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1.
We introduce a fast fell-search scheme based on the distributed sample acquisition (DSA) technique for inter-cell asynchronous DS/CDMA systems. The proposed DSA scheme enables the long-code acquisition extremely fast even without employing any passive matched filter which used to dominate synchronization circuit complexity in asynchronous DS/CDMA systems. In the DSA-based asynchronous DS/CDMA system, each base station spreads its DQPSK-modulated long-code generator information with an assigned short-period igniter sequence, and broadcasts it as a common pilot signal. A mobile station first identifies and acquires the igniter sequence of the cell group currently located, then detects the conveyed long-code generator information by despreading the acquired igniter sequence, thereby identifying and synchronizing the long-code of the current cell. The mean acquisition time of this proposed DSA-based inter-cell asynchronous DS/CDMA system, evaluated under the assumption that each of 512 cell-specific long-codes is a 10-ms segment (38400-chips for the chip rates of 3.84 Mchips/s) of complex Gold codes of period 218-1 and the igniter sequence (or, group code) set is composed of 7 complex orthogonal Gold codes of period 256, turned out even shorter than that of the inter-cell synchronous DS/CDMA systems employing the conventional serial search method. Furthermore, simulation results showed that the DSA scheme employing a passive matched filter is much superior in terms of acquisition time and robustness, to the 3GPP W-CDMA synchronization scheme having comparable complexity  相似文献   

2.
We introduce a correlation-aided distributed sample acquisition (CDSA)-based intercell synchronous direct-sequence code-division multiple-access (DS/CDMA) system for enhancing the robustness of the previously proposed distributed sample acquisition (DSA)-based system. The CDSA system incorporates the state symbol correlation process in the existing DSA process to maintain the fast acquisition performance even under very poor channel environment. For its realization, each CDSA-based mobile station stores in its memory a period of the possible state symbol sequences, which are determined by the long-period scrambling PN sequences used in the system and the sampling time parameters for the state samples. In the first stage of the synchronization procedure, the mobile station (MS) attempts to acquire the psuedo noise (PN) sequence by taking the comparison-correction based synchronization approach of the original DSA scheme. However, if it cannot acquire the synchronization until it collects a predetermined number of state symbols (e.g., a period of the state symbol sequence), then the MS determines the PN sequence timing by correlating the received symbol sequence with each shift of the prestored state symbol sequences. Performance analysis and simulation results reveal strong robustness of the CDSA-based system in low-signal-to-noise ratio, fading, and large frequency-offset channels.  相似文献   

3.
We analyze the acquisition time performance of the distributed sample acquisition (DSA) scheme proposed for a fast DS/CDMA signal acquisition. To analyze the composite acquisition mechanism, we first define several acquisition-related probability parameters which can describe all the essential events in the DSA synchronization, along with the basic states that constitute the eventual DSA state transition diagram. Then, we construct the state transition diagram employing these basic states and the moment generating functions which are entirely based on the above defined probability parameters. Applying this state transition diagram and determining the acquisition-related parameters, we finally analyze the mean acquisition time performance of the DSA  相似文献   

4.
We propose a new acquisition scheme called distributed sample acquisition (DSA) which is applicable to the direct-sequence code-division multiple-access (DS/CDMA) system with a long-period pseudonoise (PN) sequence. The proposed scheme lays its foundations on an auxiliary PN sequence called the igniter sequence, which has relatively short period, and the distributed sample scrambling (DSS) technique previously developed for the asynchronous transfer mode cell transmission. In the DSA scheme, acquisition is done in three steps. First, the igniter sequence is synchronized, which normally takes a very short time due to its short period. Second, the state samples of the long-period PN sequence generator in the transmitter, which are conveyed to the receiver over the igniter sequence stream, are determined out of the synchronized igniter sequence. Third, the long-period PN sequence is synchronized by applying the state samples to the DSS receiver. Since the operation of each step takes a very short time, the overall acquisition is done very quickly. We analyze the acquisition time performance of the proposed scheme by taking the transform domain approach, confirming that the resulting mean acquisition time is dramatically reduced. If compared with the existing serial-search scheme, the DSA scheme can perform acquisition about 100 times faster when the period of the PN sequence is 215-1. None the less, the additional circuit complexity for its implementation is very small  相似文献   

