A New Demodulation Method Improving FM System Interference Immunity

As a result of investigation of interference into FM systems, a new algorithm for the process of demodulation is proposed. When compared to the method using the conventional limiter-discriminator, it offers better immunity against the baseband interference noise. Desired signal processing is performed by the functional devices added to the conventional limiter-discriminator in such a way that this new demodulator can be optimized in the sense of the minimum baseband interference noise. The statistics of the wanted and interfering signals must be known. Several examples involving interference problems in FDM-FM radio-relay systems carrying multichannel telephone signals are elaborated to illustrate the performances of the proposed demodulator. FDM-FM, PSK, or FSK systems are considered the cause of the interference. The noise power ratio (NPR) at the output of the conventional limiter-discriminator and the improvement factor offered by the new demodulator, obtained on digital computer, are presented versus baseband frequency in the form of diagrams. Different IF filters in FDM-FM receiver and transmit filters in the interfering systems are taken into account. The improvement offered by the proposed demodulator is of such a degree that some of the important restrictions in planning different radio systems could be relaxed.     

Effects of Impulsive Noise on Phase-Locked Loop FM Demodulator

The effects of impulsive noise on phase-locked loop (PLL) FM demodulators is investigated. The PLL FM demodulator used for the experiments is basically a second order loop employing an active filter. The impulsive noise used for this work is ignition noise. Impulse response of the receiver is investigated and the PLL FM demodulator is digitally simulated. The response of the receiver employing the PLL FM demodulator used in the ground terminal to an input signal consisting of unmodulated carrier and impulses is investigated experimentally. The system margin is fouind to be degraded by about 10 dB.     

PLL FM demodulator performance under Gaussian modulation

A widespread test of the phase-locked loop (PLL) FM demodulator under Gaussian modulation is simulated using the Monte Carlo method. Unified noise-free and noise performance analyses of the PLL FM demodulator are presented. Substantial reduction of the modulation limit by the input bandpass filter is reported in the region of the input bandwidth of practical interest. Bessel bandpass filters of order greater than two are shown to compare favorably with Butterworth filters in front of the PLL FM demodulator relative to the intermodulation (IM) distortion. A lower bound on the loop noise bandwidth is found by minimizing the output click rate for given IM distortion specifications. FM threshold of 4 and 7 dB for the root-mean-square (RMS) frequency deviation-to-message bandwidth ratio 0.1 and 1.0, respectively, is reported on the worst-case IM distortion of 45 dB     

Analysis of delay-and-multiply optical FSK receivers withline-coding and non-flat laser FM response

We present a theoretical analysis of the performance of coherent optical FSK systems when the driving laser signal is AMI or Manchester (biphase) line-coded to counteract the nonideal FM characteristic of the transmit laser diode, and the received signal is heterodyned and detected by a delay-and-multiply demodulator. The analysis takes into account IF filtering by assuming linear filtering of the noisy signal phase, accounting, for small linewidths, for laser phase noise in a straightforward and accurate manner. A simple equivalent baseband model of the system is derived for performance evaluation, applicable to both cases of large demodulator delay and when the delay tends to zero (ideal discriminator). Noise statistics include the clicks due to both signal and phase noise. The problem of performance evaluation is reduced to a classical intersymbol interference problem which is solved by mead of the method of Gauss quadrature rules. The analysis accurately predicts the effectiveness of AMI and Manchester line coding, depending on several system parameters such as linewidth, modulation index, IF bandwidth and laser FM response, and can be easily extended to other line coding techniques     

Zero-crossing zero-IF demodulator

A new zero-IF digital demodulator which is applicable to M-ary narrowband digital FM signals is presented. This demodulator offers ease of integration and manufacturing and requires less power and size than conventional demodulators. The performance of this demodulator is comparable to that of conventional demodulators     

On Optimum Sampled-Data FM Demodulation

Since the introduction of large-scale integration (LSI) techniques, there has been a continuing effort to develop digitalization techniques for communication equipment amenable to LSI implementation. Hopefully, this will permit expanded capability in the equipment while taking advantage of the cost reliability attributed of LSI. In this paper, a digitalized or sampled-data FM demodulator recursive algorithm is synthesized and its signal-to-noise ratio performance compared with the optimum analog demodulator and the conventional limiter discriminator demodulator. The demodulator is shown to exhibit threshold extension capability and automatic time-varying gain (bandwidth) adjustments from acquisition through tracking of the incoming modulated signal.     

