Multiple-Access Performance Analysis of Combined Time-Hopping and Spread-Time CDMA System in the Presence of Narrowband Interference

We consider a combined time-hopping (TH) and spread-time (ST) multiple-access technique that uses an internal code. In this method, the duration of each bit is divided into $N_{s}$ frames. The outputs of the encoder and a pseudorandom (PN) sequence specify the number of the frame in which the data bit is transmitted in ST code-division multiple-access (ST-CDMA) form using the second PN sequence. We consider the correlator receiver, followed by the channel decoder. We obtain the performance of the combined method in additive white Gaussian noise (AWGN) and fading channels in the presence of multiple-access interference (MAI) and narrowband interference (NBI). We also consider the conventional ST-CDMA system and compare its performance with our method. The results indicate that the proposed method has much better performance while it has the same bandwidth and spectral efficiency as the conventional ST-CDMA system. In the new method, like in the conventional ST-CDMA system, an external error-correcting code can be applied for further performance enhancement.      

一种OFDM系统强窄带干扰消除方法

OFDM系统由于具有子载波的正交性从而可以充分利用频谱资源,鉴于当OFDM受到窄带干扰而影响较多的子载波时,会出现系统误码率性能严重恶化的现状。文中提出了一种OFDM系统窄带干扰消除技术,该技术在接收端检测出受干扰子载波,利用反馈信道告知发送端,并在发送端将受干扰的子载波不加调制的信息发送到信道中,而在信道中该部分子载波只受干扰信号的影响,接收端将干扰信息重构并储存,从而完成干扰消除确保正常通信。仿真和分析结果表明,该方法在不浪费频谱资源的情况下,能有效抑制OFDM系统的窄带干扰。     

超宽带系统在窄带干扰条件下的性能研究

超宽带（Ultra Wide-Band，UWB）系统发射信号的带宽在一个非常大的频段范围内，易与已存在的窄带无线通信系统的带宽形成重叠。因此，有必要研究UWB系统在频段重合范围内的抗干扰能力。文中首先分析了直接扩频超宽带系统在最小均方误差准则检测方式下，RAKE接收机的比特误码率（Bit Error Rate，BERl，然后研究了普通窄带系统的功率谱密度，最后做出了仿真分析。结果表明，在CM1信道传播下，窄带干扰对UWB系统不会造成很大影响，而在CM2信道传播下会照成一定影响，必须通过其他通信手段如信道编码来降低BER，实现通信的可靠性。     

OFDM系统的抗窄带干扰性能分析

目前,2.4 GHz非授权频段越来越拥挤,使得工作在此频段下的WLAN系统很容易受到窄带干扰的影响。针对这种情况,主要研究窄带干扰环境下OFDM通信系统的性能。通过理论分析和仿真可以得到,在窄带干扰比较严重的环境下,OFDM通信系统性能急剧下降。当干扰信号的中心频点不是OFDM符号基本频率的整数倍时,这一点尤其明显。因此,在窄带干扰比较严重的场合,必须要采取一定的抗干扰措施来保证系统的正常工作。     

Analysis of the Narrowband Interference Effect on OFDM Timing Synchronization

In OFDM systems, the symbol timing synchronization is needed to find an estimate of where the symbol starts. The most popular of the pilot-aided timing estimators is the one proposed by Schmidl and Cox (S&C) ["Robust Frequency and Timing Synchronization for OFDM," IEEE Transactions on Communications, vol. 45, no. 12, pp. 1613-1621, Dec. 1997]. Generally, the proper action of the timing estimator may be strongly affected by the presence of disturbances, like narrowband interference (NBI) signals. This paper investigates the effect of NBI signals, which may arise in the OFDM band as the spectrum becomes more crowded, on the timing synchronization for OFDM systems. The performance of the S&C symbol timing synchronizer is evaluated in an analytical way in the presence of narrowband interferers. Also, the probabilities of both missing and false detection of a training sequence are addressed. Further, simulations have been carried out to verify the validity of the approximations in the analysis.     

