共查询到20条相似文献,搜索用时 31 毫秒
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Suwon Kang Yong-Hwan Lee 《Selected Areas in Communications, IEEE Journal on》2001,19(6):1128-1137
We propose a new scheme for rapid acquisition of PN signals in direct-sequence spread spectrum (DS/SS) systems by estimating the phase of the received PN signal with the use of an auxiliary signal. The auxiliary signal can be generated by a sum of the phase shifted PN signals. The phase of the incoming PN signal is estimated using the properties of cross correlation between the PN signal and the auxiliary signal. True phase alignment is detected using a conventional serial search scheme, where the initial phase of the local PN generators is set to a value obtained by the phase estimator. The performance of the proposed acquisition scheme is analytically evaluated in terms of the mean acquisition time. Numerical results show that the proposed scheme can achieve acquisition at least two times faster than the conventional scheme in the nominal operating condition 相似文献
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Direct sequence spread spectrum systems require a local replica of the pseudonoise (PN) sequence to be synchronized with the received signal's spreading code. A method is proposed to improve the PN sequence acquisition time and decrease the acquisition time variability. The proposed method is based on a binary search algorithm. At each stage of the algorithm, an auxiliary signal is used to formulate a new search region within the PN sequence, and at each stage the search region is reduced by half. The region containing the incoming PN phase is therefore obtained within O(log2 (N+1)) steps. A closed loop coherent PN acquisition algorithm presented by Salih and Tantaratana (1996) motivated the use of the auxiliary signal, and the algorithm of Salih et al. is also used for comparison. Results indicate the algorithm presented in this paper can achieve a factor of two to three times improvement in the mean acquisition time with a significant decrease in the acquisition time variability 相似文献
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An acquisition method of long pseudo-noise (PN) sequences in direct-sequence spread spectrum (DS/SS) systems is presented. The concurrent cross correlation of locally generated auxiliary signals with the incoming PN sequence produces binary search estimates leading to an initial approximation of the input signal's PN offset. The PN receiver then uses a closed-loop subsystem to determine the true offset of the incoming PN signal. New phase estimates are generated from successive corrections of likely errors in the binary search. The acquisition scheme's average acquisition time and its variance are analytically determined. Simulation results show that the proposed acquisition scheme is faster than the conventional serial receiver. A hybrid serial/parallel PN acquisition receiver is used for comparing the acquisition performance given similar hardware complexity. The hybrid receiver used the same number of parallel correlators as used in the proposed receiver's input phase estimator. Simulation results show that the proposed system provides an improved performance under normal operating conditions. 相似文献
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直接序列扩频用于低轨卫星通信可以解决抗敌意干扰问题,但多普勒频移下码捕获是需要解决的关键技术。基于离散时间信号处理分析了多普勒频差对码捕获性能的影响,给出部分匹配滤波器与FFT结合的码捕获算法原理。针对大频差、长地址码直扩系统的快速码捕获问题,提出了一种二次部分匹配滤波器与FFT结合算法的实现方案,在考虑捕获性能与实现复杂度之间的折衷上,具有很强的灵活性。 相似文献
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大频差长地址码扩频系统快速捕获方案的设计与实现 总被引:2,自引:0,他引:2
该文基于离散时间信号处理分析了多普勒频移对捕获性能影响的表达式,给出部分匹配滤波器与FFT结合方案的原理。针对大频差长地址码扩频系统快速捕获问题,提出一种采用部分匹配滤波器与FFT结合算法的实现方案,在考虑捕获性能与实现复杂性间的折衷上,具有很好的灵活性。该方案应用FPGA与DSP芯片配合实现,应用结果表明该方案在移动卫星通信和直扩抗干扰通信中具有很好的应用前景。 相似文献
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We propose a closed-loop system with a pre-loop code phase estimator (PLE) for acquisition of the pseudonoise (PN) signal in direct-sequence spread-spectrum systems. It consists of two major parts: a PLE and a closed-loop acquisition subsystem. The system uses an auxiliary signal, as opposed to the PN signal itself, to correlate with the incoming signal. The PLE uses the correlation result to obtain an estimate of the incoming code phase. Then, starting with this initial estimate, the closed-loop subsystem will acquire the code phase of the incoming PN signal. With coherent carrier demodulation, mean and variance of the acquisition time of the proposed scheme are obtained and compared to those of the conventional serial-search acquisition receiver and the closed-loop system without the pre-loop estimator. Results show that, with proper choices of parameters, the proposed system acquires the PN phase significantly faster than the other two systems 相似文献
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在深空测距任务中,高精度的伪码捕获是后续执行伪码跟踪的关键前提.传统基于时频二维搜索的频偏估计算法对于深空测距中频率偏移范围较大的情况难以满足伪码捕获实时性要求.为此,提出了改进的时频二维搜索算法,通过在传统时频二维搜索算法的前端引入快速傅里叶变换(Fast Fourier Transform,FFT)算法对多普勒频偏... 相似文献
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在卫星导航系统中,普遍采用了长码扩频信号。长码扩频信号具有很强的抗干扰和保密能力,实现长码的快速直接捕获对于导航系统的军事应用和发展卫星定位系统具有重要意义。利用FFT计算可以使多次的时域伪码相位的循环相关处理转换为频域的一批乘法处理,单次计算即可获得一批相关结果,进而可加快长码的搜索和捕获速度。通过对多种基于FFT的方法进行比较,提出了适于工程应用的实现方式,并利用实际工作环境对设计进行了实际验证,结果表明该处理方法能够实现预期的目的,可以满足工程需要。 相似文献
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针对低轨(LEO)卫星高速运动引起的多普勒频移,分析了低轨卫星直扩通信信号的扩频参数侦察技术,提出了基于分段累积相关的伪随机(PN)序列周期估计方法及PN码字、PN码初始相位、多普勒频移三维空间搜索方法。理论推导和实践证明,该方法不需先验知识,可通过FFT实现快速计算,运算复杂度低,可对低轨卫星扩频信号参数进行有效侦测。 相似文献
