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GMSK信号是一种连续相位调制方式,由于它具有较好的功率效率和频谱利用率,因此在无线通信领域得到广泛的应用。在此给出一种适合于数字化处理的突发GMSK调制信号的相干解调方式,利用基于FFT的载波频偏及符号时钟误差联合估计算法,实现前导字检测以及频偏和符号定时误差的估计和补偿。采用基于匹配滤波的前向位同步技术实现位同步,对存在残留频偏误差情况下该相干解调系统的解调性能进行了计算机仿真分析。仿真和实验表明,该解调方法具有良好的误码性能。 相似文献
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Enrico Del Re Romano Fantacci 《International Journal of Satellite Communications and Networking》1988,6(3):267-281
In this paper alternatives for digital multicarrier demodulators (MCD) suitable for advanced digital satellite communications systems are presented. The MCD permits the direct on-board interfacing of FDMA and TDM communication links by digital signal processing techniques. Two main functions are implemented by a MCD: demultiplexing (DEMUX) and demodulation (DEMOD). We focus here only on a digital implementation of the MCD, looking at its advantages, flexibility, better performance and VLSI integrability. The DEMUX may be implemented in a number of ways: the analytic signal method, fast Fourier transform with polyphase network technique, or multistage methods. For all the implementation methods considered it is shown that a certain degree of integration of DEMUX and DEMOD functions is possible. To this end, in the proposed MCD schemes the receiver pulse-shaping filter has been integrated in the DEMUX structure, reducing the overall implementation complexity. It is shown that, for the per-channel structure based on the analytic signal method, a highly modular and flexible implementation can also be achieved. Coherent demodulation is used to reduce the signal-to-noise ratio required to achieve a specified bit error rate. The coherent demodulation is carried out by using the maximum likelihood (ML) estimation method. Two different approaches to receiver synchronization have been studied. For the first, the carrier phase and symbol timing estimates are independently derived by suitable techniques. The second approach makes use of the maximum a posteriori probability method to estimate both the carrier phase and symbol timing of the receivied signal. In particular, for this technique it is shown that, by a suitable choice of the architecture of the digital coherent receiver, the ML demodulator can be integrated in the joint carrier and clock recovery circuit, with no increase in the overall system complexity. The digital architecture of the proposed MCD can be adapted to different digital modulation techniques. However, here we consider only the application for QPSK signals, as this modulation scheme is the most promising for digital satellite communications. A theoretical analysis and computer simulation have been used to evaluate the performance degradation of the proposed MCD, including finite-arithmetic implementation effects. 相似文献
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Yung-Liang Huang Kang-Dar Fan Chia-Chi Huang 《Vehicular Technology, IEEE Transactions on》2000,49(3):863-874
We propose a fully digital noncoherent and coherent Gaussian minimum shift keying (GMSK) receiver architecture with joint frequency offset compensation and symbol timing recovery. Carrier phase offset can be estimated if the coherent demodulation mode is adopted. The converted base-band complex signal is first frequency discriminated and then passed through a digital filter which performs a fast Fourier transform (FFT). The frequency offset can be estimated from the DC component of the FFT, and the symbol timing error can be estimated from the phase angle of the FFT at a specified frequency which is equal to an integral multiple of half the bit rate. These two estimated parameters are then used for frequency offset compensation and symbol timing recovery during a preamble period. Coarse carrier phase can be estimated by averaging sampled in-phase and quadrature-phase signals and finding its phase angle within the preamble period after carrier frequency offset is estimated and compensated. The bit error rate (BER) performance of this GMSK receiver architecture is assessed for an additive white Gaussian noise (AWGN) channel by computer simulation 相似文献
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《Vehicular Technology, IEEE Transactions on》1984,33(3):220-226
Digital mobile radio transmission techniques and integrated circuit devices have been developed for application to a digital portable transceiver utilizing narrow-band GMSK modulation and ADM voice coding. Design and performance of a quadrature type GMSK modulator and a single-chip coherent demodulator as the GMSK modem are described. To overcome slow fading, encountered in portable applications, switching diversity using a jitter detection type sensor is proposed and shown to be effective. An experimental portable transceiver, developed to demonstrate hardware feasibility, is also described. 相似文献
