共查询到20条相似文献,搜索用时 15 毫秒
1.
Choong Lee 《Communications, IEEE Transactions on》1973,21(8):967-969
When the ratio of the frequency of the carrier to that of the modulating signal becomes less than approximately 10:1, AM detectors become unable to detect the impressed modulation in a satisfactory manner. Distortion due to transient charging and discharging phenomena in the diode circuit during detection of wide-band AM signals has imposed limitations on channel capacity in AM and FM wide-band multiplexing systems. This paper presents and analyzes polyphase envelope detection as a suitable method of solving the problem. This technique makes it possible to detect the envelope of the impressed AM signal to any desired degree of accuracy even when the ratio of the frequency of the carrier to that of the modulating signal approaches unity. The paper shows the results of an experiment that was carried out to verify the theory. 相似文献
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Sang-Hun Yoon Jong-Wha Chong Kyung-Kuk Lee 《Communications Letters, IEEE》2007,11(10):796-798
In this letter, we design and analyze a novel differentially coherent decision feedback structure for differentially bi-orthogonal code (DBOC). Proposed detector using decision feedback and partially maximum likelihood sequence estimation (DF-PMSE) can be applied to the DBOC detector irrespective of bi-orthogonal code length. Simulation and analyzed results show that the PER performance of the proposed detector is almost the same as that of the coherent detector for the various case of bi-orthogonal code length. 相似文献
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In this work, we investigate differentially encoded blind transceiver design in low signal‐to‐noise ratio (SNR) regimes for orthogonal frequency‐division multiplexing (OFDM) signaling. Owing to the fact that acquisition of channel state information is not viable for short coherence times or in low SNR regimes, we propose a time‐spread frequency‐encoded method under OFDM modulation. The repetition (spreading) of differentially encoded symbols allows us to achieve a target energy per bit to noise ratio and higher diversity. Based on the channel order, we optimize subcarrier assignment for spreading (along time) to achieve frequency diversity of an OFDM modulated signal. We present the performance of our proposed transceiver design and investigate the impact of Doppler frequency on the performance of the proposed differentially encoded transceiver design. To further improve reliability of the decoded data, we employ capacity‐achieving low‐density parity‐check forward error correction encoding to the information bits. 相似文献
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It has previously been shown that MSK modulation with correlative encoded symbols, using first- and second-order encoding polynomials, can give rise to signals with excellent bandwidth efficiency. In this paper we specify and analyze the Viterbi receiver for such signals. The receivers are not very complex as they either require four or eight states to be stored and processed during each symbol interval. Our analysis concerns the bit error rate and the transfer function bound technique is utilized. Perfect coherent operation of the receiver is assumed in the error analysis. 相似文献
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On the Energy Detection of Unknown Signals Over Fading Channels 总被引:17,自引:0,他引:17
This letter addresses the problem of energy detection of an unknown signal over a multipath channel. It starts with the no-diversity case, and presents some alternative closed-form expressions for the probability of detection to those recently reported in the literature. Detection capability is boosted by implementing both square-law combining and square-law selection diversity schemes 相似文献
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This paper is concerned with the problem of transmission errors in digitally encoded television signals. Various techniques for reducing the visibility of transmission error effects in the reconstructed signals have been evaluated using computer-produced film sequences. It is found that the visibility of errors in element difference coders is sharply reduced if an erroneous line is replaced by an average of adjacent lines. It is shown that the visibility of errors in two coders that use spatial prediction is low and can be further reduced by using a "leaky" predictor. The implications of these results for in-frame, interframe, and facsimile encoders are discussed. 相似文献
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Demonstration of a Self-Synchronized Polyphase Sampling and Demultiplexing Scheme for Radio-Frequency Analog Signals 总被引:1,自引:0,他引:1
