Adaptive bandwidth sharing mechanism for quality of service administration in infrastructure wireless networks

In infrastructure wireless networks, the wireless hop can be considered as another hop of the transmission path. With the rapid growth of wireless traffics, the future wireless network is expected to provide services for heterogeneous data traffics with different quality of service (QoS) requirements. Most proposed schemes do not have adaptive mechanisms to deal with the environment changes. In real situation, bandwidths, error rates and loss rates of wireless links vary frequently. We will base on the differentiated service model and propose a wireless differentiation (WD) scheme for user datagram protocol (UDP) flows and a wireless differentiation with prioritised ACK scheme for connections with transmission control protocol (TCP) flows. Both schemes provide QoS support for IEEE 802.11b and do not change the basic access mechanism of IEEE 802.11b.     

Differentiated cooperative multiple access for multimedia communications over fading wireless networks

The quality of service (QoS) support for multimedia communications faces a big challenge in a fading wireless network. On one hand, conventional automatic repeat request (ARQ) schemes are not effective for small-scale fading channels with correlated errors due to consecutive retransmission failures. On the other hand, large-scale fading due to propagation loss or shadowing severely limits transmission range. A novel differentiated cooperative medium access control (MAC) protocol, called DC-MAC, is proposed to enhance the QoS support for multimedia communications while supporting service differentiation based on the IEEE 802.11e architecture. By enabling cooperative ARQ, the retransmission is initiated from an appropriate transmission queue of an appropriate relay node instead of the original source. Since unnecessary and useless retransmissions may intensify the node contention and degrade the system performance contrarily, a novel negative acknowledgement feedback mechanism is introduced for loss distinguishing and channel estimation such that cooperative retransmission will be employed only when necessary and only by competent nodes. Extensive simulations are conducted on the OPNET platform to analyse the performances of DC-MAC under both small-scale and large-scale fading. Simulation results show that the proposed scheme significantly improves the performances of both multimedia applications and best-effort data applications in terms of throughput, delay and coverage with moderate user contention.     

Dynamic resource allocation for supporting real-time multimedia applications in IEEE 802.15.3 WPANs

The IEEE 802.15.3 medium access control (MAC) protocol is an emerging standard for high-rate wireless personal area networks (WPANs), especially for supporting high-quality real-time multimedia applications. Despite defining quality of service (QoS) signalling mechanisms for interoperability between devices, IEEE 802.15.3 does not specify resource allocation algorithms that are left to manufacturers. To guarantee the QoS of real-time variable bit rate (VBR) videos and utilise the radio resource efficiently, the authors propose a dynamic resource allocation algorithm. The proposed bandwidth allocation algorithm is based on a novel traffic predictor. Recently, the variable step-size normalised least mean square (VSSNLMS) algorithm was employed for on-line traffic prediction of VBR videos. However, the performance of the VSSNLMS algorithm significantly degrades due to the abrupt traffic variation occurring at the scene boundary. To tackle this problem, the authors design a novel traffic predictor based on a simple scene detection algorithm and the VSSNLMS algorithm. Analyses using real-life MPEG video traces indicate that the proposed traffic predictor significantly outperforms the VSSNLMS algorithm with respect to the prediction error. The performance of the proposed bandwidth allocation algorithm is also investigated by comparing several existing algorithms. Simulation results demonstrate that the proposed bandwidth allocation algorithm surpasses other mechanisms in terms of channel utilisation, buffer usage and packet loss rate.     

