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.     

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     

A Multimode Transmitter in 0.13 μm CMOS Using Direct-Digital RF Modulator

This paper presents a system-independent transmitter architecture based on a direct-digital RF-modulator which combines the D/A conversion, up-conversion, unwanted sideband rejection, power control, and part of the digital image-rejection filtering into a single mixed-signal circuit block. The multimode capability of the architecture is demonstrated with WCDMA, EDGE, and WLAN system requirements. The modulator achieves 90 dB of power control range and with an external power amplifier module, WCDMA EVM of less than 2% from signal powers of -20 dBm to +25 dBm. The noise floor level defined by the quantization noise at 190 MHz offset from the carrier is -150 dBc/Hz measured at the output of the PA with +25 dBm signal power. The analog power consumption with the maximum signal power level is 92 mW and scales down to 46 mW when reducing the signal level to -43 dBFS. The digital power consumption is 65 mW. The chip is implemented with a standard 0.13 mum 1.2 V digital CMOS with total silicon area of 4 mm².     

A frequency agile monolithic QPSK modulator with spectral filteringand 75 Ω differential line driver

This monolithic modulator combines both digital signal processing and analog techniques to realize a high bit-rate quadrature phase-shift keyed (QPSK) modulator. It includes a digital baseband pulse shaping network, analog quadrature modulator, agile carrier generator, spectral shaping, and transmit power control for interfacing to wireline transmission media. Nominal data rates are 256 kbit/s with a carrier range of 8.096-20.128 MHz in 32 kHz steps. Maximum output level is 62 dBmV into a 75 Ω load. The features of 1.2 μm mixed signal BiCMOS technology permit both signal processing and power line drivers to be collocated while achieving better than 85 dB cross-talk isolation     

Compatibility of FM hybrid in-band on-channel (IBOC) system fordigital audio broadcasting

A robust in-band on-channel (IBOC) digital audio broadcast (DAB) system for improved performance over existing FM broadcasting is under development by Westinghouse for USA Digital Radio. Both the analog FM and the DAB signals are transmitted simultaneously in the FM hybrid IBOC system. Broadcasters can simultaneously transmit both analog and digital signals within the allocated channel mask, allowing full compatibility with existing analog receivers. It is shown here that the solution is tolerant of interference from adjacent channels, or interference from the co-channel analog transmission, even in a multiple station, strong-signal urban market. Although the primary focus of this paper is to discuss the compatibility issues between the existing FM and the DAB signals, the paper also briefly describes spectral occupancy, power ratios, modulation formats, and coding, as well as the introduction of frequency and time diversity     

Dynamic range of coherent analog fiber-optic links

We investigate the performance of coherent analog optical links employing amplitude modulation (AM), phase modulation (PM), and frequency modulation (FM). The performance of these coherent links is compared to that of AM direct-detection (DD) links. The signal-to-noise ratios, nonlinearities, and-spurious-free dynamic ranges (SFDR's) of the foregoing links are evaluated. We calculate the SFDR for links using DFB and Nd:YAG lasers with typical linewidths of 10 MHz and 5 kHz, respectively. The performance of PM and FM links is dominated by phase noise above a critical value of received optical power. For a linewidth of 10 MHz, and SFDR's of PM and FM links are 30 and 31 dB, respectively, for a received optical power above -27 dBm in a 1 GHz bandwidth. For a linewidth of 5 kHz, the corresponding SFDR's above a received power level of 0 dBm are 51 and 53 dB. The performance of DD and AM links is dominated by RIN above a critical value of received optical power. For a RIN level of -155 dB/Hz, the SFDR's of DD and AM links are 49 and 47 dB, respectively, for a received optical power of 10 dBm in a 1 GHz bandwidth. The SFDR's of the DD and coherent links used for transmission of subcarrier-multiplexed (SCM) signals are also derived. We evaluate target laser parameters needed by a number of different applications. For AM video and antenna remoting applications, linewidths of <1 and <3 kHz are required to use PM and FM links, respectively. For FM video, linewidths of <150 and <350 MHz are required to use PM and FM links. For SCM digital applications, linewidths of <80 and <200 MHz are required to use PM and FM links. The paper concludes with a discussion of system implementation issues, including linearization, optical frequency modulation, balanced receivers, and IF issues     

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.     

