从有线电视的发展浅谈调制技术

以调制技术为主线，介绍有线电视系统中模拟调制技术、光调制技术和数字调制技术的基本原理。随着有线电视的快速发展，调制技术正在经历电到光、模拟到数字的不断发展和全面融合的过程。     

数字调制技术的进展

本文简要介绍了数字调制技术的发展状况，目的在于对当代调制技术进行选择和开展进一步的研究，以提高通信的有效性和可靠性，数字调制技术的实现，促进了通信的飞速发展。     

论半导体激光器及调制技术

在当代的通讯传输领域中，半导体激光器及调制技术展示出前所未有和不可代替的技术成就。半导体激光器及调制技术的种类较多，从其对光源进行调制的方式上来区分，可分为光强度直接调制和光强度外部调制两种方式。本分别对这两种光强度调制方式进行了论述。     

QAM调制及其应用分析

QAM调制技术是目前数字调制理论中十分成熟的技术。随着它在调制解调器及数字有线电视系统中广泛使用，巳愈来愈引起各方的重视，本文从最基本的概念入手，全面阐述了QAM调制的物理内涵和基本原理，结合具体的实践，详细地论述了QAM调制器的主要性能指标。     

综合编码和调制的格码调制（一）

本文首先介绍了有关格码调制（ＴＣＭ）的技术名词，然后重点论述了格码调制的原理、结构以及幅度／相位调制的８态格码调制，最后介绍了多维ＴＣＭ。     

可变速率调制技术

QAM是振幅和相位联合的调制技术，近年来人们对多电平QAM应用于移动环境进行了研究，例如：根据移动信道特性的好坏可自适应地改变QAM的电平数，即改变信道的传输速率，从而形成变速率QAM(VR—QAM)。本文将对近年来提出的在个人通信等领域具有很大发展前景的可变速率调制技术的原理、性能及应用做简要介绍，最后预测调制技术在移动通信中的发展趋势。     

π/4-QPSK调制方式及其与GSMK调制方式的比较

简略介绍了QPSK，π／4－QPSK调制方式及其于此的π／4－QPSK调制方法，就π／4－QPSK的调制电路原理与实现作了概述，并针对π／4－QPSK调制方法的优点及其性能与GMSK技术进行了比较。     

HDTV传输的调制技术

本文旨在阐述高清晰度电视（ＨＤＴＶ）传输的调制技术，并对其国际现状作一较全面的概括。文中扼要地分析了ＨＤＴＶ传输的基本原理，在突出全数字式地面广播的情况下，简述了三种传输调制技术的思想和特点，最后，比较三种ＨＤＴＶ传输的调制技术并分析它们的发展趋势。     

移动通信调制技术的进展

移动通信发展过程中,特别是第3代移动通信发展中,移动通信调制技术相比传统的无线通信调制技术已有相当的变革和进展。文章就现代移动通信调制技术相位调制技术、频率调制技术、多进制调制技术、自适应调制技术进行讨论,并对相关技术性能和应用进行分析,最后提出对进一步发展的看法。     

光学谐振腔增强碘分子调制转移光谱

提出了一种新的高灵敏激光光谱技术——激光双频相位调制环形腔增强调制转移光谱技术。该技术采用单一晶体实现激光双频相位调制，在满足环形腔高精度锁定的同时，又结合了调制转移光谱技术的高灵敏度、高分辨率、无多普勒背景的优点和环形谐振腔增强技术在提高谱线信噪比方面的优势；由此，实验观察到^127I2分子在532nm波段高信噪比的超精细结构光谱。与传统调制转移光谱技术相比，该技术在提高微弱吸收光谱信号的探测灵敏度方面具有明显的优势，在高灵敏、高分辨光谱检测和激光稳频方面将有很好的应用前景。     

Optimum finite-length equalization for multicarrier transceivers

A new criterion for partially-equalizing severe ISI channels to reduce the cyclic prefix overhead of the discrete multitone (DMT) transceiver, assuming a fixed transmission bandwidth, is introduced. The equalized DMT is shown to recover a significant portion of the performance loss incurred because of the use of a moderate-size FFT in the DMT to reduce latency and implementation cost. In particular, equalizers designed using our new criterion result in a higher DMT performance margin than traditional mean-square-error DMT equalizers. Finally, additional promising methods that further enhance the performance of the equalized DMT are investigated     

Optimal ISI-free DMT transceivers for distorted channels withcolored noise

The design of optimal DMT transceivers for distorted channel with colored noise has been of great interest. Of particular interest is the class of block based DMT, where the transmitter and the receiver consist of constant matrices. Two types of block- based DMT transceivers are considered: the DMT system with zero padding (ZP-DMT) and the DMT system with general prefix (GP-DMT). We derive the bit allocation formula. For a given channel and channel noise spectrum, we design the ISI-free optimal transceiver that minimizes the transmission power for a given transmission rate and probability of error. For both ZP-DMT and GP-DMT systems, the optimal ISI-free transceiver can be given in closed from. We will see that for both classes, the optimal transceiver has an orthogonal transmitter. Simulation shows that the optimal DMT system can achieve the same transmission rate and the same probability of error with a much lower transmission power compared with other existing DMT systems     

