Goodput and throughput comparison of single‐hop and multi‐hop routing for IEEE 802.11 DCF‐based wireless networks under hidden terminal existence

We investigate how multi‐hop routing affects the goodput and throughput performances of IEEE 802.11 distributed coordination function‐based wireless networks compared with direct transmission (single hopping), when medium access control dynamics such as carrier sensing, collisions, retransmissions, and exponential backoff are taken into account under hidden terminal presence. We propose a semi‐Markov chain‐based goodput and throughput model for IEEE 802.11‐based wireless networks, which works accurately with both multi‐hopping and single hopping for different network topologies and over a large range of traffic loads. Results show that, under light traffic, there is little benefit of parallel transmissions and both single‐hop and multi‐hop routing achieve the same end‐to‐end goodput. Under moderate traffic, concurrent transmissions are favorable as multi‐hopping improves the goodput up to 730% with respect to single hopping for dense networks. At heavy traffic, multi‐hopping becomes unstable because of increased packet collisions and network congestion, and single‐hopping achieves higher network layer goodput compared with multi‐hop routing. As for the link layer throughput is concerned, multi‐hopping increases throughput 75 times for large networks, whereas single hopping may become advantageous for small networks. The results point out that the end‐to‐end goodput can be improved by adaptively switching between single hopping and multi‐hopping according to the traffic load and topology. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhanced high‐performance distributed coordination function for IEEE 802.11 multi‐rate LANs

To compensate for the effects of fading in wireless channels, IEEE 802.11 systems utilize a rate‐adaptation mechanism to accomplish a multi‐rate capability. However, the IEEE 802.11 distributed coordination function results in a fundamental performance anomaly in multi‐rate networks; namely, when stations with different transmission rates collide, the throughput performance of the high‐rate station is significantly degraded by the relatively longer channel occupancy time of the low‐rate station. This study resolves this problem through the use of an enhanced high‐performance distributed coordination function (EHDCF) protocol. While most existing solutions to the multi‐rate performance anomaly problem have the form of simple contention‐based protocols, EHDCF has two modes, namely a contending mode and an active mode. In the proposed protocol, new stations joining the network are assigned a contending mode, but switch to an active node (and are therefore permitted to transmit data packets) as soon as they have gained access to the channel. Having transmitted a data packet, the active node then selects the next transmission station in accordance with a probability‐based rule designed such that the high‐rate stations within the network receive a greater number of transmission opportunities than the low‐rate stations. The simulation results show that the EHDCF protocol not only yields a significant improvement in the network throughput but also guarantees the temporal fairness of all the stations. Copyright © 2009 John Wiley & Sons, Ltd.     

Distributed point coordination function for IEEE 802.11 wireless ad hoc networks

The Distributed Point Coordination Function (DPCF) is presented in this paper as a novel Medium Access Control Protocol (MAC) for wireless ad hoc networks. DPCF extends the operation of the Point Coordination Function (PCF) defined in the IEEE 802.11 Standard to operate over wireless networks without infrastructure. In PCF, a central point coordinator polls the users to get access to the channel and data collisions are completely avoided, thus yielding high performance. In order to extend its high performance to networks without infrastructure, the DPCF is proposed in this paper as a combination of the Distributed Coordination Function (DCF) and the PCF. The general idea is to combine a dynamic, temporary, and spontaneous clustering mechanism based on DCF with the execution of PCF within each cluster. The backwards compatibility of DPCF with legacy 802.11 networks is also assessed in this paper. Comprehensive computer-based simulations demonstrate the high performance of this new protocol in both single-hop and multi-hop networks.     

