Impact of co‐channel interference on performance of dual‐hop wireless ad hoc networks over α−μ fading channels

In this work, we investigate the performance of a dual‐hop cooperative network over α?μ fading channels with the presence of co‐channel interference (CCI) at both the relay and destination nodes. Amplify‐and‐forward (AF) relaying is considered in the relay node. The upper bound of the signal‐to‐interference‐plus‐noise ratio (SINR) of the dual‐hop relay link is used to determine the system performance. The probability density function (PDF) and the cumulative distribution function (CDF) of the upper bound of the SINR are analyzed. The system performance is determined in terms of the outage and error probabilities. Numerical results are used to present the performance analysis of the system.     

噪声跟踪干扰检测算法性能分析

基于认知无线电中协作频谱感知的思想,提出了一种跳频通信中噪声跟踪干扰的检测算法。首先采用能量检测算法,研究了干扰条件下单跳信号的检测性能。在此基础上,应用“k out of n”准则,在决策融合模块实现对噪声跟踪干扰的检测,推导了AWGN信道下噪声跟踪干扰的检测性能。理论分析和仿真结果表明,随着信干噪比的逐渐减小,对于单跳信号和噪声跟踪干扰的检测概率均逐渐增大;而在相同信干噪比情况下,噪声跟踪干扰的检测概率较单跳信号的检测概率得到了提高。      

采用局部特征尺度分解的跳频信号参数盲估计算法

针对现有跳频信号参数盲估计算法存在时间分辨率和频率分辨率矛盾这一问题,提出了一种基于局部特征尺度分解的跳频信号参数估计新算法。该算法将跳频信号迭代地分解成若干个内禀尺度分量并进行降噪处理,然后对其最大瞬时幅度进行小波变换和傅里叶变换即可估计出跳频信号的跳变时刻和跳频周期,最后根据得到的跳变时刻和跳频周期可以进一步估计出跳频频率集。该算法不受时频不确定性原理的影响,能够在未知先验知识的条件下估计出跳频信号的跳周期、跳变时刻和跳频频率集。最后通过仿真验证了算法的有效性。      

Design and analysis of a fast frequency-hopped DBPSK communicationsystem. I. System description and hop timing tracking loop analysis

Design and performance analyses of a fast frequency-hopped (FFH) spread spectrum communication system employing differential binary phase shift keying (DBPSK) modulation and differentially coherent demodulation are presented. The receiver utilizes a hop timing tracking loop to lock the hop clock. Through this tracking loop, the differentially coherent demodulation of an FFH signal is made possible. The authors present the system model of an FFH/DBPSK system. A digital, full-time early-late gate timing error estimator is investigated. The tracking loop is shown to be a Markov chain, and various performance characteristics of the tracking loop are studied     

Frequency-hopped spread-spectrum transmission with band-efficientmodulations and simplified noncoherent sequence estimation

Frequency-hopped spread-spectrum transmission using band-efficient modulations that are phase-continuous during each hop, is presented. A range of system parameters is considered, including signaling spectrum, reception, system complexity, and performance in the presence of noise and jamming. The particular cases where the hopped modulation is minimum-shift-keying (MSK), duobinary minimum-shift-keying (DMSK), or tamed-FM (TFM), are studied in detail. Results are presented for various modulation indexes, rectangular and raised cosine pulse shapings, and a range of hop interval lengths. Sequence estimation on a hop-by-hop basis is considered. The noncoherent likelihood sequence receiver must keep all possible paths, and so the computation and complexity becomes large for system transmitting many bits per hop. Therefore, a simplified noncoherent Viterbi-like sequence estimation algorithm with reduced complexity is introduced. System performance has been evaluated in Gaussian noise, partial-band jamming and multiple-tone jamming, using bounds and a system simulation. The compact nature of the hopped spectrum, when a number of bits are transmitted per hop, offers greater spectrum utilization and the prospect of improved performance in the presence of multiple-tone jamming or interference     

短波差分跳频系统抗部分频带干扰性能分析

对接收端采用非相干平方律能量检测器及维特比译码器的短波差分跳频通信系统,在无衰落信道和频率非选择性慢衰落信道下抗部分频带干扰的性能进行了理论分析.若信道存在衰落,则假设每跳所经历的衰落过程是相互独立的,且服从瑞利分布.部分频带干扰被模拟为加性高斯噪声,分析中考虑了背景热噪声.结果表明:差分跳频相邻两跳频率之间的相关性为系统提供了良好的抗部分频带干扰的能力.若忽略背景热噪声,则当信干比为20dB时,在无衰落信道下最坏情况比特误码率可达10-5,而在频率非选择性瑞利慢衰落信道下最坏情况比特误码率可达10-3.     

