Variable Beam Width Selection for Improving the Throughput of IEEE 802.11ad Wireless LAN in the Contention Based Access Period

The hybrid MAC protocol specified by IEEE 802.11ad for millimeter wave wireless LANs consist of carrier sense multiple access/collision avoidance (CSMA/CA) during the contention based access periods (CBAPs) and TDMA during the service periods. To provide channel access during CBAP, the coverage area around the access point (AP) can be divided into several quasi omni (QO) beam levels. When uplink channel access during CBAP is considered, every directional multigigabit station residing within a QO level uses CSMA/CA protocol for getting the transmission opportunity. With equal beam width receive QO levels at the AP, we present an analytical model to compute the uplink throughput of the network in the CBAP, by closely following the 802.11ad MAC protocol specifications. We demonstrate that PHY layer MCS (modulation and coding scheme) dependent adaptive selection of QO levels can improve the throughput performance. In the second part of the paper, we consider that PCP/AP can have at most three radios, each tuned to operate in non-overlapping frequency bands as specified by 802.11ad PHY. We establish that such an arrangement can lead to concurrent transmissions in the network and improve the uplink throughput performance.     

Performance analysis of IEEE 802.11ah wireless local area network under the restricted access window‐based mechanism

IEEE 802.11ah is an approved amendment to IEEE 802.11 wireless local area network (WLAN) standard to support growing demand for machine‐to‐machine (M2M) applications. To enable an efficient scheme for accessing the channel by a large number of stations (STAs) within the coverage of an access point, 802.11ah has developed a novel mechanism known as Restrictred Access Window (RAW). Here, a group of STAs attempts channel access during their designated RAW slot by following the carrier sense multiple access‐collission avoidance (CSMA‐CA)‐based enhanced distributed channel access (EDCA) mechanism. In this paper, we develop an analytical model for finding the nonsaturation/saturation throughput of 802.11ah WLAN under the RAW‐based channel access mechanism. We describe an analytical model for finding the average frame delay as well. The impact of the number of STAs and number of groups on network throughput and average delay are presented. We establish that the RAW mechanism can improve the throughput while the average frame delay gets reduced. The analytical results are validated by extensive simulation studies.     

Relay-volunteered multi-rate cooperative MAC protocol for IEEE 802.11 WLANs

In IEEE 802.11, the rate of a station (STA) is dynamically determined by link adaptation. Low-rate STAs tend to hog more channel time than high-rate STAs due to fair characteristics of carrier sense multiple access/collision avoidance, leading to overall throughput degradation. It can be improved by limiting the transmission opportunities of low-rate STAs by backoff parameters. This, however, may cause unfair transmission opportunities to low-rate STAs. In an attempt to increase overall throughput by volunteer high-rate relay STAs while maintaining fairness, we propose a new cooperative medium access control (MAC) protocol, relay-volunteered multi-rate cooperative MAC (RM-CMAC) based on ready to send/clear to send in multi-rate IEEE 802.11. In the RM-CMAC protocol, we show that the effect of hogging channel time by low-rate STAs can be remedied by controlling the initial backoff window size of low-rate STAs and the reduced transmission opportunity of low-rate STAs can be compensated by the help of volunteer high-rate relay STAs. We analyze the performance of RM-CMAC, i.e., throughput and MAC delay, by a multi-rate embedded Markov chain model. We demonstrate that our analysis is accurate and the RM-CMAC protocol enhances the network throughput and MAC delay while maintaining the fairness of low-rate STAs.     

Performance improvements of HCCA scheduling in V2R environments

This paper addresses the issue of real‐time data transmission in vehicles to roadside environment by the hybrid coordination function controlled channel access (HCCA) scheme with Institute of Electrical and Electronics Engineers 802.11p protocol. The HCCA is one of the medium access protocols specified in 802.11p standard, which uses a polling scheme similar to the point coordination function to provide a reliable QoS. In this paper, we improve the HCCA polling scheme and design a new data transmission scheduling method. We also prepared a mathematical model to systematically evaluate the performance of the HCCA in terms of average delay. Moreover, we analyze the factors that could impact the average delay, throughput, and packet loss rate as well. The simulation results are compared with the original scheme specified in the standard. The simulation results demonstrate that the proposed delay model could estimate the average delay of the HCCA with a high precision, whereas the proposal of the enhancement of the HCCA has lower delay, lower loss rate, and higher throughput than the one specified in the standard. Copyright © 2013 John Wiley & Sons, Ltd.     

