packet delays or severe performance degradation due to the control overhead to exchange information between neighboring links. In this paper, we develop a novel random access scheduling scheme that does not need message passing. We pay attention to the interplay between the links and control their access probabilities targeting at a certain collision rate. We employ the Additive Increase Multiplicative Decrease (AIMD) algorithm for convergence, and show that our proposed scheme can achieve the same performance bound as the previous random access schemes with high control overhead. We verify our results through simulations and show that our proposed scheme achieves the performance close to that of the centralized greedy algorithm.ope

Application of information fusion to unreliable wireless sensor networks

Thesis is appropriated analyze to performance metric evaluation for decentralized distributed detection sensor network strategy. Performance metric investigated a typical wireless sensor network with respect to IEEE 802.15.4 standard. Distributed detection is considered with present of the fusion node as long as clustering and non-clustering sensor network. The clusters are organized uniform and non-uniform topology sensor networks with tree-based topologies and hierarchical multi-level fusion centers. Fusion centers are acting as head of cluster for decision making based on majority-like received signal strength (RSS) with comparison an optimized threshold with concerning to channel influence. FCs decisions will forward to Access point (AP). AP behaves similar as a fusion node with same channel affect but in next level of fusing. Decision error probability at Fusion node is taken into the account based on ideal and non-ideal channel with Channel State Information (CSI) impacts. Network average delay, Reliability, Packet failure, Energy consumption, Network aggregation throughput are considered as performance metric parameters versus packets generation rates and two 3,12 (dB) signal to noise ratio. An analytical Markov model IEEE 802.15.4 MAC layer is supposed which characterized the slotted CSMA/CA mechanism of beacon enable mode. Markov model drives the performance metric base on MAC and physical layer cross-layers method and Channel State Information specifications. We assumed the performance metric is evaluated with equation outcome from Markov model with mentioned topology with present of Fusion node. With this combination, a theoretical performance evaluation framework is proposed. Application of fuzzy fusion theory is considered in framework as well. Inference performed with fuzzification, rule evaluation, combination or aggregation of rules, and deffuzification based on most common methods of fuzzy logic Mamdani inference.The two inputs value are the distance of a sensor node from fusion center node (cluster head) and its available RSSI as singnal to noise ratio. Project figured out with simulations of Markov model with proposed framework. Results represent significant enhancement on performance of network and accuracy of received data to fusion nodes actions

Towards reliable geographic broadcasting in vehicular networks

In Vehicular ad hoc Networks (VANETs), safety-related messages are broadcasted amongst cars, helping to improve drivers' awareness of the road situation. VANETs’ reliability are highly affected by channel contention. This thesis first addresses the issue of channel use efficiency in geographical broadcasts (geocasts). Constant connectivity changes inside a VANET make the existing routing algorithms unsuitable. This thesis presents a geocast algorithm that uses a metric to estimate the ratio of useful to useless packet received. Simulations showed that this algorithm is more channel-efficient than the farthest-first strategy. It also exposes a parameter, allowing it to adapt to channel load. Second, this thesis presents a method of estimating channel load for providing feedback to moderate the offered load. A theoretical model showing the relationship between channel load and the idle time between transmissions is presented and used to estimate channel contention. Unsaturated stations on the network were shown to have small but observable effects on this relationship. In simulations, channel estimators based on this model show higher accuracy and faster convergence time than by observing packet collisions. These estimators are also less affected by unsaturated stations than by observing packet collisions. Third, this thesis couples the channel estimator to the geocast algorithm, producing a closed-loop load-reactive system that allows geocasts to adapt to instantaneous channel conditions. Simulations showed that this system is not only shown to be more efficient in channel use and be able to adapt to channel contention, but is also able to self-correct suboptimal retransmission decisions. Finally, this thesis demonstrates that all tested network simulators exhibit unexpected behaviours when simulating broadcasts. This thesis describes in depth the error in ns-3, leading to a set of workarounds that allows results from most versions of ns-3 to be interpreted correctly

Energy-efficient diversity combining for different access schemes in a multi-path dispersive channel

