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本文提出了一种将回波抵消器(EC)作为LD-CELP编解码器的部分工作的方法,将EC功能融入LD-CELP编解码器之中,文中讨论了用两片TMS320C30实时实现LD-CELP与EC于一个系统中的可能性。 相似文献
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1HDSL技术HDSL(高速率数字用户环路)是一种在一对或一对以上铜线上提供欧洲标准的E1(2.048Mb/s)或北美标准的T1(1.544Mb/s)传输的一种技术。HDSL通过先进的调制技术——多电平编码方式(常用的编码方式是2B1Q或CAP等)将... 相似文献
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对数字用户环路(DSL)的研究已进入单线对HDSL(HDSL2)的阶段。一个实用的HDSL2系统2要能成倍的提高HDSL的传送速率,同时应保持对ISDN、T1、HDSL、ADSL线路的频谱兼容性,文章对基于回波消除(EC)的HDSL2及频分复用(FDM)的HDSL2这两种可选择的方案进行了研究,分析了它们的噪声背景及相应的信道容量,指明了设计HDSL2系统的技术难点及研究方向。 相似文献
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文章介绍一种采用CODEC(编解码)接口芯片MC14LC5480、TMS320C31设计实现的数字话音回波抵消器硬件的设计方法。着重介绍了回波抵消器模拟接口的实现方法。 相似文献
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宁波GSM系统LAC状况 目前宁波GSM系统共有LAC区22个,每个BSC分配一个LAC(除市区BSC23,BSC24外),这样,某些BSC的Location-Update占OK-ACC-PROC的比例(后称LU-RATE)相当高,如余姚BSC8,其LU-RATE高达79.42%,其SDCCH负荷相当重,且已导致SDCCH拥塞,具体每个BSC的LU次数,LU-RATEPAGE-REQUESTS/PAGE-RESPONSE,PAGES-PER-SECOND,SD-CONGESTION-RATE,… 相似文献
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本文提出了一种新的HEMT器件非线性CAD模拟方法,即可以利用PSPICE程序中GaAsMESFET的非线性CAD模型(Statz模型)对HEMT器件进行非线性模拟,并用实验验证了这种方法的正确性。 相似文献
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EMX-500交换机系统带数据丢失的原因分析江苏省徐州邮电局朱小枫EMX-500交换机的系统带最初是由MOTOROLA公司提供的,它共有3个组成部分,即PATCH,SYSGEN(SYSTENGENARATION)和空的CHANGEJOUNAL。前两部... 相似文献
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在详细阐述了ADSL接入系统组成,设备功能模块、传输系统中数据和话音通道的频谱划分等基本原理和国内外技术标准的基础上,总结电信部门当前采用ADSL接入系统为用户提供宽带数据业务的技术特点;对目前ADSL设备市场中出现的两类线路编码和调制技术即单载波线路编码调制技术(如QAM、CP)或多载波一路编码调制技术(如DMT),以及ADSL接入网络中两种主要 数据传送模式即Pdisplay status 相似文献
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A new echo cancellation structure for discrete multitone systems is presented, where each used tone has its own per-tone echo canceller in addition to a per-tone equalizer, which provides an alternative to currently employed time domain and time/frequency domain approaches. The per-tone approach enables us to optimize the signal-to-noise ratio for each tone separately by solving a minimum mean-square error problem for each tone, with implicit so-called joint shortening. Complexity during data transmission is compared for time domain, time/frequency domain, and per-tone echo cancellation. Structures with reduced complexity are derived for an interpolated and a decimated rate setup. Finally, simulation results for an asymmetric digital subscriber line setting demonstrate improved performance over time domain (or time/frequency domain) echo cancellation. 相似文献
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This paper describes a new technique for implementing an echo canceller for full-duplex data transmission (such as in digital subscriber loops and volceband data sets). The canceller can operate in spite of time-invariant nonlinearities in the echo channel or in the implementation of the echo canceller itself (such as in the D/A converters). The basic structure of the linear echo canceller is not changed, but taps are simply added to account for the nonlinearity. The number of taps which must be added depends on the degree of nonlinearity which must be compensated. Numerical results based on computer simulation are given which show that typical nonlinearities encountered in MOS D/A converters can be compensated by a relatively small number of taps added to the linear echo canceller, and substantial improvement in the cancellation results. 相似文献
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The performance of an adaptive echo canceller at the looptimed subscriber end of a digital subscriber loop has been shown to be sensitive to jitter arising from the timing recovery subsystem. We evaluate this degradation for the common timing recovery subsystem consisting of a prefilter, a squarer, and a second-order phase-locked loop. The evaluation shows the influence of equalization, prefilter shape, and phaselocked loop parameters. A narrow-band accurately tuned prefilter, line equalizer, and a narrow-band phase-locked loop are found to be necessary for adequate performance in a 144 kbit/s bipolar-coded digital subscriber loop system employing echo cancellation. 相似文献
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Ysebaert G. Pisoni F. Bonaventura M. Hug R. Moonen M. 《Signal Processing, IEEE Transactions on》2004,52(9):2612-2624