Adaptive coordination function for IEEE 802.11 wireless LANs

Multiple access control (MAC) protocols play a significant role in wireless LANs. The IEEE 802.11 MAC protocol specifies two coordination functions that are Distributed Coordination Function (DCF) and Point Coordination Function (PCF). While both DCF and PCF are available in a wireless cell, we propose a novel access mechanism called Adaptive Coordination Function (ACF) to support various classes of traffic. The ACF superframe comprises two periods, one TDMA period designed for real-time traffic and followed by an adaptive period which adaptively employs DCF or PCF to support non-real-time traffic. In this paper, we apply the theory of M/G/1 queues to analyze the performance of adaptive period in terms of queuing delay, end-to-end delay, and saturation throughput. With our analytic model, DCF or PCF can be invoked appropriately according to the number of stations, packet arrival rate, packet payload size, and effective channel bit rate. Analytical results are derived for an extensive throughput and delay performance evaluation of both DCF and PCF.     

IEEE 802.11网络中质量驱动的视频传输技术研究综述

质量驱动的跨层技术是提高IEEE 802.11网络中视频传输服务质量的有效手段。传统传输控制技术的目标是降低分组丢失率、提高吞吐量等,但这些性能指标不能准确地反映终端的用户体验,也没有充分考虑视频数据的特点。质量驱动的跨层传输控制技术以提高终端用户的服务质量为直接目标,利用视频流的特点优化传输系统性能。介绍了IEEE 802.11协议关于服务质量的标准化进程,集中讨论了基于轮询和基于竞争的调度机制,并详细综述了两种机制下质量驱动的视频传输技术的最新研究成果及发展动向。     

A Framework for MPEG‐4 Contents Delivery over DMB

Digital Multimedia Broadcasting (DMB) is an upcoming standard in Korea used to provide mobile multimedia broadcasting service based on the Eureka‐147 Digital Audio Broadcasting (DAB) system. The current dominant multimedia coding standard, MPEG‐4, is foreseen to play an important role in forthcoming DMB services. However, the current approaches for transporting MPEG‐4 content over DMB networks are not optimized. To address this issue we propose a novel MPEG‐4 stream multiplexer, called M4SMux, which provides better stream multiplexing and delivery over DMB networks. M4SMux features an MPEG‐4 elementary‐stream interleaving mechanism that reduces the multiplexing overhead and a multiplex configuration mechanism that utilizes M4SLinkTable for easy content access. In addition, we propose an error correction method which enhances transport efficiency.     

Performance analysis of IEEE 802.11 DCF with stochastic reward nets

In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11‐based wireless local area networks (WLANs). We consider the distributed co‐ordination function (DCF) mode of medium access control (MAC). Stochastic reward nets (SRNs) are used as a modelling formalism as it readily captures the synchronization between events in the DCF mode of access. We present a SRN‐based analytical model to evaluate the mean delay and the average system throughput of the IEEE 802.11 DCF by considering an on–off traffic model and taking into account the freezing of the back‐off counter due to channel capture by other stations. We also compute the mean delay suffered by a packet in the system using the SRN formulation and by modelling each station as an M/G/1 queue. We validate our analytical model by comparison with simulations. Copyright © 2006 John Wiley & Sons, Ltd.     

Low‐Complexity MPEG‐4 Shape Encoding towards Realtime Object‐Based Applications

Although frame‐based MPEG‐4 video services have been successfully deployed since 2000, MPEG‐4 video coding is now facing great competition in becoming a dominant player in the market. Object‐based coding is one of the key functionalities of MPEG‐4 video coding. Realtime object‐based video encoding is also important for multimedia broadcasting for the near future. Object‐based video services using MPEG‐4 have not yet made a successful debut due to several reasons. One of the critical problems is the coding complexity of object‐based video coding over frame‐based video coding. Since a video object is described with an arbitrary shape, the bitstream contains not only motion and texture data but also shape data. This has introduced additional complexity to the decoder side as well as to the encoder side. In this paper, we have analyzed the current MPEG‐4 video encoding tools and proposed efficient coding technologies that reduce the complexity of the encoder. Using the proposed coding schemes, we have obtained a 56 percent reduction in shape‐coding complexity over the MPEG‐4 video reference software (Microsoft version, 2000 edition).     

