Performance of CDMA overlay system using filtering and diversity

This correspondence considers an interference suppression scheme for a direct-sequence code-division multiple-access overlay system operating in a multipath Nakagami fading environment. The receiver employs suppression filters and diversity to mitigate the effect of multipath and narrow-band jammer interference. The system performance is presented in terms of the bit error rate with different system parameters such as bit energy, jammer-to-signal power, multipath, diversity, ratio of interference bandwidth to spread-spectrum bandwidth, and number of active users. Numerical results indicate substantial improvement in system performance.     

Performance degradation of analog FM system due to spread spectrum overlay

The investigation of spectrum overlay of a spread spectrum system on the existing narrowband FM broadcasting system is presented. The overlaid spread spectrum (SS) system is assumed to utilize direct sequence (DS) spreading, using maximal length pseudorandom sequences. We studied the performance degradation of the analog FM system due to the interference produced by the SS signal, through laboratory subjective and objective measurements, for various types of spreading scenarios and for different carrier frequency differences (/spl Delta/f). The RF protection ratios for the FM receivers are derived, along with SINAD measurements. Finally, these experimental results have been compared with the theoretical study of the FM receiver's audio frequency SNR output due to SS interference.     

Analog PAL-G signal degradation due to spread spectrum overlay

Performance degradation of an analog PAL-G signal due to direct sequence spread spectrum overlay is examined. An analytical expression between RF TV protection ratio (CIR) and baseband unweighted signal-to-noise ratio (SNRv), for co-channel spread spectrum and noise interference, is derived. Computer analysis results are presented and compared to experimental measurements for different spread spectrum RF bandwidths and carrier frequency offsets between the analog and digital signal. Image quality degradation is also presented and associated to different level of spread spectrum interference.     

Approximate analysis of narrow-band interference rejectiontechnique in CDMA spread spectrum systems using nonlinear predictionfilters

The performance of code-division multiple access (CDMA) spread spectrum systems using nonlinear prediction filters in the presence of narrow-band interference is approximately analyzed. Closed-form approximate analytical expressions for the performance improvement are derived. Also, the closed-form approximate analytical results are compared with simulated results by numerical examples. The comparison results show that the analytical results are valid when the interference bandwidth is small     

基于PL3200的CDMA扩频电力线载波通信系统设计

介绍CDMA扩频通信的基本原理、PL3200型SoC的结构及其载波通信功能模块,提出一种基于PL3200的CDMA扩频电力线载波通信系统的设计方案.     

The capacity of a spread spectrum CDMA system for cellular mobileradio with consideration of system imperfections

There has been much interest in the use of spread spectrum code division multiple access (CDMA) techniques for cellular mobile radio. To date, spread spectrum has been used mainly for military applications, in which the inherent transmission security and immunity to deliberate jamming are important. Spread spectrum systems, however, possess various other features such as multiple access and multipath rejection capability, which make their use attractive within the mobile radio environment. However, the current interest has been principally motivated by the work of Gilhousen et al. (see IEEE Trans. Vehic. Technol., vol.VT-40, no.2, p.303, 1991) in which it is claimed that the CDMA option may offer capacity improvement over more conventional frequency and time division multiple access, FDMA and TDMA, techniques. Within this paper, the relative capacities of a basic FDMA and CDMA system are examined. It is shown that, in the absence of capacity-enhancing features such as voice activity detection and cell sectorization, the capacity of each system is comparable. The paper then assesses the sensitivity of the CDMA system to typical propagation conditions, power control errors, and realistic antenna patterns and shows that the capacity of a CDMA system may be significantly reduced under nonideal conditions     

CDMA通信中多址序列相关性的研究及仿真

扩频序列设计和选择是码分多址(CDMA) 扩频通信的关键技术之一,扩频码序列的设计就是构造不同结构的具有良好相关性的伪随机序列来满足CDMA 系统的要求.现主要研究了应用于CDMA通信中的m序列、Gold序列和Kasami序列的原理、性能和构造方法,且基于MATLAB软件M语言编程以上序列的实现和相关性分析,并比较了其各自特点分析了其在不同环境下的适用性.     

