Performance evaluation of COFDM for digital audio broadcasting. II.Effects of HPA nonlinearities

For pt. I see ibid. vol.43, no.1, p.64-75, 1997. The effects of the high power amplifier (HPA) nonlinearities on the performance of the Eureka 147 DAB system are studied by computer simulation. The performance is determined for three types of HPA: a travelling wave tube amplifier (TWTA), a solid state power amplifier (SSPA) and a perfectly linearized amplifier (PLA). Two related performance criteria are used: (a) the degradation, resulting from HPA nonlinearities, in the E_b /N₀ ratio required at the receiver to maintain a bit error rate of 10^-4 and (b) the total power degradation. These degradations are measured as a function of the HPA output backoff (OBO). The effect, on the E_b/N₀ degradation, of linearizing only the phase or only the amplitude transfer characteristic of the TWTA and the SSPA is also assessed. Correcting the phase distortion alone in both HPAs is found to reduce the E_b/N₀ degradation by less than 0.5 dB. Linearization of the amplitude characteristic alone, on the other hand, can reduce the E_b/N₀ degradation by several dBs at small OBO values (<2 dB). The optimum output backoff which minimizes the total power degradation is between 2 and 3 dB for both the TWTA and the SSPA in a terrestrial mobile channel and between 1 and 2 dB in an AWGN channel. The optimum output backoff for the PLA is 2 dB in the terrestrial channel and between 1 and 2 dB in the AWGN channel. At the optimal operation point, the power saved by linearizing the amplitude and phase characteristics of the TWTA or the SSPA is about 0.6 dB for the terrestrial mobile channel and 0.4 dB for the AWGN channel     

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.     

Subband-multipulse digital audio broadcasting for mobile receivers

The audio quality, robustness and implementational complexity of a novel mobile digital audio broadcast scheme are addressed. The audio codec proposed is based on an efficient combination of subband coding (SBC) and multipulse excited linear prediction coding (MPLPC). The bit allocation is dynamically adapted according to both the signal power in different subbands and a perceptual hearing model. Typically a segmental signal to noise ratio (SEGSNR) in excess of 30 dB associated with high fidelity subjective quality was achieved for 2.67-b/sample transmissions at a bit rate of 86 kb/s. Perceptually unimpaired audio quality was achieved for a bit error rate (BER) of about 10^-4, when injecting random errors, which was degraded for increased BERs. In order to provide robust error protection, the audio codec was also subjected to a rigorous bit sensitivity analysis. Four different forward error correction schemes were investigated in order to explore the complexity, bit rate, and robustness tradeoffs     

数字音频广播的进展

分析目前音频广播的现状,指出发展数字音频广播（ＤＡＢ）的必然性,并讨论数字音频广播的关键技术。最后介绍了有关数字音频广播系统的方案。     

Complementary punctured-pair convolutional codes for digital audio broadcasting

Hybrid in-band on-channel (IBOC) broadcasting systems for digital audio radio have the capability of simultaneously transmitting analog FM and digital audio of CD-like quality. Due to fading and interference in the already-crowded FM band, the signal design for the hybrid IBOC system is very challenging. It has been proposed to use a method of double sideband transmission where the digital information is transmitted by means of orthogonal frequency-division multiplexing (OFDM) on both sides of the analog host FM and where the digital information can be recovered when one sideband is partially or even totally lost. This leads to an interesting channel coding problem, where we search for optimal pairs of high-rate codes that form good combined low-rate codes, which are better than classic code combining techniques. Furthermore, we also search for rate-compatible punctured convolutional codes which can be used for two-level unequal error protection (UEP) of digital audio. Since some of the tones in the multitone modem (OFDM) are more exposed to interference than others, optimal assignments of convolutional code bits to tones depending on their spectral position are also found. A large number of new codes with memory 6 and 8 are presented both for equal error protection and UEP.     

广东数字音频广播的发展

数字音频广播(Digital Audio Broadcasting，DAB)是继调幅和调频广播之后的新一代广播，与模拟调制的广播相比具有音质好、抗多径干扰较强和恶劣环境下的接收、频谱利用率高、业务构成灵活等优点，是广播事业发展中的一个新的里程碑。     

Technical advances in digital audio radio broadcasting

The move to digital is a natural progression taking place in all aspects of broadcast media applications from document processing in newspapers to video processing in television distribution. This is no less true for audio broadcasting which has taken a unique development path in the United States. This path has been heavily influenced by a combination of regulatory and migratory requirements specific to the U.S. market. In addition, competition between proposed terrestrial and satellite systems combined with increasing consumer expectations have set ambitious, and often changing, requirements for the systems. The result has been a unique set of evolving requirements on source coding, channel coding, and modulation technologies to make these systems a reality. This paper outlines the technical development of the terrestrial wireless and satellite audio broadcasting systems in the U.S., providing details on specific source and channel coding designs and adding perspective on why specific designs were selected in the final systems. These systems are also compared to other systems such as Eureka-147, DRM, and Worldspace, developed under different requirements.     

