DSSS系统中自适应小波包干扰抵消器

本文提出了一种DSSS系统中基于小波包变换域的自适应干扰抵消算法（AWPT）,分析了小波包变抵抵消窄带干扰和脉冲干扰的机理,提出了优化准则和相应的自适应抵消算法,通过计算机仿真研究了其抗窄带和脉冲干扰的能力,并与传统的加窗DFT干扰抵消和子带变换干扰抵消作了比较。     

短波宽带OFDM的相对门限干扰消除器

短波宽带OFDM系统极容易受到拥挤频段上的窄带干扰,低信噪比工作条件下可能带来性能的急剧恶化。该文在Nilsson的宽带OFDM系统基础上设计了一种适合短波多径信道的相对门限干扰消除器。分析了低信噪比下相对门限的选取和噪声功率的估计问题,并对信道补偿做了改进,以减小噪声干扰。理论分析和仿真表明,低信噪比下,这种门限干扰消除器可以使系统在有干扰的条件下性能接近于理想干扰消除器的性能。     

Computer Modeling and Simulation of Communications Satellite Channels

Computer modeling of satellite communications channels is a valuable adjunct to analytical modeling and hardware simulation for predicting and verifying communications link performance. In the computer simulation approach, sampled signals are created in the computer and operated on by algorithms that simulate the effects of filtering, channel nonlinearities, interference, and noise. After passage through the simulated channel, the distorted signals are demodulated to determine the performance degradation introduced by the channel. This paper describes the approach used in simulating communications channels on the computer. Examples are given that apply to the communications satellite channel; however, the techniques described are applicable to general channel configurations.     

Computer-aided modeling, analysis, and design of communicationnetworks

Computer-aided design, analysis, and simulation techniques for communication networks are surveyed. The focus is on analytic and simulation techniques that are either amendable to, or require, implementation on a computer. Issues relating to the implementation of these techniques on a computer as well as their embodiment in software tools are addressed. Past and present work in these areas is surveyed, the application of these techniques to network performance modeling and analysis is discussed, and promising directions for future research are indicated     

Statistical model of downlink interference for the performance evaluation of CDMA systems

A statistical model of the downlink interference for the analytical performance evaluation of code-division multiple-access (CDMA) systems is proposed. Based on Wilkinson's approximation, the statistical model of the relative other cell interference is developed in closed form. The best base station (BS) selection in the shadowed environment with a correlation is taken into consideration. We show that interference statistics obtained by the proposed analytical model agree with simulation results. It is also shown that the proposed analytical model can replace Monte Carlo simulation in outage analysis.     

Narrow-band interference excision in spread-spectrum systems usingself-orthogonalizing transform-domain adaptive filters

Among many transform-domain interference excision techniques, transform-domain adaptive filtering has many advantages. It is based on a true optimization of some particular performance parameters such as the bit-error rate (BER). Moreover, it is insensitive to jammer frequency. However, transform-domain adaptive filtering also has the drawback of being incapable of tracking a rapidly changing interference because most adaptive algorithms require time to converge to the optimal solution. In this paper, a self-orthogonalizing transform-domain least mean square (SO-TRLMS) algorithm is used to speed up the convergence. Compared to a traditional transform-domain least mean square (TRLMS) algorithm, the SO-TRLMS algorithm can significantly improve the convergence rate of the LMS algorithm, thus making the transform-domain adaptive filtering technique more suitable for real-time processing. In order to show how the system performance is affected by various factors such as interference power and the transform used, this paper presents an analytical result for the BER performance that is applicable for arbitrary orthogonal linear transforms. Simulation results are also presented to demonstrate the validity of the analysis     

A Large Time-Bandwidth Product Signaling Technique for Nonwhite Noise Channels

AnM-ary, large time-bandwidth product signal design technique is described which is useful for signaling in channels characterized by narrow-band interference and/or wide-band noise impulses. Diversity is also provided, thereby making it a useful signaling technique for dispersive channels. The motivations for choosing this signal format are explained, and design procedures, with two candidate signal designs, are given. The performance of a fast-fast-Fourier-transform-based receiver, which employs an excision algorithm for reducing the effects of narrow-band interference, is investigated through computer simulation.     

Efficiency of error-control schemes for real-time wireless applications on the Gilbert channel

The design of a bandwidth-efficient physical layer for wireless access has always been a challenging task, due to the harsh environment, characterized by impairing phenomena such as radio interference, fading, and shadowing. With circuit switching, a bit-error rate suitable for real-time applications such as voice and video is guaranteed by adopting robust forward error correction (FEC) codes and proper power-budget margins to face fading problems. With this approach, automatic repeat request (ARQ) is used only for applications that require a much lower error rate and can tolerate high delays. The introduction of the packet technique allows the use of ARQ even for real-time traffic. We compare the efficiency of three error-recovering techniques in the presence of traffic with delay constraints, when the memory property of the wireless segment is represented by the Gilbert-Elliot channel. The techniques compared are FEC with interleaving, real-time ARQ, and erasure coding (EC). The comparisons are performed by using both analytical and simulation tools. Two new analytical models are introduced to evaluate the performance of FEC and EC. Simulation is used to validate the analytical results and to derive the performance of real-time ARQ. The numerical results show that when the channel memory increases well beyond the packet-transmission time, the performance of FEC impairs due to the limited interleaving depth, while ARQ and EC remain effective.     

