共查询到20条相似文献,搜索用时 31 毫秒
1.
Multiple Dwell Serial Search: Performance and Application to Direct Sequence Code Acquisition 总被引:1,自引:0,他引:1
The technique of multiple dwell serial search is described and analyzed. The advantage of the multiple dwell procedure is that the examination interval need not be fixed, allowing incorrect cells to be quickly discarded, which in turn results in a shorter search time than is possible with a fixed dwell time procedure. This type of search scheme is particularly useful for direct sequence code acquisition in a spread-spectrum communication system. An expression for the generating function is obtained from a flow graph representation of the multiple dwell technique. The generating function is used to develop expressions for the mean and variance of the search time in terms of the following parameters: the dwell times, the detection probability, the false alarm probability, and the false alarm penalty time. Coherent detector characteristics are then used to investigate the performance of the multiple dwell technique for direct sequence code acquisition. It is shown that the multiple dwell procedure can significantly reduce the expected acquisition time from that obtained with a single dwell system. The most significant improvement is obtained by using a two-dwell system. Additional but nominal improvement is gained when more than two dwells are employed. 相似文献
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As an alternative to the classic linear detector which only assumes noise variance, a new robust detector with noise variance estimation censoring input signals over AWGN is proposed. The results demonstrate that analytic detection probability matches the simulation results for the linear detector and that the new robust detector shows better performance than the linear detector when the number of samples increases. 相似文献
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A novel circuit implementation for an adaptive phasefrequency comparator, which can be conceived of as a 5-cell up-down counter, is proposed. This circuit can handle coincident input signals and has no dead phase zone or intermediate states. These properties greatly improve the performance of a phase-locked loop. 相似文献
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The performance of four algorithms using pseudonoise matched filters (PNMFs), for direct-sequence spread-spectrum systems, is analyzed. They are: parallel search with fix dwell detector (PL-FDD), parallel search with sequential detector (PL-SD), parallel-serial search with fix dwell detector (PS-FDD), and parallel-serial search with sequential detector (PS-SD). The operation characteristic for each detector and the mean acquisition time for each algorithm are derived. All the algorithms are studied in conjunction with the noncoherent integration technique, which enables the system to operate in the presence of data modulation. Several previous proposal using PNMF are seen as special cases of the present algorithms 相似文献
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An improved implementation of an adaptive phase comparator circuit is presented. The adaptive phase comparator can be thought of as a five-cell up-down counter that is bounded in both the outermost cells. A new design concept leads to a circuit with a higher maximum operation frequency while maintaining the basic requirements of handling coincident input signals and absence of intermediate states. The circuit is based on the application of a number of identical logic elements, which are placed in a ring structure 相似文献
6.
Biqi Long Hichan Moon 《Electronics letters》1997,33(11):926-928
The authors present the performance of double dwell acquisition using a continuous integration detector. One performance measure in an acquisition system is the mean acquisition time, which depends on detection and false alarm probability. The detection and false alarm probability of double dwell acquisition using continuous integration detector is derived 相似文献
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A symbol detector for wireless systems using space division multiple access (SDMA) and orthogonal frequency division multiplexing (OFDM) is derived. The detector uses a sphere decoder (SD) and has much less computational complexity than the naive maximum likelihood (ML) detector. We also show how to detect non-constant modulus signals with constrained least squares (CLS) receiver, which is designed for constant modulus (unitary) signals. The new detector outperforms existing suboptimal detectors for both uncoded and coded systems. 相似文献
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针对载波多普勒下的伪码捕获问题,分析了基于分段相关-视频积累方法的多驻留伪码捕获系统的最优性能。推导了正交双通道检测器的检测概率和虚警概率表达式,给出了多驻留系统的捕获时间均值表达式;通过采用遗传算法对系统进行优化设计,增大了系统的多普勒容限,降低了捕获时间;分析了驻留级数、多普勒和载噪比等对捕获系统性能的影响。研究成果可用于指导扩频系统接收机伪码捕获模块的设计。 相似文献
9.
This paper develops the mean and variance of the time to acquire for single dwell time PN-type spread-spectrum systems. A model is specified, and then exact results are obtained by use of the generating function for the acquisition process. The paper is somewhat tutorial in that the analysis technique is developed in a logical step-to-step manner for the Markov chain model and can be readily used on other models. The effects of Doppler and other imperfections of the original model are discussed. Finally the results of the double dwell time system are presented and the appropriate modifications for Doppler effect are given. 相似文献
10.
Arias-Castro E. Donoho D.L. Huo X. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2005,51(7):2402-2425
We construct detectors for "geometric" objects in noisy data. Examples include a detector for presence of a line segment of unknown length, position, and orientation in two-dimensional image data with additive white Gaussian noise. We focus on the following two issues. i) The optimal detection threshold-i.e., the signal strength below which no method of detection can be successful for large dataset size n. ii) The optimal computational complexity of a near-optimal detector, i.e., the complexity required to detect signals slightly exceeding the detection threshold. We describe a general approach to such problems which covers several classes of geometrically defined signals; for example, with one-dimensional data, signals having elevated mean on an interval, and, in d-dimensional data, signals with elevated mean on a rectangle, a ball, or an ellipsoid. In all these problems, we show that a naive or straightforward approach leads to detector thresholds and algorithms which are asymptotically far away from optimal. At the same time, a multiscale geometric analysis of these classes of objects allows us to derive asymptotically optimal detection thresholds and fast algorithms for near-optimal detectors. 相似文献
11.
