3G-ALE短波信号信道化接收机高效设计

快速选频建链对提高短波通信系统的接通率和通信质量至关重要,针对第三代自动链路建立（3G-ALE）短波信号频率较低、信道带宽窄、信道个数多的特点,设计了一种基于加权叠接相加（WOLA）滤波器组的射频直采信道化接收机,同时,提出了信道组内有效信道全覆盖的方式,能够使建链时间缩短为单路接收时的1/511。在高斯白噪声信道下进行了仿真,当SNR低至-9dB时同步捕获概率甚至可以达到100%,当SNR高于24dB时误码率为0,与单路接收相比该信道化接收机不会因为并行接收而降低信号接收质量。     

二相编码信号性能分析

二相编码信号应用于低截获自导声纳波形设计,具有较好的性能。本文着重研究了二相编码信号的模糊函数及频谱,仿真实验表明二相编码信号距离分辨力及速度分辨力与信号带宽和信号时宽分别对应相关。信号带宽越大则距离分辨力越高,信号时宽越长则速度分辨力越高。同时信号带宽亦与信号频谱幅度成反比关系。信号带宽越大,信号频谱幅度越低,功率谱密度亦越低。因此,选择适当的时宽、带宽,二相编码信号具有较好的低截获性能。     

二相编码信号性能分析

二相编码信号应用于低截获自导声纳波形设计,具有较好的性能。本文着重研究了二相编码信号的模糊函数及频谱,仿真实验表明二相编码信号距离分辨力及速度分辨力与信号带宽和信号时宽分别对应相关。信号带宽越大则距离分辨力越高,信号时宽越长则速度分辨力越高。同时信号带宽亦与信号频谱幅度成反比关系。信号带宽越大,信号频谱幅度越低,功率谱密度亦越低。因此,选择适当的时宽、带宽,二相编码信号具有较好的低截获性能。     

基于宽带阵列的数字信道化接收机设计与实现

数字化宽带接收机提高了接收信号的频域覆盖带宽,但往往灵敏度降低而难以检测弱小信号。既追求足够宽的频谱带宽,又提高强杂波背景中弱小目标检测能力,是本文研究的出发点。本文基于宽带相控阵接收机的工程实践,讨论了基于频域抽取的信道化接收机设计原理,设计了一个400M瞬时带宽阵列接收机的工程样机,并成功应用于某多波束阵列接收系统。实验结果表明,该信道化宽带接收机实现了超远程对雷达脉冲信号的检测,具有一定的工程借鉴价值和理论指导意义。     

宽带无线信道精细时延和响应联合估计方法

研究适用于无线信道测量的定时偏移和信道联合估计方法.发射机发送具有循环前缀结构的导频信号段.接收机根据粗同步信号确定快速傅里叶变换的窗口起始位置.利用改进时域最小二乘信道估计和变换域滤波,获得高精度的信道估计值.对频域接收导频信号段的定时偏移进行精细估计,对定时偏移量进行滤波并累加.最后,对频域接收导频信号段进行定时偏移补偿.信道估计器、定时延迟偏移精细估计器与补偿单元三者构成迭代相干延迟锁定环路.仿真结果表明:采用迭代相干联合估计方法进行精细定时延迟估计的性能明显优于非相干方法.     

一种新的OFDM相位编码频率步进雷达信号及其特性

OFDM相位编码脉冲雷达体制具有很多良好的性质,但工程实现上存在着一些的技术挑战,其中之一就是瞬时带宽等于信号的总带宽,当信号带宽很大时对接收设备提出了很高的要求。针对这个问题,该文提出了一种OFDM相位编码频率步进的新雷达信号,其核心思想是通过载频的频率步进,利用多个带宽较小的OFDM相位编码脉冲组成一个脉冲串,合成大的带宽。在推导这种新雷达信号的模糊函数的基础上,着重分析了信号的距离高分辨特性和多普勒特性,通过比较得出结论:OFDM相位编码频率步进信号能有效实现距离高分辨,其多普勒敏感度介于OFDM相位编码和步进频信号之间。     