Asymmetric digital subscriber lines (ADSLs) employ discrete multitone modulation (DMT) as transmission format, where subcarriers are assigned to the up- and/or downstream transmission direction. To separate up- and downstream signals, the ADSL standard allows the use of echo cancellation resulting in improved bit rates, reach, and/or noise margins. In DMT-based modems, typically, the mixed time/frequency (MTF) domain echo canceling scheme, as proposed by Ho et al., is implemented. This technique estimates the echo filter in the frequency domain using the least mean square (LMS) algorithm with the transmitted echo symbols as update directions. Since not every tone of the transmitted echo signal will carry data, i.e., will be excited, the MTF adaptation process does not lead to a good estimate for the echo channel, unless extra power on unused echo tones is transmitted. However, transmitting extra power on such tones is often undesired. In this paper, we present an alternative echo canceling scheme referred to as the circulant decomposition canceler (CDC), which works without extra power requirements and with comparable complexity as the method of Ho et al. Similar to MTF echo canceling, the CDC scheme can easily be incorporated into a multirate environment with different transmit and receive rates and can also cheaply be combined with per-tone equalization and double talk cancellation to allow fast tracking and/or convergence in the presence of a far-end signal. 相似文献
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Fukuda M. Tsuda T. Gambe H. Hino Y. 《Selected Areas in Communications, IEEE Journal on》1988,6(3):476-483
A 144-kb/s digital subscriber loop (DSL) transmission system based on hybrid transmission with an echo cancelling method is described. It incorporates advanced LSI technology to obtain compactness, low cost, and high reliability. An echo canceller (EC) LSI has been developed using CMOS technology. Combined with the multiplexing processor (MXP) LSI, the EC LSI provides basic DSL equipment functions. A specially arranged frame format with a newly developed digital phase-locked loop (DPLL) circuit for stable timing extraction, an automatic balancing network, and a two-stage echo canceller characterize the system. Using this line termination circuit, the DSL equipment showed a reach of over 6 km when used with 0.5 mm diameter cable for 160-kb/s bidirectional digital transmission 相似文献
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A discrete-time analog echo canceller is described that reduces the echo in the front end of Gigabit Ethernet twisted-pair interfaces. Echo cancellation in the analog domain by means of four taps reduces the complexity of the digital echo canceller and crosstalk cancellers. Designed in a 0.4-μm CMOS technology, the circuit employs an LMS algorithm to adapt to the cable length and impedance discontinuities, providing an echo suppression of 10 dB. The design operates at 125 MHz while consuming 43 mW from a 3-V supply 相似文献
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一种基于DSP的音频实时处理系统 总被引:1,自引:1,他引:0
声学回声消除器一直是视频会议系统不可缺少的组件。将回声消除算法结合噪音消除和静音检测算法等,提出一种改进的实时音频处理系统方法,并在TMS320C6713B上实现,能够有效改善噪音、双工检测、非线性回声等导致自适应滤波器发散的问题。该系统在保证正常双工通话的同时,对非线性回声的抑制有着明显的改善效果。 相似文献
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Tang Baomin 《中国邮电高校学报(英文版)》1997,(2)
PerformanceEvalutionof2B1QDataEchoCancelerinDigitalSubscriberAccesNetworksManuscriptreceivedOct.12,1996TangBaomin(NanjingUniv... 相似文献
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Kanemasa A. Sugiyama A. Koike S. Koyama T. 《Selected Areas in Communications, IEEE Journal on》1986,4(8):1359-1366
This paper proposes an ISDN subscriber loop transmission system based on an echo cancellation technique which fully supports the CCITT recommended basic interface for ISDN, i.e.,B + B + D over metallic cables. System design considerations of cable loss, crosstalk, impulsive noise, and system requirements such as power feeding on a caLl-by-call basis are discussed, and a transmission system is proposed. The proposed system is characterized by the use of a new line code, named "modified biphase code." The use of this code with fixed line loss equalization and coherent detection achieves circuit simplification. A special adaptation algorithm is incorporated with the echo canceller that significantly reduces convergence time. Experimental results show satisfactory performance with respect to the residual echo and the bit error rate. Since the system requires only a simple nonadaptive circuit for analog portion, it is suitable for LSI implementation. 相似文献