Increasing end‐to‐end fairness over IEEE 802.11e‐based wireless mesh networks

In this paper, we discuss the issue of fairness in the IEEE802.11e over wireless mesh networks. Fairness is an important factor that we have to achieve before talking about QoS. Inspired by social networks approximations, and to achieve fairness and provide QoS by regulating heterogeneous traffic, we extended the original IEEE802.11e protocol by introducing a new algorithm based on the ‘token bucket’ concept. We also treat the problem of exposed/hidden nodes. Simulation results show that the proposed approach offers better performance than the IEEE802.11e one. Copyright © 2011 John Wiley & Sons, Ltd.     

A Novel Event Model for Performance Analysis of IEEE 802.11 DCF

After considering the memory effect among series events occurring on the channel, we propose a novel event model to analyze the channel status more precisely. The memory effect is caused by the backoff freezing regulation of IEEE 802.11 Distributed coordination function （DCF）, which has been ignored before and thus resulted in the inaccurate evaluation of the network performance. Based on our new event model, the network performance of IEEE 802.11 DCF, including throughput, packet delay distribution and energy efficiency is analyzed. Simulation results show that our model is highly accurate.     

Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs

Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co‐ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Broadcasting System Compliant with MPEG‐2/4 IPMPX

In this paper, we present an intellectual property management and protection (IPMP) system in a broadcasting environment to provide mechanisms for copyright and contents protection that are compliant with the MPEG‐2 and MPEG‐4 IPMP Extension (IPMPX) specifications. The technology for processing IPMP related information was exploited, and a terminal model has been successfully designed and implemented. In addition, interoperability, which is the main objective of MPEG‐2/4 IPMPX, has been addressed in detail. The experimental results show that the implemented system performs the IPMP process well, meeting the requirements of a broadcasting environment.     

Performance and scalability evaluation of IEEE 802.11v/aa multicast transport

IEEE 802.11v and 802.11aa are two recent amendments that define new functionalities in order to support a reliable multicast transport over wireless networks. The first amendment introduces directed multicast service (DMS). On the other hand, 802.11aa defines the groupcast with retries (GCR) service, which proposes two retransmission policies: block acknowledgement (GCR‐BACK) and unsolicited retry (GCR‐UR). In this paper, we evaluate the throughput and the scalability of these new proposals using both analytical and simulation approaches. We show that DMS has the lowest scalability, while GCR‐BACK is not appropriate for groups with a large number of receivers. We conclude that GCR‐UR is the most appropriate for large groups. However, increasing the number of transmission retries reduces significantly the achieved throughput of the unsolicited retry policy. Copyright © 2016 John Wiley & Sons, Ltd.     

Entire network load‐aware cooperative routing algorithm for video streaming over mobile ad hoc networks

In this paper, we present an entire network load‐aware cooperative routing algorithm based on IEEE 802.11 multi‐rate for video streaming over mobile ad hoc networks. The proposed routing algorithm is designed to minimize the consumed time slots while guaranteeing the required time slots at all the pairs of adjacent nodes over the route and the contention neighbors of these nodes to support the route. Furthermore, the proposed routing algorithm can distribute the network loads well over the entire network. This technology is essential because video streaming applications require stringent quality of service and even larger network resources compared with traditional data services, and these demands may dramatically increase the entire network load and/or cause network congestion. Finally, experimental results are provided to show a performance of the proposed routing algorithm. Copyright © 2011 John Wiley & Sons, Ltd.     