COFDM数字电视广播系统中使用CSI的维特比译码器

介绍比特交织格状编码调制 ＭＱＡＭ的编译码原理,软判决译码中使用信道状态信息（ＣＳＩ）是ＣＯＦＤＭ在频率选择性衰落和干扰下获得优异性能的关键。研究ＣＯＦＤＭ数字ＴＶ广播系统中使用ＣＳＩ的维特比译码器的一种实现方法。     

数字音频广播浅谈

本文介绍了数字音频广播的一些关键技术、优点、系统组成、应用情况。     

数字电视地面广播COFDM传输中的软判决技术

深入研究了数字电视地面广播COFDM解调方案中的解映射软判决技术,提出了适用于该系统的信道状态信息CSI提取方法。在此基础上通过算法仿真分析,进一步提出一种新的克服单频和PAL模拟电视同频干扰的消除法并给出计算公式。本设计基于国家数字高清晰度电视总体组的多载波BDB-T传输方案,方案样机采用FPGA实现其相应的硬件电路,经过在实际无线环境中传输测试,证明了所提方法的易实现性和其良好性能。     

高清数字视频广播中的音频解嵌系统设计

数字视频广播的视频流中可嵌入音频数据。本文研究了符合SMPTE299M标准的高清视频流中音频嵌入原理,在FPGA上设计并实现了高清视频流音频解嵌系统,它能解出采样率为48K的16路声音通道的数字音频信号,并根据需要选择相应通道进行播放。该系统可用于数字演播室中对各个通道的声音监测及播放。     

Multi-antenna scheme for high capacity transmission in the digital audio broadcasting

In this paper, we apply multi-antenna scheme to DAB system for high-rate transmission. In the MIMO-DAB system with a number of transmitting and receiving antennas increases the transmission rate efficiently with low multiplication operations. For channel estimation in the MIMO-DAB system, we propose a new PRS structure and evaluate the channel estimation performance. The proposed PRS structure can estimate multi-channel information based on the semi-blind processing. The performance of proposed PRS is compared with that of conventional training sequence employing Tarokh's transmission matrix. And also we investigate the performance limitation due to the imperfect channel estimation in a MIMO-DAB receiver. It has been shown that the MIMO-DAB system with multi-antennas can achieve the high-rate transmission for multimedia broadcasting and the performance of MIMO-DAB system is impaired by imperfect channel information.     

DVB前端系统中的MPEG音频实时编码

随着数字技术的引入和人们不断提高的视听要求,MPEG组织在MPEG-1标准的基础上提出了新的MPEG-2标准。新的标准具有更高位率（2～50 Mbps）,接近演播室效果的图像质量,音频编码最多能支持6路声道。由于以上诸多的特点,MPEG-2标准已广泛应用于高品质的广播电视中。而在中国,MPEG技术已投入到实际应用中。MPEG第二层编码利用了人耳的听觉特性,采用MUSICAM算法对立体声进行实时压缩编码。其压缩率为6～8倍左右。本文将详细介绍DVB前端系统中采用MPEG-2标准开发的实时立体声编码模块。1 模块的结构组成DVB前端的编码系统…     

Joint encoding and decoding methods for digital audio broadcasting of multiple programs

We introduce new methods for increasing the performance of multiprogram digital audio broadcast systems, e.g., satellite digital audio broadcasting. Joint multiprogram encoding is an attractive possibility for parallel broadcasting of a large number of programs. Joint coding extended over multiple audio frames in time give further improvements. The benefits of this kind of statistical multiplexing yield improved audio quality and/or higher capacity in terms of number of programs. We describe the new Joint Multiple Program Encoding Technique in the context of the perceptual audio coding (PAC) type of algorithms. We also describe methods for multi-program transmission including Equal Error Protection (EEP) as well as Unequal Error Protection (UEP) and improved error concealment for multiple program transmission. Some of the techniques described in this paper, are currently being used in satellite digital audio broadcasting in the United States.     

Performance analysis of a COFDM/FM in-band digital audiobroadcasting system

In this paper, we present a performance analysis of a coded orthogonal frequency division multiplexing DAB system that is power multiplexed over a commercial FM station. We model the mobile channel with a time-frequency scattering function. Results show that the performance of the FM demodulator is crucial, since the level of the residual FM signal has a strong influence on the BER performance of the COFDM system. As with other mobile communication systems, the use of interleaving greatly enhances the performances     

Simultaneous broadcasting of analog FM and digital audio signals bymeans of adaptive precanceling techniques

A method for broadcasting digital audio simultaneously with existing analog frequency modulation (FM) radio is presented. The method is based on precomputing the response of the host analog FM signal at the digital receiver and precanceling it at the transmitter. As a result, the digital transmission is free from interference from analog FM. We select the rate and power level of the digital transmission in a manner that the interference the digital data incur on the analog FM signal remains at acceptably low levels. The digital transmission is based on adaptive orthogonal frequency-division multiplexing (OFDM) (adaptive multicarrier). The frequencies and number of carriers of the digital multicarrier modem are judiciously selected in a time-varying fashion so as to cause a negligible distortion in a standard receiver for analog FM. Simulations based on conservative nonoptimized signal design indicate that data rates up to about 130 kb/s inside the 200-kHz FM channel are achievable for acoustic test signals. We present a number of numerical examples where the average digital data use up to 50% of the 200-kHz power spectrum with digital signal power levels 25-35 dB below the analog signal. Due to the resulting variable-rate digital transmission, a control channel is required. A method of precanceling with multiple orthogonal direct-sequence spread-spectrum schemes is also presented