光子计数探测的非线性失真及其改进的研究和探讨—一种多路光子探测法的方

对光子计数探测中堵塞漏计引起的非线性失真现象作了一些新的探讨和分析，提出了一套新的减少漏计的方法，多路光子探测法将会大大扩展光子计数探测的线性范围，进一步提高探测的灵敏度，信噪比和精度，使探测的水平跃上一个新的台阶。     

基于FPGA的无线光通信PPM调制系统的设计

无线光通信技术具有通信容量大、传输速率高等众多优点,在许多场合都有重要的应用,是现代通信技术研究的一个热点.由于脉冲位置调制(PPM)有较高的平均功率利用率和抗干扰能力,故PPM是无线光通信系统中常用的调制方式.在研究PPM调制技术的基础上,就基于FPGA的无线光通信PPM调制系统进行设计,并用VHDL语言完成了系统的设计和仿真.仿真结果表明,该设计具有正确性和合理性.     

无线光通信中PPM的差错编码调制研究

文章推导了基于线性分组码的脉冲位置调制(PPM)通信系统纠错后的差错概率上限,分析了差错编码的纠错能力和PPM位分辨率的参数设置对差错性能的影响,并进行了仿真.结果表明,在纠错个数能被位分辨率整除时,PPM系统达到较高编码调制性能,同时指出适合PPM系统的纠错编码一般为高阶码.     

空间光通信PPM信号的软解调及其性能

PPM调制由于其较高的功率利用率而在空间光通信系统中得到了广泛的应用，PPM信号的接收部分对整个通信系统的性能起很大作用。我们对光PPM信号的解调进行分析，提出了PPM信号的软解调而不对脉冲位置作先期判决，并对软解调及其性能进行分析，最后利用计算机对用APD接收且存在热噪声下的空间光通信PPM信号的解调进行了模拟仿真。仿真结果说明软解调由于充分利用了光电探测器计数软信息而降低了误码率。     

无线光通信中PPM的RS级联编码调制研究

在脉冲位置调制(PPM)直接检测光通信系统中插入RS级联编码构成一种新的PPM光通信系统(RS-PPM),该方式对PPM直接检测光通信系统进行了改进,并用Mat l ab对编码系统和未编码系统的误比特率进行了仿真比较,仿真结果表明,基于RS级联编码的PPM系统具有较好纠错和抗干扰能力。     

一种无线光通信中脉冲位置调制的符号同步方法

脉冲位置调制(pulse position modulation,PPM)是无线光通信的经典调制方式之一.符号同步是实现PPM正确解调的关键技术.在分析帧同步码型和长度要求的基础上,设计了一种PPM帧结构,提出了利用帧同步来实现PPM符号同步的方法.论述了其工作原理,并分析了其同步性能.结果表明该方法建立时间短,同步概率高,并具有自动调整功能,可实现性强.     

FPGA技术在无线光通信PPM调制系统优化设计中的运用

无线光通信技术是目前运用比较广泛的一门通信技术,它融合了无线通信和光纤通信的优势,具有广泛的发展前景和市场,因而,相关部门应该加强对无线光通信技术的重视。下面本文就对FPGA技术在无线光通信PPM调制系统优化设计中的应用分析。     

基于自适应提升小波的APD探测信号消噪

雪崩光电二极管(APD)具有高增益、高灵敏度和响应速度快的特点,因而成为空间光通信中的首选信号探测器件.针对空间光通信的脉冲位置调制(PPM)信道,分析了空间光通信系统中雪崩光电二极管探测噪声的特点和类别,在讨论了第二代小波变换基本原理及其特点的基础上,将自适应性引入提升方案中,用先更新后预测的改进提升算法解决自适应性引起的非线性问题,并在阈值处理过程中引入了软硬阈值折衷法来恢复信号.实验仿真结果表明,采用该算法实现的雪崩光电二极管信号去噪,不仅较好地剔除信号中的噪声,而且保留了原始信号中的有效成分,是一种可行的方法.     