The coarse acquisition performance of a CDMA overlay system

The coarse acquisition performance of a code-division multiple-access (CDMA) overlay system operating in a mobile communications environment is considered. Specifically, a CDMA system supporting communication between several mobile units and one base station shares the frequency band with an existing narrowband user. At the CDMA base station receivers, narrowband interference rejection filters are used to suppress the narrowband user's energy. It is demonstrated that in a nonfading environment the presence of the narrowband user does not severely affect the acquisition performance when the ratio of its bandwidth to the CDMA bandwidth is small. As the ratio becomes larger, the acquisition performance degrades, but the use of the interference rejection filter still significantly decreases the time to acquire. When flat Rician fading is introduced, the acquisition performance of the overlay system degrades, especially when the power in the direct component is small     

DCT域的数字指纹CDMA扩频追踪

以DCT变换为基础,结合了数字图像JPEG压缩和通信CDMA技术的特点,提出了一种基于双DCT变换、扩频技术的二维数字指纹追踪算法。通过像素值和DCT系数两种平均合谋方式攻击和追踪性能分析验证,该追踪方案能够有效抵抗多用户合谋和抗JPEG压缩,同时具有较高的峰值信噪比和良好的追踪特性。     

Design of spread spectrum multicode CDMA transport architecture formultimedia services

We investigate a new application of the well-known spread spectrum code division multiple access (SS-CDMA) techniques to multimedia services related to the development of the next-generation wireless mobile networks interconnecting with a wireline ATM-based broadband network. Such services allow users to share novel multimedia applications without any geographical restrictions. However, since the mobile radio channel has a fixed limited bandwidth, the traditional SS-CDMA system may not be sufficient to accommodate the variable bit rate (VBR) multimedia services requested by multiple mobile users simultaneously. Moreover, the traffic load at the base station can change dynamically due to the time-varying throughput requirement of these requested multimedia services. To tackle this difficulty, a multicode CDMA (MC-CDMA) technique is proposed to provide multirate multimedia services by varying the number of spreading codes assigned to each user in order to meet its throughput requirement. In MC-CDMA, a spreading code can be used to transmit information at a basic bit rate. Users (video or data) who need higher transmission rates can use multiple codes in parallel. Meanwhile, the maximum available number of codes in the MC-CDMA system is still limited. Hence, a cost-effective dynamic code allocation scheme has then been proposed to dynamically assign an appropriate number of codes to each user for achieving the maximum resource utilization for multiuser multimedia services via the mobile radio channel. Finally, a number of real multimedia titles generated from the well-known MacroMind Director are conducted to evaluate performance     

频率复用DS/CDMA系统中自适应盲多用户检测的一种方法

该文给出一种工作于强窄带干扰(NBI)多径衰落信道中DS/CDMA系统盲多用户检测接收机模型。它具有RAKE接收机的基本结构,在每一条并行支路中利用MMSE准则跟踪各路径信号。因此具有抗多径衰落,同时抑制NBI和多址接入干扰(MAI)的能力。模拟结果证明,它的性能优于未考虑NBI抑制的多用户检测接收机。     

Novel spatial spread spectrum based fiber optic CDMA networks forimage transmission

Novel code division multiple access (CDMA) fiber optic networks based on spatial frequency spread spectrum for image transmissions are proposed. Two key technologies are the parallel fiber optic transmission of spatially encoded images and parallel access to image data through optical spatial encoding and decoding. The temporal signature sequences used in conventional time-domain CDMA are replaced by two-dimensional (2-D) signature patterns to encode and decode binary image pixels. This enables the fully parallel access and transmission of images. The fundamental rules and methodology to construct optical orthogonal signature patterns (OOSP) are presented. Furthermore, it is shown that the all-optical implementation of the proposed system is feasible by utilizing optically addressable spatial light modulators in both the spatial encoder and the decoder along with multicore fibers as the parallel image transmission medium. The predicted overall throughput can reach 10 Tb/s     