Design and theoretical analysis of throughput enhanced spatial reuse distributed coordination function for IEEE 802.11

The IEEE 802.11 distributed coordination function (DCF) employs a carrier sensing mechanism, a simple and effective mechanism to mitigate collisions in wireless networks. But the carrier sensing mechanism is inefficient in terms of shared channel use because an overcautious channel assessment approach is used to estimate interference at a receiver. A DCF node simply blocks its transmission when it senses that the channel is busy. However, in many cases this channel assessing node?s own transmission may not generate enough interference to disrupt the ongoing transmission at the receiver. This overcautious channel assessment unnecessarily blocks transmission attempts, and thus degrades the overall network throughput. To avoid this unnecessary blocking, the authors propose a spatial reuse DCF (SRDCF), which utilises location information and transmission parameters to make accurate channel assessments and to permit concurrent transmissions by adjusting the transmission power. SRDCF also resolves the contention between opportunistic concurrent transmissions with a secondary backoff counter. Consequently, the proposed scheme improves the overall network throughput because of more concurrent transmissions. The authors theoretically analyse the performance enhancement of SRDCF over the original IEEE 802.11 DCF by using a Markov chain model and verify it through simulations.     

Survey and Analysis of VoIP Frame Aggregation Methods over A-MSDU IEEE 802.11n Wireless Networks

The IEEE 802.11n standard has provided prominent features that greatly contribute to ubiquitous wireless networks. Over the last ten years, voice over IP (VoIP) has become widespread around the globe owing to its low-cost or even free call rate. The combination of these technologies (VoIP and wireless) has become desirable and inevitable for organizations. However, VoIP faces a bandwidth utilization issue when working with 802.11 wireless networks. The bandwidth utilization is inefficient on the grounds that (i) 80 bytes of 802.11/RTP/UDP/IP header is appended to 10–730 bytes of VoIP payload and (ii) 765 µs waiting intervals follow each 802.11 VoIP frame. Without considering the quality requirements of a VoIP call, be including frame aggregation in the IEEE 802.11n standard has been suggested as a solution for the bandwidth utilization issue. Consequently, several aggregation methods have been proposed to handle the quality requirements of VoIP calls when carried over an IEEE 802.11n wireless network. In this survey, we analyze the existing aggregation methods of VoIP over the A-MSDU IEEE 802.11n wireless standard. The survey provides researchers with a detailed analysis of the bandwidth utilization issue concerning the A-MSDU 802.11n standard, discussion of the main approaches of frame aggregation methods and existing aggregation methods, elaboration of the impact of frame aggregation methods on network performance and VoIP call quality, and suggestion of new areas to be investigated in conjunction with frame aggregation. The survey contributes by offering guidelines to design an appropriate, reliable, and robust aggregation method of VoIP over 802.11n standard.     

Cross-layer design for block subchannel allocation and admission control in the IEEE 802.16 OFDMA networks

The flexibility of orthogonal frequency-division multiple access (OFDMA) technology necessitates a compromise between spectrum efficiency and quality of service (QoS) in IEEE 802.16 broadband wireless networks. This article proposes a complete solution with the nice feature of adaptive modulation and a coding scheme to provide both delay and loss rate guarantees for real-time services. The proposed method first determines the subframe boundary according to the current downlink and uplink backlogs. To comply with the IEEE 802.16 standard, the proposed method then groups contiguous subchannels and allocates them to proper connections based on the current loss rate and available modulation and coding schemes for each connection. By modeling the aggregated required subchannels as a Gaussian distribution, this study develops a simple admission control algorithm by checking if there are enough resources for a new connection. Simulation results show that the proposed solution can provide QoS guarantee with high spectrum efficiency.     

Integrated quality-of-service differentiation over IEEE 802.11 wireless LANs

The fundamental medium access control mechanism in IEEE 802.11 wireless LANs (WLANs)-distributed coordination function (DCF) only supports the best-effort service and does not support quality-of-service (QoS) differentiation. Enhanced distributed channel access (EDCA) in IEEE 802.11e supports delay differentiation. A new approach, EDCA+ , is proposed to enhance QoS over WLANs. It simultaneously achieves bandwidth, delay and jitter differentiation by distinguishing the minimum contention window, the maximum backoff stage or persistent factor and packet-loss rate differentiation by distinguishing the retry limit. Analytical models are proposed to analyse the performance of EDCA+ in terms of throughput, bandwidth, delay, jitter and packet-loss rate. Extensive simulations are also carried out to evaluate the accuracy of the proposed performance models and to compare the performance of DCF, EDCA and EDCA+. The simulation results show that EDCA+ performs better than DCF and EDCA in ensuring integrated QoS, and that the proposed analytical models are valid.     