Bit error rate performance of orthogonal frequency‐division multiplexing relaying systems with high power amplifiers and Doppler effects

This paper analyzes the bit error rate performance of orthogonal frequency‐division multiplexing systems in mobile multihop relaying channels. We considered the uplink scenario and quantified the effects of mobile channel impairments such as Doppler shift due to user mobility per hop, high power amplifier distortions when amplifying the transmitted/relayed orthogonal frequency‐division multiplexing symbol per hop, and the cumulative effects of these impairments on multihop relaying channels. It was shown that the resulting intercarrier interference due to the cumulative effects of the phase noise generated by these impairments per hop becomes very significant in a multihop relaying communication system and severely degrades the bit error rate performance of the system. Simulation results agree well with and validate the analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Global hop length analysis for millimeter-wave radio links

For the CCIR 14-rain climatic zones of the globe, we present a simplified hop length versus fade margin analysis with link reliability as a parameter. The analysis uses Laws-Parsons values for the a and b parameters of A(dB/Km)=a R^b (mm/hr), and considers the two cases of (i) limited rain-cell and (ii) “entire hop in rain”. The result is a family of fade margin vs. hop length curves for various reliability objectives, obtained for each of the 14-rain zones at a frequency of 50 GHz. A simple frequency scaling rule is also devised to enable similar analysis at frequencies in the range 30–70 GHz. It is particularly concluded that an extended hop length of 10–20 Km is possible with reasonable reliability if the reduced cell-size concept is applied. If the entire hop is in rain, a limited hop length of one to five kms can't be exceeded even with modest reliability. It is also demonstrated that high resolution global rain map, together with an accurate cell size definition are mandatory for reliable radio link design at mm-wave lengths.     

Opportunistic Decode‐and‐Forward Cooperation in Mixed Rayleigh and Rician Fading Channels

We consider a two‐hop multiple‐relay network implemented with opportunistic decode‐and‐forward cooperative strategy, where the first hop and second hop links experience different fading (Rayleigh and Rician). We derive the exact expressions of end‐to‐end outage probability and analyze the approximate results in high signal‐to‐noise ratio region. The analysis shows that the same diversity order can be achieved even in different mixed fading environments. Simulation results are provided to verify our analysis.     

Turbo codes for noncoherent FH-SS with partial band interference

Turbo codes are investigated in a slow frequency-hopped spread spectrum (FH-SS) system with partial band jamming. In addition, full-band thermal noise is present. The channel model is that of a partial-band jammer in which a fraction of the frequency band is jammed and the remaining fraction is unjammed. This paper focuses on the implementation and performance of a modified turbo decoder for this model. We refer to the knowledge that each transmitted bit is jammed as channel state information. We consider cases of known or unknown channel state and variable number of bits per hop. Our approach is to modify the calculation of branch transition probabilities inherent in the original turbo decoder. For the cases with no side information and multiple bits per hop, we iteratively calculate channel state estimates. Analytical bounds are derived and simulation is performed for noncoherent demodulation. The performance of turbo codes is compared with a Reed-Solomon and a concatenated code comprised of a convolutional inner code and Reed-Solomon outer code     

基于STFD&SCMUSIC的多跳频信号DOA估计与网台分选

为了在欠定条件下利用跳频信号的空域特征参数进行网台分选,该文提出一种基于STFD&SCMUSIC的跳频信号DOA估计算法。首先在时频域提取跳频信号的有效跳(hop),并建立该hop的空时频矩阵(STFD);然后在MUSIC算法基础上,利用噪声子空间降维思想构造SCMUSIC空间谱;最终通过半谱搜索实现DOA快速估计,进而利用DOA信息完成信号的分选;同时为了提高低信噪比算法的性能,采用形态学滤波的方法对时频图进行修正,在修正的时频图上完成跳频信号有效hop的提取。理论分析和仿真实验表明了该算法的有效性和良好的估计性能。      

