基于FFT的双基地综合脉冲孔径雷达发射阵校准

本文结合高频岸-舰双基地综合脉冲孔径雷达(SIAR)的特点,利用接收到的直达波信号以及全球定位系统(GPS)测得的接收站位置信息,提出基于FFT的发射阵增益、相位以及位置误差校准方法.仅存在增益和相位误差时,校准需已知一个接收站方位;增益、相位和位置误差都存在时,需要三个接收站方位.文中推导了对这三个接收站方位的要求,研究了接收平台运动和存在多径效应时的校准方法,分析了GPS角定位误差对校准的影响.计算机仿真表明了该方法对发射阵的增益、相位以及位置误差具有良好的校正性能.由于无需精确校准的辅助阵元或方位精确已知的辅助信源,并且运算量小,该方法易于工程实现.     

收发分置的地波SIAR发射波束形成

针对在运动平台上收发分置的地波综合脉冲孔径雷达,研究了在接收站进行发射波束形成的处理方法及其性能;推导其距离-方位二维模糊函数;介绍该雷达试验系统的组成,并给出了发射数字波束形成的试验结果。     

双/多基地综合脉冲孔径地波雷达的信道化接收技术研究

双/多基地综合脉冲孔径地波雷达在发射站为多载频信号同时辐射,在接收站综合形成发射方向图之前需要对各发射信号分量进行分离.尽管采用数字混频和低通滤波器组可以对各发射分量进行分离,但运算量太大,难以实时实现.为此提出采用多相滤波器组信道化接收技术,设计该雷达的多相滤波器组信道化接收机.这种多相滤波器组信道化接收机与低通滤波器组信道化接收相比,运算量减少N²倍(N为信道数).最后给出了该雷达试验系统的实测数据处理结果,验证了这种多相滤波器组信道化接收技术在该雷达信号处理中的有效性.     

舰载无源综合脉冲/孔径雷达及其若干关键问题

本文根据综合脉冲/孔径雷达采用多个天线同时向全空域辐射多个载频信号,而在接收端通过信号处理获得发射方向图的特点,提出一种新的雷达体制——舰载无源综合脉冲/孔径雷达.该雷达既利用在岸上发射、在舰船上接收而构成岸-舰双/多基地"广播式"雷达,又由于在接收站不发射信号而相当于无源定位.本文介绍该雷达的基本组成、工作原理及其特点;分析其性能;讨论该雷达需解决的关键问题.     

基于综合脉冲与孔径技术的多基地"无源"定位系统

本文根据综合脉冲／孔径雷达采用多个天线同时向全空域辐射多个载频信号,而在接收端通过信号处理获得发射方向图的特点,提出一种新的多基地“无源”定位雷达系统。该系统既利用在岩上发射,在舰船上接收而构成岩－舰多基地雷达,又由于在接收站不发射信号而相当于无源定位系统,本文介绍该系统的基本组成,工作原理及其与常规地波超视距雷达、双／多基地雷达相比的显著特点,给出计算机模拟结果;最后讨论了该雷达需解决的关键问题。     

基于运动补偿的长时相干积累方法研究

稀布阵综合脉冲孔径雷达（SIAR）是一种全新体制的数字综合孔径雷达,其发射信号在空间全向辐射,不存在波束扫描问题,可对接收回波进行长时积累。本文首先对目标回波信号建模,分析了长时相参积累存在距离走动、多普勒扩散等问题。提出了一种对回波信号先分组多普勒滤波再非相参积累的方法,并给出了工程实现途径。通过仿真和实际工程的验证,证明了该算法的有效性。     

多载频FMCW在MIMO雷达中的应用研究

 介绍多载频MIMO雷达的特点和工作原理,对多载频线性调频连续波(FMCW)信号及其回波进行了分析,并详细论述了MIMO雷达中静止目标和运动目标情况下多载频FMCW信号处理方法以及其中的一些关键问题,如通道分离滤波器的设计、距离分辨率分析、速度补偿精度分析、相参积累周期数的选取等.针对该体制雷达各发射天线间载频不同的特点,提出了采用IFFT相参合成的方法来精测目标距离,获得距离高分辨,具有运算速度快、受目标运动影响小的优点;对运动目标情况下距离多普勒的耦合问题进行了详细分析,并提出了利用相参积累进行补偿的解决方案.     

