广播电视卫星数字传输技术第四章卫星传输广播电视信号及多工利用

(上接2008年第05期)1卫星传输数字电视信号1.1传输电视信号的质量要求(1)采用MPEG-2/DVB-S标准,上行编码码率在2~8Mb/s灵活可调,一路电视按8Mb/s压缩编码,图像质量可达到演播室水平。(2)音频处理采用杜比AC-3或MUSICAM方式,取样频率为48kHz或44.1kHz,传输速率为96~384kb/s,当传     

16kb/s话音波形编码技术

本文首先介绍了采用自适应噪声谱整形的话音预测编码和直接查表多级矢量量化话音编码,以及我们对这两种方法进行计算机模拟的结果;然后,介绍了对这两种方法的改进,即对预测编码中的残余信号和矢量量化编码中的话音信号实行帧分类处理,分别采用了自适应量化技术和维数自适应技术,在此基础上,速率由96kb/s压缩到16kb/s,量化噪声明显降低至难以察觉。     

一种符合ITU-T指标要求的嵌入式立体声语音频编码方法

 基于国际电信联盟标准化组织(ITU-T)编码标准G.729.1,本文提出了一种嵌入式变速率立体声语音与音频编码方法.本算法利用G.729.1和改进的调制叠接变换(Modulated Lapped Transform,MLT)编码技术对输入信号的中值与边带信息进行分层编码,形成具有嵌入式结构的码流.编码器可处理宽带和超宽带的立体声信号,宽带立体声信号编码的最大码率为48kb/s,超宽带立体声信号编码的最大速率为64kb/s.实现结果表明,本编码器的编码质量均达到了ITU-T对G.EV-VBR立体声编码的指标要求.     

数字电路倍增设备技术发展及应用

一、引言 在传统的数字通信网中,模拟的语音信号是以8kHz抽样,每样值经8bit编码,以64kbit/s的速率在链路中传输的,这就是通常所说的脉冲编码调制(PCM).话带数据及传真信号也包封在64kbit/s信道中,以相同的带宽传输.数字电路倍增设备(DCME)是随着低比特率数字话音编码技术的发展于90年代初发展并逐步完善起来的.DCME采用低速率编码(LRE)、可变比特率(VER)、数字信号插空(DSI)、VBD处理及传真解调/再调制(FAX-DEM/REMOD)等关键技术,对链路中的不同信号采取不同的压缩处理方法,从而使相同的传输带宽上的传输容量实现几倍甚至几十倍的增益.     

一种新的8~32kb/s宽带嵌入式变速率语音编码方法

 本文基于ACELP和TCX编码技术,提出了一种8~32kb/s五层宽带嵌入式变速率语音编码方法,其中,前三层采用ACELP实现了8kb/s、12kb/s和16 kb/s的嵌入式编码,后两层采用TCX技术实现了24 kb/s和32 kb/s嵌入式编码.实验结果表明,该嵌入式语音编码方法的质量在纯净语音、办公室噪声和层间转换方面接近于ITU-T G.VBR的TOR要求.     

1.5 Mbit/s高压缩率编码方式

众所周知,电视会议、电视电话等图象信号的传输频带大约是电话传输频带的1000倍,因此它的传输成本很高。为了降低传输费用和普及电视会议和电视电话业务,压缩图象信号的传输频带便成为一个重要的研究课题。最近,日本电报电话公司电信研究所在原来32Mbit/s和6.3Mbit/s两种频带压缩编码基础上,研究成功一种高压缩率的1.5Mbit/s图象信号编码传输方式。32Mbit/s压缩编码传输方式是在一幅图象画面内利用相邻画面间连接处的相同部分,取其不同部分的信号进行     

低中速保密通信语音编码器:概论

1 引言语音加密最有效的途径之一,是先把模拟语音信号变成数字信号,然后用数字加密方法对得到的比特流进行加密。但是,许多通信信道无力以常规的64kb/s的速率传输数字化语音. 可以用声码器技术把传输速率降到2.4kb/s甚至更低,具体多少取决于所采用的参     

话音编码技术的进展

本文是数字语音技术与标准的回顾。随着通信的进展已建立了许多高质量数字语音的新业务,例如象ISDN终端,个人通信业务,移动电话,卫星小站和声音信号存储系统等等应用。 按传统电话学概念达到网络质量的语音传输速率已降到32kb/s并且目前已到16kb/s;用于蜂窝无线传输的通信质量语音在欧洲已以13kb/s GSM标准实现于移动电话网,同时8kb/s IS-54标准已在美国应用,目前的焦点是实现高质量半速率4 kb/s数字语音技术。     