Performance of FHSS systems employing carrier jitter againstone-dimensional tone jamming

The performance of a frequency-hop spread-spectrum system employing carrier jitter against one-dimensional tone jamming (n=1 band multitone jamming) is investigated. First, noncoherent BFSK signaling under continuous-wave (CW) tone interference with arbitrary frequency offset is analyzed. A closed-form expression is derived for the error probability when there is one interfering CW tone and the background noise is negligible. When the background noise is significant, an expression involving one numerical integration is derived for the probability of error. It is shown that an interfering CW tone with power less than that of the signal can still cause errors with significant probability for certain ranges of carrier offsets. Next, the authors apply these results in analyzing the performance of a FHSS communications system under one-dimensional tone jamming when the communicator pseudorandomly jitters his carrier frequency from hop to hop. Two different methods of carrier jittering are considered. It is found that one of the schemes offers approximately a 3 dB gain in signal-to-noise ratio over a system without carrier jittering while the other scheme offers no significant gain     

同信道干扰条件下的多天线放大转发中继中断概率分析

该文研究了基于波束形成技术的双跳多输入多输出(MIMO)放大转发(AF)中继系统的中断概率,该系统在发射端、中继端和接收端都配置了多根天线。假设每条链路的发射端采用最大比传输(MRT)技术,接收端采用最大合并比(MRC)技术,该文得出了中继端受到同信道干扰时的信干噪比(SINR),推导了基于固定增益中继方案的中断概率(OP)闭合表达式。计算机仿真结果不仅验证了性能分析的有效性,而且还分析了关键参数对系统性能的影响以及配置多天线带来的好处。     

Effect of imperfect channel state information and co‐channel interferences on two‐hop fixed gain amplify‐and‐forward relay networks with beamforming

This letter investigates the joint effects of imperfect channel state information and co‐channel interferences on a two‐hop fixed gain amplify‐and‐forward (AF) relay network with beamforming. Specifically, the analytical expressions of the outage probability and the average symbol error rate for the AF relaying are derived. Moreover, the asymptotic analysis at high signal‐to‐noise ratio is also presented to reveal the diversity order and array gain of the considered AF relay system. Finally, computer simulations are given to confirm the validity of the analytical results. Copyright © 2014 John Wiley & Sons, Ltd.     

Symbol error probability evaluation for PSK modulation schemes in generalized non‐Gaussian noise channels

The average symbol error probability (ASEP) performance over the faded radio frequency (RF) link when the noise is additive in nature and has generalized Laplacian distribution is evaluated in this paper. The additive white generalized Laplacian noise (AWGLN) distribution can model different impulsive and non‐Gaussian noise environments often encountered in practice and provides a robust alternative to Gaussian distribution. A new expression for evaluating the exact symbol error probability over a multilevel M‐ary PSK‐modulated AWGLN channel is derived. Based on the obtained expression, the ASEP for the single‐hop RF link that models the shadowing and fading conditions over the RF channel by a generalized –K (GK) distribution is derived. Further, the error performance of a decode‐and‐forward relayed and GK‐distributed two‐hop RF link is discussed, and the results are validated through numerical plots.     

Iterative estimation and decoding for FH-SS with slow Rayleighfading

The performance of turbo codes is investigated in a frequency-hopped spread-spectrum (FH-SS) system with full-band thermal noise and Rayleigh fading. For cases where the data rate exceeds the hopping rate (i.e., there exists multiple bits per hop) and fading side information (SI) does not exist, our approach is to iteratively estimate the fading levels. Simulation is performed for coherent and noncoherent reception, variable number of bits per hop, and cases where fading SI is available or unavailable to the decoder. It is shown that iterative channel estimation performed in conjunction with iterative decoding can improve the overall decoding performance. Finally, the performance of an FH-SS system using standard fading assumptions is compared to the performance of a measured fading channel. Due to flaws in the assumptions, the measured fading channel yields several decibels of performance loss relative to the ideal fading channel     