Digital Whitening Techniques for Improving Spread Spectrum Communications Performance in the Presence of Narrowband Jamming and Interference

Narrowband jamming and interference due to other users in spread spectrum communication systems can be effectively suppressed by using digital whitening. As a result, an impressive improvement in receiver performance can be obtained. The digital whitening is accomplished using a transversal filter whose coefficients are selected by either a Wiener algorithm or a maximum entropy algorithm. Filters obtained by use of these algorithms are evaluated for various jamming and signaling conditions and are found to exhibit comparable performance over a wide range of input signal-to-noise ratios.     

基于循环平稳性的异构网OFDM系统窄带干扰消除

在异构网正交频分复用系统中,异系统窄带干扰会造成系统性能的下降。该文提出一种基于信号循环平稳性的异系统窄带干扰消除算法,对干扰进行估计和消除,推导了干扰消除的信干噪比增益。仿真结果表明,与传统的线性预测滤波算法相比,该文提出的方法可以更为准确地估计窄带干扰信号,消除异系统干扰,提高系统性能。     

Narrowband Interference Avoidance in OFDM-Based UWB Communication Systems

In this letter we present a new method for mitigating narrowband interference in orthogonal frequency-division multiplexing-based ultra-wideband communication systems. The proposed narrowband interference avoidance (NBIA) method performs spectral shaping of the transmitted signal using binary signature sequences with minimum total squared correlation (TSC) to avoid the narrowband interfering signal. We illustrate the proposed method with plots that show the spectrum of the transmitted signal with and without NBIA, and also present numerical results obtained from simulations showing improvement in the bit error rate (BER) performance of the system when NBIA is employed.     

Unified Analysis of UWB Transmitted-Reference Schemes in the Presence of Narrowband Interference

Transmitted-Reference (TR) signaling, in conjunction with an autocorrelation receiver (AcR), offers a low- complexity alternative to Rake reception in ultrawide bandwidth systems. This paper provides a unified performance analysis of various TR schemes by developing an analytical framework based on the sampling expansion approach. Specifically, we derive the uncoded bit error probability (BEP) of different TR signaling schemes, including TR and differential TR (DTR) signaling valid for a broad class of fading channels. We consider both AcRs and modified AcRs with noise averaging. We further develop a quasi-analytical method as well as an approximate analytical method to extend the BEP analysis to include the effect of narrowband interference (NBI). We show that the approximate analytical method is particularly useful in obtaining BEP expressions that provide insight into the effect of NBI. We quantify the effects of NBI and channel power dispersion profile on the optimum integration interval of an AcR. Finally, we compare TR and DTR signaling in terms of their sensitivity to NBI.     

基于FB-FDE的地空通信窄带干扰抑制方法

提出了一种基于滤波器组的单载波频域均衡(FB-FDE)技术的窄带干扰抑制方法,该方法在多径时延较大的地空宽带通信中具有很强的窄带干扰抑制能力。从理论上详细分析了基于滤波器组的窄带干扰抑制技术能够克服基于FFT频域均衡缺点的主要原因,并在此基础上提出了基于自适应子带合并的算法。理论分析和仿真试验均表明,该方法抑制窄带干扰能力强,运算简单,适于工程实现。     

Performance Analysis of Narrowband Interference Suppression in Orthogonal Code ModulationSpread Spectrum System

1IntroductionInaspreadspectrumsystem,theuser'ssignalisspreadtoawidebandsignalfortransmission,thenthereceivedsignalswillbedecorrelatedbacktotheoriginalone.Theprocessinggainresultedfromthisprocessprovidestheadvantagesofperformanceimprovementtocombatint...     