5.
In this paper, a theory is developed to support the synchronization of shift register generators (SRGs) in the general class of distributed sample scramblers (DSSs). In the general DSS, the samples transmitted to the descrambler for its synchronization are freely generated out of the scrambler SRG, a special case of which is to take samples directly from the SRG sequence. To describe this general sampling method, the concept of sampling vectors is introduced. The delayed sample-transmission problem, which is a real problem in practical transmission systems, can be resolved by adopting the sampling vectors. This paper provides a systematic solution to the synchronization problem of the general DSS based on mathematical modeling. It first considers the sampling problem of the SRG state information, and then discusses the correction problem of the descrambler SRG state using the transmitted samples. Applications are attached at the end to demonstrate the developed theory for simple realizations of the DSS for use in the cell-based ATM transmission environment  相似文献   

6.
We propose a parallel distributed sample acquisition (PDSA) scheme applicable to a direct-sequence code-division multiple-access (DS/CDMA) system employing M-ary signaling for data transmission. While the primitive distributed sample acquisition scheme can be employed only for the binary signaling systems which transmit 1 bit per symbol, the proposed PDSA scheme extends its applicability to the general signaling systems allowing multibit transmission per symbol. The proposed PDSA technique can also be applied to fast acquisition of the scrambling code in multicarrier DS/CDMA cellular systems with a slight modification of the transceiver circuitry  相似文献   

7.
In this paper, we consider how to apply the sequence space and the shift register generator (SRG) theories to distributed sample scrambling (DSS), which exhibits the best performance in scrambling of small frame-sized signals. We first consider how to predict scrambling sequences using their samples, which is a basic problem for a proper synchronization within the DSS systems. Then for DSS scramblers, we consider how to determine the scrambler SRGs and the sampling times for conveying information on the scrambling sequence; and for DSS descramblers, we consider how to determine the descrambler SRGs, the correction times, and the correction vectors for a proper synchronization. We further examine how to realize the scramblers and the descramblers with minimized circuit complexity. Finally, we demonstrate how to apply the results to DSS scramblers and descramblers for application in cell-based asynchronous transfer mode (ATM) transmission  相似文献   

8.
同步是扩频通信中的关键问题,它一般分为同步捕获和同步跟踪两个阶段。3GPP标准中采用了具有良好非周期相关特性的序列集,快速哈达玛变换(FHT)等技术来实现快速同步捕获,本文对DS/WCDMA中小区同步捕获的原理进行了阐释并给出了具体实现方法。  相似文献   

9.
扩频通信系统的软件无线电实现结构及性能分析   总被引:21,自引:0,他引:21       下载免费PDF全文
叶中付  吴涛  徐旭 《电子学报》2001,29(1):120-123
本文主要论述了直接序列(DS)扩频通信系统中的软件无线电实现结构.首先从软件无线电的基本概念出发,论述了直接扩频通信系统中采用软件无线电结构的可能性和必要性;其次详细论述了直接扩频通信系统中软件无线电结构的实现形式,包括发射方、接收方的实现结构,扩频编码的同步(包括扩频编码相位的捕获与跟踪)以及多址通信的实现等.对文章中提出的方法进行了计算机模拟试验,结果是令人满意的.  相似文献   

10.
The well-known linear decorrelating detector (LDD) for direct-sequence code-division multiple-access (CDMA) systems provides near-far resistant performance when the timing of each user is accurately known. Traditional CDMA acquisition techniques suffer from high differences in power levels. The estimation accuracy for a user overwhelmed by stronger ones is likely to be unsatisfactory; at the same time, the interference from a user undergoing acquisition or tracking is not removed by the standard LDD. In this paper, a fully near-far resistant technique for acquisition and tracking for asynchronous CDMA systems applying the LDD is proposed, considering realistic band-limited signals. This technique is based on the adoption of a pair of special sequences equivalent to a dedicated access channel and is shown to provide a relatively fast and robust means to perform channel estimation both in case of single- and multipath channels  相似文献   