Analysis of adaptive multistage interference cancellation for CDMAusing an improved Gaussian approximation

We consider a simple model for adaptive multistage interference cancellation within a CDMA system, and seek to develop an accurate analytical expression for the performance of this system. Previous work on interference cancellation has relied heavily on simulation techniques or a simple Gaussian approximation (GA). The standard GA ran lead to bit-error rate (BER) results which are optimistic for the conventional receiver, and this also occurs when the approximation is applied to the interference cancellation problem. Additionally, this approximation does not allow the second order effects of the multiple access interference (MAI) to be included in the performance estimates. Several improvements on the standard GA have been suggested which result in accurate performance results for a standard CDMA receiver. This paper presents an analytical expression for the probability of bit error for an adaptive multistage interference canceller, using an improved Gaussian approximation (IGA) for MAI. The BER at any stage of interference cancellation can be recursively computed from the signal-to-noise ratio (SNR), the statistics of the random powers of users, and the processing gain of the CDMA system. The performance of the resulting EER expression is compared with simulation results. Since the second order effects of MAI can be included, the analytical framework presented here can also be used to evaluate the performance of multistage interference cancellation in arbitrary fading environments, and we present results for the performance of interference cancellation in lognormal fading environments     

Radiometric detection of direct-sequence spread-spectrum signals using interference excision

Direct-sequence spread-spectrum (DS-SS) transmission are difficult to intercept. The theoretical analysis of intercept performance against such systems has always been a difficult task if the noise samples are correlated. Thus, many results are purely experimental and lack a generality which can only be achieved from theoretical considerations. The target system described is a DS-SS communications system operating environment which consists of additive white Gaussian noise and continuous wave interference. The interceptor uses a radiometer in conjunction with interference excision techniques to detect the presence of the target signal. It is shown that much of the interceptor's effectiveness is restored by the interference excision.<>     

An analytical method for assessing interference in interference environments involving NGSO satellite networks

An Erratum has been published for this article in International Journal of Satellite Communications 2000; 18(3):219. This paper presents an analytical approach to assess interference involving NGSO satellite networks. The proposed method can be implemented through numerical techniques, and is intended to perform the analysis of interference sensitivity to system and network parameters without the reliability problems and the very excessive computer time associated, sometimes, with direct computer simulation methods. The method is based on the knowledge of the probability density function of the position of a single satellite placed in an orbit with an arbitrary inclination, which is derived in the paper. To illustrate the applicability of the proposed method to complex interference environments, results for two specific situations are presented. Comparisons of the results obtained using the proposed method and those generated by a widely used commercially available simulation software have indicated that the proposed method can generate reliable and precise results with less computer time. Copyright © 1999 John Wiley & Sons, Ltd.     

Suppression of narrowband jammers in a spread-spectrum receiverusing transform-domain adaptive filtering

The author investigates the use of transform-domain adaptive filtering for the suppression of narrowband jammers in a direct-sequence (DS) spread-spectrum receiver. An input signal consisting of the DS signal, white Gaussian noise, and a narrowband jammer is transformed into the frequency domain where adaptive filtering acts to suppress the jammer. Weight leakage is used to allow jammer suppression while preserving the desired DS signal. Bit error rate (BER) results obtained by computer simulation are presented to illustrate performance for a single-tone jammer and for a jammer consisting of a second DS signal with a lower chip rate. These results are compared to those for a transform-domain exciser. Expressions for the converged tap weights are derived and the results are verified via the simulation. Finally, the convergence properties of the adaptive suppressor are illustrated     

天波超视距雷达空域干扰抑制

天波超视距雷达杂波会妨碍自适应波束形成抑制副瓣干扰."空阔区"脉冲压缩后作副瓣相消可以改善干扰的影响,而降维的旁瓣相消降低了算法的计算量.分析了所提方法的性能,仿真试验验证了所提方法运算量相对较少,干扰抑制效果好的特点.     

On the performance of interference cancelation in D2D‐enabled cellular networks

Device‐to‐device (D2D) communication underlaying cellular networks is a promising technology to improve network resource utilization. In D2D‐enabled cellular networks, interference among spectrum‐sharing links is severer than that in traditional cellular networks, which motivates the adoption of interference cancelation (IC) techniques at the receivers. However, to date, how IC can affect the performance of D2D‐enabled cellular networks is still unknown. In this paper, we present an analytical framework for studying the performance of two IC methods, that is, unconditional IC and successive IC, in large‐scale D2D‐enabled cellular networks using the tools from stochastic geometry. To facilitate the interference analysis, we propose an approach of stochastic equivalence of the interference, which converts the two‐tier interference (interference from the cellular tier and D2D tier) to an equivalent single‐tier interference. Based on the proposed stochastic equivalence models, we derive the general expressions for the successful transmission probabilities of both cellular uplinks and D2D links in the networks where unconditional IC and successive IC are respectively applied. We demonstrate how these IC methods affect the network performance using both analytical and numerical results. Copyright © 2016 John Wiley & Sons, Ltd.     