一种全计算波束形成的数字阵列雷达

介绍一种全数字阵列雷达——综合脉冲孔径雷达,雷达采用收发全数字波束形成。发射时,每个发射单元采用直接产生正交编码波形,从而波形在空间不相干叠加形成聚集波束;接收时,单元接收信号通过一匹配滤波器组,其中每个匹配滤波器对应一路发射信号,由于每个发射和接收单元的空间位置准确已知,从而可以对匹配滤波器组的输出信号进行调相并相加,同时形成多个指向的发射波束。     

新型米波三坐标雷达自适应波束形成性能分析

稀布阵综合脉冲孔径雷达（SIAR）是一种新型米波分布阵体制雷达,采用稀布阵列天线,通过各个阵元全向发射正交编码频率信号以使各向同性照射,在接收端通过DBF和发射脉冲综合形成接收和发射波束。本文采用正交化自适应波束形成算法对米波三坐标雷达的抗干扰性能做了仿真,取得了良好的干扰抑制效果,有着较小的运算量,具有工程实用价值。     

基于相位编码的稀布阵综合脉冲孔径雷达的脉冲压缩性能分析

稀布阵综合脉冲孔径雷达(SIAR)采用多个频率信号同步全向照射工作方式,通过脉冲综合可以获得一定的脉压比。根据其距离模糊函数知,距离分辨率仅取决于发射信号带宽,增大发射信号的时宽带宽积则存在距离栅瓣效应。为此本文利用相位编码调制各阵元的发射信号,讨论其脉冲压缩性能。结果表明:这时不仅可以大大提高脉压比,而且可以降低距离旁瓣,同时可以满足SIAR对各向同性照射的要求。从而有利于提高其作用距离和距离分辨能力.     

自由空间光通信系统中弱大气湍流引起的相位波动和强度闪烁对DPSK调制系统的影响

大气湍流是自由空间光通信链路系统的主要限制因素。大气湍流造成光束的强度闪烁和相位起伏。因此,基于MZI-DPSK调制,考虑大、小湍流尺度引起的强度闪烁和相位噪声对误码率的影响且强度闪烁满足逆高斯分布和相位波动满足高斯分布。利用分布式天线阵接收技术,研究了大气湍流下自由空间光通信链路的误码率性能,推导了在内外尺度下,分布式天线阵接收的误码率关于相位误差的函数表达式。为了提高误码率的性能,天线阵接收采用了最大比合并技术。仿真结果得出相位误差对误码率的影响很大;内外尺度对误码率的影响可以忽略不计。采用天线阵接收可以降低系统的误码率,提高通信系统的性能,且得出天线阵接收的最佳子天线个数。     

低相噪光子式微波接收机的研制

首次对微波接收机的相噪进行了理论建模,并提 出了一种基于光子技术的新型微波接收机,该接收机采用微波光子 链路来代替电缆,使用光电振荡器代替电子振荡器来作为本振源,并基于上述理论模型分析 了该种接收机较传统电子式接收 机在相噪指标上的优越性。让10 GHz载波信号分别通过电、光两种接 收机,对比输出信号的相噪情况,实验结果表明:通 过传统电子接收机接收后,载波信号相噪在1kHz频偏增加了30 dB; 而对于本文所提新型光子式接收机,载波信号相噪在 1kHz频偏仅增加10 dB,说明了该种新型接收机在集成了微波光子链 路与光电振荡器两种新型光子技术后,相噪指标得到了显著提高。     

Analysis of phase noise effects in OFDM modems

The effects of the phase noise (PN) on orthogonal frequency-division multiplex modems are evaluated. Three receivers are studied: a coherent receiver, a common phase error correction receiver (which is a receiver specially designed to combat PN) and a differential receiver. The impact of the PN on the decision signal-to-noise ratio (SNR) of each of these receivers is computed as a function of the PN spectrum. The resulting formulas are extremely simple. The theory is applicable to a wide range of PN models, and unifies and extends previous results on the topic. The conditions under which the decision SNR yields correct symbol error rate predictions are discussed. Simulations are reported that confirm the results.     

偏振部分相干激光斜程湍流大气传输的漂移扩展

采用光场的一阶矩和二阶矩作为评价参数,研究了偏振部分相干激光波束在斜程湍流大气传输中的漂移效应和扩展效应。根据推广的惠更斯-菲涅耳原理,以椭圆偏振部分相干激光波束为研究对象,推导了斜程传输情况下波束的重心坐标、扩展半径和扩展角的表达式,数值分析了偏振波束两正交分量的相位差、方向角、波长、初始束腰半径和接收机高度对波束漂移及扩展的影响。结果表明,在确定的斜程传输距离和接收机高度下,随着偏振波束两正交分量相位差的增大,漂移效应先增大后减小,在确定的斜程传输距离下,接收机高度越高,波束的漂移效应和扩展效应越小。     

Doppler-corrected differential detection of MPSK

An open-loop technique is presented for estimating and correcting Doppler frequency shift in an M-ary differential phase-shift-keyed (MDPSK) receiver. The novelty of the scheme is based on the observation that whereas the change in phase of the received signal over a full symbol contains the sum of the data (phase) and the Doppler-induced phase shift, the same change in phase over half a symbol (within a given symbol interval) contains only the Doppler-induced phase shift. Thus, by proper processing, the latter can be estimated and removed from the former. Analytical and simulation results are given for the variance of the above estimator, and the error probability performance of the MDPSK receiver is evaluated in the presence of the Doppler correction. Next, the practical considerations associated with the application of this technique on bandlimited Nyquist channels are discussed and incorporated into the final design. It is shown that the receiver can, in the absence of timing jitter, be designed to allow combined Doppler correction and data detection with no penalty due to intersymbol interference (ISI). The effects of ISI due to timing jitter are assessed by computer simulation     

