什么是杜比AC-3?

杜比数字环绕声系统ＤＯＢＬＹＤＩＧＩＴＡＬ（ＡＣ－３）是一种全数字化的音频编解码技术,共有６个完全独立的声音通道３个位于前方的通道（左,中,右）和左右２路环绕声道,这５个声道（包括环绕声道）都是全频带的（２０ＨＺ－２００００ＨＺ）,ＡＣ－３还备有一个独立的低音效果声道,用于表现效果声,由于ＡＣ－３的低音声道的频率响应有限（３－１２０ＨＺ）,不能算一个完整的声道,与其余５个全频带声道合在一起称为ＤＯＢＬＹＤＩＧＩＴＡＬ５．１声道,由于各声道的信号都是数字化的,在传输过程中不会损失,也彻底解决了矩阵…     

Motorola环绕声DSP解决方案

ＴＨＸＳｕｒｒｏｕｎｄＥＸＴＭ（环绕声）是当今优秀的声频技术,它由ＬｕｃａｓｆｉｌｍＴＨＸ和Ｄｏｌｂｙ实验室共同开发,并运用了ＭｏｔｏｒｏｌａＳｙｍｐｈｏｎｙ的ＤＳＰ技术和Ｍｏｍｅｎｔｕｍ数据系统的经验。使用环绕声技术的摩托罗拉ＤＳＰ５６３６２芯片,为用户提供首款家庭ＴＨＸ超级产品,它允许特别编码胶片解码,提供包括现有的５个声道的环绕声背景声道。新款环绕声道和背景环绕声扬声器允许音响设计师设计逼真的“过顶音响”（ｆｌｙ－ｏｖｅｒ）和“四周背景音响”（ｆｌｙ－ａｒｏｕｎｄ）效果,使声音效果更流畅、…     

数字电视广播系统的基础技术(三)

（上接2002年第8期第17页）2.5 声音编码声音编码采用的是MPEG-2 AAC（Advance AudioCoding：高级声音编码）中的LC(Low Complexity 低复杂度)协议，该协议于1998年成为ISO国际标准。由于在DVB广播制定阶段没有采用MPEG-2的技术规范，所以1994年采用了向下兼容的BC国际标准。而美国的DTV采用的是杜比AC-3（Dolby AC-3）规范。用AAC方式可以提供144kps（双声道立体声）类似于CD光盘效果的声音。在数字电视广播中使用的声音编码的技术参数见表7。采样频率48kHz,44.1kHz,32kHz量化比特数至少16bit声道数［多声道1(单声道)，2…     

环绕声音频编/解码格式知多少

诸多不同的音频编码格式,在解码还原后的声音效果上也有诸多不同,其体现方式一般包括声道数目、频带宽度、各声道之间分离度和音质音色等等。这些不同的音频编码格式有的是逐步发展进化而来,因而新旧产品在技术档次和声音效果的优劣上显现得较为明显(例如最初的杜比环     

ONKYO TX-SR606 AV放大器

ONKYO（安桥）的TX—SR606Av放大器是最近正式推出的全新产品,是针对中国影音市场而设计的新一代AV放大器。此机为7．1声道声音处理的设计,对最新的DTS—HD Master Audio、DTS—HD Htgh ReSolution Audi0、DolbyTrueHD、及Dolby Digital Plus等环绕声编码格式提供了解码的支持。     

DRA分层音频编码技术

提出了一种与DRA编码算法兼容的分层音频编码算法,其中环绕声分层编码采用了声道分类方式,而单声道/立体声分层编码则以残差再编码作为增强层的框架。分析和测试结果表明该DRA分层编码算法能够提供较好的声音质量,可作为信源编码与信道编码和分层调制技术完美结合应用于我国数字音频广播。     

数字式音响控制器的原理及设计

提出了一种采用数字电路技术,替代原来的模拟元器件控制音响的声道选择和音量调节的音响控制器.系统包括在8个声道之间进行依次转换以达到8种不同音效的通道选择系统和将声音量化成8个级别以达到音量的大小控制的音量控制系统.     