Fair scheduling with rate control for IEEE 802.16 broadband wireless networks

Although the scheduling problem of the uplink transmission in the IEEE 802.16 broadband wireless access network is extensively discussed, most of the results are limited to the quality of service (QoS) upon throughput and delay requirement. But as in practice only limited wireless resources are made available, a fairness-based scheduling upon each connection?s QoS provides better outcomes. In this study, the authors propose a new fair uplink scheduling for real-time polling service and non-real-time polling service with the proportional sharing of excess bandwidth of the network. To implement the proposed fair scheduling that satisfies the delay requirement and full bandwidth utilisation, the authors introduce the rate control algorithm. With the proposed scheduling, we guarantee the fairness, delay requirement and full bandwidth utilisation which are not fully achieved in the existing results.     

A cross-layer adaptive algorithm for multimedia QoS fairness in WLAN environments using neural networks

The authors address the problem of providing fair multimedia quality-of-service (QoS) in IEEE 802.11 distributed co-ordination function-based wireless local area networks in the infrastructure mode where mobile hosts experience heterogeneous channel conditions due to mobility and fading effects. It was observed that unequal link qualities can pose significant unfairness of channel sharing, which may thereby lead to the degradation of multimedia QoS performed in adverse conditions. A cross-layer adaptation scheme that provides fair QoS by online adjusting the multidimensional medium access control layer backoff parameters in accordance with the application-layer QoS requirements as well as the physical-layer channel conditions was proposed. The solution is based on an optimisation approach, which utilises neural networks to learn the cross-layer function. Simulation results demonstrate that the proposed adaptation scheme can tackle heterogeneous channel conditions and random joining (or leaving) of hosts to achieve fair QoS in terms of throughput and packet delay.     

MAC-layer channel utilisation enhancements for wireless mesh networks

The authors focus on a wireless mesh network, that is, an ad hoc IEEE 802.11-based network whose nodes are either user devices or Access Points providing access to the mesh network or to the Internet. By relying on some work done within the IEEE 802.11s TG, the network nodes can use one control channel and one or more data channels, each on separate frequencies. Then, some problems related to channel access are identified and a MAC scheme is proposed that specifically addresses the problem of hidden terminals and the problem of coexisting control and data traffic on different frequency channels. An analytical model of the MAC scheme is presented and validated by using the Omnet++ simulator. Through the developed model, we show that our solution achieves very good performance both in regular and in very fragmented mesh topologies, and it significantly outperforms the standard 802.11 solution.     

Enhancing enhanced distributed channel access function based on cross-layer information for multirate wireless networks

IEEE 802.lie provides guaranteed quality of service (QoS) by proving different transmission priorities. IEEE 802. lie improves the media access control layer of IEEE 802.11 to satisfy the different QoS requirements by introducing two new channel access functions: the enhanced distributed channel access (EDCA) and the hybrid coordination function-controlled channel access. The available bandwidth and transmission rate may be easily affected by the signal quality, because the communication channel in a wireless environment operates in a random time-variation manner. Generally, a station using a low transmission rate will occupy the communication channel for a long time and degrade system performance, which causes bandwidth waste and unfairness; thus the guaranteed QoS for stations with higher transmission rates cannot be provided. An enhancing EDCAF (E DCAF) is proposed that consolidates the cross-layer concept and the IEEE 802.1 le EDCAF protocol. After simulation experiments, E DCAF obviously improves performance, especially in throughput and fairness. E DCAF scheduling also allows the different QoS requirements to be processed efficiently and flexibly.     