A Beacon-Based Collision-Free Channel Access Scheme for IEEE 802.11 WLANs

In IEEE 802.11 based WLAN standard, distributed coordination function is the fundamental medium access control (MAC) technique. It employs a CSMA/CA with random binary exponential backoff algorithm and provides contention-based distributed channel access for stations to share the wireless medium. However, performance of this mechanism drops dramatically due to random structure of the backoff process, high collision probability and frame errors. That is why development of an efficient MAC protocol, providing both high throughput for data traffic and quality of service (QoS) support for real-time applications, has become a major focus in WLAN research. In this paper, we propose an adaptive beacon-based collision-free MAC adaptation. The proposed scheme makes use of beacon frames sent periodically by access point, lets stations enter the collision-free state and reduces the number of idle slots regardless of the number of stations and their traffic load (saturated or unsaturated) on the medium. Simulation results indicate that the proposed scheme dramatically enhances the overall throughput and supports QoS by reducing the delay, delay variation and dropping probability of frames.     

A spatial clustering group division-based OFDMA access protocol for the next generation WLAN

The next generation wireless local area network (WLAN) needs to significantly improve the area throughput in high-dense deployment scenario. Orthogonal frequency division multiple access (OFDMA), considered as the key technology of the next generation WLAN, has been adopted by IEEE 802.11ax. However, most existing studies have one tricky problem: interference extension problem, i.e., the stations (STAs) placed at dispersive locations from one basic service set (BSS) access channel and transmit data simultaneously through OFDMA, thereby interfering a large area and suppressing the potential transmissions around this BSS. Unfortunately, high-dense deployment scenario exacerbates interference extension problem. This article proposes a spatial clustering group division-based OFDMA (SCGD-OFDMA) protocol, which enables the geographically close STAs to form spatial clustering groups, named SCGs. Each SCG has a leader STA and several member STAs. Each SCG’s leader STA contends for channel resources. After that, the leader STAs that successfully contending channel are scheduled by the access point one by one to trigger its member STAs to transmit uplink data by using OFDMA. Therefore, the geographical interference area is reduced and the area throughput is improved since the concurrent STAs in one SCG are located in limited area. This article theoretically analyzes the optimal SCG establishment, and throughput and area throughput of SCGD-OFDMA. Theoretical analysis is consistent with simulation results. The simulation results also show that when the number of STAs is 200 and all resource units are used for random access, SCGD-OFDMA outperforms IEEE 802.11ax and OMAX in area throughput by 56.13% and 190.97%, respectively.

     

A Hybrid Collision Avoidance Scheme for Ad Hoc Networks

A novel hybrid collision avoidance scheme that combines both sender-initiated and receiver-initiated collision-avoidance handshake is proposed for multi-hop ad hoc networks. The new scheme is compatible with the popular IEEE 802.11 MAC protocol and involves only some additional queue management and book-keeping work. Simulations of both UDP- and TCP-based applications are conducted with the IEEE 802.11 MAC protocol, a measurement-based fair scheme and the new scheme. It is shown that the new scheme can alleviate the fairness problem with almost no degradation in throughput. More importantly, it is shown that without explicit information exchange among nodes, the fairness problem cannot be solved conclusively if reasonable throughput is to be maintained. Hence it calls for further work to integrate the new collision avoidance scheme with other schemes that approximate fair queueing and use more contention information in channel access to achieve some QoS assurances in ad hoc networks.     

Delay guaranteed MDP scheduling scheme for HCCA based on 802.11p protocol in V2R environments

In recent years, the vehicular ad hoc network has attracted worldwide attention from academe and industry. Many researches have been executed to improve the quality of services (QoS) of the intelligent transportation system. However, current existing channel access schemes at the medium access control layer specified in 802.11 protocol, including hybrid coordination function control channel access (HCCA) and enhanced distributed channel access, could not efficiently achieve the QoS requirements in some special situations. This paper proposes a delay guaranteed HCCA (DG‐HCCA) scheduling scheme, which works based on a Markov decision process model and the measurement of historic performance, to guarantee the QoS enhanced data transmission for vehicles to roadside unit. Besides, this paper also presents a performance analysis model to systematically evaluate the system performance of the channel utility and the average delay. The performance of the proposed delay guaranteed HCCA scheduling scheme is compared with that of original HCCA scheme specified in 802.11p standard and other 2 HCCA improved schemes by the simulation experiments. The simulation results demonstrate that the proposed solution could highly fulfill the transmission delay requirements with a better channel utility and less loss rates than those by the standard HCCA scheme and other 2 schemes.     

