PoC技术探析

PTT又称为“一键通”,是一种实现walkie—talkie功能的移动话音业务。基于公众蜂窝移动通信网络的PTT业务称为PoC业务。文章主要介绍PoC技术、PoC协议和发展趋势。     

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.     

应用VoIP网关实现呼叫中心远端座席

集中式呼叫中心系统以其投资少、易维护及异地只设置座席等特点在企业建设客户服务中心工程中被广泛使用。在集中式呼叫中心应用方案中,介绍了如何通过VoIP(因特网电话)语音网关来实现远端座席的方法,并提供了实现电话状态同步的工作原理。就实现方案进行了详细分析和介绍,并描述了该方案的具体实现配置方式和步骤。     

基于H.323的VoIP系统QoS实现研究

文章提出了一种QoS增强的VoIP体系结构，增加了连接准入控制功能，提供了语音分组的IP优先服务，并改进了抖动缓冲的设计，使VoIP系统的QoS得到很大改善。     

基于GPRS的IP电话技术研究

文章研究了一种的新的无线IP电话技术GPRS-VoIP,是一种基于GPRS接入的IP电话技术,可以实现和传统的基于电路交换的语音通话进行无缝切换.文中分析了该技术下的通话和传统GSM语音通话的无缝切换.文中还详细的分析了时廷、丢包、通话不连续等因素对基于GPRS接入的IP通话的影响和其对于带宽的需求,并提出了相应的解决方法.     

A New Buffer Algorithm for Speech Quality Improvement in VoIP Systems

Jitter buffer plays an important role in Voice over IP (VoIP) applications because it provides a key mechanism for achieving good speech quality to meet technical and commercial requirements. The main objective of this paper is to propose a new, simple-to-use jitter buffer algorithm as a front-end to conventional static or adaptive jitter buffer algorithms to provide improved performance, in terms of enhanced user-perceived speech quality and reduced end-to-end delay. Supported by signal processing features, the new algorithm, the so-called Play Late Algorithm, alters the playout delay inside a speech talkspurt without introducing unnecessary extra end-to-end delay. The results show that the new algorithm achieves the best performance under different network conditions when compared to conventional static and adaptive jitter buffer algorithms. The results reported here are based on live tests and emulated network conditions on real mobile phone prototypes. The mobile phone prototypes use AMR codec and support full IP/UDP/RTP stack with IPSec function in some of the tests. The method for perceived speech quality measurement is based on the ITU-T standard for speech quality evaluation (PESQ).

海事卫星通信系统VoIP技术的应用分析

随着VoIP技术的发展,VoIP技术结合卫星通信网络的应用越来越广泛。Inmarsat卫星系统是地球同步轨道系统,网络传播时延大,卫星VoIP电话的语音通信是否可行值得研究。结合VoIP关键技术和海事卫星通信语音通信应用场景,探讨了基于Inmarsat卫星网络实现VoIP技术的方案,并分析出此方案下VoIP系统通话过程的单向时延为350 ms,低于ITU G.114的400 ms的要求。在实际使用环境中进行了测试和验证,结果表明,基于Inmarsat网络下实现VoIP的方案是可行的。该方案实现复杂度低,可以方便地实现Inmarsat网络与地面电话网之间的互联互通,也可以为我国自主研制的宽带卫星通信系统实现VoIP技术提供参考。     

Steganalysis of Low Embedding Rates LSB Speech Based on Histogram Moments in Frequency Domain

As wavelet packet transform is able to focus on minute change of signals, this study proposes an analytic approach of low embedding steganograpy based on high order Histogram moments in frequency domain (HMFD), which provides a key solution to the feature selection and extraction of HMFD. The detection results are tested with the LSB matching steganograpy of different embedding rates in speech signals, respectively, it is proved that the detection performance with HMFD applied is greater than that of histogram statistical moments. HMFD by Wavelet packet decomposition (WPD) can effectively detect low embedding rates Least significant bit (LSB) speech steganography, its accuracy can be 60.8％ while the embedding rate is only 3％.     