Performance analysis of IEEE 802.11 DCF and 802.11e EDCA based on queueing networks

The authors propose a new analytical model based on BCMP closed queueing networks in order to evaluate the performance of IEEE 802.11 DCF MAC protocol when all nodes are in the transmission range of each other, that is, a single hop wireless ad hoc network. By the proposed model, some performance metrics such as saturation and non-saturation throughput, distributions of channel access delay and the number of packets in the MAC buffer are derived. An extension of the proposed model is used for the analysis of IEEE 802.11e EDCA and the same performance metrics are evaluated for this protocol. Analytical results on IEEE 802.11e prove that differentiation in service is possible and channel share for each service type may be well assigned by tuning the MAC protocol parameters. Simulation results show consistency with our analytical results.     

Direction finding in IEEE802.11 wireless networks

A novel direction-finding method for stations of IEEE802.11 wireless local area networks is presented in this paper. The method uses a switched beam array for determining the direction of arrival of the incident electromagnetic field in a time efficient way and associates certain medium access control (MAC) layer functions with different radiation patterns of the switched antenna array, in order to determine the proper orientation of directional beams on both entities of a communication link. The application of the proposed method to an IEEE802.11 wireless network is presented and it is depicted how the method improves the network performance without requiring any modifications to the existing MAC protocol.     

无线局域网上IP语音传输的容量分析

由于无线媒介的易变性，IP语音在无线局域网上传输受到极大的限制。通过对无线局域网媒体接入层机制的分析，考虑了碰撞概率因素，提出了采用马尔可夫链模型来推导在IEEE 80211b/a/g标准下单个接入点同时支持IP语音用户最大容量的方法，计算出针对不同IP语音编码标准如G711, G729和G723.1下的用户容量上限。并在NS2仿真环境下进行结果验证。     

Quality of service supporting downlink scheduling scheme in worldwide interoperability for microwave access wireless access systems

IEEE 802.16 is a standardisation for a broadband wireless access in metropolitan area networks (MAN). Since the IEEE 802.16 standard defines the concrete quality of service (QoS) requirement, a scheduling scheme is necessary to achieve the QoS requirement. Many scheduling schemes are proposed with the purpose of throughput optimisation and fairness enhancement, however, few scheduling schemes support the delay requirement. In this study, the authors propose a new scheduling scheme reflecting the delay requirement. Specifically, the authors add the delay requirement term in the proportional fair scheduling scheme and the scheduling parameters are optimised with respect to the QoS requirement. Therefore the QoS requirement is achieved without the excessive resource consumption.     

Performance measurement of IEEE 802.11b-based networks affected by narrowband interference through cross-layer measurements

Researches and development efforts in wireless networking and systems are progressing at an incredible rate. Among them, measurement and analysis of performance achieved at network layer and perceived by end users is an important task. In particular, recent advances concerning IEEE 802.11b-based networks seem to be focused on the measurement of key parameters at different protocol levels in a cross-layered fashion, because of their inherent vulnerability to in-channel interference. By adopting a cross-layer approach on a real network set-up operating in a suitable experimental testbed, packet loss against signal-to-interference ratio in IEEE 802.11b-based networks is hereinafter assessed. Results of several measurements aimed at establishing the sensitivity of IEEE 802.11b carrier sensing mechanisms to continuous interfering signals and evaluating the effects of triggered interference on packet transmission.     

A pinwheel packet scheduling scheme for broadband wireless networks

Abstract

A frame‐based packet scheduling scheme, the pinwheel scheduling (PWS) scheme, is proposed and investigated at the medium access control (MAC) layer in broadband wireless networks. The objective of the proposed scheduling scheme is to provide low delay and low jitter for real‐time traffic. We have demonstrated in this paper that the proposed PWS scheme not only satisfies the packet‐level QoS requirements but also has low implementation cost. The PWS scheme gives the highest priority to CBR connections in a service cycle to minimize their delay and jitter. For ABR traffic, a number of slots are allocated to fit their MCR. The remaining time slots are then allocated to VBR traffic according to their PCR. Thus, the VBR traffic may suffer large delay and jitter when the number of CBR connections increases. The PWS with modular strategy (PWS/MS) is proposed to improve the performance of the VBR traffic. We also introduce three different slot‐reuse strategies named real‐time traffic first (RTF), non‐real‐time traffic first (NRTF) and longest queue first (LQF), respectively, to improve resource utilization. In order to demonstrate the performance of the PWS and PWS/MS schemes, comparisons are made with existing schemes such as the round‐robin (RR) and weighted‐round‐robin (WRR) by using OPNET software. Simulation results show that the proposed schemes are capable of maintaining the lowest delay and jitter for VBR and CBR traffic while not sacrificing the available bit rate (ABR) traffic.     

