Logistic映射扩频序列的相关分布

本文由Ｌｏｇｉｓｔｉｃ映射产生用于直扩码分多址（ＤＳ／ＣＤＭＡ）系统的扩频序列,证明了周期为Ｎ的此类扩频序列的偶相关和奇相关均服从均值为０、方差为Ｎ的高斯分布,采用混沌扩频序列的ＣＤＭＡ系统的容量怀传统扩频序列相同。     

采用多重TCM的室内无线DS／SSMA系统性能分析

本文将多重ＴＣＭ技术应用于室内慢衰落信道下的直接序列扩频多址（ＤＳ／ＳＳＭＡ）系统中，提出了一种发射端和接收端分别采用多重伪码扩频和多重相关接收的ＤＳ／ＳＳＭＡ系统模型及其理论分析方法。在系统用户数、用户信源比特速率和伪码周期相同的条件下，模拟结果表明采用多重ＴＣＭ的ＤＳ／ＳＳＭＡ系统性能显著优于一重ＴＣＭＤＳ／ＳＳＭＡ系统的性能     

同步CDMA系统中一类新的扩频序列

码分多址（ＣＤＭＡ）技术已作为第三代数字移动通信及个人通信系统的无线接入技术进行广泛的研究和应用。而ＣＤＭＡ系统中扩频序列问题一直是ＣＤＭＡ技术中的关键问题。文献４给出了Ｓ－ＣＤＭＡ系统中的扩频序列实数加编码的新方法,但对构造具有纠错能力的扩序列至今尚未发现。本文给了了Ｓ－ＣＤＭＡ系统中具有纠错能力的一类新的扩频序列和它的译码算法。     

广电宽带网上S-CDMA电缆接入系统技术方案

1　Ｓ -ＣＤＭＡ技术介绍ＣＤＭＡ技术由于其抗干扰能力强 ,保密性能好 ,用户容量大 ,在无线通信领域正得到重视和应用 ,若能充分发挥其优点 ,ＣＤＭＡ在ＨＦＣ网络中也会有较好的应用前景。ＣＤＭＡ的基本原理 :ＣＤＭＡ基本原理如图 1所示。在各发送端用各不相同、相互正交的扩频码 (一般采用直接扩频 -ＤＳ ,扩频码采用伪随机码 -ＰＮ序列码 )调制发送数据信号 ,由于ＰＮ码速率比数据码率高几百倍 ,调制后的信号频谱就被扩展了 ,在接收端用与发端相同的ＰＮ码对收到的信号进行相关处理 ,当两个信号同相时得到最大相关峰值 ,窄带噪声及干…     

正交序列扩频多码CDMA系统在AWGN信道的性能分析

在直接序列扩频通信（ＤＳ－ＣＤＭＡ）系统中，为了有效地实现用户高数据率的传输，本文提出了一种正交扩频多码ＣＤＭＡ系统（称为ＯＭＣ－ＣＤＭＡ）。相似于多载波调制，传输的高数据率首先进行串－并转换，然后对转换后的低数据流用正交序列进行扩频调制。不同于多载波调制，各支路扩频信号用同一载波进行调制。这里，我们对此系统在ＡＷＧＮ信道的性能进行了计算，并对数值结果进行了分析。     

用于CDMA的四相混沌扩频序列

本文由混沌映射产生用于直扩码分多址（ＤＳ／ＣＤＭＡ）系统的四相扩频序列，证明了周期为Ｎ的此类扩频序列的四种广义奇相关均服从均方值为Ｎ的瑞利分布。混沌四相序列的相关峰值较混沌二相序列有显著的下降，多址性能与传统四相扩频序列相同。     

网格编码MQAM直扩多址系统的性能分析

本文将非恒包络高效网格编码调制ＴＣ－ＭＱＡＭ应用于瑞利慢衰落信道下的直接序列扩频多址系统中。针对衰落信道和ＴＣ－ＭＱＡＭ的特点，提出了一种分析ＴＣ－ＭＱＡＭ用于衰落信道下ＤＳ／ＳＳＭＡ系统性能的方法，数值模拟表明在系统用户数、用户信源比特速率以及码相同的条件下，本文所构造的非恒包络１／４ＴＣ－１６ＱＡＭ性能优于同状态数３／４ＴＣ－１６ＱＡＭ和恒包络２／３ＴＣ－８ＰＳＫ。这说明通过增大最小分支数等适     

采用正弦移频键控调制的直接序列扩频系统的性能分析

正弦移频键控调制信号具有恒包络和平滑的相位变化特性，把它作为直接序列扩频信号的切普基本波形，将使扩频信号具有带外辐射低，而相应的系统受非线性影响小等特点。分析表明，采用ＳＦＳＫ调制的直接序列扩频系统较ＱＰＳＫ－ＤＳ／ＳＳＭＡ及ＭＳＫ－ＤＳ／ＳＳＭＡ系统有更好的多址能力。     

