利用准时相关值的PN码定时误差检测器

从利用准时支路相关值的角度出发,研究了用于DS/CDMA系统的改进型PN码定时误差检测器,分析了其性能,并与传统的定时误差非相干检测器和相干检测器进行对比,给出了数值和计算机仿真结果。研究表明,NCIELG型非相干检测器的性能较传统非相干定时误差检测器有明显改善,并且硬件电路更为简化。     

利用自适应滤波器实现扩频码的捕获

使用自适应滤波器对扩频信号进行扩频码捕获,不仅理论上是可行的,而且此方法还能够实现快速捕获,同时还可以对输入信号内的多种干扰信号起到抑制的作用。自适应滤波器法结构简单,易于实现;同时跟踪采用与捕获同一个支路,不需要额外硬件实现,从而节省硬件资源。自适应滤波器法扩频码捕获时,只需期望扩频码的周期与长度,并不期望码型与干扰信号的任何信息。在稳态时,此方法还具有对多径信号分集接收的潜力。     

PN code acquisition using signed-rank-based nonparametric detectorsin DS/SS systems

In this paper, signed-rank based nonparametric detectors are used for pseudonoise (PN) code acquisition in direct-sequence spread-spectrum (DS/SS) systems. We first derive the locally optimum rank (LOR) detector and then propose the locally suboptimum rank (LSR) and modified signed-rank (MSR) detectors using approximate score functions. We compare the single-dwell scheme without the verification mode using the proposed LSR and MSR detectors with that using the conventional squared-sum (SS) and modified sign (MS) detectors. From the simulation results, it is shown that the proposed LSR and MSR detectors perform better than the MS detector by about 2-3 dB and are nearly optimum     

Noncoherent sequential PN code acquisition using slidingcorrelation for chip-asynchronous direct-sequence spread-spectrumcommunications

Noncoherent sequential pseudonoise (PN) code acquisition using sliding correlation is proposed in this paper. Noncoherent detection and chip asynchronization should be taken care of to handle a severely noisy environment, while frequency offset and data modulation effects can be simultaneously dealt with in the proposed technique. To realize sequential detection, the cross-correlation sequences at the output end of the integrate/dump (LID) filter under out-of-lock conditions have to be modeled as either a Gaussian random sequence for chip-asynchronous applications or as their upper bound for chip-synchronous applications in order to avoid significantly high probabilities of false alarm caused by the conventional zero-sequence model. Meanwhile, the in-lock sequence also has to be modified by taking the frequency offset and chip-asynchronization effects into account in order to avoid the occurrence of high probabilities of miss. Extensive computer simulation results indicate that the proposed technique can achieve low probabilities of false alarm and miss and can outperform its fixed-sample-size (FSS) counterparts by roughly 2~4 dB. This superiority, furthermore, increases with decreasing SNRs and/or decreasing desired error probabilities     

A simple expression for the optimization of spread-spectrum code acquisition detectors operating in the presence of carrier-frequency offset

In this letter, we present a simple expression for the optimization of the threshold detection performance for direct-sequence spread-spectrum code acquisition in the presence of carrier-frequency offset. The proposed scheme divides the total integration time into subintervals, and the results of the coherent integrations performed over these subintervals are noncoherently combined prior to detection. The proposed expression allows obtaining the optimum number of coherent-integration subintervals for a given total integration time.     

PN code acquisition using smart antenna for spread-spectrum wireless communications. I

The smart antenna (a blind adaptive antenna array) has brought much attention to its ability to improve the future code-division multiple-access (CDMA) wireless communications systems. However, Adachi et al. (1998), employed only one out of M elements that are in a smart antenna array during the pseudonoise (PN) code acquisition process due to the difficulty in obtaining the weight coefficients of the smart antenna and PN code acquisition jointly and adaptively. Yet, as the PN code is acquired, all M elements are used by Adachi et al. to improve the signal-to-noise ratio (SNR) at a reverse link. We propose an efficient PN code acquisition scheme where all elements are employed during PN code acquisition. Also, we show that by using all elements, the PN code acquisition time can be shortened by at least 40% for a given signal-to-noise ratio and M=5, compared to the single element case. Furthermore, the power of a random access user signal in the reverse link can be lowered at least 3 dB. The additional computational load and complexity to use the proposed PN code acquisition are insignificant.     