The Effects of Vestigial Sideband Passband Characteristics upon Television Transient Response

The task of ensuring acceptable detected transient response in consumer television receivers is complicated by the large variety of different transmitter vestigial sideband and receiver IF filter characteristics in use. In this paper, the effects of different typical transmitter and receiver passband characteristics in the vestigial sideband region upon detected transient response are analytically examined. Both envelope and synchronous demodulation systems are investigated, and various levels of carrier modulation are assumed. In addition, the effects on transient response of alternate methods for transmitter vestigial sideband filter (VSBF) phase correction are described. In general, it is found that even with the substantial response of many receiver IF filters in the 1-MHz region of the vestigial sideband, acceptable transient response can be obtained provided that appropriate phase correction of the transmitter VSBF is used. Experimental verification of the analytical results is also presented.     

An integrated framework for MC-CDMA reception in the presence of frequency offsets, phase noise, and fast fading

The combination of code-division multiple-access and multicarrier (MC) modulation has been proposed to develop high data-rate wireless communication systems. Due to the longer symbol duration in comparison with single-carrier systems, MC systems are more sensitive to various imperfections, including phase noise and frequency offsets due to local oscillators and Doppler spreading due to motion that results in temporal channel variations. The performance of current systems is significantly limited by these imperfections because they disperse the transmitted power in a particular subcarrier into adjacent subcarriers, thereby causing interference between the subcarriers at the receiver. We consider a single-user communication system and use a canonical model for the received signal that efficiently captures the effects of all impairments. The model uses Fourier basis functions that are fixed for all imperfections while the expansion coefficients depend on imperfections. Using the model, we introduce a receiver structure that implements the matched filter (MF), and hence, optimal. The MF is implemented through a Rake receiver in the frequency domain. The receiver fully compensates for frequency offsets as well as phase noise, thereby eliminating the performance loss due to these factors. Furthermore, in contrast to existing designs, it delivers improved performance under fast fading by exploiting Doppler diversity. Finally, the same integrated receiver structure works for all imperfections eliminating the need for devising a separate correction technique for each.     

一种采用光学相位分集接收技术的相干光正交频分复用远端接入系统

提出了一种采用基于光学相位分集接收技术实现远程相干光正交频分复用(CO-OFDM)信号的远程光接入方案,并进行了理论研究和仿真验证。在本方案中,没有使用色散补偿光纤(DCF)或者色散补偿模块(DCM)补偿光纤信道色散导致的负面效应,原因是CO-OFDM信号能有效抵抗传输过程中色度色散(CD)和偏振模色散(PMD)引起的负面效应。仿真结果表明,10Gbit/s CO-OOFDM信号在标准单模光纤(SMF-28)传输320km后,采用相位估计技术得到的OFDM电信号,其时域波形的相位抖动幅度更小;与采用光载波自提取技术接收相位调制COOFDM的方案进行比较,测试误差向量幅度(EVM)的结果表明,本文方案可以获得更好的COOFDM信号接收性能,星座图中星座点收敛更加紧凑,接收的CO-OFDM信号质量更高。     

Amplitude demodulation of filtered AM/PM signals

The input signal is assumed to be simultaneously amplitude and phase modulated (AM and PM), and the bandpass filter may be unsymmetrical and mistuned. The demodulator output is the magnitude of the filtered signal for an AM receiver or its phase for a PM receiver. For such a system with amplitude demodulation, the results are found and presented in the form of an expansion in which the leading term is the linear (i.e., undistorted) reproduction of the input AM and the successive terms represent the distortion and crossmodulation. The significant effects are given by the first few terms of the expansion because the applications of interest are those in which the distortion is small. A spectral analysis is performed on the output of an AM receiver. The leading DC, linear, and nonlinear terms of the output power spectrum are derived by assuming that the amplitude- and phase-modulating signals are uncorrelated zero-mean random Gaussian processes     

Reduced complexity sequence detection for nonminimum phaseintersymbol interference channels

Controlled intersymbol interference may be used to design bandwidth efficient coded modulation schemes. The performance of the optimum receiver depends only on the free distance of the code and is independent of its phase. Large reductions in receiver complexity are obtained by using reduced search detection techniques like the M-algorithm (MA). However, we show that MA detector performance depends critically on phase, and is characterized by the partial energy of the encoder or channel. The minimum phase encoder needs by far the least detector searching. We propose modifications to the receiver, so that the reduced search can operate on all nonminimum phase channels at this same low complexity