A client‐side design and implementation for push to talk over cellular service

This paper proposes a client architecture for the push to talk over cellular (PoC) service based on the open mobile alliance (OMA) PoC specifications v1.0 release. We show that most standard VoIP modules can be reused for the PoC client, and the VoIP software can be easily extended to support PoC service. Then we present the detailed message flows between the PoC client and other network entities in the PoC system. A PoC client prototype has been implemented in the Industrial Technology Research Institute (ITRI) and National Chiao‐Tung University (NCTU) Joint Research Center. Copyright © 2006 John Wiley & Sons, Ltd.     

基于可量化性能分级的自适应IP语音隐写方法

论文以客观语音质量评价和信噪比为量化手段,分析了参数编码中语音帧的每个比特位对重构语音质量影响的不均衡性,并提出了一种载体可隐藏位的分级方案,以达到充分利用各载体位的目的.以此为基础,进一步提出了一种基于载体位置分级的自适应IP语音隐写方法.该方法可自适应地选择最佳的隐写位置,以提高隐蔽通信的不可感知性.以大量的语音样本为载体,对提出的方法进行了实验验证.结果表明,本文的分级方案是正确可行的,且提出的分级隐写方法较之传统方法具有更好的隐写性能.     

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.     

Design and Realization of a Novel Header Compression Scheme for Ad Hoc Networks

IP header compression schemes offer a valuable measure for bandwidth preservation. Such schemes have been practically implemented in infrastructure‐based IP networks for point‐to‐point links. However, minimal research and practical implementation efforts have been conducted in the direction of an IP header compression strategy that can meet the peculiar requirements of multi‐hop ad hoc wireless networks. In this paper, we present a practically implemented multi‐hop IP header compression scheme using the Robust Header Compression (ROHC) protocol suite. The scheme runs on a novel identifier (ID) based networking architecture, known as an ID‐based ad hoc network (IDHOCNET). IDHOCNET additionally solves a number of bottlenecks of pure IP‐based ad hoc networks that have emerged owing to IP address auto‐configuration service, distributed naming and name resolution, and the role of an IP address as an identifier at the application layer. The proposed scheme was tested on a multi‐hop test bed. The results show that the implemented scheme has better gain and requires only O (1) ROHC contexts.     

Effects of gratification-opportunities and gratifications-obtained on preferences of instant messaging and e-mail among college students

The traditional approach of using gratifications-obtained in the study of motives in the adoption and use of media puts much emphasis on the users’ perspectives and pays less attention to the attributes of the medium. This exploratory research confirms the important role of gratification-opportunities in studying media preference for computer-mediated communication.     

适用于大规模MIMO系统的低复杂度RZF-SOR预编码算法

在大规模多输入多输出(MIMO)系统中,为了降低传统预编码算法的复杂度,在原有正则化迫零(RZF)预编码算法的基础上,提出用超松驰迭代(SOR)法代替矩阵求逆的高复杂度运算,得到一种改进算法RZF-SOR,并应用随机矩阵原理得出其最优相关参数的近似表达式和取值的必要条件.实验仿真表明,提出的RZF-SOR预编码算法与RZF预编码相比有效地降低了一个数量级的复杂度,在很小的迭代次数下达到接近于RZF预编码的误码率性能,并且优于基于Neumann级数预编码算法的误码率性能.     

IP over WDM网络中能耗自感知的混合疏导专有保护算法

针对绿色生存性IP over WDM网络中资源开销大、网络阻塞率高的问题,提出一种能耗自感知的混合疏导专有保护(HG-PA-DPP)算法。首先在IP层的核心路由器对低粒度业务请求集中疏导;然后通过实时感知WDM层的链路负载和双层器件带来的链路能耗状态定义链路权值,基于分层图在不同波长平面上为各业务请求寻找权值小且链路分离的工作路径和保护路径,同时在业务的中间节点处对不需要光-电-光转换的光路进行光旁路处理;最后,将空闲或保护资源设置为休眠模式以实现节能。仿真结果表明,所提算法在高负载时有着更好的节能效果,且在大网络拓扑下资源开销(RO)为传统算法的76.5%,阻塞率(BP)仅为传统算法的61.1%。     