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e ComputadoresThe forthcoming generation of mobile communications, 5G, will settle a new standard for a larger bandwidth and better Quality of Service (QoS). With the exploding growth rate of user generated data, wireless standards must cope with this growth and at the same time be energy efficient to avoid depleting the batteries of wireless devices. Besides these issues, in a broadband wireless setting QoS can be severely affected from a multipath dispersive channel and therefore be energy demanding. Cross-layered architectures are a good choice to enhance the overall performance of a wireless system. Examples of cross-layered Physical (PHY) - Medium Access Control (MAC) architectures are type-II Diversity Combining (DC) Hybrid-ARQ (H-ARQ) and Multi-user Detection (MUD) schemes. Cross-layered type-II DC H-ARQ schemes reuse failed packet transmissions to enhance data reception on posterior retransmissions; MUD schemes reuse data information from previously collided packets on posterior retransmissions to enhance data reception. For a multipath dispersive channel, a PHY layer analytical model is proposed for Single-Carrier with Frequency Domain Equalization (SC-FDE) that supports DC H-ARQ and MUD. Based on this analytical model, three PHY-MAC protocols are proposed. A crosslayered Time Division Multiple Access (TDMA) scheme that uses DC H-ARQ is modeled and its performance is studied in this document; the performance analysis shows that the scheme performs better with DC and achieves a better energy efficiency at the cost of a higher delay. A novel cross-layered prefix-assisted Direct-Sequence Code Division Multiple Access (DS-CDMA) scheme is proposed and modeled in this document, it uses principles of DC and MUD. This protocol performs better by means of additional retransmissions, achieving better energy efficiency, at the cost of higher redundancy from a code spreading gain. Finally, a novel cross-layered protocol H-ARQ Network Division Multiple Access (H-NDMA) is proposed and modeled, where the combination of DC H-ARQ and MUD is used with the intent of maximizing the system capacity with a lower delay; system results show that the proposed scheme achieves better energy efficiency and a better performance at the cost of a higher number of retransmissions. A comparison of the three cross-layered protocols is made, using the PHY analytical model, under normalized conditions using the same amount of maximum redundancy. Results show that the H-NDMA protocol, in general, obtains the best results, achieving a good performance and a good energy efficiency for a high channel load and low Signal-to-Noise Ratio (SNR). TDMA with DC H-ARQ achieves the best energy efficiency, although presenting the worst delay. Prefix-assisted DS-CDMA in the other hand shows good delay results but presents the worst throughput and energy efficiency

Centralized random backoff for collision free wireless local area networks

Over the past few decades, wireless local area networks (WLANs) have been widely deployed for data communication in indoor environments such as offices, houses, and airports. In order to fairly and efficiently use the unlicensed frequency band that Wi-Fi devices share, the devices follow a set of channel access rules, which is called a wireless medium access control (MAC) protocol. It is known that wireless devices following the 802.11 standard MAC protocol, i.e. the distributed coordination function (DCF), suffer from packet collisions when multiple nodes simultaneously transmit. This significantly degrades the throughput performance. Recently, several studies have reported access techniques to reduce the number of packet collisions and to achieve a collision free WLAN. Although these studies have shown that the number of collisions can be reduced to zero in a simple way, there have been a couple of remaining issues to solve, such as dynamic parameter adjustment and fairness to legacy DCF nodes in terms of channel access opportunity. Recently, In-Band Full Duplex (IBFD) communication has received much attention, because it has significant potential to improve the communication capacity of a radio band. IBFD means that a node can simultaneously transmit one signal and receive another signal in the same band at the same time. In order to maximize the performance of IBFD communication capability and to fairly share access to the wireless medium among distributed devices in WLANs, a number of IBFD MAC protocols have been proposed. However, little attention has been paid to fairness issues between half duplex nodes (i.e. nodes that can either transmit or receive but not both simultaneously in one time-frequency resource block) and IBFD capable nodes in the presence of the hidden node problem

Achieving Low latency and High Packet Reception Ratio in Media Access Control Layer in VANET

Vehicular ad hoc networks (VANETs) or inter-vehiclecommunication (IVC) makes possible the development of a number ofinnovative and powerful transportation system applications. VANETtechnology proves an important extension of both cellular andwireless local area networks (WLANs) currently used in thetransportation industry. It is widely recognized that thetransportation industry serves as an ideal platform for a largenumber of existing and future wireless applications, many of whichhave yet to be developed for commercial use.Safety messaging is one of the most critical uses for VANET,supporting a number of potential safety applications, e.g. emergencyelectronic brake lights, lane change and pre-crash warning, amongothers. Many applications require extremely low latency (less than100ms) and highly reliable (over 99\% packet delivery ratio)communication services. In order to satisfy these criticalrequirements, an efficient media access control (MAC) layer isnecessary. At the time of this writing, a de facto standard of VANETMAC is being developed.Extensive VANET MAC research with regard to safety applications hasyet to be done. The proposed base for the VANET future standard usesan 802.11a media access layer whose performance-although studied-isknown to contain deficiencies and was accomplished outside theVANET context. These factors motivated the author to initiate thestudy of VANET and MAC.In this work, MAC for VANET MAC is extensively researched, and ahistory of MAC is initially reviewed. The special and criticalrequirements of VANET MAC are presented and four major categorieswere investigated and analyzed. Because the under-development of802.11p is based on the IEEE 802.11a, special consideration is givenwith regard to the performance of 802.11a MAC and associatedrequirements. Extensive research enhancements centering on safetyapplications of the 802.11 MAC are conducted. The author's researchgenerated a platform in which VANET performance can bequantitatively evaluated, analyzed, and verified. The quantitativebehavior of the current protocols/algorithms, which include delayand packet delivery ratio, are presented on this platform.Furthermore, the future protocol and algorithm proposals can beadded into this platform so that a faster research cycle can beachieved. Through theoretical analysis and simulation, thisinvestigation shows that current proposed VANET MAC and 802.11a MACenhancements have yet met the critical requirements of VANET. Thefuture work may focus on how to use this theoretical model andsimulation tool to assist MAC layer protocol design. Meanwhile, whennew algorithms are proposed or accepted by the standard, this modeland tool can serve as a fast and convenient platform, where the newalgorithm can be easily added for the sake of evaluation andverification. The feasibility of relaxing some assumptions includedtherein, such as the hidden node problem in a two dimensional space,may also be studied to make the platform closer to a real system