数字化副载频解调的研究

副载频解调器是频分制遥测系统中的重要组成部分。由于工程实施中的实时性以及较低的系统复杂度难以达到要求,即过高的数据传输量造成滤波器阶数的提高,导致处理过程产生延时且消耗大量硬件资源。提出了针对实际工程中数字化副载频解调器性能优化的实施方案。在实际解调过程中,首先利用半带滤波器对原始数据进行抽取滤波,可以减少数据的处理量,降低数据输入频率,达到计算效率高以及实时性强的效果。最后用MATLAB对该解调方案进行了仿真,以此证明方案的正确性和有效性。     

A novel digital FM receiver for mobile and personal communications

A digital baseband receiver called zero-intermediate frequency zero-crossing demodulator (ZIFZCD) was developed for digital FM signal detection. ZIFZCD is applicable to many worldwide mobile and personal communications systems. In addition, ZIFZCD offers lower power consumption and simpler implementation, compared to the conventional analog implementation [e.g., a limiter-discriminator integrator and dump (LDI)] and the conventional digital implementation [e.g., the cross-differentiate-multiply demodulator (CDM)]. This paper introduces the ZIFZCD and reports the bit-error rate (BER) of the ZIFZCD under both static and fading environments. The analyzed and simulated BER results show that the ZIFZCD is comparable to the conventional CDM for narrowband digital FM with a modulation index of 0.5, and the ZIFZCD is significantly better than the CDM for wideband digital FM with a modulation index larger than 1.5     

The Performance of a Digital FM System with Discriminator: Intersymbol Interference Effects

The error performance of a digital FM system is studied in the presence of additive Gaussian noise. This system is a conventional one employing a voltage-controlled oscillator as the modulator and a limiter-discriminator followed by a low-pass filter as the demodulator. The notion of "clicks" introduced by Rice, and used by Mazo and Salz, is adopted and the performance of the above system is theoretically studied when the intersymbol interference caused by band limitation cannot be neglected. Special consideration has been given to binary frequency-shift keying (FSK) systems. For such systems, the probability of error is given in a closed form.     

Decision feedback postprocessor for zero-crossing digital FMdemodulator

A baseband digital narrow-band FM receiver, called zero-intermediate frequency zero-crossing demodulator (ZIFZCD), has been developed. This demodulator may offer low complexity and simple implementation. However, the bit error rate (BER) performance of the ZIFZCD is inferior to that of the limiter-discriminator-integrate-and-dump (LDI) demodulator. In this paper, a simple decision feedback postprocessor (DFP) is proposed to improve the performance of the ZIFZCD. Analysis and simulation BER results of the ZIFZCD with the DFP are presented for minimum-shift keying (MSK) and Gaussian MSK (GMSK) signals under additive white Gaussian noise (AWGN) and mobile fading environments     

Surface transverse wave based FM modulator/demodulator

An FM modulator/demodulator system employing three identical surface transverse wave (STW) resonators is described. It operates at a centre frequency of 1012 MHz and can transmit data at over 100 kbit/s. This low cost system has a low noise and can detect FM signals with a deviation of less than 0.1 ppm.<>     

A 5-MHz IF digital FM demodulator

Key requirements for digital frequency-modulation (FM) demodulators are wide spurious-free dynamic range in the intermediate-frequency quantizer, linear-phase passband filtering, and accurate frequency discrimination. The proposed FM demodulator implemented digitally achieves high linearity by numerical differentiation performed at a 112× oversampling rate, suppresses adjacent channels by placing zeros of the SINC function on them, and rejects amplitude-modulation (AM) components by numerical division. A 5-MHz FM demodulator integrated with a fourth-order bandpass delta-sigma front end exhibits 74.7 dB signal-to-noise ratio, -80.7 dB total harmonic distortion, and 61 dB AM rejection within a 9-kHz message bandwidth. The 0.65-μm CMOS chip occupies 3.5×3.5 mm² of active area and consumes 180 mW with 4-V supply when clocked at 20 MHz     

Compound AFC-APC FM demodulators

In this letter two different types of FM demodulators, called compound AFC-APC (automatic frequency control--automatic phase control) FM demedulators, have been considered. It is shown that the tracking capability of either of the systems is much higher than that of an ordinary phase-locked demodulator. Experimental results are also presented in support of the conclusions of the analyses.     