11.
In this paper, we discuss recovery schemes for errors occurring when image data encoded with variable length coding (VLC) is transmitted through additive white Gaussian noise (AWGN) and multiple–access interference in direct sequence code division multiple access (DS/CDMA) systems. VLC such as JPEG is so sensitive to channel errors that severe degradation in decoded images occurs even if only one or two bits have errors. This is due to the loss of synchronization at the image decoder. We propose a resynchronization scheme using a power allocation method in wireless DS/CDMA transmission. Through simulation, we know that the proposed method has a more robust resynchronization capability and higher objective and subjective quality than the conventional method.  相似文献   

12.
Spread spectrum techniques have become very useful in modern communications. A common spread spectrum technique is to directly modulate a pseudorandom noise (PN) code onto the carrier. Systems employing this technique are called direct sequence (DS) systems. A primary concern with direct sequence systems involves PN code synchronization (acquisition) of the incoming and local signals to within at least one PN symbol followed by a fine alignment (tracking) which must be maintained throughout transmission. This paper is concerned with the PN acquisition aspect of code synchronization. Specifically, a dual threshold sequential detection receiver is analyzed and a general expression is derived which addresses the probability that the sequential detection procedure ceases after an arbitrary number of samples. This expression is needed in order to support a characteristic function approach in deriving acquisition Probability as a function of time which will be the topic of a subsequent paper.  相似文献   

13.
该文基于由电子科技大学提出的作为中国地面数字多媒体电视广播传输标准候选方案之一的SMCC+系统和OFDM系统,提出了一种在低信噪比下利用特殊构造的短PN序列进行快速精确的大范围频率同步的方法。经仿真证明,信噪比在-20 dB范围以上时,该法在AWGN,单抽头瑞利衰落信道和等值双径瑞利衰落信道环境纠正大范围频偏的性能比Tufvesson等人(1999)同类常规算法性能更优,从理论上而言,该算法可以估计1/2带宽范围内的频率偏移,显然,该算法优于常规同类算法。  相似文献   

14.
This paper investigates the impacts of array weight errors (AWE) in an antenna array (AA) on a parallel interference cancellation (PIC) receiver in uplink synchronous and asynchronous direct sequence code division multiple access (DS‐CDMA) systems. The performance degradation due to an AWE, which is approximated by a Gaussian distributed random variable, is estimated as a function of the variance of the AWE. Theoretical analysis, confirmed by simulation, demonstrates the tradeoffs encountered between system parameters such as the number of antennas and the variance of the AWE in terms of the achievable average bit error rate and the user capacity. Numerical results show that the performance of the PIC with the AA in the DS‐CDMA uplink is sensitive to the AWE. However, either a larger number of antennas or uplink synchronous transmissions have the potential of reducing the overall sensitivity, and thus improving its performance.  相似文献   

15.
A hybrid scheme is proposed for the purpose of suppressing the effects of external modulation and/or laser nonlinearities in subcarrier multiplexing (SCM) fiber optic communications systems. Hybrid CDMA/FDMA combines two schemes in such a way that the resulting hybrid network is robust against interference and is much more spectrally efficient than a CDMA system. Several possible architectures are introduced for the hybrid CDMA/FDMA subcarrier fiber optic local area network (LAN). The networks utilize CDMA and SCM, an asynchronous multiple access scheme. Direct sequence spread spectrum multiple access (DS/SSMA), the most common form of CDMA is employed. It is shown that by using the code sequence sets for which the shift-and-add property holds, intermodulation products (IMPs) and harmonics have a similar interference-like effect as nonmatching sequences do. Owing to the fact that the shift-and-add property holds for conventional spreading sequences, suppression of nonlinear distortions is examined. An average error probability performance evaluation of the selected configuration is presented for a transceiver pair. In analysis of the system, the authors assume the interference term arising from other users is Gaussian distributed. The results are compared to that obtained by exact evaluation of interference distribution using Gauss quadrature rule integration method. The authors compare the performance of this scheme for two different code sequence lengths. They also present some preliminary experimental results on the proposed LAN implementation as well as its measured transmission performance  相似文献   