Use of Inferential Statistics to Design Effective Communication Protocols for Wireless Sensor Networks

This thesis explores the issues and techniques associated with employing the principles of inferential statistics to design effective Medium Access Control (MAC), routing and duty cycle management strategies for multihop Wireless Sensor Networks (WSNs). The main objective of these protocols are to maximise the throughput of the network, to prolong the lifetime of nodes and to reduce the end-to-end delay of packets over a general network scenario without particular considerations for specific topology configurations, traffic patterns or routing policies. WSNs represent one of the leading-edge technologies that have received substantial research efforts due to their prominent roles in many applications. However, to design effective communication protocols for WSNs is particularly challenging due to the scarce resources of these networks and the requirement for large-scale deployment. The MAC, routing and duty cycle management protocols are amongst the important strategies that are required to ensure correct operations of WSNs. This thesis makes use of the inferential statistics field to design these protocols; inferential statistics was selected as it provides a rich design space with powerful approaches and methods. The MAC protocol proposed in this thesis exploits the statistical characteristics of the Gamma distribution to enable each node to adjust its contention parameters dynamically based on its inference for the channel occupancy. This technique reduces the service time of packets and leverages the throughput by improving the channel utilisation. Reducing the service time minimises the energy consumed in contention to access the channel which in turn prolongs the lifetime of nodes. The proposed duty cycle management scheme uses non-parametric Bayesian inference to enable each node to determine the best times and durations for its sleeping durations without posing overheads on the network. Hence the lifetime of node is prolonged by mitigating the amount of energy wasted in overhearing and idle listening. Prolonging the lifetime of nodes increases the throughput of the network and reduces the end-to-end delay as it allows nodes to route their packets over optimal paths for longer periods. The proposed routing protocol uses one of the state-of-the-art inference techniques dubbed spatial reasoning that enables each node to figure out the spatial relationships between nodes without overwhelming the network with control packets. As a result, the end-to-end delay is reduced while the throughput and lifetime are increased. Besides the proposed protocols, this thesis utilises the analytical aspects of statistics to develop rigorous analytical models that can accurately predict the queuing and medium access delay and energy consumption over multihop networks. Moreover, this thesis provides a broader perspective for design of communication protocols for WSNs by casting the operations of these networks in the domains of the artificial chemistry discipline and the harmony search optimisation algorithm

Timestepped Stochastic Simulation of 802.11 WLANs

Performance evaluation of computer networks is primarily done using packet-level simulation because analytical methods typically cannot adequately capture the combination of state-dependent control mechanisms (such as TCP congestion control) and stochastic behavior exhibited by networks. However, packet-level simulation becomes prohibitively expensive as link speeds, workloads, and network size increase. Timestepped Stochastic Simulation (TSS) overcomes scalability problems of packet-level simulation by generating a sample path of the system state S(t) at time t=d,2d,... rather than at each packet transmission. In each timestep [t,t+d], the distribution Pr[S(t+d)|S(t)] is obtained analytically, and S(t+d) is sampled from it. This dissertation presents TSS for shared links, specifically, 802.11 WLAN links. Our method computes sample paths of instantaneous goodput N_i(t) for all stations "i" in a WLAN over timesteps of length "d". For accurate modeling of higher layer protocols, "d" should be lesser than their control timescales (e.g., TCP's round-trip time). At typical values of "d" (e.g, 50ms), N_i(t)'s are correlated across timesteps (e.g., a station with high contention window has low goodput for several timesteps) as well as across stations (since they share the same media). To model these correlations, we obtain, jointly with the N_i(t)'s, sample paths of the WLAN's state, which consists of a contention window and a backoff counter at each station. Comparisons with packet level simulations show that TSS is accurate and provides up to two orders of magnitude improvement in simulation runtime