Digital audio broadcasting in the FM band by means of contiguous band insertion and precanceling techniques

A low-complexity method of linearly combining an analog frequency-modulation (FM) signal with a low-level multitone signal for simultaneous broadcasting of digital data and analog FM is proposed and evaluated. The analog FM signal can be recovered with a standard FM receiver. The digital multitone signal is added symmetrically at the band edges of the 200-kHz FM signal in contiguous bands with variable width. To maximize the data rate, the digital bandwidth is maximized subject to a maximum allowed distortion of the demodulated analog FM signal. The impact of the analog FM signal on, digital reception is cancelled by means of transmitter precanceling techniques. Conditions for precanceling techniques for multipath channels are formulated. The main advantage of the contiguous band insertion method is that the rate of the control channel is considerably lower compared to previously proposed methods of carrier insertion without significant reduction in data rate. We present a number of numerical results for acoustical signals.     

Postcanceling techniques for simultaneous broadcasting of analog FM and digital data

We consider simultaneous broadcasting of low-power digital data and analog FM and present reliable receivers for the digital data. Due to the relatively low power level of the digital data and the interference suppression capability of analog FM, standard analog FM receivers can reliably recover the analog FM audio signal. To recover the digital data, an extended Kalman filter front end is developed that exploits the capture capability of analog FM to reconstruct and postcancel the analog FM component from the received composite signal. Simulations are conducted with artificial analog FM signals, suggesting that postcanceling schemes can provide higher data rates than their precanceling counterparts, at a lower transmission delay penalty but higher digital receiver complexity. For analog FM to digital signal power level ratios in the range of 30-50 dB, the postcanceler digital signal recovery appears fairly robust, providing digital signal-to-noise ratios of 2-7.5 dB. The corresponding uncoded bit error rates strongly depend on the power level difference between the host analog FM and the digital data signal. In particular, at 260 kb/s and E/sub b//N/sub o/=10 dB they range between 1% to about 15%, and can be reduced to acceptable levels using standard channel coding techniques.     

Precoded Modulo-Precanceling Systems for Simulcasting Analog FM and Digital Data

We present techniques for simulcasting low-power digital data and analog FM over fading channels. Our methods have strong connections to what are referred to as dirty paper coding techniques in that a low-power digital data signal is modulo-added to the host analog FM signal. Due to the low power levels of the digital data and the suppression capability of analog FM, a standard analog FM receiver can be used to reliably recover the analog audio signal. We develop digital receivers that work reliably over fading channels given imperfect channel state information. Spreadresponse precoding is exploited to not only provide rate-1 temporal diversity benefits, but also to simplify the design of the modulo-precanceler and the receiver. Our theoretical and simulation-based performance analysis of the digital receivers and our MSE-based analog FM distortion analysis suggest that precoded modulo-precanceling schemes provide substantially higher data rates than existing precanceling strategies at the cost of transmission delay and transmitter and receiver complexity. The systems we present are also readily compatible with conventional channel coding techniques as well as with analog FM postcancelers, which can improve the digital receiver bit-error-rate performance at the expense of receiver complexity.     

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.     

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.     

Broadband multicarrier communication receiver based on analog to digital conversion in the frequency domain

This paper introduces a multicarrier communication receiver for broadband applications based on analog to digital conversion (ADC) of the received signal in the frequency domain. The samples of the spectrum of the received signal are used in the digital receiver to estimate the transmitted symbols through a matched filter operation in the discrete frequency domain. The proposed receiver is aimed at the reception of high information rates in a multicarrier signal with very large bandwidth. Thus, the receiver architecture provides a solution to some of the challenging problems found in the implementation of conventional wideband multicarrier receivers based on time-domain ADC, since It efficiently parallelizes the A/D conversion reducing the sampling speed requirements. We show that the sampling rate requirements are relaxed as the number of frequency samples is increased, which introduces a trade-off between complexity and sampling rate. The new receiver possesses additional advantages, including scalability with increasing frequency samples, the possibility of optimally allocating the available number of bits for the ATD conversion across the frequency domain samples which potentially reduces the distortion introduced by the high-speed ADC, narrowband interference suppression that can be directly carried out in the frequency domain, and inherent robustness to frequency offset which makes it an attractive solution when compared with traditional multicarrier receivers. We also investigate how the proposed receiver responds to common multicarrier communication receiver problems such as phase noise and channel frequency selectivity.     