16.
Differential space–time modulation (DSTM) schemes were recently proposed to fully exploit the transmit and receive antenna diversities without the need for channel state information. DSTM is attractive in fast flat fading channels since accurate channel estimation is difficult to achieve. In this paper, we propose a new modulation scheme to improve the performance of DS‐CDMA systems in fast time‐dispersive fading channels. This scheme is referred to as the differential space–time modulation for DS‐CDMA (DST‐CDMA) systems. The new modulation and demodulation schemes are especially studied for the fast fading down‐link transmission in DS‐CDMA systems employing multiple transmit antennas and one receive antenna. We present three demodulation schemes, referred to as the differential space–time Rake (DSTR) receiver, differential space–time deterministic (DSTD) receiver, and differential space–time deterministic de‐prefix (DSTDD) receiver, respectively. The DSTD receiver exploits the known information of the spreading sequences and their delayed paths deterministically besides the Rake‐type combination; consequently, it can outperform the DSTR receiver, which employs the Rake‐type combination only, especially for moderate‐to‐high SNR. The DSTDD receiver avoids the effect of intersymbol interference and hence can offer better performance than the DSTD receiver. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

17.
There has been significant interest in cellular systems employing direct sequence (DS) code division multiple access (CDMA), with no synchronization requirement between base stations (BS), especially in the context of the so-called third-generation (3G) wireless systems. In this case, since neighboring BSs use different spreading sequences, the mobile must first determine the spreading sequence being used by the BS(s) from which the mobile receives sufficiently strong signals. To facilitate acquisition, the total set of spreading sequences is divided into groups, and the group identification is transmitted over a synchronization channel. This paper describes a novel mechanism for transmitting the group identification (ID) using cyclically permutable (CP) codes; this scheme results in significant reduction in the search space, allowing for rapid acquisition. The technique described is currently a component of the radio access technology in the 3G partnership project (3GPP) proposal to the International Telecommunications Union (ITU) for 3G wireless systems (IMT-2000). An analysis of the three-stage search process required for acquisition and cell search is also presented, and simulation results are shown to demonstrate the efficacy of this approach  相似文献   

18.
A quasi‐timing synchronous code division multiple access (CDMA) system called ZCZ‐CDMA, which uses a set of sequences with a zero‐correlation zone called ZCZ code as a spreading code, is useful for short‐range wireless communications because of its excellent properties such as co‐channel interference‐free performance, simplified hardware design, and low transmit power as well as fast frame synchronization capability. In this paper, a ZCZ‐CDMA system with binary frequency‐shift keying (BFSK) modulation called BFSK‐ZCZ‐CDMA is proposed. This system is characterized by using a pair of balanced ZCZ codes for spreading and transmitting the two spread components over the respective keying carrier frequencies. Its bit error rate performance, compared with those of existing BPSK‐ZCZ‐CDMA, ASK‐ZCZ‐CDMA, and CDMA systems using the other spreading codes, is evaluated in theory and simulation. The bit error rate performance of the three ZCZ‐CDMA systems over additive white Gaussian noise and Rayleigh fading channels are formulated. It is proved that BFSK‐ZCZ‐CDMA is much more robust in anti‐fading performance and low transmit power in such an environment that fading distributions on the keying frequencies are independent mutually. Fading versus frequency characteristics are also investigated. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

19.
The problem of blind channel identification for direct-sequence/code-division multiple-access (DS/CDMA) multiuser systems is explored. For wideband DS/CDMA signals, multipath distortion is well modeled by a finite-impulse response filter. In this work, a blind channel identification technique based on second-order statistics is investigated. The method exploits knowledge of the spreading code of the user of interest via matched filtering, as well as properties of spreading codes. The current scheme focuses on a method appropriate for randomized long sequence DS/CDMA. This access scheme poses special challenges as the spreading codes are time varying. An analytical approximation of the mean-squared error is derived using perturbation techniques. The performance of the algorithm is studied via simulation and through the mean-squared error approximation, which is observed to be tight  相似文献   

20.
PN (PseudoNoise)码捕获技术是DS CDMA (DirectSequence CodeDivisionMultipleAccess)蜂窝移动通信系统的关键技术。文中提出了一种基于能量窗的捕获技术 ,有效地利用了CDMA系统固有的多径分集能力 ,捕获对象是多径信号 ,研究结果表明 :对有效多径成分进行捕获有比单径捕获和跟踪有更好的性能。  相似文献   

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