环绕声音频编／解码格式知多少

诸多不同的音频编码格式．在解码还原后的声音效果上也有诸多不同，其体现方式一般包括声道数目、频带宽度、各声道之间分离度和音质音色等等。这些不同的音频编码格式有的是逐步发展进化而来．因而新旧产品在技术档次和声音效果的优劣上显现得较为明显(例如最初的杜比环绕声发展成为后来的杜比专业逻辑系     

实现三维声效果的多媒体技术

１引言 计算机声音效果可分为简单立体声和三维立体声这两种。与普通的家用高保真的音响的立体声相似，计算机立体声也使用两个声道。在个人微机的Ｗｉｎｄｏｗｓ操作系统下的应用程序，可以利用多媒体控制接口（即ＭＣＩ）或Ｄｉｒｅｃｔ Ｓｏｕｎｄ技术回放预先录制的双声道声音。但听众在声场中与声源之间是相对固定的，由录音时传声器的位置决定。应用程序也可以通过分别改变左右两个声道的音量，模拟声源位置在三维空间中发生变化，从而产生声源在声场中应用的效果。立体声效可以让使用者判断左、右和前方３个声源位置。三维声效果比立…     

大显：DC-528E经济型数字电视机顶盒

针对现有和日渐浮现的应用．体现最大的压缩灵活性．哈雷公司展出的DiviCom Electra^TM 5000能以多种编码格式编码一个通道，一种编码格式编码多个通道．或多种不同的编码格式编码多个通道节目。基本配置可以同时用MPEG-4AVC（H-264）或MPEG-2编码两个全分辨率节目．并以MPEG-2和MPEG-4AVC格式编码其他小分辨率节目。     

550型电视频道变换器的原理与设计

随着有线电视和卫星电视的开通，节目数量的不断扩大，尤其是增补频道的使用，使相当数量的电视机已不能适应现有电视节目的收看。而频道变换器是专门为有线电视系统设计的终端接收设备，它能覆盖有线电视网包括增补频道在内的６０个频道。利用频道变换器可准确地调到任一有线电视频道，并经频道变换器内的调制器变频到固定的频道（１频道，４９．７５ＭＨｚ）输出。该变换器中心是８０３１单片机，选台用数字频率合成。具有红外遥控，开关电视机电源，频道频率微调、定时自动关机、直呼、递增／递减、最后呼出等功能。本文简要介绍其原理与设计。     

Frequency-selective multiple-input multiple-output channel estimation with transmitter non-linearities

The authors propose an algorithm based on the knowledge of training sequences to obtain an asymptotically unbiased estimator of non-linear multiple-input multiple-output (MIMO) channels, which involves the radio frequency front-end non-linearity and linear frequency selective MIMO channels. Although the impact of non-linearity in the transmitter side has been widely studied, most work on the channel estimation assumes linear channel models and ignores the non-linear effects. In this study, we develop a nonlinear channel estimator that can simultaneously estimate the linear MIMO channel model and non-linearity of the transmitter is developed. With these two sets of parameters, the non-linear channel model can be fully described. This channel estimation algorithm is implemented over an empirical MIMO channel model using an orthogonal frequency division multiplexing system.     

OFDM系统中信道编码对系统性能的影响

正交频分复用（OFDM）技术是下一代移动通信的核心技术之一。其最突出的优点是频谱利用率高和抗多径时延能力强,适合未来高速宽带无线通信的应用。OFDM技术通过将频率选择性多径衰落信道在频域内转换为平坦信道,减小了多径衰落的影响。根据OFDM基本原理特构建了一个OFDM通信系统仿真模型,分析了在不同调制方式、不同信道下信道编码对系统性能的影响。仿真结果表明,采用信道编码可有效的降低OFDM系统的误码率。     

Multiple-access channels with memory with and without framesynchronism

The capacity region of frame-synchronous and frame-asynchronous, discrete, two-user multiple-access channels with finite memory is obtained. Frame synchronism refers to the ability of the transmitters to send their code words in unison. The absence of frame synchronism in memoryless multiple-access channels is known to result in the removal of the convex hull operation from the expression of the capacity region. It is shown that when the channel has memory, frame asynchronism rules out nonstationary inputs to achieve any point in the capacity region, thereby allowing only coding strategies that involve cooperation in the frequency domain but not in the time domain. This restriction drastically reduces the capacity region of some multiple-access channels with memory, and in particular the total capacity of the channel, which is invariant to frame asynchronism for memoryless channels     

高频地波雷达相位补偿系统

OSMAR2000采用的是“一发八收,收发共用”模式的相控阵高频地波雷达.为了扩大其探测的范围,在新的雷达系统中将采用多发多收的模式,从而导致当信号通过通道后,信号的相位会因受到通道的调制而发生改变,使得雷达无法正常工作,因此需要对通道的相位进行实时监控和补偿.在参考了低频段的相位测量原理和射频段的相移电路的设计理论的基础上,该文提出了基于差分放大器、容阻和容感器件的高频地波雷达收发通道的相位控制系统.     

