Performance evaluation of COFDM for digital audio broadcasting. I.Parametric study

This paper describes the performance of COFDM (coded orthogonal frequency division multiplexing) for digital audio broadcasting (DAB) over various multipath mobile radio channels. COFDM is a channel coding and modulation scheme which mitigates the adverse effects of fading by using wideband multicarrier modulation combined with time interleaving and a convolutional error correcting code. A guard interval is inserted at the transition between successive symbols to absorb the intersymbol interference created by the time domain spread of the mobile radio channel. The decoding process is performed using differential demodulation in conjunction with a soft decision Viterbi decoder. The COFDM evaluation is done by means of computer simulations. A parametric study of the proposed COFDM system is done in this first of a series of papers to determine the optimal system parameter values for operation at a radio frequency of 1.5 GHz. The results show that the parameter values proposed in the standard are indeed well suited for operation at 1.5 GHz. Using the set of optimal parameter values found, the COFDM performance is then evaluated in mobile radio channels typical of different geographical environments. Simulation results confirm the benefit that the system gains from frequency diversity found in the urban and hilly terrain areas     

关于编码正交频分复用中同步的研究

编码正交频分复用(COFDM)是一种多载波数字通信调制技术,其基本原理是将频域中的一个宽带信道划分成多个重叠的子信道进行窄带传输.在接收端,虽然频谱相互重叠,但是只要保证各子信道上信号的正交性,就可以将各信道上的信号正确分离.文章重点研究了COFDM 通信系统中的同步技术.     

低信噪比下SMCC+系统精确大频偏估计方案

该文基于由电子科技大学提出的作为中国地面数字多媒体电视广播传输标准候选方案之一的SMCC+系统和OFDM系统,提出了一种在低信噪比下利用特殊构造的短PN序列进行快速精确的大范围频率同步的方法。经仿真证明,信噪比在-20 dB范围以上时,该法在AWGN,单抽头瑞利衰落信道和等值双径瑞利衰落信道环境纠正大范围频偏的性能比Tufvesson等人(1999)同类常规算法性能更优,从理论上而言,该算法可以估计1/2带宽范围内的频率偏移,显然,该算法优于常规同类算法。     

基于COFDM技术的电缆调制解调器的设计

文中对采用编码正交频分复用技术的调制解调器进行了分析研究,并完成了用数字信号处理器实现的COFDM调制解调器的系统方案。这种新型高速通信传输技术不仅可以满足测井电缆传输系统数据传输的要求,而且具有良好的抗噪声能力。所有主要功能和算法均由软件编程实现,不用改动硬件就可以进行算法的升级改进。     

Field trials of an MPEG2 distributed single frequency network

The digital terrestrial television standard approved by the European Telecommunications Standards Institute (ETSI) is based upon the work of the Digital Video Broadcasting group (DVB). This standard using coded orthogonal frequency division multiplexing (COFDM) facilitates the establishment of single frequency networks (SFN). The first MPEG2 distributed SFN was established by RTE and other partners of the European Commission sponsored project VALIDATE (Verification and Launch of Integrated Digital Advanced Television in Europe) in Ireland. This paper describes the network established and details some of the measurements performed. Two co-channel UHF transmitters were synchronised using the MPEG2 megaframe identification packet (MIP). A 155 Mbit/sec STM-1 microwave link system was used for signal distribution     

Transmission techniques for dab by satellite

This study is a comparison between the CDMA and COFDM transmission techniques for digital audio broadcasting. Since broadcasting is used to establish a mobile or fixed link, it is necessary to set up a transmission technique which allows the optimum use of fading and multipath channels, particularly in urban locations. This paper sums up a comparative case study between the two transmission techniques mentioned above. The interest of this paper is to point out the added value brought by these transmission techniques for requirements such as multiple path problems with digital broadcasting with mobiles, frequency mapping and synchronization, capacity of the system, jamming protection capability, BER specifications, signal processing complexity, power control, spectrum efficiency and error correction operations. Finally, this paper tries to bring the appropriate conclusion which leads the OFDM process in Europe.     