话音编码技术的进展

本文是数字语音技术与标准的回顾。随着通信的进展已建立了许多高质量数字语音的新业务,例如象ISDN终端、个人通信业务、移动电话、卫星小站和声音信号存储系统等等应用。按传统电话学概念达到网络质量的语音传输速率已降到32kb/s,并且目前已到16kb/s;用于蜂窝无线传输的通信质量语音在欧洲已以13kb/sGSM标准实现于移动电话网,同时8kb/sIS-54标准已在美国应用,目前的焦点是实现高质量半速率4kb/s数字语音技术。     

基于二维非负矩阵分解的1kb/s WI语音编码算法

 本文针对波形内插（WI）语音编码模型和参数量化等技术进行了研究,并最终提出了一种基于二维非负矩阵分解的1kb/s波形内插（2DNMF-WI）语音编码算法. 文中采用二维非负矩阵分解（2D-NMF）方法来分解语音特征波形（CW）,该分解方法在行和列两个方向上同时压缩CW幅度谱矩阵的维数,使得CW幅度谱矩阵降维后得到的编码矩阵维数较小,易于量化. 此外,在甚低速率语音编码中,由于没有足够的比特数来描述编码参数,往往很难得到高质量的合成语音. 本算法采用两帧联合编码、帧间后向预测三级矢量量化、离散余弦变换（DCT）和分裂式矩阵量化等技术来降低编码速率和改善音质. 非正式主观听觉测试显示,1kb/s 2DNMF-WI编码器合成语音的质量稍差于2kb/s的NMF-WI语音编码算法.     

PowerCell——一种支持多业务类型的广域网技术

主要介绍一种支持多业务类型的广域网技术,它通过对数据、话音及其他类型数据流的协议排队、分段压缩和复用,使得多业务在一个广域网中快速可靠地传输,特别是保证延迟敏感数据的加速处理同时避免不敏感数据的处理。PowerCell无论对数据还是对话音的处理都只有很小的延迟,与ACELP-CN语音压缩算法的配合使用能提供高质量低带宽的话音通信。由于PowerCell优越的性能,它不但被应用于地面的广域网,还被广泛应用于VSAT（甚小孔径地面站）卫星通信网络中。     

Time-Multiplexed Analog Transmission of Three Broadcast-Quality Television Channels Through One Satellite Transponder

This paper describes a TV signal compression scheme which may become a common practice for analog video transmission and broadcast via satellite by the year 2000. The technique uses twodimensional interfield processing to reduce the video bandwidth with minimum degradation in subjective quality, and time multiplexed with analog multiplexing technique for transmission in component format. Computer simulations of the processing technique on the test slides, and analysis of subjective quality andS/Nexpected over a typical satellite link, are reported. A proof-of-concept prototype being developed at COMSAT Laboratories is also outlined.     

Application of 32 and 16 kb/s speech encoding techniques to digital satellite communications

This paper describes the performance of various voice encoding techniques at 32 and 16 kb/s for applying to digital satellite communication systems. The subjective performances of adaptive differential PCM (ADPCM), adaptive predictive coding (APC), subband coding (SBC) and adaptive delta modulation (ADM) are compared under various satellite channel environments, that is, random and burst channel errors in satellite link and an ambient noise in the ship-to-shore direction in a maritime satellite channel. The performance of the voiceband data at 4·8 and 2·4 kb/s is also evaluated for these coders. ADPCM encoding at 32 kb/s is very attractive for conventional fixed satellite systems, keeping the equivalent quality to 64 kb/s PCM. On the other hand, APC encoding at 16 kb/s is also most suitable for maritime satellite communication systems at the sacrifice of a small degradation of speech quality.     