Single tone jamming elimination scheme of multicarrier spread spectrum system

The proposed scheme is based on Discrete Fourier Transform (DFT) domain processing. The key technology of this scheme is jamming parameters‘ accurate estimation and jamming reconstruction. Compared with the “threshold exciser”scheme.the proposed scheme can eliminate more jamming energy on the whole frequency band with the minimum loss of useful signal energy. As shown in the research and simulation, the proposed scheme is much better than the “threshold exciser” scheme, especially in the case of high power jamming whereas the “threshold exciser” scheme might be invalid.     

Performance of various multistage interference cancellation schemesfor asynchronous QPSK/DS/CDMA over multipath Rayleigh fading channels

The performance of multistage interference cancellation (MIC) and three combining techniques, i.e., multipath decorrelating (MIC-DECO), optimum combining (MIC-OPTM), and RAKE combining (MIC-RAKE) for asynchronous quadrature phase-shift keying/direct-sequence code-division multiple access over frequency-selective multipath Rayleigh fading channels is studied. The analytical bit-error probabilities of the MIC-DECO and MIC-OPTM are derived and shown to be in a good agreement with simulation results. Both analytical and simulation results show that the MIC-DECO, MIC-OPTM, and MIC-RAKE in a multiuser environment provide a good performance close to the ideal performance in a single-user system even in the presence of channel estimation error     

Minimum Mean-Square Error Timing Recovery Schemes for Digital Equalizers

Two algorithms are presented for optimum timing recovery in digitally implemented equalizers. The first one is a polarity-type algorithm based on the conventional minimum mean-square error criterion. A theoretical analysis is made to characterize the algorithm phase detector and evaluate its steady-state phase jitter variance. Influence of various channel and system design parameters on the algorithm performance is illustrated using phase jitter probability densities obtained by means of computer simulations. Interaction of the algorithm with decision-directed carrier recovery is also examined. It is shown that interaction with carrier recovery may considerably degrade the timing acquisition performance, and a second algorithm is then presented which eliminates this interaction. The second algorithm is based on the minimization of a modified mean-square error criterion which provides a measure of the intersymbol interference, independently of the carrier phase. Decision-directed timing and carrier recoveries are thus decoupled and the system startup period is considerably reduced. Phase detector characteristic and steady-state jitter performance of the second algorithm are evaluated by analytical means and computer simulations, as in the first algorithm.     

变换域窄带干扰检测算法研究

基于数据链的应用背景,在直接序列扩频系统下,研究了不同变换域窄带干扰检测算法的基本原理,包括基于一、二阶矩的门限算法、K谱线法、条件中值滤波法及连续均值剔除算法。通过仿真对比了不同算法的干扰检测抑制性能。仿真结果表明,在几种干扰检测算法中,连续均值剔除算法对于典型窄带干扰的检测能力最优,能够实现干扰的快速实时检测处理。     

Narrow-band interference excision in spread spectrum systems usinglapped transforms

In order to mitigate narrow-band interference in spread spectrum communications systems, novel communications receivers incorporating transform domain filtering techniques are designed. In this paper, lapped transforms are used to transform the received data signal to the transform domain wherein adaptive excision is performed. Transform domain detection algorithms, which yield bit decisions based on the remaining signal energy, are analyzed and, together with excision, are employed on a block-by-block basis to suppress single-tone and narrow-band Gaussian interference. System performance is analytically quantified in terms of the overall system bit-error rate (BER). Subsequent results are presented for a variety of channel conditions and compared to those obtained using excision algorithms based on orthonormal block transforms (Medley 1995). These results demonstrate the improved performance and increased robustness with respect to jammer frequency and bandwidth of lapped transform domain excision techniques relative to similar algorithms based on nonweighted block transforms     

Signal interception in non-Gaussian noise

The interception of weak signals in nonGaussian noise is discussed. The spectral correlation property exhibited by all cyclostationary signals is exploited to synthesize multi-cycle and single-cycle detectors which assure a superior tolerance (as compared to radiometric techniques) to one of the most challenging problems in interception, namely accommodating unknown and changing noise level and interference activity. The proposed detectors perform a maximum likelihood estimate of the noise level and use the estimate to form the detection statistic. To obtain some analytical information about the performance of the multi-cycle and single-cycle detectors, the deflection, which is a useful measure of the output (signal-to-noise ratio), especially appropriate for weak-signal SNR interception, has been evaluated. The receiver operating characteristics, carried out via computer simulation, confirm the superiority of the proposed cycle detector with respect to the traditional radiometer