The COFDM modulation system: the heart of digital audiobroadcasting

Digital audio broadcasting offers the potential to give every radio in Europe the sound quality of a compact disc. To accomplish this, it requires a rugged method of transmission. The coded orthogonal frequency division multiplexing (COFDM) modulation system was developed to meet this need. The paper describes the reasons why a new modulation process was needed, and explains how the COFDM system has been optimised to meet the requirements     

COFDM技术及其在DVB-T系统中的应用

COFDM技术是一种多载波数字通信技术。他是较为完备的移动接收和传输技术,可以大大降低每个子载波内的符号间干扰,节省了用于均衡的系统开销。对欧洲数字地面广播标准DVB T中的COFDM(编码的正交频分复用)调制方式进行了研究,阐述了COFDM技术的基本原理,并且介绍了其适合应用于地面数字电视广播系统的主要特性。     

基于FPGA的DVB-T COFDM调制模块的设计

研究了DVB-T标准中的COFDM编码调制模块,阐述了COFDM编码调制的基本原理,并以FPGA为硬件平台进行了半实物仿真。最后结合DVB-T标准分析了COFDM适用于地面数字电视广播的特性。     

CD by radio-digital radio broadcasting

Engineers have been looking at ways of broadcasting a digital radio service to the general public, which would ideally have the following features: sound quality comparable with that of the CD; reliable reception to all listeners in the coverage area; capability of offering coverage of all listeners; capability of fixed, mobile and portable reception using simple low grains antennas; simple push-button programme selection-no tuning; frequency efficiency, so that many services can be provided in any spectrum available; and capability of operation from terrestrial transmitters and/or satellite. The author describes the requirements of a digital audio broadcasting system regarding intersymbol interference and then discusses COFDM, coded-orthogonal frequency division multiplex. The author also discusses low-bit-rate sound, terrestrial transmission, satellite broadcasting, receivers, frequency allocation and system testing     

Performance of cofdm for satellite digital audio broadcasting

This paper analyses the performance of a coded orthogonal frequency division multiplexing (COFDM) based system for digital audio broadcasting using a highly inclined orbit satellite constellation. The sources of performance degradation considered are non-linear amplification in the satellite transponder and multipath propagation for mobile reception. Despite its strong peak-to-mean amplitude variation, COFDM has been found to be very robust against non-linear amplification. In the multipath channel, practical cases demonstrate low performance losses even in highly populated areas when highly inclined elliptical orbits (HEO) are used.     

Digital/analogue co-channel protection ratio field measurements

The digital terrestrial television standard approved by the European Telecommunications Standards Institute (ETSI) using coded orthogonal frequency division multiplexing (COFDM) facilitates the establishment of complex networks including single frequency networks (SFN) and multiple frequency networks (MFN). RTE and other partners of European Union (EU) sponsored projects such as MOTIVATE and VALIDATE have established and tested these networks in order to understand the important parameters of digital networks. Protection ratios are needed in order to plan the coverage of digital networks and minimise interference from co-channel transmitters. This paper describes a network established to field test protection ratios and details the measurements performed. Three co-channel UHF transmitters were installed at RTE mainstations in the Dublin area     

Multi-resolution 64-DAPSK modulation in a hierarchical COFDMtransmission system

Two alternative modulation schemes of 64-QAM (quadrature amplitude modulation) and 64-DAPSK (differential amplitude and phase shift keying) with a coherent and incoherent demodulation have been proposed for digital terrestrial video broadcasting (DTVB) in combination with the coded orthogonal frequency division multiplexing (COFDM) technique (Schafer 1995, and Engels and Rohling 1995). Additionally, a hierarchical transmission system based on a multi-resolution (MR) 64-QAM is described in Engels and Rohling which extends the service area of a TV programme in decoding a stepwise reduced data rate with increasing transmitter distance (graceful degradation). This procedure corresponds to a decreasing picture quality. In this paper MR concepts for the 64-DAPSK are developed. A performance comparison between the hierarchical transmission systems (MR-64-QAM/OFDM and MR-64-DAPSK/OFDM) is described for the uncoded and coded case     

数字电视技术分析

DVB—H手机电视技术从传统的数字电视技术演进而来并广泛应用于3G移动通信中，回顾数字电视技术的历史，比较ATSC 8-VSB、DVB—T COFDM和ISDB—T BST—OFDM3种不同调制方式的数字电视技术的优缺点，并分析3种传输系统在不同网络环境中的运行性能。     

