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.     

A CDMA overlay system using frequency-diversity spread spectrum

The frequency bands currently used by existing narrow-band users might be shared with a code-division multiple-access (CDMA) spread-spectrum (SS) overlay system. Thus, the spectral efficiency is improved, providing more capacity for future personal communications services. Since both narrow- and wide-band signals interfere with each other, an SS modulation scheme with a good resistance to narrow-hand interference results in an increased number of acceptable overlay users. We study a frequency-diversity SS modulation scheme for which optimal detection in the presence of narrow-band interference is easy to implement. The acceptable number of overlay users is evaluated and compared to that of conventional direct-sequence SS (DS-SS) modulation schemes with and without interference rejection filters. The proposed system also presents the following advantage: by suppressing transmission of replicas where narrow-band signals (NBSs) are present, the mutual interference can be avoided completely     

Performance of DS spread spectrum systems

In a direct sequence (DS) spread spectrum communication system the processing gain is approximately the ratio of chip rate to the data rate. Here a more accurate formulation is obtained in terms of signaling, system, and noise parameters. It is useful for performance comparisons since it is valid for all possible parameter values.     

Performance of MSK spread spectrum systems

An exact expression for the processing gain of a direct sequence spread spectrum communication system using MSK spreading is derived. This extends previous results for systems using QPSK spreading.     

多载波扩频系统的载波频率偏移性能分析

讨论了在载波频率偏移作用下多载波扩频系统的误码性能。详细研究了载波频率偏移对系统的信噪比和误码的影响。并且用MATLAB进行仿真。研究结果表明多载波扩频系统对很小的相对频率偏移也是非常敏感的,载波频率偏移引起的系统性能下降不仅与频率偏移量有关而且与子载波个数有关。     

扩频通信系统中Rake接收性能仿真研究

在扩频通信中,Rake接收是抵抗多径衰落的有效方法。本文首先介绍无线移动通信的信道特性,然后对Rake接收的基本原理和接收机结构进行详细描述,并对Rake接收性能进行了仿真比较。仿真结果表明,在多径信道条件下,Rake接收方式能很好的改善接收系统误码性能;采用GOLD序列扩频比m序列扩频方式时,Rake接收方法性能提高的更明显。     

M进制直扩系统在平坦衰落下的性能分析

分析了采用RS(n，k)编码的一种在MSK调制方式下基于循环移位的M进制直接序列扩频通信系统在Rayleigh衰落信道中的性能，给出了准确的误码率公式。并通过SPW软件仿真给出了该系统在Rayleigh衰落环境下的性能曲线，仿真得到的误码率与公式推导的结果完全吻合。     

Performance degradation of Jaumann absorbers due to curvature

The normal-incidence flat-plate performance of radar absorbers can seldom be realized when the absorbers are used on cylindrical structures. This is also true of Jaumann absorbers, which consist of alternating layers of resistive sheets and light-weight spacers. A method based on Richmond's stepping theory [4] is used to predict the performance more accurately for cylindrical structures.     

Performance degradation of DOA estimators due to unknown noisefields

A statistical performance analysis of subspace-based directions-of-arrival (DOA) estimation algorithms in the presence of correlated observation noise with unknown covariance is presented. The analysis of five different estimation algorithms is unified by a single expression for the mean-squared DOA estimation error which is derived using a subspace perturbation expansion. The analysis assumes that only a finite amount of array data is available     

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...     

Rician慢衰落信道下的正交循环码M元扩频系统性能分析

本文提出了一种基于正交循环码的M元扩频系统,在发端将一条原型扩频码循环移位构成M个相互正交的扩频码,实现M元扩频,而接收机利用一个时频变换域复数匹配滤波器就可实现正交循环码M元非相干解扩解调.与传统的M元扩频系统相比较,正交循环码M元扩频系统具有很低的复杂度.本文推导出该接收机在Rician慢衰落信道条件下的误比特率的计算公式,给出并分析了计算机仿真结果.     

Performance degradation of phase-modulated systems due to nonlinear phase noise

The error probability is calculated for phase-modulated systems with nonlinear phase noise. Using the assumption that the phase of amplifier noise and nonlinear phase noise are independent of each other, the error probability and penalty are calculated for both phase-shift keying (PSK) and differential phase-shift keying (DPSK) systems. The mean nonlinear phase shift must be less than about 1.00 and 0.63 rad for a penalty less than 1 dB for PSK and DPSK systems, respectively.     