Supporting multimedia streaming and best‐effort data transmission over IEEE 802.11e EDCA

As demand for broadband multimedia wireless services increases, improving quality of service (QoS) of the widely deployed IEEE 802.11 wireless LAN (WLAN) has become crucial. To support the QoS required by a wide range of applications, the IEEE 802.11 working group has defined a new standard: IEEE 802.11e. In this paper, we propose a measurement‐based dynamic media time allocation (MBDMTA) scheme combined with a concatenating window scheme to support real‐time variable bit rate (rt‐VBR) video and best‐effort (BE) data transmission using IEEE 802.11e enhanced distributed channel access (EDCA). To provide the QoS guarantee for rt‐VBR video, the proposed MBDMTA scheme dynamically assigns channel time to the rt‐VBR video based on the estimate of the required network resources. On the other hand, the concatenating window scheme controls the contention window (CW) ranges of different priority flows such that real‐time services always have higher channel access probability, thus achieving the capability of preemptive priorities. In addition, the concatenating window scheme preserves fairness among flows of the same class and attains high channel utilization under different network conditions. Simulation results demonstrate that the throughput and delay performance improve significantly for the transmission of rt‐VBR video and BE traffic as compared to those for the 802.11e EDCA specification. It is also revealed that combining the two proposed schemes provides seamless integration and reliable transmission of digital video and data service within the 802.11e EDCA framework. Copyright © 2007 John Wiley & Sons, Ltd.     

Study on bandwidth control for multiple transmission rates in IEEE 802.11e EDCAF

IEEE 802.11e supports the guaranteed quality of service (QoS) by providing different transmission priorities. IEEE 802.11e improves the media access control layer of IEEE 802.11 to satisfy the different QoS requirements by introducing two channel access functions: the enhanced distributed channel access (EDCA) and the hybrid coordination function (HCF) controlled channel access (HCCA). Signal quality may affect the available bandwidth and transmission rate, because the characteristic of communication channel in wireless environment is in random time‐variation manner. Generally a station using a lower transmission rate will occupy communication channel for a longer time and degrade system performance, which causes unfairness and cannot provide the guaranteed QoS for the stations with higher transmission rates. We propose a bandwidth control scheme (BCS) by combining the IEEE 802.11e enhanced distributed channel access function (EDCAF) protocol to overcome the guaranteed bandwidth issue in multirate environments. A multirate discrete Markov chain model is analyzed for the multirate transmission system in this paper. According to the obtained results, BCS improves performance especially in throughput and makes the different QoS requirements be processed efficiently and flexibly. Copyright © 2009 John Wiley & Sons, Ltd.     

A fuzzy logic cooperative MAC for MANET

In both wireless local area networks（WLAN） and mobile ad hoc networks（MANET）, the 1EEE 802.11e medium access control （MAC） protocol is proposed for an effective quality of service （QoS） solution. A number of studies have been done to enhance the performance of 802.11e in MANET by independently adjusting contention window （CW） size of each access category （AC） in every node. However, without the cooperation between the high priority flows and lower priority flows, the QoS goal of high priority flows cannot achieve effectively. In this article, a fuzzy logic based cooperative MAC protocol （FLCMAC） is proposed to cooperate amongst network flows and dynamically adjust access probability of each low priority flow affecting the high priority flows to satisfy their QoS requirement. The simulation results indicate that compared to the enhanced distributed channel access （EDCA） scheme of 802.11e, the FLCMAC consistently excels, in terms of throughput and delay under moderate and heavy background traffic both in single-hop and multi-hop scenarios.     