一种改进的通信测距复合系统抗窄带干扰性能的研究

该文介绍了一种改进的通信测距复合系统,即应用自适应组合滤波器和Gardner于1986年的基于循环谱分析法的SPECCORR_TDOA估计模型,来改进系统的抗窄带干扰和高斯白噪声的能力,并建立了系统仿真平台。同时提出了应用峰值比对复合系统的抗干扰能力进行评估。仿真结果证明,改进的复合系统具有强抗干扰能力。     

超宽带通信系统及实现

全双工超宽带(UWB)通信冲激无线电收发信机由一个发射冲激脉冲的发射机与一个接收冲激脉冲的接收机组成。采用脉冲交错技术使发射机或接收机能同步于收发冲激无线电信号脉冲。脉冲交错也避免了收发冲激脉冲信号间的相互干扰。     

Performance Analysis of Optimum Combining Technique in OFDM Based Full Duplex Multiantenna DF Relay Network with Narrowband Interference

In this paper, optimum combining technique is applied to minimize the effect of Narrowband Interference (NBI) in Orthogonal Frequency Division Multiplexing based full duplex relay network. The NBI signal is assumed to be quasi-static over the duration of a transmitted signal. Multiple antennas are employed at Decode and Forward relay and destination nodes. The Probability Density Function of Signal to Interference Ratio at relay and destination nodes is derived using Hotelling’s T ² distribution. Analytical expression for the end-to-end outage probability of the proposed network is derived using the hypergeometric functions. As the weight vector of the optimal combiner is determined using the statistics of the interference channels, the performance of the proposed network becomes better than the network with maximal ratio combining.     

Coarse Acquisition Performance of Spectral-Encoded UWB Communication Systems in the Presence of Narrow-Band Interference

It is known that a major practical implementation challenge of ultra-wideband (UWB) receivers is the design of the coarse acquisition stage. Due to the fine time resolution of UWB signals, the acquisition stage has to acquire a large number of low-energy multipath components, with no or little knowledge of the state of the channel. In addition, the complexity further increases with the presence of narrowband interference due to the proposed spectral overlay. Our goal in this paper is to evaluate the affects of the lack of a priori knowledge of the channel state and the presence of narrowband interference during acquisition. Maximum-likelihood and maximum a posteriori procedures for estimation in the presence of narrowband interference are formulated, and two different interference mitigation techniques are evaluated. In particular, this paper considers UWB communication systems that use spectral encoding as both the multiple access scheme and the interference suppression technique. The qualitative results are, however, believed to be valid for any UWB system implementation. It is shown that the acquisition performance strongly depends on the amount of a priori knowledge of the channel state at the receiver, and on whether or not interference suppression is employed.      

OFDM系统中载波间干扰消除方法性能分析

OFDM系统面临的一个主要问题是对频率偏移的敏感性,频率偏移将导致载波闻干扰(ICI)的产生,从而大大 降低系统性能。对由频率偏移而导致的ICI进行了理论分析,并对抑止ICI的三种方法:自消除方法(SC)、最大似然估计方法 (MLE)及扩展Kalman滤波方法(EKF)进行了仿真和性能比较。     

Performance of Non-Polarized Noise Modulated Communications System in the Presence of Interference

The noise modulated non-polarized communication system, developed by us recently, is an ultra-wideband transmitted-reference system designed for secure interferencefree communications. By using ultra-wideband random noise to spread the signal and by using polarization diversity for transmitting the spread message and the reference signal, we make the transmitted signal appear totally featureless and noise-like. However, the system may encounter intentional and non-intentional interference since its operating bandwidth is very large. This paper derives analytical models to characterize system performance in partial-band jamming channels and channels containing narrowband interference. Models compare very well with simulations and results validate successful system operation under low signal-to-interference ratio conditions. Research also reveals that the center frequency of transmitted signal must be suitably protected to prevent link outage due to the presence of cross-interference terms. Since multipath acts as self-interference for communication systems, a new method which can improve system performance in multipath environments is also introduced in this paper.     

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。