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。     

A 10.7-MHz IF-to-baseband ΣΔ A/D conversion system forAM/FM radio receivers

ΣΔ modulation with integrated quadrature mixing is used for analog-to-digital (A/D) conversion-of a 10.7-MHz IF input signal in an AM/FM radio receiver. After near-zero IF mixing to a 165 kHz offset frequency, the I and Q signals are digitized by two fifth-order, 32 times oversampling continuous-time ΣΔ modulators. A prototype IC includes digital filters for decimation and the shift of the near-zero-IF to dc. The baseband output signal has maximum carrier-to-noise ratios of 94 dB in 9 kHz (AM) and 79 dB in 200 kHz (FM), with 97 and 82 dB dynamic range, respectively. The IM3 distance is 84 dB at full-scale A/D converter input signal. Including downconversion and decimation filtering, the IF A/D conversion system occupies 1.3 mm² in 0.25-μm standard digital CMOS. The ΣΔ modulators consume 8 mW from a 2.5-V supply voltage, and the digital filters consume 11 mW     

Analog AGC Circuitry for a CMOS WLAN Receiver

The IEEE 802.11a standard uses orthogonal frequency division multiplexing (OFDM) to allow high data rates in multipath WLAN environments. The high peak-to-average power ratio (PAPR) of OFDM signals, along with stringent settling-time constraints, make conventional closed-loop automatic gain control (AGC) schemes impractical for WLAN receivers. In a direct conversion receiver, AGC and channel-select filtering are performed by analog baseband circuitry. A baseband signal processor using a new open-loop analog gain-control algorithm for OFDM is described. The new AGC algorithm uses switched coarse gain-setting steps followed by an analog open-loop fine gain-setting step to set the final gain of variable gain amplifiers (VGAs). The AGC was implemented in a 0.18-$muhbox m$CMOS process using newly designed circuits including linear VGAs, RMS detectors, and current-mode computation circuitry. Simulation and measurement results verify that the new AGC circuit converges with gain error less than 1dB to the desired level within 5.6$muhbox s$.     

A 1.2 mW RDS receiver for portable applications

A 0.9 V 1.2 mA fully integrated radio data system (RDS) receiver for the 88-108 MHz FM broadcasting band is presented. Requiring only a few external components (matching network, VCO inductors, loop filter components), the receiver, which has been integrated in a standard digital 0.18 /spl mu/m CMOS technology, achieves a noise figure of 5 dB and a sensitivity of -86dBm. The circuit can be configured and the RDS data retrieved via an I/sup 2/C interface so that it can very simply be used as a peripheral in any portable application. A 250 kHz low-IF architecture has been devised to minimize the power dissipation of the baseband filters and FM demodulator. The frequency synthesizer consumes 250 /spl mu/A, the RF front-end 450 /spl mu/A while providing 40 dB of gain, the baseband filter and limiters 100 /spl mu/A, and the FM and BPSK analog demodulators 300 /spl mu/A. The chip area is 3.6 mm/sup 2/.     

IF-sampling fourth-order bandpass /spl Delta//spl Sigma/ modulator for digital receiver applications

Bandpass modulators sampling at high IFs (/spl sim/200 MHz) allow direct sampling of an IF signal, reducing analog hardware, and make it easier to realize completely software-programmable receivers. This paper presents the circuit design of and test results from a continuous-time tunable IF-sampling fourth-order bandpass /spl Delta//spl Sigma/ modulator implemented in InP HBT IC technology for use in a multimode digital receiver application. The bandpass /spl Delta//spl Sigma/ modulator is fabricated in AlInAs-GaInAs heterojunction bipolar technology with a peak unity current gain cutoff frequency (f/sub T/) of 130 GHz and a maximum frequency of oscillation (f/sub MAX/) of 130 GHz. The fourth-order bandpass /spl Delta//spl Sigma/ modulator consists of two bandpass resonators that can be tuned to optimize both wide-band and narrow-band operation. The IF is tunable from 140 to 210 MHz in this /spl Delta//spl Sigma/ modulator for use in multiple platform applications. Operating from /spl plusmn/5-V power supplies, the fabricated fourth-order /spl Delta//spl Sigma/ modulator sampling at 4 GSPS demonstrates stable behavior and achieves a signal-to-(noise + distortion) ratio (SNDR) of 78 dB at 1 MHz BW and 50 dB at 60 MHz BW. The average SNDR performance measured on over 250 parts is 72.5 dB at 1 MHz BW and 47.7 dB at 60 MHz BW.     

All-optical gain control of in-line erbium-doped fiber amplifiers for hybrid analog/digital WDM systems

Automatic gain control using an all-optical feedback loop in in-line erbium-doped fiber amplifiers (EDFA's) used in hybrid analog/digital wavelength division multiplexing (WDM) systems was studied. It is found that the signal level variation for the digital channels can be maintained within a range /spl les/3-dB between the presence and dropout of the analog channel when the narrowband feedback is centered at the amplified spontaneous emission (ASE) peak (/spl sim/1532 nm) with loop loss ranging between 13-22 dB. Robust transmission at 2.5 Gb/s without measurable power penalty was obtained for the digital channels when the EDFA was saturated by either the analog or the control lasing signal.     

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.     