An interpolative bandpass converter on a 1.2-μm BiCMOSanalog/digital array

The architecture and performance of an interpolative bandpass A/D converter (ADC) and digital quadrature demodulator dedicated for digital narrowband transmission systems, like the cellular radio mobile receiver, are presented. A prototype version has been implemented on a 1.2-μm/7-GHz BiCMOS analog/digital array. A bandpass signal centered at 6.5 MHz with 200-kHz bandwidth is demodulated and converted with a 55-dB signal-to-noise ratio giving 9-b performance     

An adaptive coding scheme with code combining for mobile radiosystems

The authors propose and study an adaptive error-control coding scheme for binary digital FM (BFM) mobile radio transmission. The scheme employs code combining through packet retransmissions. The number of transmissions of a packet is in proportion to the channel fading/noise levels, which is in contrast to time diversity techniques where a fixed number of repetitions of a data packet is performed even in the absence of channel errors. Furthermore, the receiver uses received signal envelopes as channel state information, which significantly improves the throughput and bit error rate (BER) performance. Performance of the proposed scheme is analyzed for frequency-flat Rayleigh fading channels with additive white Gaussian noise (AWGN), co-channel interference and random FM noise     

Optimization and performance evaluation of multicarriertransmission

Optimization of the performance of multicarrier transmission over a linear dispersive channel is presented. The optimum data and power assignment to the subcarriers are derived for both the conventional error probability criterion, and a new criterion based on the normalized mean-square error. The assignments and algorithms hold for channels where performance is degraded by additive noise, intersymbol and interchannel interference. Lower bounds on throughput are derived and are used to compare multicarrier performance with conventional single-carrier quadrature amplitude modulation (QAM) with both linear and decision feedback equalization. It is seen that multicarrier transmission can provide a significant improvement at low and intermediate channel signal-to-noise ratios. As an example, the optimization is applied to the high-speed digital subscriber loop, and multicarrier transmission is demonstrated to be superior to decision feedback equalized single-carrier QAM     

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.     

An iterative maximum SINR receiver for multicarrier CDMA systems over a multipath fading channel with frequency offset

A robust iterative multicarrier code-division multiple-access (MC-CDMA) receiver with adaptive multiple-access interference (MAI) suppression is proposed for a pilot symbols assisted system over a multipath fading channel with frequency offset. The design of the receiver involves a two-stage procedure. First, an adaptive filter based on the generalized sidelobe canceller (GSC) technique is constructed at each finger to perform despreading and suppression of MAI. Second, pilot symbols assisted frequency offset estimation, channel estimation and a RAKE combining give the estimate of signal symbols. In order to enhance the convergence behavior of the GSC adaptive filters, a decisions-aided scheme is proposed, in which the signal waveform is first reconstructed and then subtracted from the input data of the adaptive filters. With signal subtraction, the proposed MC-CDMA receiver can achieve nearly the performance of the ideal maximum signal-to-interference-plus noise ratio receiver assuming perfect channel and frequency offset information. Finally, a low-complexity partially adaptive (PA) realization of the GSC adaptive filters is presented as an alternative to the conventional multiuser detectors. The new PA receiver is shown to be robust to multiuser channel estimation errors and offer nearly the same performance of the fully adaptive receiver.     

Simultaneous Transmission of Digital Phase-Shift Keying and of Analog Television Signals

A method for transmission of a 1.544-Mbit/s data channel in a frequency band which is above the baseband of sound and vision signals of color television in FM microwave systems is described. The impact of the interfering video signal on phaseshift keyed (PSK) performance is evaluated. The probability of error as a function of the receiver carrier-to-noise ratio in the data channel for the case of Gaussian noise, sinusoidal interference, and various video test waveform (color bar, stair step, etc.) interference and combinations of these is measured. Analog and also novel digital methods of insertion of the television sound subcarrier signal are described. Data above video (DAVID) transmission measurement results which have been performed on an RCA 6-GHz microwave hop are presented.     

A CMOS ADSL codec for central office applications

A CMOS central office codec that supports Full Rate and G.Lite asymmetric digital subscriber line (ADSL) transmission is described. The transmit channel consists of application-dependent digital filters, a 14-bit, 8.832-MSample/s current steering DAC, a 1.104-MHz analog filter, and a programmable attenuator. Due to extensive on-chip digital signal processing, the codec complies with the ADSL transmit power spectral density standards without external filtering. The receive channel contains -17.5 to 33.5 dB of programmable gain staggered strategically across three stages, a 138-kHz analog low-pass filter, a 14-bit, 2.208-MSample/s pipeline ADC, and a digital 138-kHz low-pass filter. The receive channel has a wide input range that can accommodate large line voltages present at the line hybrid circuit. The IC occupies 55.2 mm² and dissipates 450 mW from a 3.3-V supply     

基于频率调制的多载波Chirp信号雷达通信一体化研究

为了减少电子战平台的体积和电磁干扰,一种有效的途径就是实现雷达与通信的一体化.该文针对雷达通信一体化信号设计中存在的不兼容和互干扰问题,根据信号能量共享的原则,提出了基于频分准正交多载波Chirp 信号的雷达通信一体化波形及其相应的系统实现方法.并采用宽带模糊函数对多载波一体化信号特性进行了详细分析,进一步研究了一体化信号的处理过程以及其系统性能.在均衡子载波准正交性和通信频谱效率下,通过理论分析和仿真结果表明在多载波频谱重叠率为20％的情况下,一体化信号能够满足雷达的常规探测,并且具有较低的误码特性.     