Spectral overlay of multicarrier CDMA on existing CDMA mobilesystems

A spectral overlay of a narrow-band code division multiple access (CDMA) system and a wide-band multicarrier CDMA system is considered as a means for existing CDMA mobile networks to evolve into a future CDMA network. The achievable joint capacity of the overlaid system is provided and compared with that of another network evolution strategy of spectrally overlaying wide-band single-carrier CDMA to the existing CDMA systems     

Multicarrier CDMA overlay for ultra-wideband communications

In this letter, the performance of multicarrier code-division multiple-access (CDMA) systems is studied in the presence of narrowband interference for future ultra-wideband (UWB) communications. A Nakagami fading channel is assumed, and notch filters along with diversity techniques are used in the multicarrier CDMA receiver. A complete performance analysis of error probability is given. It is shown that when the number of subcarriers jammed by narrowband interference is small, the multicarrier receiver without notch filters can work well, due to the gain of frequency diversity from nonjammed subcarriers. On the other hand, when the number of subcarriers jammed by the narrowband interference is large, using notch filters can improve the multicarrier system performance significantly.     

Multicarrier CDMA for cellular overlay systems

A code-division multiple access (CDMA) cellular overlay system is investigated, employing the idea of multicarrier CDMA, which has previously received significant attention as an alternative to traditional single-carrier CDMA. Overlay is pursued here as a means of long-term transition from narrowband cellular to CDMA cellular. A major result of this paper is the demonstration that the use of multicarrier CDMA in a fading channel is particularly beneficial to the narrowband system, as the CDMA users can reduce their transmitted powers as a result of diversity. Another significant conclusion is that the use of transmitter notching in the CDMA system in order to avoid active narrowband users outperforms a strategy in which a narrowband user is avoided by simply dropping the particular carrier which overlays it. Finally, results on the use of the minimum mean-squared error (MMSE) receiver in a fading channel are extended for use in the overlay scenario     

Adaptive lattice filters for CDMA overlay

This paper presents the behavior of reflection coefficients of a stochastic gradient lattice (SGL) filter applied to a code division multiple-access overlay system. Analytic expressions for coefficients for a two-stage filter are derived in a Rayleigh fading channel with the presence of narrow-band interference and additive white Gaussian noise. It is shown that the coefficients of the lattice filter exhibit separate tracking and convergent properties, and that compared to an LMS filter, the lattice filter provides fast rate of convergence, while having good capability of narrow-hand interference suppression     

基于ISCP-DPSK调制的直接序列扩频技术

使用符号内连续相位差分相移键控(ISCP-DPSK)调制的直接序列扩频方法可以在实现扩频抗干扰的同时保留ISCP-DPSK调制信号的准恒包络特性和优良的频谱特性,有利于非线性和功率受限的应用场合。由于采用非相干的信号解扩解调方法,避免了低信噪比下的载波和相位估计与跟踪,简化了系统设计。计算机仿真表明,基于ISCP-DPSK调制的直接序列扩频能有效对抗本振偏离、多普勒频移等引起的符号间相位变化影响,8倍扩频和16倍扩频的增益仅与理论值分别相差0.1 dB和0.2 dB。     

TIME DOMAIN PROCESSING MODE SPREAD SPECTRUM SYSTEM

The construction and specifications of a surface acoustic wave storage correlator are described. A time domain processing mode spread spectrum system is presented. An analysis of the interference rejection for this system is provided. The formula for calculating the probability of error of the system is given. The experimental results agree with the theoretical analysis.     

直序扩频系统中扩频码同步技术的研究

针对扩频通信中伪随机序列的快速捕获问题,文中提出了扩频信号快速捕获方法,来解决低信噪比条件下伪码序列的捕获问题.首先对直接扩频通信系统的基础理论做了探讨,而后重点研究了两种基带扩频信号同步捕获方案--序列相位搜索捕获法和不连续相位滑动相关法,序列相位搜索捕获法主要适用于m序列码周期较短的情况,而不连续滑动相关法则克服了...