IEEE 802.11n标准下的4G关键技术解析

第四代移动通信将是一种超高速无线网络。OFDM可以最大限度地利用频谱资源,MIMO系统进一步提高无线通信系统容量、提高频谱效率。MIMO—ODFM已经成为第四代移动通信技术研究中的热点。本文结合IEEE802．11n标准分析了4G中的关键技术,并对其应用前景进行了一定展望,对于我国无线局域网标准的选择,具有一定研究意义：     

Analytical Study of TCP Performance over IEEE 802.11e WLANs

IEEE 802.11 Wireless LAN (WLAN) has become a prevailing solution for broadband wireless Internet access while the Transport Control Protocol (TCP) is the dominant transport-layer protocol in the Internet. Therefore, it is critical to have a good understanding of the TCP dynamics over WLANs. In this paper, we conduct rigorous and comprehensive modeling and analysis of the TCP performance over the emerging 802.11e WLANs, or more specifically, the 802.11e Enhanced Distributed Channel Access (EDCA) WLANs. We investigate the effects of minimum contention window sizes and transmission opportunity (TXOP) limits (of both the AP and stations) on the aggregate TCP throughput via analytical and simulation studies. We show that the best aggregate TCP throughput performance can be achieved via AP’s contention-free access for downlink packet transmissions and the TXOP mechanism. We also study the effects of some simplifying assumptions used in our analytical model, and simulation results show that our model is reasonably accurate, particularly, when the wireline delay is small and/or the packet loss rate is low.

Disparity‐Compensated Stereoscopic Video Coding Using the MAC in MPEG‐4

The MPEG‐4 multiple auxiliary component (MAC) is a good mechanism to achieve one‐stream stereoscopic video coding. However, there is no syntax or semantics for the residual texture data of the disparity‐compensated image in the current MAC. Therefore, we propose a novel disparity‐compensated coding method using the MAC for stereoscopic video. We also define a novel MAC semantics in MPEG‐4 so as to support the proposed coding algorithm. The major difference between the existing and proposed coding methods using the MAC is the addition of the residual texture coding.     

IEEE802.11b无线局域网视频传输特性分析

论述了目前成熟的无线局域网(WLAN)技术的特点,在此基础上对IEEE802.11b进行IP组播的传输特性进行研究与分析,为在无线局域网上进行视频实时传输提供信道的应用特性.     

A novel self‐adaptive transmission scheme over an IEEE 802.11 WLAN for supporting multi‐service

The IEEE 802.11 wireless local area network (WLAN) media access control (MAC) specification is a hybrid protocol of random access and polling when both distributed coordination function (DCF) and point coordination function (PCF) are used. Data traffic is transmitted with the DCF, while voice transmission is carried out with the PCF. Based on the performance analysis of the MAC protocol for integrated data and voice transmission by simulation, this paper puts forward a self‐adaptive transmission scheme to support multi‐service over the IEEE 802.11 WLAN. The simulation results show that, on the premise of satisfying the maximum allowable delay of packet voice, the self‐adaptive transmission scheme can improve the data traffic performance and increase the WLAN capacity through dynamic and appropriate adjustment of the protocol parameters. Especially, voice traffic is sensitive to delay jitter, and the self‐adaptive scheme can effectively decrease it. Finally, it is worth noting that the adaptive scheme is easy to be realized, whereas no change in the MAC protocol is needed. Copyright © 2006 John Wiley & Sons, Ltd.     

Hardware‐Software Implementation of MPEG‐4 Video Codec

This paper presents an MPEG‐4 video codec, called MoVa, for video coding applications that adopts 3G‐324M. We designed MoVa to be optimal by embedding a cost‐effective ARM7TDMI core and partitioning it into hardwired blocks and firmware blocks to provide a reasonable tradeoff between computational requirements, power consumption, and programmability. Typical hardwired blocks are motion estimation and motion compensation, discrete cosine transform and quantization, and variable length coding and decoding, while intra refresh, rate control, error resilience, error concealment, etc. are implemented by software. MoVa has a pipeline structure and its operation is performed in four stages at encoding and in three stages at decoding. It meets the requirements of MPEG‐4 SP@L2 and can perform either 30 frames/s (fps) of QCIF or SQCIF, or 7.5 fps (in codec mode) to 15 fps (in encode/decode mode) of CIF at a maximum clock rate of 27 MHz for 128 kbps or 144 kbps. MoVa can be applied to many video systems requiring a high bit rate and various video formats, such as videophone, videoconferencing, surveillance, news, and entertainment.