带内同频道数字音频广播关键技术进展

基于编码正交频分复用的数字音频广播(DAB)具有鲁棒性高和激光唱盘(CD)音质等优良性能。带内同频道(IBOC)制式的DAB能够在已有的模拟广播频道内同播模拟和数字两种信号,完全兼容现有的模拟接收机,以较低成本实现向全数字化DAB的平滑过渡。作者论述了FM IBOC DAB的频谱分析,综述了混合模式FM IBOC DAB的发射(接收)机的基本结构和感知音频编码、前向纠错编码、OFDM、第一邻频道干扰消除、时间延迟分集和音频混合等关键技术,提出了发展我国的 IBOC DAB的一些建议。     

Combining digital and analog signals for US IBOC FM broadcasting

IBOC DAB (In-Band On-Channel Digital Audio Broadcasting) requires the simultaneous broadcast of an analog and a digital signal within one channel of the FM band. Because broadcasters are adding IBOC to their existing systems, it is vital that they achieve maximum power efficiency while working within their existing space and power limitations. There are currently three different strategies proposed for accomplishing this goal, each having its own advantages and disadvantages. One strategy is to establish a separate, second antenna for the digital service. The other two strategies involve combining the analog and digital signals, either in a single hybrid transmitter or at the output of separate analog and digital transmitters. This paper discusses the equipment required for accomplishing this last strategy.     

Robust modem and coding techniques for FM hybrid ICOC DAB

The design of robust modem and FEC (forward error correction) code techniques with application to the transmission of an FM hybrid analog/digital in-band on-channel (IBOC) digital audio broadcast (DAB) signal is presented here. The FEC codes are derived from an original lower rate convolutional code (R=1/3). The original code is segmented into a pair of “complementary” components, which form independent codes, each with a higher rate (less redundancy) than the base code. The exploitation of channel state information (CSI) and special interleaving techniques are described for application to FM hybrid IBOC DAB with its unique interference environment and selective fading due to multipath. Simulation results confirm the robustness of the design     

创新的中国数字调频广播技术方案——CDRadio与HD Radio的简介与比较

数字化正对中国广播电视行业产生着深刻的影响,传统的FM音频广播也面临着数字化改造.在DAB,HD Radio,DRM及CDRadio几种先进数字音频广播技术方案中重点比较了HD Radio与CDRadio.中国数字调频广播技术方案CDRadio实现了真正的带内数模混叠同播,并通过使用非规则频谱分配、LDPC纠错编码、时...     

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.     

Detailed Analysis of Split-Level Combining

High level combining is a practical way to upgrade existing FM transmitters to IBOC. Very well understood, with readily available 10 dB couplers, it is a very attractive method with which to upgrade even the highest power levels in the field. Unfortunately, if offers only a combining efficiency of 83%, as 90% of the IBOC power is wasted into a dummy load, along with 10% of the generated FM power. Additionally, the power headroom demanded from the FM transmitter is proving to be an unsurpassable requirement for some existing sites ready to upgrade. This paper presents an innovative combining technique that minimizes the FM and IBOC power loss in high level combining. Instead of combining two totally incoherent signals with its known resulting losses, this method first achieves partial coherence of the signals, and only then combines them at an optimum coupling ratio. A system implemented this way offers two main benefits; a higher overall system efficiency, and the elimination of the need for FM headroom. Though the paper focuses on the particular case of FM HD radio upgrade, this technique can also be used whenever low loss is needed when combining dissimilar signals.     

HD Radio传输系统实验室性能测试

HD Radio是美国AM与FM波段的数字广播标准,为了了解其信号的传输性能及其在我国实际播出环境及广播频道规划条件下,与邻频道广播电台之间相互干扰的情况,需要对其传输性能进行实验室测试和场地测试,为我国调频频段广播数字化提供技术参考依据。本文主要探讨实验室性能测试的相关技术和方法。     

美国数字音频广播带内同频技术的实现方案

带内同频技术以其兼容性,频谱有效性,灵活性和可靠性成为美国数字音频广播（ＤＡＢ）极具吸引力的数字化方案。目前有两家机构开发了ＩＢＯＣ系统;ＵＳＡＤＲ和ＬｕｃｅｎｔＤＲ。详细介绍了这两套系统,包括编,解码和调制技术。     