Deployment of a reliable 802.11e experimental setup for throughput measurements

This paper describes an experimental setup for measuring the throughput of an 802.11 network that supports Quality of Service (QoS) mechanisms, addressing some issues concerning the comparison between experimental and theoretical results. The setup is an ad hoc network in which the nodes implement the Multiband Atheros Driver for Wireless Fidelity (MADWiFi). There are three main contributions of this study. The first one describes the adjustments to the MADWiFi source code that guarantee the control of the QoS parameters in ad hoc mode. The second contribution aims to provide a practical method for verifying if the backoff generated by a given wireless card is uniformly distributed, as dictated by the 802.11 standard. This represents a key point when theoretical and experimental results must be compared, since many vendors adopt nonuniform backoff distributions in their commercial cards. As a third contribution, this paper presents a theoretical nonsaturated analysis that provides the throughput and the successful packet delay of an 802.11 network supporting QoS in presence of nonuniform backoff. The throughput derived from this analysis using a uniform backoff, which is included in the proposed model as a particular case, is compared to the measurements provided by the deployed setup. Copyright © 2010 John Wiley & Sons, Ltd.     

Quality‐of‐service‐aware cluster‐based service discovery approach for mobile ad hoc networks

This paper presents a quality‐of‐service (QoS) distributed service discovery approach for mobile ad hoc network environments. The approach builds upon a clustered topology, where the clusterhead (CH) is assigned additional roles having to do with maintaining a directory of services in the network and aggregating and computing QoS scores about service providers (SPs) from requesting nodes (RNs) and the providers themselves. To reduce the amount of overhead traffic, the design makes extensive use of piggybacking for relaying and updating the CHs with QoS scores. A mobile device that is interested in a certain service submits a request to its CH, which uses cached QoS data to return a ranked list of SPs that offer the type of requested service. On the basis of its interaction with the SP, the device sends the CH next time it makes a request a score reflecting its perception of the SP's QoS. Over time, the CH develops robust QoS data that it uses to help devices obtain the best available service. Theoretical analysis and experimental evaluation based on simulations prove the advantages of the proposed system and the effectiveness of its operations. Copyright © 2013 John Wiley & Sons, Ltd.     

Provisioning QoS controlled media access in vehicular to infrastructure communications

The emerging IEEE 802.11p standard adopts the enhanced distributed channel access (EDCA) mechanism as its Media Access Control (MAC) scheme to support quality-of-service (QoS) in the rapidly changing vehicular environment. While the IEEE 802.11 protocol family represents the dominant solutions for wireless local area networks, its QoS performance in terms of throughput and delay, in the highly mobile vehicular networks, is still unclear. To explore an in-depth understanding on this issue, in this paper, we develop a comprehensive analytical model that takes into account both the QoS features of EDCA and the vehicle mobility (velocity and moving directions). Based on the model, we analyze the throughput performance and mean transmission delay of differentiated service traffic, and seek solutions to optimally adjust the parameters of EDCA towards the controllable QoS provision to vehicles. Analytical and simulation results are given to demonstrate the accuracy of the proposed model for varying EDCA parameters and vehicle velocity and density.     

A traffic control system for IEEE 802.11 networks based on available bandwidth estimation

To support Quality of service (QoS)‐sensitive applications like real‐time video streaming in IEEE 802.11 networks, a MAC layer extension for QoS, IEEE 802.11e, has been recently ratified as a standard. This MAC layer solution, however, addresses only the issue of prioritized access to the wireless medium and leaves such issues as QoS guarantee and admission control to the traffic control systems at the higher layers. This paper presents an IP‐layer traffic control system for IEEE 802.11 networks based on available bandwidth estimation. We build an analytical model for estimating the available bandwidth by extending an existing throughput computation model, and implement a traffic control system that provides QoS guarantees and admission control by utilizing the estimated available bandwidth information. We have conducted extensive performance evaluation of the proposed scheme via both simulations and measurements in the real test‐bed. The experiment results show that our estimation model and traffic control system work accurately and effectively in various network load conditions without IEEE 802.11e. The presence of IEEE 802.11e will allow even more efficient QoS provision, as the proposed scheme and the MAC layer QoS support will complement each other. Copyright © 2006 John Wiley & Sons, Ltd.     

Performance analysis of differentiated QoS in IEEE 802.11e WLANs

This paper proposes a multi‐dimensional Markov model to analyse the performance of the IEEE 802.11e EDCF MAC protocol. Based on this model, we present extensive performance evaluation in terms of throughput, throughput ratios, and access delay of flows of distinct priorities under RTS/CTS mode. We also provide quantitative analysis of the impact of prioritized parameters, i.e. Arbitration InterFrame Space (AIFS), Contention Window (CW) on Quality of Service (QoS) differentiation. The accuracy of the proposed model is verified by means of comparing the numerical results obtained from both analytical model and simulations. Our research can be used as a guideline for the prediction of how flows belonging to a certain Traffic Category (TC) perform with their TC‐specific parameters, as well as designing EDCF‐based WLANs and tuning the parameters to achieve the desirable differentiated QoS objectives. Copyright © 2005 John Wiley & Sons, Ltd.     