3@—W—CDMA系统的扩频结构与扩频码

本文结构３ＧＰＰ Ｗ－ＣＤＭＡ的最新协议,介绍了Ｗ－ＣＤＭＡ系统的两次扩频结构,讨论了其中使用的ＯＶＳＦ码与扰码的主要特性及其在Ｗ－ＣＤＭＡ系统中的应用,文章的最后讨论了在工程实际中实时产生扩频码的方法。     

第三代移动通信系统CDMA的关键技术

在３Ｇ系统中,ＣＤＭＡ系统成为了最具竞争力、最具发展前景的无线多址技术。虽然ＣＤＭＡ扩频技术可以采用直接序列扩频(ＤＳ)、跳频(ＦＨ)、跳时(ＴＨ)以及它们的组合等,但在移动通信中一般选用直接序列扩频,它构成了我们常说的ＤＳ－ＣＤＭＡ系统。３Ｇ系统结构如图１所示,它的核心网是在ＧＳＭ系统的核心网ＧＳＭ—ＭＡＰ和ＡＭＰＳ、ＩＳ—９５的核心网ＡＮＳＩ—４１的基础上发展而来的,其空中接口和相应的２Ｇ系统后向兼容。它的３种工作模式为:单载波频分双工、多载波频分双工和时分双工方式。     

Enhancing the capacity of DS-CDMA system using hybrid spreading sequences

A new direct-sequence code-division multiple-access (DS-CDMA) system using hybrid spreading sequences in order to increase system capacity is proposed. This scheme permits accommodating more than N users, where N is the processing gain of the spreading sequences. Users are divided into two classes. The centerpiece idea is to synchronously assign N mutually orthogonal codes to class-1 users, and asynchronously assign quasi-orthogonal codes to class-2 users. The proposed architecture is realized through the DS-CDMA and multicode CDMA (MC-CDMA) techniques for class-1 and class-2 users, respectively, and the system capacity is considerably enhanced as compared with Sari et al.. The new approach still excels over Vanhaverbeke et al. when the number of class-1 users K/sub 1/ is large; but our desire is to expand system capacity. Compared with Sari et al. and Vanhaverbeke et al., the new design is able to support multirate applications, and is especially suitable for high-speed multimedia transmissions. Furthermore, the performance of the MC-CDMA system over an additive white Gaussian noise channel is evaluated for various primary codes and mutually orthogonal subcodes. It is shown that orthogonal Gold codes concatenated with Hadamard sequences yield the lowest bit-error rate when the signal-to-noise ratio lies between 0 and 30 dB.     

DS/CDMA with two sets of orthogonal spreading sequences anditerative detection

In this letter we introduce a direct-sequence code-division multiple access (DS/CDMA) concept which accommodates a higher number of users than the spreading factor N. Each of the available orthogonal spreading sequences of length N is assigned to one of the first N users which employ a common pseudonoise (PN) scrambling sequence. When the number of users K exceeds N, say K=N+M with MN. The proposed technique thus accommodates N users without any mutual interference and a number of additional users at the expense of a small signal-to-noise ratio penalty     

CONVOLUTIONAL CODED DS／CDEMA WITH TWO SETS OF ORTHOGONAL SPREADING SEQUENCES AND ITERATIVE DETECTION

In this letter a convolutional coded Direct-Sequence Code-Division Multiple Ac-cess(DS/CDMA) concept is introduced. The number of the users it can accommodate is greater than the spreading factor N. Each of the available orthogonal spreading sequences of length N is assigned to one of the first N users which employ a common Pseudo-Noise (PN) scrambling sequence. When the number of users K exceeds N, say K= N + M with M < N, the M additional users reuse M of those orthogonal spreading sequences but in combination with another PN scrambling sequence. An iterative multistage detection technique aided by Viterbi decoding is used to cancel the interference between the two sets of users when K > N. The proposed technique thus accommodates N users without any mutual interference and a number of additional users almost without signal-to-noise ratio penalty.     

Experimental evaluation of combined postdetection diversity andconcatenated channel coding

The combined effects of postdetection diversity reception and concatenated channel coding are experimentally evaluated for π/4-shift QDPSK signal transmission over a Rayleigh fading channel. Two-branch postdetection diversity reception using maximal ratio combining (MRC) and selection combining (SC) are considered. The concatenated channel coding uses the Reed-Solomon (15,k) code of GP(2 ⁴) as the outer code and the BCH (7,4) code as the inner code (k=9,11,13). Measured bit error rate (BER) performance results are presented under cochannel interference (CCI) and multipath channel delay spread, as well as additive white Gaussian noise (AWGN)     

Differential preamble detection in packet-based wireless networks

A novel hypothesis-based preamble detection method for uncoordinated, high-density packet-based communication over an additive white Gaussian noise channel is proposed and analyzed. Received samples are observed over a window of length equal to that of the preamble and a metric is computed for each sample shift of the window. A metric exceeding a noise dependent pre-computed threshold flags the presence of a preamble. The preamble sequence consists of concatenated sections of spreading sequences whose length is at most the coherence time of the channel. These sections are then differentially combined. A differential correlation-based detection is employed to locate the boundaries of the preamble. A theoretical framework is developed to provide exact analytical solutions for missing and falsely detecting a preamble using matrix analysis of quadratic Gaussian statistics. Furthermore, the robustness of the proposed methodology in a two path channel is studied. The effects of frequency and timing offsets on the system performance is evaluated. Simulation results are presented to validate the analytical expressions. Additionally, a performance comparison of the proposed differential detection scheme with that of a noncoherent square-law detector is presented.     