Blind acquisition characteristics of PSP-based sequence detectors

The blind acquisition characteristics of binary sequence detection algorithms based on per-survivor processing (PSP) are demonstrated via computer simulations. These capabilities are impressive as compared to those of traditional blind equalizers. It is demonstrated that the short-term acquisition performance of PSP-based algorithms is dominated by the poor performance obtained when certain sequences are transmitted. These sequences are those that cannot be distinguished by the joint maximum likelihood (ML) channel and sequence estimator or do not allow for a complete identification of the channel impulse response. Such sequences are defined and analytically characterized, resulting in asymptotic results on performance for joint ML channel and sequence estimators. Typical misacquisition conditions, the effects of initialization, and the impact of increased tree search complexity are also all characterized by simulations and motivated by the analytical results     

电能量表码采集过程分析

电能量采集及计费自动化系统(简称电量系统)是集电能自动采集、传输、统计结算于一体的自动化系统。电量系统帮电网推行商业化运营和管理,是电力走向市场的技术保障之一。文中结合渭南变电站渭化电厂渭化I线、渭化II线电量表码信息传输实例,论述了电量表码信息如何经电量子站系统维护采集,通过通信传输通道传送至电量计量主站系统,经主站系统采集处理后,送至调度中心结算工作站,供结算工作人员使用的全过程。对同类的工厂专线电能量信息的采集与应用具有普遍的借鉴意义。     

Serial search code acquisition using smart antennas with single correlator or matched filter

This paper investigates three code acquisition methods for direct sequence spread spectrum systems (DS/SS) utilizing smart antennas. The methods are suitable especially for receivers that consist of a smart antenna followed by a single correlator or a matched filter (IMF). The first method is the known fixed beam strategy where the whole angular uncertainty region is divided into small cells using conventional beamforming techniques. Therein, the receiver searches through all angular and delay cells via a serial search procedure. In the second method, the fixed division is made using advanced beamforming techniques, which provide improved tolerance against interference. In the third strategy, the direction-of-arrival (DOA) of incoming signals are estimated and utilized in the acquisition process. An advantage of this DOA estimation-based strategy, when compared to fixed beamforming methods, is a decrease in the region of uncertainty. Disadvantages are increased computational complexity and signal-to-noise ratio (SNR) limitations. The acquisition strategies are compared when the serial search acquisition of the code phase is made using either the correlator or the matched filter. The results indicate that a single antenna receiver gives the best acquisition performance when SNR is high. However, single antenna methods are sensitive to interference. On the other hand, DOA estimation-based methods offer shorter mean acquisition times than fixed beam methods, especially when the number of arriving signals is small.     

A new approach to rapid PN code acquisition using iterative message passing techniques

Iterative message passing algorithms on graphs, which are generalized from the well-known turbo decoding algorithm, have been studied intensively in recent years because they can provide near-optimal performance and significant complexity reduction. In this paper, we demonstrate that this technique can be applied to pseudorandom code acquisition problems as well. To do this, we represent good pseudonoise (PN) patterns using sparse graphical models, then apply the standard iterative message passing algorithms over these graphs to approximate maximum-likelihood synchronization. Simulation results show that the proposed algorithm achieves better performance than both serial and hybrid search strategies in that it works at low signal-to-noise ratios and is much faster. Compared with full parallel search, this approach typically provides significant complexity reduction.     

Two-dimensional code acquisition in time and angular domains

The extension of conventional delay-domain code acquisition to the angular domain is explored. The uncertainty region is partitioned into a number of delay and angular cells. In single-path channels where the interference is modeled as temporarily and spatially white, there exists an optimum number of angular cells minimizing the mean acquisition time. Mean acquisition times up to three times shorter can be attained with the two-dimensional approach. A rather similar behavior is in general found in Lth-order equal amplitude multipath channels, where paths are contiguous in the delay or angular domains. The strategy employed to search through the uncertainty region may have a considerable impact on acquisition performance. The results reveal that the search should proceed not in the direction of the multipath spread but in the other available domain. Proper selection of the search strategy can reduce the synchronization time by a factor of up to two. Two-dimensional code acquisition in scenarios with spatially nonuniform interference is also investigated. In general, the acquisition performance is degraded by the presence of nonuniform interference in the angular domain     