TV Tuning Systems with SAW Comb Filter

We have successfully developed two TV tuning systems which apply a SAW comb filter device in a new way. One is an automatic channel indicating system and the other is a frequency synthesizer. The SAW comb filter has comb peaks at the frequencies where channels are allocated. A channel number is recognized by counting the number of comb peaks which the local oscillator signal of a tuner goes through. The SAW comb filter has a minimum electrode width of 1 mu m. It has four sets of IDT's to cover all TV channels, fabricated on a single chip.     

Measured Characteristics of 800/900 MHz Fading Radio Channels with High Angle Propagation Through Moderately Dense Foliage

The probability of error for the transmission of digital information on fading radio channels is influenced by the statistical behavior of fading. This is characterized by the cumulative distribution function (CDF) for the received signal envelope, and the correlation of random variations across the channel bandwidth. It is therefore important for system design purposes to determine the distribution function for envelope fading, and the frequency correlation characteristics of radio channels in propagation environments where the use of digital radio systems is planned. This paper details experiments that were conducted under conditions similar to those which would be typical on 800/900 MHz band satellite-mobile channels in rural environments. The impulse response functions of measured channels were estimated by operating a pseudonoise channel probe from a 65 m tower through deciduous trees to a receiver at close range. Measurement results include: channel impulse response estimates, envelope fading statistics, and double-sided frequency correlation plots. Comparisons are made between channel characteristics during the summer and during the autumn after the leaves have fallen from the trees. Estimates of digital channel capacity limitations are also given. Aside from the fading statistics, these channel characteristics have not previously been reported.     

DFT-modulated filterbank transceivers for multipath fading channels

The orthogonal frequency division multiplexing (OFDM) transceiver has enjoyed great success in many wideband communication systems. It has low complexity and robustness against multipath channels. It is also well-known that the OFDM transceiver has poor frequency characteristics. To get transceivers with better frequency characteristics, filterbank transceivers with overlapping-block transmission are often considered. However these transceivers in general suffer from severe intersymbol interference (ISI) and high complexity. Moreover costly channel dependent post processing techniques are often needed at the receiving end to mitigate ISI. We design discrete Fourier transform (DFT) modulated filterbank transceivers for multipath fading channels. The DFT modulated filterbanks are known to have the advantages of low design and implementation cost. Although the proposed transceiver belongs to the class of overlapping-block transmission, the only channel dependent part is a set of one-tap equalizers at the receiver, like the OFDM system. We show that for a fixed set of transmitting or receiving filters, the design problem of maximizing signal-to-interference ratio (SIR) can be formulated into an eigenvector problem. Experiments are carried out for transmission over random multipath channels, and the results show that satisfactory SIR performance can be obtained.     

Two‐stage channel assignment scheme in wireless networks

This paper presents a new channel assignment scheme that efficiently improves the spatial frequency–spectrum reuse in a wireless network with heterogeneous demands, in which the cells are partitioned into a lot of clusters. Since the channel demands of each cell are different, this scheme adopts two stages to effectively assign channels. In the first stage, the cluster‐based scheme allocates a number of channels to the cells of each cluster for satisfying the requirement of co‐channel reuse. The channel demand of majority cells will be satisfied in this stage. In the second stage, when the channel requirement of most cells has been fulfilled, the tree‐based assignment scheme allocates channels for the minority cells, which are still lacking of channels. Simulation results showed that the proposed scheme is superior to the previous schemes. Copyright © 2005 John Wiley & Sons, Ltd.     

通道响应失配对DBF天线旁瓣电平的影响

本文研究了通道响应失配对数字波束形成(DBF)天线旁瓣电平的影响,然后分析了通道频率响应失配与脉冲响应失配的关系,进而得到通道间频率响应失配对天线旁瓣电平的影响。结果表明,用DBF技术实现超低旁瓣天线对通道频率匹配的要求相当高。最后计算机模拟验证了理论分析结果。