基于多级信道化的超宽带搜索接收机设计与实现

针对大瞬时带宽和高频率分辨率的实时侦察需求,联合采用模拟信道化和数字信道化技术完成了超宽带信号搜索接收机的设计与实现,并重点讨论了数字信道化接收机的高速FPGA数字系统设计.数字没计中,充分考虑了高速数据的可靠接收以及片内数字处理速度和资源的优化配置,确保系统良好的性能.实现和测试结果表明接收机性能稳定,能够完成大瞬时带宽内的无线电信号搜索任务.     

瞬时测频接收机探测混存信号

用于测频的带有延迟线鉴频器的瞬时测频(IFM)接收机在脉冲调制的信号环境中具有良好特性。但是,对于时间重叠信号或混同信号接收效果差。本文针对以下各种信号做了分析,并以实验给以验证;像脉冲调制信号、连续波(CW)、线性调频信号和相位编码信号.对二个时间重叠脉冲调制信号进行了更详尽地分析.此外,由于强信号在限制前置放大器中的过激造成的——对弱信号的压缩效应,我们用一个比例因子给予考虑.下面是本文采用的基本符号:h(t)=视频滤波器脉冲响应函数BW=视频带宽t_0=鉴频器线延迟θ(t)=信号相位函数φ(t)=延迟线相位函数ω_0=角载波频率T=脉宽T_0=双相编码信号子脉冲间隔R=两时间重叠信号功率比C=经验换算系数     

一种新的低截获概率雷达信号的设计与分析

从信号频谱、模糊函数等方面对二相编码信号、步进频率信号两种典型的低截获概率雷达信号进行了分析,提出一种脉内二相编码——脉间步进频率复合调制雷达信号,并对其优缺点进行了比较。研究结果表明,复合调制信号既能克服步进频率信号较严重的距离——多普勒耦合和相位编码信号的多普勒频移敏感的缺点,同时又具备相位编码信号的大带宽特性和步进频率信号的高距离分辨率特性,是一种较理想的低截获概率雷达信号。     

多天线超宽带通信中的一种盲接收机

针对多天线冲激无线电超宽带通信系统,提出了一种盲的线性接收机。在不需要信道信息的情况下,可以利用经过预编码的空时分组码给接收信号带来的特定结构,直接得到接收机系数,从而恢复出发送符号。仿真表明,随着用于估计的数据块的增加,盲接收机的性能逐渐接近于相关接收。     

具有连续相位的8PSK调制

连续相位的QPSK信号具有恒定包络,解决了传统QPSK信号由于相位跳变所带来的包络起伏问题,但其频带利用率没有8PSK高,为提高频带利用率,提出了连续相位8PSK(CP8PSK)调制。本文首先利用差分编码规则来表征8PSK信号一个符号周期的相位变化,进而将其表示为连续相位调制(CPM)的形式,再使用频率脉冲对其相位进行脉冲整形,最终得到具有连续相位的CP8PSK表达式。为了降低系统的整体复杂度,本文还对CP8PSK进行了Laurent分解。根据理论分析CP8PSK信号应当具有恒定包络,而且比连续相位的QPSK调制要有更高的带宽效率和更平滑的频谱,通过MATLAB进行仿真之后,得到的CP8PSK具有恒定包络,且带宽效率在同等情况下要高于整形的交错QPSK(SOQPSK)和8PSK,频谱也更加平滑,抗误码性能与理想8PSK相比损失也不大。      

The relationship between fading and bandwidth for multipath channels

A signal transmitted over a multipath channel experiences fading, the variability of which is a function of: 1) signal bandwidth; and 2) power delay profiles of the channel's specular and diffuse components. We analyze this general relationship and, for several important classes of multipath channel, we derive simple, closed-form approximations for what we call the stability bandwidth, W/sub 0/. For signal bandwidths greater than W/sub 0/, the local area variation in the received signal power is acceptably small, e.g., less than 1 dB standard deviation of decibel power. We demonstrate the accuracy of our W/sub 0/ approximations for some representative cases. Moreover, we show that the root mean square delay spread-a statistic commonly used to characterize multipath channels-has limited utility in estimating W/sub 0/.     