本文关注的是多路信号之间时延差异的联合估计问题。不同于传统的自适应时延估计算法,本文以合成信号作为自适应时延估计的参考信号,给出了基于信号合成的联合自适应时延估计算法。同时本文推导和仿真了该算法时延估计的均值、学习曲线及方差特性。性能分析和仿真结果均显示,本文提出的基于合成的多路信号自适应时延估计为渐进无偏的时延估计。在不明显增加计算量的条件下,当算法收敛时,联合时延估计算法的方差显著低于传统的两路信号之间自适应时延估计算法方差。 相似文献
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14.
Dongmin Lim 《Communications, IEEE Transactions on》2004,52(10):1643-1647
In this letter, we propose a modified version of the Gardner detector for symbol timing recovery of M-ary phase-shift keying (M-PSK) signals. Simulation results show that the proposed modification leads to significant performance improvement when M-PSK signals are highly bandlimited and M is small. Specifically, the reduction in the level of self-noise due to the modification amounts to 10.7 dB for quaternary phase-shift keying signals with the rolloff factor of 0.25 and the normalized noise-equivalent loop bandwidth of 0.005. In terms of computational complexity involved, the proposed method has an advantage over the known self-noise reduction methods for M-PSK signals with small M. 相似文献
15.
Maximum likelihood detection of superimposed signals in code-division multiple access (CDMA) communication systems has a computational complexity that is exponential in the number of users, and its implementation is practically prohibitive even for a moderate number of users. Applying the expectation maximization algorithm to this problem, we decompose the multiuser detection problem into a series of single-user problems, and thus present an iterative computationally efficient algorithm for detection of superimposed signals in synchronous direct-sequence CDMA communication systems. The resulting structure includes the well-known multistage detector as one of its special cases. With a proper choice of its parameters, the new detector can achieve the advantages of both the multistage and conventional detector and have good performance for both strong and weak users 相似文献
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《Digital Communications & Networks》2016,2(4):218-224
In massive multiple input and multiple output (MIMO) systems the challenge is the detection of the individual signals from the composite signal with a large system limit. The optimal detector becomes prohibitively complex. The approximate message passing (AMP) algorithm, designed for compressed sensing, has attracted researchers to counter this problem due to its reduced complexity with a large system limit. For this reason the AMP algorithm has been used for detection in massive MIMO systems. In this paper, we focus on implementing this algorithm in a fixed-point format. To obtain an implementation friendly architecture, we propose approximations for the mean and variance estimation functions within the algorithm. These estimation functions are obtained using the log-sum approximation, then taking the exponent of the result. The log-sum approximation is obtained by the Jacobian logarithm with a correction function. We also provide a modification of the correction function for the approximations that best suits our case. We then transform the algorithm with the approximated functions to fixed-point and provide a BER performance for the algorithm with the variables set to 16-bit word lengths using the hybrid “ScaledDouble” data types. 相似文献
18.
Presents a new approach for adaptive control of blood pressure using vasoactive drugs. The idea is to use an adaptive controller that incorporates the concept of duality in the sense of Feldbaum (1965) and to consider the cost functional M-steps ahead in time. The dual property means that the control signal is chosen in such a way that estimation of the model parameters and regulation of the output signals are optimally balanced. Extensive computer simulations for different values of M shows that the sample mean of the achieved cost tends asymptotically to a limiting value while the variance is reduced. The proposed suboptimal adaptive controller has also an improved transient response when compared to a certainty equivalent controller 相似文献
19.
This study investigates mobility patterns in microcellular wireless networks, based on measurements from the 802.11 based system that blankets the Carnegie Mellon University campus. We characterize the distribution of dwell time, which is the length of time that a mobile device remains in a cell until the next handoff, and sign-on interarrival time, which is the length of time between successive sign-ons from the same mobile device. Many researchers have assumed that these distributions are exponential, but our results based on empirical analysis show that dwell time and sign-on interarrival time can be accurately described using heavy-tailed arithmetic distributions that have infinite mean and variance. We also show that the number of handoffs per sign-on can be modeled accurately with a heavy-tailed distribution. 相似文献
20.
The well-known Norris-Landzberg acceleration factor (N-L AF) empirical equation was developed based on the accelerated thermal cycling (ATC) test. It has been widely used for many years to predict product lifetimes. However, some recent test results have shown the insufficiency of this equation when the ramp rates change. The AF equation predicts a longer lifetime when the ramp rate is higher, which contradicts the experimental test data. The reason for this discrepancy is that the N-L AF equation combines both ramp rate and dwell time factors in one frequency term. Thus, modifying the current AF equation to more precisely predict product lifetimes has become an important topic.This study proposes a new AF equation to decouple the effects of the ramp rate and dwell time during an ATC test, replacing the frequency term used in the N-L equation with two new terms. One is related to the ramp rate for the strain rate effect, and the other is related to the dwell time for the creep effect of the packaging solder joint material. The new AF equation produces a good correlation between the simulation and test results for different package types discussed in the literature with various ramp rates and dwell times. 相似文献