Quality assurance of voice over WLANs (VoWLANs) with differentiated services

Several technical issues make commercial and large voice over wireless local area network (VoWLAN) services difficult to provide. The most challenging issue when voice over Internet Protocol (VoIP) services are ran over IEEE 802.11-based WLANs is the bandwidth inefficiency due to the considerable overhead associated with WLAN packet transmission. In this work, we propose a session-based quality-of-service management architecture (SQoSMA) to overcome the low number of VoIP calls in IEEE 802.11 Wireless LANs and the negative effect of new call addition when the WLAN reaches its capacity. The SQoSMA combines data and control planes to detect VoWLAN QoS degradations and performs either an adaptive audio codec switching or a call stopping to fix VoWLAN issues in a differentiated services manner. In addition, our solution deals with user sessions information, by considering user priority (from its agreement) to guarantee a certain level of its multimedia applications. Performance evaluation using a real test-bed shows that call codec change and call stopping techniques can easily assure high-priority calls with acceptable call blocking probability.     

Variable bit rate VOiP in IEEE 802.11e wireless LANs [medium access control protocols for wireless LANs]

WLANs have become a ubiquitous networking technology deployed everywhere. Meanwhile. VoIP is one popular application and a viable alternative to traditional telephony systems due to its cost efficiency. VoIP over WLAN (VoWLAN) has been emerging as an infrastructure to provide low-cost wireless voice services. However, VoWLAN poses significant challenges due to the characteristics of contention-based protocols and wireless networks. In this article we propose two mechanisms to provide quality of service for variable bit rate VoIP in IEEE 802.11e contention-based channel access WLANs: access time-based admission control and access point dynamic access. Simulation results are conducted to study these schemes.     

PIANO: A power saving strategy for cellular/VoWLAN dual-mode mobiles

The integration of cellular and VoIP over WLAN (VoWLAN) systems recently has attracted considerable interest from both academia and industry. A cellular/VoWLAN dual-mode system enables users to access a low-cost VoIP service in a WLAN hotspot and switch to a wide-area cellular system without WLANs. Unfortunately, cellular/VoWLAN dual-mode mobiles suffer the power consumption problem that becomes one of the major concerns for commercial deployment of the dual-mode service. In this study, we present a novel power saving mechanism, called PIANO (paging via another radio), for the integration of heterogeneous wireless networks, and further apply the proposed methods to implement a cellular/VoWLAN dual-mode system. Based on the proposed mechanisms, a dual-mode mobile can completely switch off its WLAN interface, only leaving the cellular interface awake to listen to paging messages. When a mobile receives a paging message from its cellular interface, it wakes up the WLAN interface and responds to connection requests via WLAN networks. Therefore, a dual-mode mobile reduces the power consumption by turning off the WLAN interface during idle, and can also receive VoWLAN services. Measurement results based on the prototype system demonstrate that the proposed methods significantly extend the standby hours of a dual-mode mobile.     

基于WLAN的VoIP终端移动性管理研究

目前,随着WLAN的发展,VoIP(Voice over Internet Protocol)技术在其中的应用也越来越广泛。但VoWLAN仍然面临着移动终端切换时延过长、话音容量低、安全隐患以及QoS保证等技术上的挑战。文章简要介绍了VoIP技术,重点研究了VoWLAN终端的移动性管理,在现有支持移动性管理协议的基础上,融合各层协议提出了一种改进的移动性管理新方案。     

VoWLAN通信平台的设计与实现

VoWLAN也叫VoWiFi或者WiFi VoIP。它是基于无线网络技术和VoIP网络,是两者的有机结合。即是通过WLAN提供VoIP业务,使得终端用户通过WLAN拨打IP电话成为现实。本文提出了在基于Linux操作系统的SIP应用服务器及VoIP网关中,如何通过SIP信令和传统的PSTN数据通信线路与无线网络无缝连接方案,从而实现IP网络与传统电话间的实时语音通信、电话会议、语音信箱、视频通信、短消息、数据传输等业务。本设计已成功应用于某企业的实时语音通信平台,获得良好的效果。     

WLAN技术在软交换系统中的应用

文章主要讨论无线局域网（WLAN）如何接入软交换系统,通过对WLAN技术标准、网络架构及承载能力的探讨,揭示了软交换系统无线应用面临的挑战,在此基础上给出了一些有前景的应用,如VoWLAN、远程无线监控、无线即时消息和定位服务等的解决方案。文章认为宽带无线接入标准WiMAX有望成为WLAN的升级版,一旦成熟,并与软交换等NGN技术相结合,将会实现人们追求的。网络无所不在,信息随手可得”的美好愿望。     

An energy‐efficient transmission mechanism for VoIP over IEEE 802.11 WLAN

Voice over IP (VoIP) over WLAN (VoWLAN) is an important application for public and private WLANs. However, VoWLAN systems suffer from several technical challenges such as power consumption of a WLAN station (STA) and service capacity of an access point (AP), making the commercial deployment of a large‐scale VoWLAN service problematic. This study presents a cross‐layer and energy‐efficient mechanism for transmitting VoIP packets over IEEE 802.11 WLAN. The proposed mechanism considers the characteristics of voice packets that can tolerate certain loss, and dynamically disables the medium access control (MAC) layer acknowledgement for voice packets. In doing so, the time and energy consumed to transmit and receive voice packets for an STA can be reduced. Simulation results demonstrate that the mechanism improves the energy efficiency of a VoWLAN STA and WLAN utilization without sacrificing voice qualities. Copyright © 2009 John Wiley & Sons, Ltd.     