Perfect discrete multitone modulation with optimal transceivers

Previously, discrete Fourier transform (DFT)-based discrete multitone modulation (DMT) systems have been widely applied to various applications. In this paper, we study a broader class of DMT systems using more general unitary matrices instead of DFT matrices. For this class, we show how to design optimal DMT systems over frequency-selective channels with colored noise. In addition, asymptotical performance of DFT-based and optimal DMT systems are studied and shown to be equivalent. However, for a moderate number of bands, the optimal DMT system offers significant gain over the DFT-based DMT system, as is demonstrated by examples     

The effect of timing jitter on the performance of a discretemultitone system

The transmission of high-speed data over severely band-limited channels may be accomplished through the use of discrete multitone (DMT) modulation, a modulation technique that has been proposed for a number of new applications. While the performance of a DMT system has been analyzed by a number of authors, these analyses ignore the effect of timing jitter on system performance. Timing jitter becomes an increasingly important concern as higher data rates are supported and larger constellations are allowed on the DMT subchannels. Hence, in this paper, we assume that synchronization is maintained by using a digital phase-locked loop to track a pilot carrier, Given this model, we derive error rate expressions for an uncoded DMT system operating in the presence of timing jitter, and we derive an expression for the interchannel distortion that results from a varying timing offset across the DMT symbol. In addition, we investigate the performance of trellis-coded DMT modulation in the presence of timing jitter. Practical examples from the asymmetric digital subscriber line (ADSL) service are used to illustrate various results     

A dual-metal-trench Schottky pinch-rectifier in 4H-SiC

Characteristics of high-voltage dual-metal-trench (DMT) SiC Schottky pinch-rectifiers are reported for the first time. At a reverse bias of 300 V, the reverse leakage current of the SiC DMT device is 75 times less than that of a planar device while the forward bias characteristics remain comparable to those of a planar device. In this work, 4H-SiC pinch-rectifiers have been fabricated using a small/large barrier height (Ti/Ni) DMT device structure. The DMT structure is specially designed to permit simple fabrication in SiC. The Ti Schottky contact metal serves as a self-aligned trench etch mask and only four basic fabrication steps are required     

A discrete multitone transceiver system for HDSL applications

A discrete multitone (DMT) transceiver design for high bit rate digital subscriber line (HDSL) access is presented and analyzed. The DMT transmitter and receiver structure and algorithms are detailed, and the computational requirements of DMT for HDSL are estimated. At a sampling rate of 640 kHz, using an appropriate combination of a short finite-impulse-response (FIR) equalizer and a length-512 DMT system, 1.6 Mb/s data transmission is possible within the carrier serving area (CSA) at an error rate of 10^-7 on a single twisted pair. A significant performance margin can be achieved when two coordinated twisted pairs are used to deliver a total data rate of 1.6 Mb/s. In terms of a performance-per-computation figure of merit, the DMT system is an excellent candidate for HDSL implementation     

针对DMT调制技术的自适应均衡方法

介绍了离散多音频技术（ＤＭＴ）的原理及其实现方法，提出了一种针对ＤＭＴ调制技术的自适应均衡方法，并通过计算机仿真实验证明了该方法是简单的有效的。     

New equalisation approach for maximising data rate in discrete multi tone systems

This article presents a new time domain equaliser (TEQ), which can be used in discrete multi-tone (DMT) systems to maximise the bit rate. The proposed TEQ is tested in the fast Fourier transform based discrete multi-tone (FFT–DMT) system, and in a proposed discrete cosine transform based discrete multi-tone (DCT–DMT) system. The objective of the proposed DCT–DMT system is to make use of the energy compaction property of the DCT to reduce the channel effects on the transmitted signals. A mathematical model of the proposed TEQ is presented. Simulation experiments have been carried out to test the effect of the proposed TEQ with the FFT–DMT system and the proposed DCT–DMT system. The results show that the performance of the DCT–DMT system with the proposed TEQ is better than the FFT–DMT system with this TEQ over the eight standard carrier serving area (CSA). The results also show that employing the proposed TEQ in the DCT–DMT system can achieve a high bit rate, ranging from 2.899?Mbps to 5.369 Mbps.     

Digital RFI suppression in DMT-based VDSL systems

We propose a method for suppressing radio frequency interference (RFI) in discrete multitone (DMT) based very high bit rate digital subscriber line (VDSL) systems. The method operates in the frequency domain of a DMT system. First, we derive a model of how an unknown narrow-band RF signal is mapped onto the DMT carriers. Then, by measuring the RFI on a few unused DMT carriers we are able to subtract RFI estimates from every modulated subcarrier. Simulation results show that this method, applied to an RFI signal with the same average power as the VDSL signal, suppresses the RFI with 40-50 dB, which reduces the average SNR loss from about 20 to less than 0.3 dB.     

A coded and shaped discrete multitone system

Shows how coding and constellation shaping may provide significant gains to a discrete multitone (DMT) system transmitting over spectrally-shaped channels. First, the authors present and analyze a concatenated coding scheme consisting of an inner trellis code and outer block code when applied to DMT modulation, and address some of the implementation issues associated with this scheme. Some laboratory test results for a DMT prototype employing the coding scheme are presented. Next, they propose a method for applying Forney's trellis shaper across the tones in a DMT system to realize significant shaping gain. To illustrate the coding and shaping gains achieved, they use scenarios indicative of the newly introduced asymmetric digital subscriber line service. By combining a powerful coding scheme, shaping, and DMT modulation, they arrive at an implementable transceiver that can provide very high data rates over spectrally-shaped channels