A 48-16-MHz CMOS SC decimation filter

This paper presents a CMOS switched-capacitor decimation filter for prefiltering operations in video communications systems, reducing the complexity of continuous-time antialiasing filters and alleviating dynamic range requirements of analog-to-digital converters. As a consequence of the structure's low sensitivity to process variations, predicted by theory and verified in the laboratory by measurements on all samples of the same batch, it was possible to apply capacitor arrays having minimum feasible size units of 100 fF to implement the filter coefficients, leading to substantial savings in power consumption. Implemented in a standard 0.8-/spl mu/m CMOS process with poly-poly capacitors, the experimental device samples the incoming continuous-time analog signal at 48 MHz and presents a filtered sampled-data output at 16 MHz, with a measured pass-band deviation smaller than 0.22 dB up to the cutoff frequency of 3.6 MHz, output noise power spectrum of 1.1 nV/sub RMS///spl radic/(Hz) and a signal handling ability of 1.4 V/sub pp/, resulting in a dynamic range of 48 dB, meeting the usual specifications for video-frequency signal processing.     

Three-Channel FM Stereo Multiplex System for Compatible Broadcasting

A system for transmitting and receiving three independent stereophonic channels by FM multiplex is described. This system has the advantage of being compatible with monophonic and two-channel stereophonic FM receivers without any significant loss in their output signal-to-noise ratios (less than 1 dB) and without having to utilize any part of the SCA band. Compatibility of the three-channel stereophonic receiver with a one-or two-channel broadcast is achieved by the use of an additional pilot signal that does not cause any increase in the instantaneous frequency deviation of the FM carrier. The additional noise in the output of the three-channel receiver appears to be less than 6 dB above the noise that is now present in two-channel receivers.     

An efficient baseband modem technique for data transmission overanalog FM links

In mobile radio where data are transmitted over existing analog FM systems, the receive bandpass bandwidth, which is adapted to the analog speech transmission, is larger than would be required by data transmission. This results in poor error performance. A novel baseband modem technique which drastically improves the error performance is proposed and analyzed. A smearing filter is used to convert the compound baseband noise at the limiter discriminator output to approximately Gaussian noise. This optimizes the performance at large carrier-to-noise ratios (CNRs). A baseband click detection and elimination scheme, which improves the performance at small CNR is proposed. Simulation results show that this system requires 3.8 dB less CNR than the conventional digital FM system to achieve a bit error probability of 10^-4. It is concluded that the technique is attractive for data transmission over analog FM links     

Design and implementation of an all-CMOS 802.11a wireless LAN chipset

The tremendous growth in wireless LANs has generated interest in technologies that provide higher data rates and greater system capacities. The IEEE 802.11a standard, based on coded OFDM modulation, provides nearly five times the data rate and at least 20 times the overall system capacity compared to the incumbent 802.11b wireless LAN systems. This article describes the design challenges and circuit implementation of a two-chip set that forms a complete 802.11a solution in 0.25 /spl mu/m CMOS technology. Wherever possible, sophisticated digital signal processing techniques are used to compensate for possible analog impairments associated with integrating RF circuitry in a CMOS technology. The analog portion of the chip set implements a 5 GHz transceiver comprising all the necessary RF and analog circuits of the 802.11a standard integrated on a single chip. Some features of this IC include 22 dBm peak transmitted power, 8 dB overall receive-chain noise figure, and -112 dBc/Hz synthesizer phase noise at 1 MHz frequency offset. The digital portion of the chip set, the baseband and MAC processor, contains dual ADCs/DACs and all the digital circuits for synchronization, detection, and 802.11 MAC layer data processing. This IC delivers up to 54 Mb/s in a 20 MHz channel according to the 802.11a standard, and includes proprietary modes supporting up to 108 Mb/s in a 40 MHz channel.     

基于FPGA的2CPFSK全数字中频调制器的设计与实现

针对飞行器数据链中高码速率要求,需要使用数字技术实现传统模拟调制,以得到更好的调制性能,增加系统作用距离。本文介绍了二进制连续相位频移键控(2CPFSK)调制原理,提出了基于软件无线电架构的2CPFSK正交调制算法。该算法利用2CPFSK相位累加特性实现了基带数据的分数倍内插,从而适应宽范围码速率的调制。设计了提高频谱纯度的数字滤波器、基于FPGA+DAC架构的数字调制器硬件平台并实现算法。通过与传统模拟频率调制(FM)比较,该设计提升了1.7 dB调制性能,增加了系统作用距离。     

基于CDR 数字音频广播的外辐射源雷达信号模糊函数分析与处理

CDR (China Digital Radio)数字音频广播是我国自主研发的FM 频段(87-108 MHz)数字音频广播新标准,它兼容我国现有模拟FM 广播的频谱规划,能够满足我国FM 频段声音广播从模拟到数字平滑过渡的需求。该文从CDR 信号结构入手,重点探讨了基于该广播的外辐射源雷达信号特性及相关处理方法。首先分析其信号特性以及作为外辐射源雷达照射源的模糊函数特性;然后针对因循环前缀引起的模糊函数副峰、同步信号引起的多普勒模糊带以及信号频谱不连续导致的距离副峰对目标探测的不利影响,分别提出了相应的副峰抑制方法,并通过仿真验证了该方法的有效性。