Impact of phase noise in weakly coherent systems: a new andaccurate approach

Coherent optical systems for future broadband local loops may use lasers with significant phase noise, manifest as broad linewidths. This phase noise can be accommodated if the receiver is correctly designed, i.e. if nonsynchronous (envelope or square-law) IF demodulation is used and sufficient IF bandwidth is provided. It is difficult to analyze the performance of a coherent optical receiver when the signals are corrupted by phase noise. The central theoretical problem arising from filtering a signal with phase noise is defined in a particular form which permits the derivation of the forward or Fokker-Planck partial differential equation for probability density of the output voltage of the receiver. The results are used to discuss the IF bandwidth required for optical heterodyne receivers for amplitude-shift-keying (ASK) signals     

Interference Cancellation System for Satellite Communication Earth Station

A new interference cancellation system was devised to suppress the mutual interference between satellite and terrestrial communication systems and to expand the number of potential earth station locations for effective frequency reuse. This system basically adopts the sidelobe canceller concept and has main and auxiliary antennas. The originality of this system lies in that the auxiliary channel signal to be combined with the main channel signal is modulated by a low frequency signal, and the amplitude and phase controlling voltages are obtained by means of envelope detection, to get the envelope of the residue, and then by phase detection, using the envelope signal and the low frequency signal. As a result of experiments, more than 40 dB cancellation was achieved over a 50 MHz range for CW, FM(TP, TV) and PSK signals, even if the desired and interference signals are in the cochannel. In the field test on a 45 km path, sufficient cancellation performance and response were obtained even during fading periods.     

Design considerations for multi-band OFDM polar transmitter of UWB system

The requirements for the envelope and phase paths in a multi-band orthogonal frequency division modulation (OFDM) polar transmitter for ultra-wideband (UWB) are studied at system level. The results show that the bandwidth of the envelope of the polar signal require at least 1.1 times the bandwidth of in-phase (I) and quadrature-phase (Q). But the bandwidth of the phase of polar signals should be at least 7.1 times in order to pass the error vector magnitude requirement in the ECMA standard. In addition, time delay mismatch of less than 0.36 ns is also required.     

The effects of polarization rotation and phase delay with frequency on ionospherically propagated signals

When a CW skywave signal is received on a linearly polarized antenna, polarization (Faraday) rotation produces a variation of received signal strength with radio frequency. The resulting dependence of received signal amplitude on radio frequency may impose a bandwidth limitation on pulsed signals where waveform preservation is important. A measure of this limitation, termed polarization bandwidth, is defined to correspond to the bandwidth in which the plane of polarization rotates90deg. Computer ray-tracing calculations were performed using a single Chapman-layer ionospheric model to determine the 1-hop polarization bandwidth as a function of geomagnetic azimuth and radio frequency. The polarization bandwidth was found to decrease with increasing radio frequency and with increasingly close alignment of the propagation path with the longitudinal component of the earth's magnetic field. Assuming a critical frequency of 9 MHz and a path length of 2000 km, the polarization bandwidth increased from a minimum of 140 kHz at 10.5 MHz and from a minimum of 70 kHz at 17.5 MHz, as the propagation direction varied from geomagnetic north to east. A model for the 1-hop ionospheric signal channel is proposed whose parameters are the rate of change of polarization rotation with frequency and the phase versus frequency characteristic of the path. These two parameters are shown to be readily determined from FM-CW or equivalent oblique-path sounding records. Using this model, predictions are made of the effects of polarization rotation with frequency, and also of ionospheric dispersion or phase distortion, on the envelope shape of short-pulse signals (of from 1.5 to50 mus duration). A pronounced waveshape distortion due to the effects of polarization rotation on the pulse envelope was observed when the signal bandwidth appreciably exceeded the "polarization bandwidth" for the path.     