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.     

Bit-error rate of PSK heterodyne optical communication system and its degradation due to spectral spread of transmitter and local oscillator

In a PSK heterodyne optical communication system, the FM noise of the transmitter and local oscillator degrades the bit-error rate (BER). A theory is presented giving the BER of such a system considering the FM-noise effect. To verify the theory, BER measurement is performed using a simulation model of the PSK heterodyne system.     

正确认识扩频通信系统

随着计算机网络的迅速发展,扩频通信由于其便于为计算机网络提供物理接口信道而得到日益广泛的应用。然而有些厂家为一己私利误导用户,宣称：扩频通信系统在国外是免许可的,台站不用审批,言外之意在国内也不用办理设台审批手续;即使无线电管理部门进行监测,也难以发现,因为其信号可以在噪声下传输;同时扩频通信不用审批的原因是系统不怕干扰,所以也就不用无线电管理部门管理。上述的种种说法给我国实施对扩频台站的审批管理加大了难度,使扩频通信系统的干扰矛盾日趋增多,造成空中电波秩序的混乱。本文从扩频通信系统的基本原理出…     

FM spectrum of video signals

A simple model for the FM spectrum of color TV signals is presented; based on the assumption that the luminance and chrominance components are uncorrelated Gaussian processes. Unlike existing models of the video FM spectrum, the present model accounts for the important spectral components at the color subcarrier frequency and its harmonics.     

Performance of sequential estimation for direct sequence spread spectrum code acquisition

The Sequential Estimation (SE) technique introduced by Ward was designed for the acquisition of pseudo-noise (PN) signals. It proves to be an effective model in medium SNRs as long as inverted PN sequences are not encountered. Recognizing that negative data bits invert PN sequences in spread spectrum transmissions, Chiu and Lee developed an Improved Sequential Estimator (ISE) that processes both types of sequences. The ISE design, however, erroneously despreads the incoming signal by inverting it during negative bit acquisitions. In some applications, this could be a problem, hence a Dual Correlating Sequential Estimator (DCSE) is proposed in this paper. The DCSE detects modulation errors by gathering correlation measurements from resident SE and ISE subsystems and corrects for them with an inverting mechanism. Key performance parameters such as mean timing and the variance of acquisition for the sequential estimator designs are derived via the generalized signal flow graph method and verified through simulation. In an additive White Gaussian noise (AWGN) environment, the DCSE design is shown to outperform the SE for every tested signal-to-noise ratio (SNR).Abbreviations SE sequential estimation - PN pseudo-noise - ISE improved sequential estimator - DCSE dual correlating sequential estimator - AWGN additive white gaussian noise - SNR signal-to-noise ratio     

Performance analysis of spread spectrum packet radio network withchannel load sensing

A continuous-time Markov-chain model for an asynchronous communication spread-spectrum code-division-multiple-access (CDMA) packet radio network is developed. The network is composed of mutually independent users. The receiver-based code is considered; a terminal with a packet to send looks up the destination's code and transmits on that code. Each user senses the channel load and refrains from transmission if the channel load exceeds the channel threshold. The model makes it possible to study the threshold effect of channel load on the performance of the CDMA packet radio network. Improvements in performance of spread-spectrum packet radio networks due to channel-load sensing are shown. Steady-state results for throughput are obtained     

Performance analysis of instantaneous frequency-based interferenceexcision techniques in spread spectrum communications

Jammers characterized by their instantaneous frequencies can be effectively mitigated in direct sequence spread spectrum communications by using open-loop adaptive excision filters. The primary requirement for these filters is that they must possess a notch in tune with the jammer instantaneous frequency (IF) to annihilate the interference power at every time sample. The interference time-varying frequency can be obtained using existing IF estimators, including quadratic time-frequency distribution methods. Without focusing on any specific estimator, we develop expressions for the receiver performance using a general class of multiple-zero FIR excision filters and show the dependence of the bit error rate (BER) on the filter order and its group delay. The effect of inaccuracies in the jammer instantaneous frequency information on the receiver performance is considered and evaluated as a function of the filter notch bandwidth. The latter is defined by the filter zero multiplicity, which is shown to be an important factor in the analysis of the correlator signal-to-noise ratio (SNR)