A novel self-synchronizing optoelectronics polyphase scheme for sampling and demultiplexing radio-frequency (RF) signals is demonstrated. One unique feature of this approach is that the optically sampled RF signal always remains in the electrical domain and thus eliminates the need for electrical-to-optical and back to electrical conversions. Furthermore, the simplicity and ease of construction of the scheme readily allows it to be scaled to obtain high sampling rates. As a proof of concept, a 100-MHz RF electrical signal sampled at the rate of 1.28 GS/s and then demultiplexed into four 320-MHz signals was experimentally demonstrated. 相似文献
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基于多相滤波法的中频信号正交解调的CPLD实现 总被引:2,自引:0,他引:2
正交相干检波可以将复包络的所有信息进行保留,所以在数字信号处理中得到广泛应用。该文讨论了数字信号正交相干检波的多相滤波实现方法,并且给出了基于 CPLD 的 IC 实现。计算机仿真结果表明,多相滤波方法可以提高信噪比,实现高性能数字信号处理的要求。 相似文献
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PAM data transmission receivers accomplishing maximum likelihood sequence detection (MLSD) usually require a matched filter prefilter, a sampler at the symbol rate, and a Viterbi algorithm detector. When the channel is unknown or slowly changing, one must use an adaptive matched filter prefilter. We examine an alternative optimum receiver whose optimality is independent of the matched filter prefilter and which is applicable when the channel is effectively band-limited. The sampler in the proposed receiver operates at a rate faster than the data symbol rate, enabling one to replace the matched filter by a fixed low-pass filter and still ensure that the maximum likelihood detector is supplied with a set of sufficient statistics. It is shown that the matched filter is incorporated within a modified Viterbi detector without increasing the number of states in the algorithm, although the Viterbi detector must perform computations at approximately twice the usual rate. Simulations support the optimality of the new receiver and quantitatively indicate the degradation in performance experienced by some adaptive receivers previously proposed. 相似文献
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A true envelope detector is presented and compared with the polyphase envelope detector. It theoretically has no carrier feedthrough. 相似文献
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研究了基于多相滤波结构数字信道化接收机的雷达信号检测技术,在提出接收机具体实现模型的基础上,分析了不同形式雷达信号的检测方法,并对信号检测中可能出现的问题进行了讨论。仿真结果验证了该算法的正确性和有效性。 相似文献
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多相滤波在合成孔径雷达数字正交解调中的应用 总被引:5,自引:0,他引:5
在一般的雷达和通信系统中,实现中频或射频的直接采样,需要完成数字正交解调过程,数字乘积检波(DPD)是实现数字正交解调的一种工程上易于实现的方法,但该方法获得的I/Q数据是需要修正的。该文结合合成孔径雷达信号处理,提出了多相滤波法来修正通过DPD获得的I/Q通道数据,并和Bessel滤波进行了比较。仿真实验结果表明,该方法简便灵活,且工程上易于实现;在滤波器阶数相同的情况下,多相滤波器的最大绝对修正误差为5.839410-4,而Bessel滤波的最大绝对修正误差为9.30710-4,而且,多相滤波很容易实现非等距滤波。 相似文献
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《Signal Processing, IEEE Transactions on》2008,56(5):2003-2016
This paper focuses on the symbol detection problem of random pulse-position modulation (PPM) ultrawideband (UWB) signals in the absence of interframe interference. Particular attention is devoted to severely time-varying channels where optimal detectors are proposed for both uncorrelated and correlated scattering scenarios. This is done by assuming the received waveforms to be unknown parameters. In UWB communication systems, the assumption of unknown random waveforms is consistent with the fact that the received waveform has very little resemblance with the original transmitted pulse. In order to circumvent this limitation, a conditional approach is presented herein by compressing the likelihood ratio test with the information regarding the second- order moments of the end-to-end channel response. Both full-rank and rank-one detectors are derived. For the reduced complexity rank-one detector, an iterative procedure is presented that maximizes the J-divergence between the hypotheses to be tested. Finally, simulation results are provided to compare the performance of the proposed detectors in different propagation environments. 相似文献
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低截获概率(LPI)雷达的广泛应用导致电子侦察系统难以从噪声中检测到LPI信号的存在。针对这一问题,提出一种基于多相滤波器组和高阶累积量联合处理的121雷达信号检测算法。该算法首先利用多相滤波器组实现信号在频域上的快速均匀划分,然后对输出的每个子带信号进行三阶累积量对角切片短时估计,有效抑制高斯噪声,并设计检测器对每个子带信号进行信号存在性检测,进而判断整个信号中是否含有有用信号。仿真结果表明,该方法的检测性能远优于传统的能量检测器,在信噪比大于-20dB时具有较高的检测概率。 相似文献
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层析成像合成孔径雷达(Tomography SAR)结合空间谱估计技术解决层叠效应时,首先要估计出高度维信号源数目,信号源数估计得正确与否直接关系到后续处理的估计性能。用传统的信息论方法估计时,由于数据受乘性噪声影响,估计性能下降。该文提出一种新的信号源数估计方法:双向平滑多视幅相估计(FB-MAPES)滤波器算法。通过Monte Carlo仿真对信息论方法中的GMDL算法和FB-MAPES方法的估计性能进行了比较,试验结果表明该文提出的方法能够更好地适应乘性噪声的影响,因而在估计Tomography SAR高度维信号源数时性能优于传统的信息论方法。 相似文献