An optimum design of deep‐space downlinks affected by tropospheric attenuation

In the paper, we propose an optimum design of deep‐space downlinks made with 2 hops, at K_a band and above, in which each hop should be designed for providing half of the total noise‐to‐signal power ratio. We have derived this result from maximizing the ratio between the tropospheric attenuation in the 2‐hop downlink and that in the 1‐hop downlink. The design of the 1st hop (free‐space) of the 2‐hop downlink can reduce the spacecraft power, for the same antennas physical size, by increasing the carrier frequency from K_a band (32 GHz) to W band (80 GHz). This choice is not available in 1‐hop downlink design because of the huge Earth tropospheric attenuation expected in the W frequency band. To show a practical design, we have applied the theory to compare 1‐hop downlink design at 32 GHz to 2‐hop downlink design that adopts 32 or 80 GHz in the 1st hop. The calculations refer to spacecrafts located at two astronomical units (300×10⁶ km, about planet Mars) and to NASA and ESA receiving stations located in Goldstone (California), Cebreros (Madrid, Spain), Canberra and New Norcia (Australia). At 0.1% outage probability, in an average year or in the worst month, 1‐hop downlinks show performance critical or close to fail, because of the large tropospheric attenuation (except at Goldstone), while 2‐hop downlinks always work. Copyright © 2009 John Wiley & Sons, Ltd.     

Adaptive recovery of a chirped sinusoid in noise. II. Performanceof the LMS algorithm

For pt.I see ibid., vol.39, no. 3, p.583-94 (1991). The authors present a methodology for evaluating the tracking behavior of the least-mean square (LMS) algorithm for the nontrivial case of recovering a chirped sinusoid in additive noise. A complete closed-form analysis of the LMS tracking properties for a nonstationary inverse system modeling problem is also presented. The mean-square error (MSE) performance of the LMS algorithm is calculated as a function of the various system parameters. The misadjustment or residual of the adaptive filter output is the excess MSE as compared to the optimal filter for the problem. It is caused by three errors in the adaptive weight vector: the mean lag error between the (time-varying mean) weight and the time-varying optimal weight; the fluctuations of the lag error; and the noise misadjustment which is due to the output noise. These results are important because they represent a precise analysis of a nonstationary deterministic inverse modeling system problem with the input being a colored signal. The results are in agreement with the form of the upper bounds for the misadjustment provided by E. Eweda and O. Macchi (1985) for the deterministic nonstationarity     

基于延迟相乘的相关跳频信号鲁棒检测

从相关跳频扩谱系统在每一跳中发送频率恒定的正弦波这一典型特征出发,对相关跳频扩谱信号在经过延迟相乘低通处理后所具有的基于跳驻留时间的恒值特性进行了研究。提出了一种可实现对相关跳频扩谱信号侦察检测的有效方法——基于延迟相乘低通滤波的相关分析法。计算机仿真显示该方法不但能在低信噪比环境下凸现相关跳频扩谱信号的特征,而且同时能够实现对跳驻留时间的估计。     

Performance analysis of a variable‐gain amplify‐and‐forward relayed mixed RF‐FSO system

In this work, an amplify‐and‐forward variable‐gain relayed mixed RF‐FSO system is studied. The considered dual‐hop system consists of a radio frequency (RF) link followed by a free space optical (FSO) channel. The RF link is affected by short‐term multipath fading and long‐term shadowing effects and is assumed to follow the generalized‐K fading distribution that approximates accurately several important distributions often used to model communication channels. The FSO channel experiences fading caused by atmospheric turbulence that is modeled by the gamma‐gamma distribution characterizing moderate and strong turbulence conditions. The FSO channel also suffers path loss and pointing error induced misalignment fading. The performance of the considered system is analyzed under the collective influence of distribution shaping parameters, pointing errors that result in misalignment fading, atmospheric turbulence, and path loss. The moment‐generating function of the Signal power to noise power ratio measured end‐to‐end for this system is derived. The cumulative distribution function for the Signal power to noise power ratio present between the source and destination receiver is also evaluated. Further, we investigate the error and outage performance and the average channel capacity for this system. The analytical expressions in closed form for the outage probability, symbol and bit error rate considering different modulation schemes and channel capacity are also derived. The mathematical expressions obtained are also demonstrated by numerical plots.