CMA-based code acquisition scheme for DS-CDMA systems

In direct-sequence code-division multiple access, a code synchronization must take place before the multiuser detector. As the initial synchronization stage, a code acquisition scheme is used to estimate the relative timing phase for the desired transmission within one chip interval. In this paper, a blind code acquisition scheme using adaptive linear filtering based on a linearly constrained constant modulus algorithm (CMA) is proposed. The uncertainty of a desired user's delay is initially discretized and translated into a number of hypotheses. The lock convergence property of CMA is exploited, where the filter at the steady state can lock onto the desired user while nulling all other interfering users (i.e., a decorrelator). For each delay hypothesis, the filter is initialized as the corresponding shifted spreading sequence of the desired user. It is shown that lock convergence always occurs for the correct hypothesis, while all incorrect hypotheses will be hovered around some saddle regions, given sufficiently small step sizes. Then, the correct hypothesis is the one which has the converged filter to yield the maximum lock onto the desired user, or a maximum output energy     

Rapid code acquisition algorithm employing PN matched filters

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     

Modeling of code acquisition process in CDMAnetworks-quasi-synchronous systems

We present a model of serial code acquisition process in code-division multiple-access networks. The difference between this model and the existing work is in using the assumption that in each cell of delay uncertainty region the probability of false alarm, is different. This is caused by the fact that in each cell cross correlations between the local code and the codes used by the other users in the network are different. A closed-form expression for the average acquisition time is derived and discussed     

Modeling of code acquisition process in CDMA networks-asynchronoussystems

In this paper, we discuss modeling of the serial code acquisition process in a code division multiple access (CDMA) network. Due to multiple access interference (MAI), the process is characterized by a different probability of signal detection P_D and probability of a false alarm P_FA in each cell of the code delay uncertainty region. We derive exact expressions for average code acquisition time and its variance. In addition to this, we also present several useful approximations, which enable easy engineering use of these results for practical applications in future Universal Mobile Telecommunications System (UMTS) solutions. Numerical results based on this analysis are used for decision threshold optimization in code acquisition process for asynchronous CDMA networks     

DS-SS code acquisition based on simultaneous search andverification

A double-dwell acquisition system that can simultaneously operate search and verification processes, by employing two correlation blocks, is proposed. The search block continuously looks for threshold-crossing instants, and at those instants, the verification block is reset and reinitiated. The threshold is time varying and updated depending on the partial correlation. Computer simulation results indicate that the proposed technique can perform better than existing double-dwell systems which alternate between search and verification modes     

Adaptive PN code acquisition using instantaneous power-scaled detection threshold under Rayleigh fading and pulsed Gaussian noise jamming

An adaptive serial search pseudonoise (PN) code acquisition scheme is proposed, in which the detection threshold is scaled by the instantaneous received power measured prior to PN code correlation. We observe that the proposed scheme achieves significantly improved mean acquisition times compared to the conventional nonadaptive schemes under Rayleigh fading and pulsed Gaussian noise jamming. Furthermore, the proposed scheme is shown to be optimum under pulsed Gaussian noise jamming in the sense that it forces the worst case jamming fraction to unity.     

Signal recognition and signature code acquisition in CDMA mobilepacket communications

Fast and reliable signal sense and signature code synchronization for direct-sequence spread-spectrum (DS-SS) signals are key issues in the design of the receiver for modern packet code-division multiple-access (CDMA) radio networks for mobile communications; this motivates the study of the signal recognition and code-acquisition (SR/CA) scheme we describe in this paper. Specifically, starting from elementary estimation and detection theory criteria, we work out a noncoherent parallel SR/CA algorithm that is suited to a full-digital implementation in a single application-specific integrated circuit (ASIC). The results of a theoretical analysis of such a scheme, encompassing additive white Gaussian noise (AWGN) and multiple-access interference (MAI), are integrated and validated by an overall time-domain system simulation. We also evaluate through a simplified approach the impact of some degradation factors on the overall circuit performance, namely, sampling epoch and carrier frequency offset and 1-b signal quantization, to allow optimization of the design parameters as a function of the characteristics of the received signal     

Low-power adaptive pseudo noise code acquisition for spread-spectrum systems

A novel pseudo noise code acquisition combined with the newly proposed adaptive sampling rate and threshold control (ASTC) algorithm is derived for low-power spread-spectrum systems with complementary metal-oxide-semiconductor implementations. Low-power performance can be achieved by reducing the sampling rate of the proposed system while maintaining the system performance. The sampling rate is dynamically updated due to the change of the channel noise level. Under the assumptions that the channel is additive white Gaussian noise slow-fading channel, up to 74.3% reduction in power consumption compared to the conventional fixed-sampling rate and fixed-threshold architecture is demonstrated with insignificant increase of system complexity. The proposed architecture can be applied to the design of low-power and controllable-performance spread-spectrum communication systems.