Multilevel RS/convolutional concatenated coded QAM for hybridIBOC-AM broadcasting

Bandwidth efficient modulation schemes using Reed-Solomon (RS) codes are proposed for hybrid in-band-on-channel (IBOC) systems that broadcast digital audio signals simultaneously with analog amplitude modulation (AM) programs in the AM band. Since both the power and bandwidth allocated for digital audio transmission are limited in this application, the system cannot afford to add enough redundancy for error control using conventional concatenated coding schemes. We show that by using multilevel RS and convolutional concatenated coded quadrature amplitude modulation (QAM), an efficient modulation schemes can be obtained for applications such as IBOC-AM broadcasting     

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     

调频段DRM数字广播信道技术研究

2009年8月ETSI颁布的DRM(Digital Radio Mondiale)标准将调频段DRM数字广播囊括其中,介绍该标准中调频段DRM数字广播的优势与信道部分的技术特性。调频段DRM数字广播通过信道编码技术、信道复用、OFDM调制等技术,实现调频段广播信号的传输,与DAB相比可快速而平滑地实现FM波段广播由模拟向数字的过渡。     

Performance of an in-band adjacent-channel DAB system forfrequency-selective Rayleigh and Ricean slow fading channels underanalog FM interference

In support of the 1995-1997 DAB (digital audio broadcasting) testing conducted by the NRSC (National Radio Systems Committee), an IBAC (in-band adjacent-channel) scheme was developed by AT&T. Although not for use in the United States, bit error rate (BER) system performance under both fading environments and the existing analog FM broadcasting is important to quantify. This is because there may still exist other countries and environments where an IBAC approach to DAB is feasible and economical. Given this situation, an IBAC simulation model has been developed to allow for a performance analysis study within the mobile reception environment, which is dominated by Rayleigh and Ricean fading statistics. This paper presents the simulation results for coherent quadrature phase-shift-keying (QPSK) with nonlinear equalization for both frequency-selective Rayleigh and Ricean slow fading channel environments, along with co-channel, 1st-adjacent and 2nd-adjacent analog FM interference. The results indicate that for a country where spectrum availability dictates an IBAC solution, this approach may perform well under various fading and interference environments     

Digitized speech transmission at VHF using existing FM mobile radios

An extensive study of digitized speech transmission over existing VHF FM mobile radio sets is presented. Objective criteria expressed in terms of bit error rate (BER) are determined for the performance evaluation of analog FM radios when transmitting digital voice. These criteria are used to define the technical characteristics such as the receiver sensitivity, co-channel rejection, and adjacent channel selectivity in the case of digital FM transmission. The concept of performance measurements of existing sets in the digital mode of operation is suggested. The results of performance measurements reported here include the following: 1) radiated FM spectra, 2) bit error rate curves, 3) receiver sensitivity, 4) BER performance in the presence of analog or digital FM interference on the same or adjacent channel, 5) signal plus noise plus distortion to noise plus distortion ratio (SINAD) performance in the presence of co-channel or adjacent channel interference for both types of interfering signals, 6) co-channel rejection and adjacent channel selectivity for various combinations of the wanted and interfering signals, 7) receiver selectivity for both modes of operation, and 8) adjacent-signal selectivity for various combinations of the desired and undesired signals. Optimum values of design parameters of digital voice radio system are deduced from the obtained results. Finally, the implications of digitized speech transmission on the technical characteristics, operating range, channel reuse distance, and adjacent channel interference performance of analog FM radios are discussed.     

一种适用于带内同频道数字音频广播的互补卷积码的构造方法研究

针对带内同频道数字音频广播系统中存在的第一临频道干扰问题,该文提出了一种基于互补结构的卷积编码构造方法。采用频率分集联合传输这种互补对卷积码,能够有效地克服信道干扰导致的传输数据破坏或丢失等问题。仿真结果和分析表明,与基于相同卷积码对的编码组合传输相比,互补卷积码联合传输可以得到1～2个dB的渐进编码增益。     

Broadcasting with digital audio

Digital audio broadcasting will come on-line worldwide in the next few years. The technology-also known as digital audio radio or digital sound broadcasting-promises to provide sound of compact-disk quality, nearly free from multipath distortion or other transmission interferences. And digital audio broadcasting (DAB) is not just for sound: all sorts of information, digitally encoded, will be transmitted. Testing is already under way around the world for systems that deliver DAB signals from satellites, from terrestrial systems using newly assigned spectral bands, and from in-band (that is, currently assigned) AM and FM systems. The author discusses spectra for DAB, perceptual coding, Europe's Eureka 147 system, and DAB research in Canada, the USA, and Japan     