16 Kb/s high quality voice encoding for satellite communication networks

This paper describes applications of adaptive predictive coding (APC) with maximum likelihood quantization (MLQ) which can cover a wide range of coding rates from 4.8 to 16 kb/s for low C/N satellite communication systems, such as maritime, aeronautical mobile and thin-route satellite communication systems, and also for speech and data integration, including digital circuit multiplication equipment (DCME) in business communication systems, such as INTELSAT business services (IBS). A 16 kb/s APC–MLQ hardware codec has been implemented by NEC–7720 DSP chips and the performance has been confirmed in subjective quality of speech through conversational tests. The objective performance has also been evaluated for non-voice signals, such as single and multi-frequency tones, and 1200 and 2400 b/s voiceband data signals. The APC-MLQ codec can transmit the voice-band data at 1200 b/s over two asynchronous tandem links and at 2400 b/s over one link. It was noted that the APC-MLQ codec is superior in speech performance at 16 kb/s to a narrow-band companded FM and meets requirements for low C/N satellite communication systems. For voice and data integration into 16 kb/s for 64 kb/s links, we propose a multi-media multiplexing for low C/N digital satellite communication systems and also a small-scale circuit multiplication system for business use. In these systems, a variable rate coding of APC-MLQ from 4.8 to 16 kb/s can be effectively introduced for voice and data integration.     

Planning considerations for domestic replacement satellites

Several domestic satellite systems have been more than 10 years in operation. During this time, the world has experienced a dramatic growth in communication. While the demand for more telephony and data circuits and television channels is still on the rise, new methods of signal transmission and circuit compression have been developed which may balance or reduce the need for more satellite trunk capacity. And while whole national networks are converting to digital transmission, new transmission media like optical fibre, are finding application, and may take over some of the heavy traffic routes previously carried by satellite. On the other side, business data communication between roof-top terminals, thin route traffic to remote users, television distribution by direct satellite broadcasting are becoming more popular and satellite land mobile communication may soon be a reality. Thus the domestic satellite's role appears to be slowly changing towards thin route and mobile traffic and DBS-type distribution and perhaps even radio position determination. System planners are adapting to the new trends in satellite communication and are trying to accommodate the various service payloads on a single satellite. This article discusses some aspects of the emerging multi-purpose domestic satellite, which carries fixed and mobile services, TV direct broadcasting and radio position determination, in view of network digitalization, network expansion, circuit compression, synchronization. The discussion centres on transponder supply and demand, satellite replenishment, K_u-band vs. C-band for TV direct satellite broadcasting, choice of modulation/multiple access for mobile communication, and expected accuracy in radio position determination.     

Advanced techniques for circuit multiplication: Celtic 3G

The Celtic 3G is Alcatel CIT's new digital circuit multiplication system designed to enhance the cost-effectiveness of long-haul links by increasing their capacity by a factor of between 5 and 8. The Celtic 3G offers an effective, versatile solution to congestion problems on 2048 and 1544 kb/s digital transmission links. The paper describes the compression modes used by Celtic 3G family to transmit the various types of signals (speech, voice band data, 64 kb/s digital data), the applications and the operating principles of the equipment. A number of telecommunication administrations and agencies have adopted and will this year deploy the Celtic 3G because of its benefits, technical qualities and the savings which it will achieve on digital links.     

机载移动通信卫星中继链路的高效传输方法

为了提高机载移动通信卫星中继链路的数据传输效率,给出了一种高效传输方法,先通过转换话音编码方式对语音进行压缩,再把话音数据作为有效负载封装成IP数据包,采用RTP复用和IP/UDP/RTP报头压缩等技术来提高话音数据的传输效率.最后通过仿真说明了这种高效传输方法能提升给机载移动通信的性能.     

基于AMBE2000的新型无线同播系统

在无线多通道语音通信中,距离长短使各接收机接收信号的时间不一,同步输出需要精确的延时。介绍一种新型的基于AMBE2000和AD73311的高质量语音同步通信系统的设计与实现。该系统能够在2.0～2.4kb/s的低比特速率产生高话音质量,实现最小步长为1us的输出延时,达到多路同步传输效果。因此,该系统可以广泛应用于软件无线电,多模式电台及多路广播等场合。     

基于AMBE-2000的数字语音传输系统

介绍了AMBE-2000的工作原理及其应用,并结合实例给出了数字语音传输系统中AMBE-2000与TLV320AIC10的A/D、D/A接口电路。AMBE-2000是DVSI(Digital Voice System·Inc)公司的语音压缩解压缩芯片,它采用AMBE语音压缩技术,具有语音音质好和编码波特率低、功耗低等优点;TLV320AIC10是TI公司的低功耗∑-Δ型16位A/D、D/A音频接口芯片。应用AMBE-2000的数字语音传输系统可以在低速率下提供优良的语音质量,并能实现全双工、实时语音压缩解压缩功能,因此在卫星通信、移动通信等领域有着广泛的应用。