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Digital mobile radio transmission techniques and integrated circuit devices have been developed for application to a digital portable transceiver utilizing narrow-band GMSK modulation and ADM voice coding. Design and performance of a quadrature type GMSK modulator and a single-chip coherent demodulator as the GMSK modem are described. To overcome slow fading, encountered in portable applications, switching diversity using a jitter detection type sensor is Proposed and shown to be effective. An experimental Portable transceiver, developed to demonstrate hardware feasibility, is also described. 相似文献
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A carrier recovery circuit implementation with an all-digital reverse modulation approach for coherent detection in the GSM/GMSK system as well as the GMSK compatible improved efficiency cross-correlated FQPSK system is presented. The proposed carrier recovery implementation utilizes all-digital reverse modulation circuit in a feedback loop to remove the modulated signal from the received intermediate frequency (IF) signal and to estimate the phase error of this carrier signal using a phase-locked loop (PLL). The digital reverse modulation approach avoids the multipliers required in an analog reverse modulation design, so that it can be implemented in a single chip FPGA. Hardware implementation of the coherent detection demonstrates that cross-correlated FQPSK is completely compatible with GMSK in the system performance and the receiver structure for GSM. Experimental performance evaluations show that the proposed carrier recovery circuit provides a Bit Error Rate (BER) performance within 0.3 dB in a non-linearly amplified channel corrupted by additive white Gaussian noise (AWCN) as compared with the simulated performance of the GSM/GMSK system 相似文献
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The paper describes in detail various digital modulation techniques for mobile and personal communication systems. Among others, these include π/4-shift quadrature phase-shift keying (QPSK), used in the second generation digital cellular mobile systems in North America and Japan, and Gaussian minimum-shift keying (GMSK), employed in the GSM system in Europe. It then briefly discusses the current research activities in modulation schemes for future systems 相似文献
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An analysis of a symbol timing recovery (STR) technique using digital processing is presented. The ratio of the discrete spectral power at the symbol rate frequency to the nearby continuous spectral power is used as a criterion of STR performance. It is shown that this power ratio equals the quality factor of the narrow bandpass filter and that it does not depend on the value of the delay element. The performance of the STR subsystem is consequently determined by the quality factor of the bandpass filter rather than by the specific delay. In addition to this, some experimental evidence that the additive channel noise has little effect on the power ratio is given. A modified phase-locked loop with anLC prefiiter is proposed to extract the symbol timing clock. This prefilter improves the acquisition and synchronization performance of the PLL. The STR technique presented here has the advantages of lower cost and simpler hardware implementation over other serial STR techniques. 相似文献
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This paper is concerned with digital modulation for future mobile radio telephone services. First, the specific requirements on the digital modulation for mobile radio use are described. Then, premodulation Gaussian filtered minimum shift keying (GMSK) with coherent detection is proposed as an effective digital modulation for the present purpose, and its fundamental properties are clarified with the aid of machine computation. The constitution of modulator and demodulator is then discussed from the viewpoints of mobile radio applications. The superiority of this modulation is supported by some experimental test results. 相似文献
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The Effects of Time Delay Spread on Portable Radio Communications Channels with Digital Modulation 总被引:3,自引:0,他引:3
Frequency-selective fading caused by multipath time delay spread degrades digital communication channels by causing intersymbol interference, thus resulting in an irreducible BER and imposing a upper limit on the data symbol rate. In this paper, a frequencyselective, slowly fading channel is studied by computer simulation. The unfiltered BPSK, QPSK, OQPSK, and MSK modulations are considered first to illustrate the physical insights and the error mechanisms. Two classes of modulation with spectral-shaping filtering are studied next to assess the tradeoff between spectral occupancy and the performance under the influence of time delay spread. The simulation is very flexible so that different channel parameters can be studied and optimized either individually or collectively. The irreducible BER averaged over fading samples with a given delay profile is used to compare different modulation/detection methods, while the cumulative distribution of short-term BER is employed to show allowable data symbol rates for given values of delay spread. It is found that both GMSK and QPSK with a raised-cosine Nyquist pulse are suitable for a TDM/TDMA digital portable communications channel. 相似文献