Frequency demodulator for DBS using an SAW adaptive filter

A frequency demodulator for DBS using an SAW adaptive filter is described. It gives quasioptimal performance with the D2-MAC/packet system and can also be useful with C-MAC/packet when a single FM demodulator is used. The SAW device is described and experimental results arc given     

A novel demodulator/detector for digital and analog signals on LMRchannels

The design, implementation, and performance of an all-digital demodulator/detector suitable for differential phase-shift keying (DPSK), continuous-phase frequency-shift keying (CPFSK), frequency-shift keying (FSK), and analog FM are discussed. In this modulator/detector, two detectors, one noncoherent and another differentially coherent, operate simultaneously to provide data detection and automatic frequency control (AFC). Test results indicate that the system provides improved performance over the conventional analog quadrature detector for two-period raised-cosine (2RC) CPFSK modulation in additive white Gaussian noise (AWGN) and Rayleigh fading channels. Being all-digital, the demodulator/detector is well suited for integrated circuit implementation. In addition, the system performs as well as the analog quadrature detector for analog FM voice transmissions, thereby maintaining full compatibility with analog land mobile radio (LMR) transmissions     

GaAs digital IC for FM demodulator

A middle-scale GaAs digital IC for a pulse-counting FM demodulator has been designed and fabricated for use in microwave communication systems. The IC is constructed with the normally-on (depletion) MESFET logic with epitaxial active layers. It exhibits a high-speed pulse train with a rise time of 150 ps and with an output voltage of 2.3 V into a 300-Ω load. Output pulsewidth can be altered by the external voltage for tuning the IC to give the highest demodulation sensitivity. By merely implementing a low-pass filter at the output of the chip, the pulse-counting FM demodulator can be realized at high frequencies where the use of Si IC's has never before been possible. We estimate the demodulation sensitivity to be 20 mV/MHz at the microwave IF band.     

一种高性能CMOS单片中频接收机

研制了一种CM O S低压低功耗中频接收机芯片,它包含混频器、限幅放大器、解调器以及场强指示、消音控制等模块,可用于短距离的FM/FSK信号的接收和解调。该接收机采用1st s ilicon 0.25μm CM O S工艺,芯片的测试结果表明整机接收灵敏度为-103 dBm,最高输入射频频率可以达到100 MH z,解调器的线性解调范围为±10 kH z,典型鉴频灵敏度为40 mV/kH z,输入FM信号(调频指数3,信号频率1 kH z)时解调信号的SFDR为41.3 dB。芯片的工作电源电压范围为2~4 V,工作电流3 mA,有效面积0.25 mm2。     

Acquisition Behavior of the Cross-Coupled Phase-Locked Loop FM Demodulator

In this work, the acquisition behavior of a cross-coupled phase-locked loop (CCPLL) FM demodulator capable of suppressing cochannel and adjacent channel interferers is examined. This novel detector consists of two phase-locked loop (PLL) demodulators interconnected in such a manner as to permit one PLL to lock onto and track the stronger received signal, while the other loop tracks and demodulates the weaker of two received signals. The demodulator has two separate outputs, namely, the outputs of each PLL, and thus possesses the capability of demodulating both the stronger as well as the weaker received signals even though they are cochannel and share the same frequency band. The transient response of the CCPLL system is obtained using computer-aided analysis of the defining coupled nonlinear differential equations. From these results, steady-state "stability regions" are derived which reveal that range of loop parameters where successful separation and demodulation of the received cochannel signals is assured. The CCPLL receiver has numerous technological applications in suppressing unintentional or intentional CW, AM, FM, and AM/FM interferers. Experimental results demonstrating such potential are included.     

The Capture Effect in FM Receivers

In this paper a theoretical explanation of the capture effect is given by calculating the instantaneous frequency of the output signal of a limiter when two frequency modulated (FM) signals are present at the limiter input. When this signal is applied to a demodulator with unlimited bandwidth, the output signal of the demodulator proves to have an extreme capture effect. When however the demodulator bandwidth is limited, the capture effect is shown not be be extreme. This phenomenon is explained and possibilities are given to minimize the capture effect. Some of the results of measurements on limiters and demodulators are given in this paper; they prove that a weak capture effect can be obtained. A method of calculating the degree of capturing is included.