VoWLAN企业级应用模式及解决方案

VoWLAN是指通过WLAN提供VoIP业务,它的技术优势在于综合了VoIP和移动电话的优势,既有VoIP的低价格和强大的增值功能,又有移动电话的漫游便利性。VoWLAN应用有运营商的企业级VoWLAN和企业自建VoWLAN两种方案,为所有运营商都带了新的机遇和挑战,是在新一轮竞争中抢占先机的一个重要应用。VoWLAN为企业带来通信便利和通信费用的节约,使电信设备商可以同时切入运营商市场和企业通信市场,成为综合服务商的一个应用方向。     

无线局域网上的VoIP

VoiceoverIPonWLAN(无线局域网上的VoiceoverIP)是一种新兴技术,它能使IP语音在802.11无线局域网中传送。通过所设计的一个网络体系,对VoWIP技术进行了较详细的分析,并对VoWIP技术所面临的一些挑战进行了介绍。     

Guest Editorial Cross-layer Optimized Wireless Multimedia Communications

The 19 papers in this special issue focus on cross-layer optimized wireless multimedia communications. The papers are organized into four sections: quality of service support for wireless networks; system architecture for multimedia over wireless networks; resource allocation in wireless multimedia communications, and multimedia coding and scheduling issues in wireless networks.     

VoWLAN监听系统的设计与实现

将WLAN与VoIP两项技术结合起来的VoWLAN业务目前发展迅速,随之而来的VoWLAN监听问题也为人们所重视。现有的VoWLAN监听装置大都架设不便,容易被目标发现且精准度不高。论文提出了一种VoWLAN监听系统的实现方法,使用方便灵活,可对无线局域网内的语音通话进行安全有效的监听。本系统采用分布式架构,系统按功能分开物理模块,重点介绍了语音还原技术,并对系统的实现进行了详细说明。测试表明,该系统能够有效地实现VoWLAN监听。     

Broadcast/multicast MPEG-2 video over broadband fixed wirelessaccess networks

With the emergence of broadband fixed wireless access networks, there is an increasing interest in providing broadband video services over outdoor wireless networks. We investigate some fundamental issues related to the broadcasting or multicasting of CBR MPEG-2 videos over fixed wireless channels in B-FWANs using FEC strategies. In B-FWANs, high-frequency wireless channels are used and a direct or indirect LOS propagation path is usually required between a transmitter and a receiver. The wireless channel is modeled by a K factor Rician fading model instead of a Rayleigh fading model. The unique characteristics of the physical channel require special consideration at the system design level. In order to evaluate the overall system performance properly, a set of parameters for objective video quality assessment is introduced and used in our simulation studies, including a definition of the objective grade point value, the number of reconstructed frames, and the conventional peak signal-to-noise ratio value. The feasibility of cell interleaving is also addressed. MPEG-2 control information (i.e., the control blocks) plays a critical role in the decoding process and can influence the reconstructed video quality dramatically; special consideration and excess protection should be given to this information. The concept of a new FEC strategy, header redundancy FEC, is introduced to address this issue. In HRFEC, selected important (high-priority) MPEG-2 control blocks (such as sequence header, sequence extensions, and picture header and corresponding extensions) are replicated before transmission, and duplicate copies are transmitted over the wireless link. Our results indicate that HRFEC is a simple, flexible, and effective error control strategy for broadcasting or multicasting MPEG-2 videos over error-prone and time-varying wireless channels     

Advances in wireless sensor communications and applications for smart space

Research progresses in wireless sensor communications and applications have been recently and widely explored. This special issue on advances in wireless sensor communications and applications for smart space provides high quality contributions addressing related theoretical and practical aspects of wireless sensor communications. We have selected eight research papers whose topics are strongly related to the wireless and sensor technology.     

Guest editorial - Wireless technologies advances for emergency and rural communications

The eight articles in this special issue focus on wireless technologies advances for emergency and rural communications.     

Next-Generation CDMA vs. OFDMA for 4G Wireless Applications

The six articles in this special issue focus on next-generation CDMA- and OFDMA-based technologies for 4G wireless applications.     

Guest editorial broadband access networks: architectures and protocols

The 13 papers in this special issue cover a diversity of topics on the design of network architectures and protocols for passive optical networks (PONs), WiMAX networks, and integrated optical and wireless access networks.     

Guest Editorial Special Issue on Multifunctional Circuits and Systems for Future Generations of Wireless Communications—I

The 17 papers in this first part of the special issue focus on multifunctional circuits and systems for future generations of wireless communications.     

Evolution toward 4G wireless networking [Guest Editorial]

This special issue serves as a stimulus to promote and accelerate technological evolution toward 4G networking. The response to the call for papers for this issue is indicative of the great interest with which the community views this topic. Of the many high quality in depth and breadth papers received from both academia and industry around the world, we could only accommodate a selected few in this issue. The research on the next generation wireless networking involves many cutting-edge research topics, which are presented in some articles included in this special issue     

Medium access control protocols for wireless LANs [guest editorial]

The six papers in this special issue focus on medium access control protocols for wireless LANs. The papers are summarized here.     

Technologies on the futute converged wireless and mobility platform [Guest Editorial]

The articles in this special issue focus on technologies on the future converged wireless and mobility platform. The issue presents recent research and development on this emerging topic focusing on security, quality of service (QoS), mobility management, system architecture, resource management, admission control, and medium access control.