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This paper addresses Gaussian minimum-shift keyed (GMSK) receiver performance analysis for limiter discriminator detection with cochannel interference resulting from a combined cellular voice and packet radio network. A specific example is cellular digital packet data (CDPD), which shares spectrum with cellular voice users; thus, the CDPD receiver will see both narrow-band frequency modulation (NBFM) voice and GMSK data interference. Previous studies investigated the performance of a GMSK receiver with a single GMSK interferer and multipath delay. In this paper, we extend earlier work to multiple Rayleigh fading (Doppler spread) interferers having NBFM (fdm=12 kHz) analog modulation and/or GMSK modulation. Probability of bit-error expressions are derived for the frequency modulation (FM) and GMSK interferer cases assuming medium-to-high signal-to-noise ratio regions. For scenarios of from one to six NBFM interferers, having the same total power, a corresponding Gaussian approximation is within 1.5 dB. Simulation results are also presented for various combinations of FM and GMSK interference. FM interference is only slightly worse than GMSK interference. Delay spread representing an urban scenario resulted in only a slight increase in the error floor 相似文献
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GMSK is the world's most widely used modulation technique for mobile digital telephony and digital wireless applications. We describe two GMSK modulator structures, the voltage controlled oscillator (VCO) and the quadrature modulator structure. The tremendous advantages of the quadrature modulator structure for practical GMSK modulator implementations are emphasized. We present the results of computer simulations and hardware experimental measurements performed on GSM-standardized IC chips which are used by several million subscribers in order to illustrate the operation of a GMSK modulator. Since quadrature modulator structures are used in nearly all practical GMSK chipsets, the properties of this structure are of wide interest. In this paper we highlight the crosscorrelation properties of the GMSK in-phase and quadrature-phase baseband signals, which are part of the quadrature modulator structure. While uncorrelated in-phase and quadrature-phase baseband signals are used in traditional QPSK and OQPSK modulated systems, we demonstrate that there is strong crosscorrelation between the in-phase and quadrature-phase baseband signals. The crosscorrelation is stronger if the observation interval is shorter. Nonobvious quadrature modulator/radio crosscorrelation advantages were patented by Kato/Feher (1986). Design with crosscorrelated quadrature transmitter is “contrary to the wisdom of classical linear communications theory”. Crosscorrelated quadrature modulated systems include FQPSK-KF and GMSK 相似文献
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In burst digital transmission using PSK (phase shift keying) modulation with coherent detection, the recovery of the carrier reference phase and the symbol clock is a key aspect. If all users have a common clock synchronization, symbol timing needs not to be recovered in each burst. A digital processor for carrier recovery without preambles, in the presence of frequency offset, is considered. As an example, a 2 Mb/s QPSK transmission system is considered in which E b/N o=10 dB, and the burst and estimation interval length L =15. Using the algorithm described and averaging eight successive estimated frequency offsets, in order to eliminate anomalous errors, the BER (bit error rate) degradation is equal to 0.14 dB when Δf =20 kHz 相似文献
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Wei-Ping Zhu Yupeng Yan Ahmad M.O. Swamy M.N.S. 《IEEE transactions on circuits and systems. I, Regular papers》2005,52(11):2490-2500
In this paper, a new feedforward symbol timing recovery technique using timing estimation followed by interpolation is presented for digital receivers with two samples/symbol or higher sampling rate. A few timing estimation algorithms are proposed to estimate the timing offset accurately. The basic algorithm uses only the in-phase (I) or quadrature (Q) signal for timing detection, which applies to a BPSK communication system. It is shown that the basic algorithm, when applied in quadrature modulation systems where both I and Q signals are available, can be modified slightly to yield an improved estimation precision. The mean and variance of the resulting timing estimate are analyzed and simulated, supporting a satisfactory estimation performance. It is also shown that by applying a postprocessing scheme, such as the Kalman filter, the variance can be further reduced, resulting in a smoothed timing estimate. Some of the issues concerning the implementation of the proposed technique are also addressed. 相似文献