Routing protocol development for quality of service optimization of video‐on‐demand system over mobile ad hoc networks

A video‐on‐demand (VoD) application system over mobile ad hoc networks typically requires particular quality of service (QoS) parameters to be achieved. In this paper, we have proposed a novel QoS‐based routing protocol called as mobile VoD protocol. This protocol has been developed for improving the QoS of the mobile VoD system (normal Mobi_VoD approach). The protocol uses customer caching scheme for storing the first fragment of the entire video in the mobile customers and thereafter broadcast them when the new mobile customers missed the portion of the already transmitted first fragment for reducing the service delay of the customer, consequently optimizing QoS parameters. Various scenarios have been studied, and the efficacy of simulation results proves that the proposed system architecture in which the mobile customers use an ad hoc network caching scheme (mobile VoD protocol) is more efficient and performs better than the existing system (ad hoc on‐demand distance vector protocol) when compared in terms of QoS parameters such as the end‐to‐end delay, energy consumption, packet delivery ratio, throughput, and overhead.     

基于Ad hoc网络的新EDCA参数调整方案

IEEE802.11e标准中业务优先级不同的AC（access category）是通过设置不同的竞争窗口最大、最小值CWmax,CWmin和仲裁帧间隔值来体现的,如高优先级AC设置小的CWmin,CWmax和AIFS值.研究表明,EDCA对每个AC指定的默认参数值只适用于中等负载、节点数目少的网络场景,并不适用于负载较重、节点数目较多且链路动态变化的Ad hoc网络环境.提出了一种根据网络状况动态调整IEEE 802.11e EDCA的QoS参数的新方案I-ED-CA,该方案根据网络状态调整竞争窗口CW,并通过修改退避计数器值调整AIFS参数,使I-EDCA适合动态变化的Ad hoc网络环境,采用NS2仿真软件对EDCA改进协议I-EDCA进行仿真.仿真结果表明,随着网络中负载的增加,I-EDCA的吞吐量表现平稳,而EDCA吞吐量是下降的.另外,在业务公平性方面,对优先级不同的业务I-EDCA比EDCA的表现更公平.     

Dynamic bandwidth management in IEEE 802.11-based multihop wireless networks

In this paper, we propose a new protocol named dynamic regulation of best-effort traffic (DRBT) which supports quality of service (QoS) throughput guarantees and provides a distributed regulation mechanism for best-effort traffic in multihop wireless networks. By adapting dynamically the rate of best-effort traffic at the link layer, DRBT increases the acceptance ratio of QoS flows and provides a good use of the remaining resources through the network. Our protocol also provides an accurate method to evaluate the available bandwidth in IEEE 802.11-based ad hoc networks which is able to differentiate QoS applications from best-effort traffic. Through extensive simulations, we compare the performance of our proposal scheme with some others protocols like QoS protocol for ad hoc real-time traffic for instance.     

Performance analysis and comparison of burst transmission schemes in unsaturated 802.11e WLANs

Contention free bursting (CFB) and block acknowledgement (BACK) are two innovative burst transmission schemes specified in the IEEE 802.11e standard for reducing the contention overheads and further improving the channel utilization of wireless local area networks (WLANs). Existing studies on performance analysis of the CFB and BACK schemes have been primarily focused on the system throughput and have not taken into account the realistic factors, such as unsaturated traffic loads and finite buffer capacity. To fill this gap, this paper proposes a new and comprehensive analytical model for evaluating the Quality‐of‐Service (QoS) metrics including throughput, end‐to‐end delay, and frame loss probability of both burst transmission schemes under unsaturated traffic conditions. The proposed model is validated through extensive simulation experiments and then is used to conduct performance analysis and comparison of the burst transmission schemes under various working conditions. The analytical results reveal that (1) both CFB and BACK schemes can substantially improve the QoS performance; (2) BACK scheme outperforms the CFB scheme when the transmission opportunity (TXOP) limit exceeds a threshold; (3) the analytical model can be used to identify the optimal configuration of system parameters for the burst transmission schemes subject to QoS constraints. Copyright © 2010 John Wiley & Sons, Ltd.