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Elias A. Alwan Sidharth Balasubramanian Jad G. Atallah Matthew LaRue Kubilay Sertel Waleed Khalil John L. Volakis 《Analog Integrated Circuits and Signal Processing》2014,78(3):691-703
We propose a novel transceiver architecture for cognitive sensing. The architecture supports agile beam forming, jamming mitigation, as well as MIMO communications. An essential aspect of the new architecture is its departure from the traditional digital beamforming approaches. Specifically, a single ADC is assigned to a group of array elements instead of having one ADC per element. To facilitate this approach, code division multiplexing is applied to each received antenna signal prior to combining them for digitization using a single ADC. Thus full signal recovery is possible at digital baseband via decoding. The proposed architecture significantly reduces the number of ADCs and I/O channels and hence drastically improves size, weight, area, power and cost of the system with minimal impact on receiver signal-to-noise ratios. 相似文献
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A. P. Clark A. Aftelak M. Savjani C. Ang 《International Journal of Satellite Communications and Networking》1990,8(5):349-361
This paper describes a novel technique for the measurement and correction of the Doppler shift (frequency offset) in a received QPSK signal that has been transmitted over a satellite link. The satellite is here assumed to be in a non-geostationary orbit, and correction of the Doppler shift is required to be achieved as soon as the satellite rises above the horizon, when the Doppler shift may be very high and the signal/noise ratio very low. The receiver now has no prior knowledge of the transmitted data, so that a non-data-aided system must be used, capable of operating under seriously adverse conditions. The selected technique measures the DFTs of successive blocks of samples of the received and demodulated signal, and from the DFTs it derives a control signal for the VCO, which generates the in-phase and quadrature reference carriers for the coherent demodulator. The frequency of the latter is adjusted to reduce the residual Doppler shift in the demodulated signal to a sufficiently small value, so that correct phase synchronization of the VCO on to the received signal carrier can then be achieved by means of an appropriate conventional system (not considered here). The paper describes the new technique of Doppler shift correction, and presents the results of computer-simulation tests to measure the time taken to correct an initial Doppler shift of 5 kHz in the received QPSK signal, at very low signal/noise ratios. 相似文献
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《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1968,56(11):1801-1811
One approach to phased-array antenna beam forming and steering is to multiplex the element signals into a single channel. Appropriate "sampling" of the resulting multiplexed signal can provide electronically steered and shaped beams. This paper describes four practical system concepts for linear and ring arrays based on this approach and discusses significant interrelationships between the various concepts. For linear arrays of elements, the two alternatives are to frequency or time multiplex the element signals. Frequency multiplexing of the element signals produces time-multiplexed beam output signals, and time multiplexing the element signals produces frequency-multiplexed beam output signals. It is also shown here that appropriate correlation "sampling" may be used with either of these to produce easily one or more continuously and electronically steered signal bandwidth beam outputs. Ring arrays of elements may be multiplexed and "sampled" in a somewhat analogous pair of techniques. It is also pointed out that the beam steering in this case may be visualized as the linear phase steering of a set of linear phase modes into which the signal received at the array may be resolved. Ring array beam forming and steering may thus be directly understood in terms of the previous linear array techniques. 相似文献
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扩频接收机系统中,载波的捕获是衡量系统性能的重要指标。当系统接入多路叠加并行信号时,若需要在二维对信号进行捕获,所需捕获时间、所耗资源和接收机功耗将成倍增加。文中针对此问题,提出了一种基于差分滤波器的分集接收方案,大幅降低了系统资源的占用,从而减少了功耗、成本和捕获时间。利用伪随机码的双极性和差分滤波结构减少了所用加法器的数量,并结合对伪随机码并行分集的结构,在多路中对滤波结果进行复用。通过对传统快速相关捕获算法、快速捕获算法、频率相关法以及文中基于差分滤波的并行分集结构进行了复杂度对比。其结果显示,基于差分滤波的并行分集结构在节省资源、提高效率上均具有较大优势。 相似文献
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A. P. Clark A. Aftelak 《International Journal of Satellite Communications and Networking》1990,8(5):337-347
The paper describes a novel development of a previously described technique for the measurement and correction of the Doppler shift (frequency offset) in a received UQPSK signal that has been transmitted over a satellite link. The satellite is here assumed to be in a non-geostationary orbit, so that it introduces a large and time-varying Doppler shift into the transmitted data signal. Correction of the Doppler shift must be achieved as soon as the satellite rises above the horizon and with no prior knowledge at the receiver of the transmitted data. Furthermore, under the given conditions, the signal/noise ratio can be very low and the Doppler shift very high. A non-data-aided technique has therefore been selected, capable of operating under seriously adverse conditions. Results of computer-simulation tests are presented to measure the time taken to correct an initial Doppler shift of 5 kHz in the received UQPSK signal, at low signal/noise ratios. 相似文献