Effective transmission opportunity allocation scheme for real-time variable bit rate traffic flows with different delay bounds

The medium access control of IEEE 802.11e defines a novel coordination function, namely, hybrid coordination function (HCF), which allocates transmission opportunity (TXOP) to stations taking their quality of service (QoS) requirements into account. However, the reference TXOP allocation scheme of HCF controlled channel access, a contention-free channel access function of HCF, is only suitable for constant bit rate traffic. For variable bit rate traffic, packet loss may occur seriously. The authors propose a TXOP allocation scheme to efficiently allocate bandwidth and meet the QoS requirements in terms of both delay bound and packet loss probability. To achieve high bandwidth efficiency, the authors take advantage of not only intra-flow multiplexing gain of traffic flows with large delay bounds, but also inter-flow multiplexing gain of multiple traffic flows with different delay bounds. According to numerical results obtained by computer simulations, the proposed TXOP allocation scheme results in much higher bandwidth efficiency than previous algorithms under the same constraints of delay bounds and packet loss probability.     

WiMA: Towards a Multi-Criterion Association in Software Defined Wi-Fi Networks

Despite the planned installation and operations of the traditional IEEE 802.11 networks, they still experience degraded performance due to the number of inefficiencies. One of the main reasons is the received signal strength indicator (RSSI) association problem, in which the user remains connected to the access point (AP) unless the RSSI becomes too weak. In this paper, we propose a multi-criterion association (WiMA) scheme based on software defined networking (SDN) in Wi-Fi networks. An association solution based on multi-criterion such as AP load, RSSI, and channel occupancy is proposed to satisfy the quality of service (QoS). SDN having an overall view of the network takes the association and reassociation decisions making the handoffs smooth in throughput performance. To implement WiMA extensive simulations runs are carried out on Mininet-NS3-Wi-Fi network simulator. The performance evaluation shows that the WiMA significantly reduces the average number of retransmissions by 5%–30% and enhances the throughput by 20%–50%, hence maintaining user fairness and accommodating more wireless devices and traffic load in the network, when compared to traditional client-driven (CD) approach and state of the art Wi-Balance approach.     

Software architecture design,implementation, and evaluation of DCF-based MAC protocol on a low-power transceiver

The carrier-sensing multiple access with collision avoidance (CSMA/CA) protocol is the most well-known medium access control (MAC) protocol for wireless networks. Both the distributed coordination function (DCF) defined in IEEE 802.11 and the MAC layer defined in IEEE 802.15.4 are based on the CSMA/CA protocol. Nevertheless, these two standards have quite different carrier-sensing mechanisms. Different to continuous carrier sensing in DCF, an IEEE 802.15.4 node only senses the channel once just after a backoff. Sensing-once mechanism can reduce the computation loading on the CPU. However, it significantly increases the probability of failure transmission because a node is not fully aware of channel activity. This paper first proposes a software architecture integrating proper hardware features for designing a DCF-based MAC protocol and then successfully implements it on a low-power transceiver. In addition, this paper conducts experiments in a star topology network to compare the performance of the above DCF-MAC protocol with the IEEE 802.15.4 MAC protocol. Experimental results show that, without continuous sensing, the IEEE 802.15.4 network suffers a high transmission failure probability as the network size increases. Consequently, the proposed DCF-based MAC protocol outperforms the IEEE 802.15.4 MAC protocol in terms of packet loss probability and throughput.