Transmission scheme of high-capacity FM multiplex broadcastingsystem

FM multiplex broadcasting is a system for providing additional text and graphics, while maintaining compatibility with existing stereo sound broadcasting. The digital signals are multiplexed in a higher frequency band than baseband FM stereo signals. This paper describes a modulation method and an error correction method for a new high-capacity FM multiplex broadcasting system called DARC (Data Radio Channel), which has a bit rate of 16 kbit/s. Simulation results show that stereo sound signals interfere with a multiplexing signal under multipath conditions. LMSK (level controlled MSK) is proposed as a modulation scheme to ensure good transmission quality. It is shown that an error correction scheme using a product code of (272190) codes has a good performance for mobile reception. Field tests on the DARC for mobile reception are conducted in the service area of the NHK Tokyo FM station. These show that the correct reception rate can be obtained at more than 80% when transmitting information of 6 kbytes     

Transmission of block turbo coded digital audio over FM-SCA

In this paper, an efficient coded scheme for transmitting digital audio over the existing FM channel, by multiplexing it with the baseband FM signal, is described. Transmission of multiplexed signals in the FM baseband called FM-SCA (subsidiary communications authorization) has been previously used for low quality analog content and some low rate digital content. The investigated scheme opens up the possibility of achieving CD quality audio over FM-SCA by enabling high bitrate transmission using MPEG-I layer 3 and MPEG-AAC audio coding for the digital audio. These schemes provide CD quality audio at or below 128 kbps, MPEG-AAC being able to do so at rates as low as 96 kbps. Block turbo codes (BTC), which offer near Shannon's limit performance with relatively low hardware complexity requirements, provide the error protection. Block turbo codes have been shown to be particularly effective for high coding rates. The system uses OFDM in conjunction with 8PSK/16PSK to modulate the digital bitstream and fit it in the 44 kHz (54 to 98 kHz) band available in the FM baseband. Simulation results show an optimal system configuration for digital audio transmission in FM-SCA.     

HD Radio系统中预留子载波降低PAPR的方法研究

HD Radio标准中使用的“带内同频（ IBOC）”技术在现有FM模拟广播的同频带内实现数字广播,无需打破现有的频率规划,是调频模拟广播数字化的最佳选择。然而模拟信号和数字信号同时通过混合天线发射时产生的耦合损耗非常大,降低数字信号的峰均比是减小损耗的有力措施。在降低峰均比的所有方案中,预留子载波法由于不引起信号的失真而受到广泛的关注,而预留子载波法的核心即是预留子载波位置的选取。基于HD Radio系统提出一种基于度量的预留子载波位置的选取方法,该方法通过一个度量值来衡量每个子载波对时域大幅度采样值的贡献,并选取具有最大的正度量值的子载波作为预留子载波。仿真结果表明,当使用30个预留子载波时,在概率为10-3时,提出的方案至少能带来0.79 dB的PAPR增益。     

Digital audio broadcasting in the FM band based on continuous phase modulation

A method for broadcasting digital audio signals simultaneously with existing analog frequency modulation radio (88-108 MHz) in adjacent channels is presented. The digital transmission is based on continuous phase modulation (CPM) and a proper reduced-state sequence estimator. With the proposed method, the power level and the symbol rate of the transmitter signal is determined in a manner that the interference the CPM signal poses for the analog FM signal in adjacent channels remains below a level according to the radio frequency emission mask defined by international rules. Due to the multipath propagation of the transmitted signal, the transmission behavior of the radio channel is determined by high dispersion up to 85 /spl mu/s. With the selected bit rate, the receiver has to cope with a channel memory of up to 17 bits. Since Viterbi detection is not feasible due to the number of channel states, detection is performed by a reduced-state sequence estimator that is able to eliminate the complete channel interference by decision feedback. Simulation results show that the detector almost achieves the detection quality of the optimum receiver. CPM achieves data rates of up to 200 kb/s inside a 200 kHz FM channel, which is sufficient for transmission of digital compressed audio signals at compact disc quality. The encouraging results of field tests will be published in another paper.