Digital video broadcasting

A new kind of “wireless video” is currently entering consumers' homes-digital television. The term digital video broadcasting (DVB) is used as a synonym for digital television in many countries of the world. Whereas one may tend to think that digital television means just a new, digital, form of signal representation not necessarily affecting the information content of what one has always called TV, the truth is that digital television becomes multiple-channel data broadcasting. This article reviews some of the results of the work in the worldwide DVB Project and explains some of the fundamental concepts behind the work of this group. It then concentrates on the terrestrial transmission system (DVB-T) as one example of the many transmission technologies DVB has developed over the last few years. The COFDM modulation scheme which is a key ingredient of DVB-T is described in some detail. The performance of the system is presented. The use of DVB for data broadcasting and the accompanying return channel technologies are explained     

COFDM: an overview

The research and development of OFDM/COFDM for digital television broadcasting has received considerable attention and has made a great deal of progress in Europe. OFDM/COFDM has already been implemented in digital audio broadcasting and is being considered for terrestrial digital television and HDTV broadcasting. The advantages of COFDM claimed by the advocates in Europe have also caught the attention of US broadcasters and generated enthusiasm although a digital modulation technique called 8-VSB has been selected by the FCC Advisory Committee on Advanced Television Service (ACATS) for the final testing. There is considerable debate in the industry over the use of COFDM vs. VSB or QAM for terrestrial HDTV broadcasting. In this paper, the history of research and development on OFDM and COFDM is reviewed. Then, the basic principles, performance and implementation of OFDM and COFDM are examined. Analysis is given to enable the selection of key elements for meeting the constraints of the required applications. Based on the ATV channel model, performance expectation of COFDM under imperfect channel conditions and implementation issues are examined in details     

中波数字AM广播实现方案

提出一种上下兼容的中波数字广播系统方案。该方案的数字基带传输方式为COFDM,与DRM和IBOC相同,射频调制仍采用保留载波的双边带调幅,不需要对现有广播发射机进行改动或更换,接收机可沿用目前中波收音机的包络检波或采用相干解调,实现复杂度低,便于形成规模生产。讨论了该方案实现的关键技术,并给出了发展和应用前景。     

COFDM技术用于无线图像传输系统的优势

本文主要介绍了COFDM技术的基本原理,论述了该技术应用于无线图像传输系统的优点以及该技术在无线图像传输系统中的实际应用。     

Hardware nonlinearities in digital TV broadcasting using OFDMmodulation

FFT-based coded orthogonal frequency division multiplexing (COFDM) is one of the techniques for digital TV broadcasting over multipath fading channels. A FFT-based OFDM signal is subject to various hardware nonlinearities in both the transmitter and receiver. Hardware nonlinearities not only affect the in-band performance of an FFT-based OFDM system but also may affect the system performance of an adjacent channel signal because of regenerated sidelobes of the transmitted signal. The paper investigates the in-band and out-of-band behaviour of a 64QAM-OFDM system under various nonlinear devices. It is shown that the inherent signal clipping in the IFFT processors with a limited word length reduces the required RF amplifier output backoff (OBO) where adjacent channel interference is the limiting factor. For a 0.25% clipping rate, an additional 2 dB OBO is required for the COFDM signal to achieve the same level of adjacent channel interference as for the single carrier system. The loss in SNR due to signal clipping is negligible in a coded OFDM system     

Coded orthogonal frequency division multiplex [TV broadcasting]

Technological evolution and the ever-increasing demand for higher-quality services give broadcasters a strong incentive to completely digitize their broadcasting networks. This digitization, which is already well advanced in many program production areas and transmission links, now has to be extended to complete the last link in the broadcast chain; i.e., from broadcast transmitter to consumer receivers. It is therefore necessary to develop wholly new techniques for the broadcasting of digitally coded TV programmes. Thus an efficient baseband digital coding must be combined with a robust digital modulation and channel coding scheme that can meet the requirements of every mode of broadcast reception. This article presents the research work related to the coded orthogonal frequency division multiplex (COFDM) technology, which has now been completed in the field of digital radio (DAB), and which is under progress in the field of digital terrestrial TV