Maximum likelihood sequence detection using a pilot tone

This paper derives, analyzes, and simulates a maximum likelihood (ML) sequence detector (MLSD) for a linearly modulated signal transmitted with a pilot tone (PT-MLSD). The transmitted signal is distorted by a time-varying frequency-selective Rayleigh fading channel and corrupted by additive Gaussian noise. The received signal is unsynchronized in that there are residual carrier frequency, carrier phase, and symbol timing offsets. The PT-MLSD treats the channel as a stochastic process, and so symbol sequences are distinguished by their autocovariances. Coherent communication is possible even in overspread channels. As the sequences' autocovariances explicitly account for the channel's time variation, the PT-MLSD's bit error rate (BER) floor is normally lower than the BER floor suffered by receivers that estimate the channel impulse response conventionally. Both the data-bearing signal and pilot tone are used together for synchronization, equalization, and detection. The pilot tone is only needed to remove the constellation's phase ambiguity and provide a stable amplitude reference for QAM constellations. It is not needed for estimating the channel impulse response. The pilot tone does not require a spectral null for its insertion, and it does not significantly degrade the peak-to-average or maximum-to-minimum power ratios. Thus, many of the disadvantages of other pilot tone systems are avoided, as there is no bandwidth expansion, and linear amplification is not made appreciably more difficult     

Signal Design for the Amplitude-Limited Gaussian Channel by Error Bound Optimization

A necessary and sufficient condition is presented for an input signal alphabet to optimize the random coding exponent for a time-discrete channel with signals restricted in amplitude. It is applied to the white noise Gaussian channel for signals in one and two dimensions. By use of this theorem the best input signal quantizafion is determined by numerical optimization. Results are presented on the number of amplitude or envelope levels needed to maximize the error bound parameter R0at different signal-to-noise ratios. For one-dimensional (baseband) signals a binary antipodal configuration is optimum, in the sense of maximizing R0, for signal-to-noise ratios below 6.9 dB. For two-dimensional (passband) signals with limited envelope, phase modulation is shown to be optimum for signal-to-noise ratios below 7.35 dB.     

一种相控阵雷达射频域自干扰对消方法

在相控阵雷达系统中,为了保证回波信号的正确接收,需要在接收阵元天线的射频前端对自干扰信号进行对消处理。随着雷达信号带宽的增加,其形成的自干扰信号的消除难度加大。针对该问题,提出了一种射频域自干扰分段对消方法。该方法利用同一个自干扰对消通道对不同时间段的自干扰信号进行对消处理。对带宽为300 MHz 的线性调频信号进行仿真验证发现:当抽头个数为4时,自干扰分段对消方法的性能可达50 dB,比抽头个数为7时的传统的多抽头对消方法高出18 dB。因此,相较于传统的多抽头对消方法,所提出的自干扰分段对消方法可以在更低的硬件复杂度下实现更高的对消性能。     

Deterministic Blind Channel Estimation for a Block Transmission System Using Fractional Sampling and Interpolation

This paper introduces a blind channel estimation method for a block transmission system using fractional sampling at a receiver. In most digital communication systems, low-pass filters are placed at a transmitter to confine the transmitting waveform to an allocated bandwidth and at a receiver to improve the signal-to-noise (SNR) power ratio. Consequently, if the received waveform is sampled with sufficiently fast rate, the resulting discrete-time signal is band-limited and exhibits a smooth waveform. The method exploits this property for estimating the channel impulse response, via an interpolation formula. The method does not require knowledge of input statistics or the autocorrelation of the received signal. It is free of channel order estimation and thus robust against its overestimation. Moreover, the algorithm is quite efficient because it does not need to compute eigenvalues of a matrix.