Mixed BB-IF predistortion of OFDM signals in non-linear channels

It is well known that power amplifier induced non-linear distortions produce a signal spectral regrowth at the IF transmitter output of digital radio communication systems. This effect is responsible for both adjacent channel interference and BER degradation. Signal predistortion is a technique that counteracts such phenomena. Technological advances in the last decade, renewing the interest in this technique, led to the realization of digital baseband (BB) predistorters that overcome the performance of the existing analog IF (intermediate frequency) ones. However, the substitution of an analog IF predistorter with a digital BB one forces one to partially redesign the system architecture. An alternative approach is proposed in this paper, based on digital and analog techniques, which combines the precision of the digital BB solution with the practicality of an IF architecture. This solution is particularly interesting to substitute an old analog IF predistorter simply plugging-in the new digital one, without further changes in the transmitter architecture. Critical aspects, predistortion algorithms and simulation performance are presented with respect to a digital video broadcasting system which is based on an OFDM modulation and is very sensitive to non-linear distortions because of the adopted multicarrier modulation     

Analysis of new methods for broadcasting digital data to mobileterminals over an FM-channel

Two new methods using an FM-radio channel for transmission of digital data to mobile terminals are examined: 1. A modification of the radio data system (RDS). In RDS, additional digital information is multiplexed with a stereo sound signal. A new system is suggested where the data signal can be multiplexed with a mono audio signal. This causes extension to the bandwidth available for the data signal, and therefore the RDS bitrate can be increased. Error calculations are performed both for the original RDS system and for the new system. 2. Orthogonal frequency division multiplexing (OFDM). OFDM is used in the digital audio broadcasting system (DAB), which is designed to transmit digital audio in the FM band. In OFDM a signal is divided over a large number of 2- or 4-PSK modulated orthogonal subcarriers. The subcarriers of 6 different programmes are multiplexed in one beam to reduce the effects of frequency selectivity of the transmission channel. A new system based on OFDM is proposed, in which the carriers of each programme are transmitted in one FM-channel with a bandwidth of 200 kHz instead of multiplexed with the carriers of other programmes. Error calculations are performed for the subcarriers used in the OFDM modulation method     

A Utility-Based Joint Resource Allocation Approach for Multi-Service in CoMP Networks

One of the premier mechanisms used in extracting unobserved signals from observed mixtures in signal processing is employing a blind source separation (BSS) algorithm or technique. A prominent role in the sphere of multicarrier communication is played by orthogonal frequency division multiplexing (OFDM) techniques. A set of remedial solutions taken to mitigate deteriorative effects caused within the air interface of an OFDM transmission with aid of BSS schemes is presented. Two energy functions are used in deriving the filter coefficients. They are optimized and performance is justified. These functions with the iterative fixed point rule for receive signal are used in determining the filter coefficients. Time correlation properties of the channel are taken advantage for BSS. It is tried colored noise and interference components to be removed from the signal mixture at the receiver. The method is tested in a slow fading channel with a receiver containing equal gain combining to treat the channel state information values. The importance is that, these solutions can be noted as quite low computational complexity mechanisms.     

多通道数字接收机的设计与实现

为了解决传统模拟中频接收机相位分辨率低等缺点,提出一种基于软件无线电的中频数字接收机技术。针对雷达信号的特点提出了脉宽匹配滤波器的设计方法。采用基于多相滤波的正交变换理论,以及基于脉宽匹配的数字滤波器方法完成了一种五通道中频数字接收机的设计。接收机利用五路高速A/D变换器对输入的模拟信号进行采样,然后将采样数据送入FPGA进行处理,最终完成了每两路信号相位差的提取。实验结果表明系统具有成本低、精度高、结构简单等特点,而且具有一定的工程应用价值。     

Evaluation of 16 kbit/s digital voice transmission for mobile radio

In this paper 16 kbit/s digital voice transmission with conventional channel spacing of 25 kHz, employing a 16 kbit/s adaptive delta modulation (ADM) coder-decoder (CODEC) is evaluated. The main characteristics of narrow-band digital FM modulation schemes, such as tamed FM, Gaussian filtered minimum shift keying (GMSK), four-level FM and phase locked loop-quaternary phase shift keying (PLL-QPSK), are compared by laboratory tests. Digitized voice quality in a digital channel incorporating a 16 kbit/s ADM CODEC and GMSK coherent detection was compared with voice quality of a conventional analog FM channel. Bit error ratio (BER) performance is shown to depend primarily on demodulation schemes. Digital voice quality is inferior to that of analog voice with an opinion score difference of about 0.5 in fading environments. This kind of digital voice transmission will be applicable for those systems that require high security at an expense of speech quality.