基于DWT-IRLS算法的超声断层成像方法研究

超声成像因非侵入式、成本低且实时性好而被广泛应用。超声系统需要大量的采集通道数据和较高的采样率来提高图像重建质量,导致成像耗时,系统复杂。压缩感知(compressed sensing, CS)算法能够在欠采样的条件下用较少的测量值重构出原始信号。因此,针对系统面临的采样率高,数据量大的问题,本文将CS理论中的DWT-IRLS算法应用在超声成像中,通过离散小波变换基(discrete wavelet transformation, DWT)对超声数据进行稀疏转换,对高低频系数进行采样测量,并使用迭代重加权最小二乘法(iterative reweighted least squares, IRLS)进行测量系数重构,最后对变换域系数进行DWT逆转换得到重建图像。通过实验分析,以50%原始数据重建图像效果逐渐趋于稳定,在均方误差和峰值信噪比方面进行对比分析,DWT-IRLS算法相比较于DWT-OMP、DWT-CoSamp和DCT-IRLS等重构算法,成像质量更高,细节特征更为明显。     

用于SoC集成的IP核质量评测方法研究

采用IP核进行SoC设计是集成电路的发展趋势。然而,IP核的质量参差不齐,如何选用高质量IP核成为困扰SoC用户的难题。针对IP核可重用的特点及其在SoC集成应用中的难点,提出了一种主客观相结合的IP核质量评测方法。重点描述了主观质量评测方法的实现和客观质量评测方法的策略,实现了主观质量评测平台,并完成一款数模转换IP核的质量评测。     

IMS域的位置管理策略研究

UMTS(Universal Mobile Telecommunications System)R6中IMS(IP Multimedia Subsystem)域的用户的位置都要注册到归属地网络,而且终端的所有SIP信令都要经过注册服务器,导致用户在漫游状态下控制信令的迂回路径变长并限制了用户对网络中应用的使用.该文对UMTS R6的IMS位置管理方案进行了改进,提出了IMS用户位置信息的分布式管理和联系人位置信息自适应缓存机制,使得其漫游状态下的位置注册和呼叫建立过程更加迅速.分析及仿真显示:新的位置管理策略从网络信令花费上优于原位置管理策略.     

基于GMM聚类的空调机组多未知模态辨识方法研究

智能建筑空调机组故障检测与诊断是保证建筑环境安全、舒适、节能的基本方法.然而,多未知模态辨识仍是其中的关键难点之一.鉴于高斯混合模型(GMM)不受特定概率分布局限,可在区分类别的基础上直接得出数据的统计分布,具有优越的计算性能,且能拟合任意连续分布,本文提出一种基于GMM的空调机组多未知模态辨识方法.仿真试验结果表明,GMM聚类方法在空调机组运行模态辨识中具有较高的准确性与可靠性.     

QoS aware traffic grooming and integrated routing on IP over WDM networks

In this article, we consider traffic grooming and integrated routing in IP over WDM networks. The challenges of this problem come from jointly considering traffic grooming, IP routing, and lightpath routing and wavelength assignment (RWA). Due to the high bandwidth of optical fiber, there exists a mismatch between the capacity needed by an IP flow and that provided by a single lightpath. Traffic grooming is therefore used to increase the network utilization by aggregating multiple IP flows in a single lightpath. However, traffic grooming incurs additional delays that might violate Quality-of-Service (QoS) requirements of IP users. In this work, the tradeoff between traffic grooming and IP QoS routing is well-formulated as a mixed integer and linear optimization problem, in which the revenue from successfully provisioning IP paths is to be maximized. Problem constraints include IP QoS, routing, optical RWA, and the WDM network capacity. We propose a novel Lagrangean relaxation (LGR) algorithm to perform constraint relaxation and derive a set of subproblems. The Lagrangean multipliers are used in the proposed algorithm to obtain a solution in consideration of grooming advantage and resource constraints simultaneously. Through numerical experiments and comparisons between the proposed algorithm and a two-phase approach, LGR outperforms the two-phase approach under all experimental cases. In particular, the improvement ratio becomes even more significant when the ratio of IP flow to the wavelength capacity is smaller.