ML approaches to channel estimation for pilot-aided multirateDS/CDMA systems

This paper analyzes the asymptotic performance of maximum likelihood (ML) channel estimation algorithms in wideband code division multiple access (WCDMA) scenarios. We concentrate on systems with periodic spreading sequences (period larger than or equal to the symbol span) where the transmitted signal contains a code division multiplexed pilot for channel estimation. First, the asymptotic covariances of the training-only, semi-blind conditional maximum likelihood (CML) and semi-blind Gaussian maximum likelihood (GML) channel estimators are derived. Then, these formulas are further simplified assuming randomized spreading and training sequences under the approximation of high spreading, factors and high number of codes. The results provide a useful tool to describe the performance of the channel estimators as a function of basic system parameters such as number of codes, spreading factors, or traffic to training power ratio     

Quadriphase DS-CDMA with pulse shaping and the accuracy of the Gaussian approximation for matched filter receiver performance analysis

Probability of bit-error (P/sub e/) performance of asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems is analyzed. In particular, the effects of pulse shaping, quadriphase (or direct-sequence quadriphase shift keying (DS-QPSK)) spreading, aperiodic spreading sequences and the coherent correlator or, equivalently, the matched filter (MF) receiver are considered. An exact P/sub e/ expression and several approximations: one using the characteristic function (CF) method, a simplified expression for the improved Gaussian approximation (IGA) and the simplified improved Gaussian approximation (SIGA) are derived. Two main results are presented. Under conditions typically satisfied in practice and even with a small number of interferers, the standard Gaussian approximation (SGA) for the multiple-access interference component of the MF statistic and for MF P/sub e/ performance is shown to be accurate. Moreover, the IGA is shown to reduce to the SGA for pulses with zero excess bandwidth. Second, the P/sub e/ performance of quadriphase DS-CDMA is shown to be superior or equivalent to that of biphase DS-CDMA. Numerical examples with Monte Carlo simulation are presented to illustrate P/sub e/ performance for square-root raised-cosine (Sqrt-RC) pulses and spreading factors of moderate to large values.     

Concatenated orthogonal/PN spreading sequences and theirapplication to cellular DS-CDMA systems with integrated traffic

In this paper, we investigate the application of the concatenated orthogonal/PN spreading scheme for a cellular direct sequence code-division multiple access (DS-CDMA) system with integrated traffic. The performance of the system is evaluated in terms of user capacity. In order to incorporate traffic with a wide range of source rates, line rates (adjusted data rates before spreading) have to be selected for transmission. For traffic with source rates higher than the line rate of concern, we propose the use of concatenated orthogonal/PN spreading sequences to subdivide a high rate stream into parallel line rate streams. Therefore, in this paper, we first analyze the properties of the concatenated orthogonal/PN spreading sequences. The results are used to evaluate their performance for homogenous voice traffic in various cellular mobile environments with multipath fading, lognormal shadowing, and path loss. Our results show that the proposed spreading scheme offers a significant improvement in the forward link capacity as compared to using the conventional nonconcatenated long PN sequence, especially if the multipath fading is Rician (e.g., microcellular and indoor picocellular systems). Incorporating the notion of line rate, we then evaluate the performance of a system with integrated voice and video traffic. Special emphasis is placed on the effect of line rate selection on the overall capacity which leads to the optimal selection of line rates     

Large-system performance analysis of blind and group-blindmultiuser receivers

We present a large-system performance analysis of blind and group-blind multiuser detection methods. In these methods, the receivers are estimated based on the received signal samples. In particular, we assume binary random spreading, and let the spreading gain N, the number of users K, and the number of received signal samples M all go to infinity, while keeping the ratios K/N and M/N fixed. We characterize the asymptotic performance of the direct-matrix inversion (DMI) blind linear minimum mean-square error (MMSE) receiver, the subspace blind linear MMSE receiver, and the group-blind linear hybrid receiver. We first derive the asymptotic average output signal-to-interference-plus-noise ratio (SINR) for each of these receivers. Our results reveal an interesting "saturation" phenomenon: The output SINR of each of these receivers converges to a finite limit as the signal-to-noise ratio (SNR) of the desired user increases, which is in stark contrast to the fact that the output SINR achieved by the exact linear MMSE receiver can get arbitrarily large. This indicates that the capacity of a wireless system with blind or group-blind multiuser receivers is not only interference-limited, but also estimation-error limited. We then show that for both the blind and group-blind receivers, the output residual interference has an asymptotic Gaussian distribution, independent of the realizations of the spreading sequences. The Gaussianity indicates that in a large system, the bit-error rate (BER) is related to the SINR simply through the Q function