空间光通信PPM信号的软解调及其性能

PPM调制由于其较高的功率利用率而在空间光通信系统中得到了广泛的应用,PPM信号的接收部分对整个通信系统的性能起很大作用。我们对光PPM信号的解调进行分析,提出了PPM信号的软解调而不对脉冲位置作先期判决,并对软解调及其性能进行分析,最后利用计算机对用APD接收且存在热噪声下的空间光通信PPM信号的解调进行了模拟仿真。仿真结果说明软解调由于充分利用了光电探测器计数软信息而降低了误码率。     

光子计数探测的非线性失真及其改进的研究和探讨──一种多路光子探测法的方案论证（二）

对光子计数探测中堵塞漏计引起的非线性失真现象作了一些新的探讨和分析，提出了一套新的减少漏计的方法，多路光子探测法将会大大扩展光子计数探测的线性范围，进一步提高探测的灵敏度、信噪比和精度，使探测的水平跃上一个新的台阶。     

Carrier phase tracking from turbo and LDPC coded signals affected by a frequency offset

This contribution considers carrier phase estimation from coded signals, affected by a frequency offset at low operating signal-to-noise ratio (SNR). We derive a maximum likelihood (ML) based iterative code-aided feedback phase-tracker suited for receivers with iterative maximum-a-posteriori (MAP) detection. Simulations indicate that the proposed synchronizer is considerably more robust against frequency offsets than a feedforward synchronizer.     

Simultaneous clock phase and frequency offset estimation

Residual frequency offsets may often result in poor functioning of a digital receiver. This is particularly true in a frequency selective environment where an adaptive equalizer may be required. In this paper, a frequency offset estimation algorithm is presented which is based on applying a nonlinear operation on the received sampled baseband signal. Tones at multiples of the clock frequency are produced and the phases of these tones provide both the desired frequency offset and clock phase information. This algorithm is intended to operate without knowledge of the pulse shape and therefore may be suitable for frequency selective environments. Additionally, the clock phase may be estimated with very little overhead. Simulations with AWGN, flat and frequency selective fading channels are included     

Optimal detection of random phase signal with Doppler frequency offset in Chirp-BOK multi-antenna system

When there are Doppler frequency deviation and phase noise in channel,the MIMO-OFDM system with coherent detection requires complicated and accurate frequency offset estimation and Doppler compensation.Based on this,an optimal random phase detection was proposed in multi-antenna Chirp-BOK system,which improved the system capacity by space division multiplexing in the condition of anti-interference and anti-frequency deviation.The equivalent MIMO channel coefficient matrix of multi-antenna Chirp-BOK system was derived as a real matrix,so as to reduce the complexity of channel estimation and avoid to be affected by random phase.A two plus two wireless transceiver system was built on the NI USRP-2942R platform.Simulation and experiment results show that the MIMO-Chirp-BOK system inherits the advantages of low complexity,insensitivity to phase shift and frequency offset of Chirp-BOK communication system.It achieves multiplied communication capacity by increasing the number of antennas.     

PILOT－BASED FREQUENCY OFFSET DETECTION SCHEME IN OFDM SYSTEM

The frequency offset information is extracted from local pilot amplitude characteristics, which suffer much less distortion in frequency-selective fading channels than those utilizing frequency domain correlation techniques. Simulation shows that the performance of this scheme has better performance than the existing frequency domain pilot-based frequency offset detection scheme.     

利用改进相频检测器实现大频偏M-PSK信号的快速载波同步

卫星通信中,接收机经常要在较大频偏下实现对M-PSK信号的载波同步;频偏较大的条件下,使用锁相环对信号进行载波同步需要较长的捕获时间,而且如果频偏超出锁相环捕获范围,将无法实现捕获。基于传统的相频检测器,提出了一种改进方案,通过增加相频检测器的"保持"区间,增大了频偏较大时相频检测器输出的直流分量,从而可以更快地实现对频偏的捕获。仿真结果表明,该方案可以帮助锁相环实现更大的频偏捕获范围和更快的捕获速度。     

激光脉冲偏频锁定技术的发展

综述了偏频锁定技术的意义、应用及其在国内外的发展状况,并详细介绍了各种脉冲外差频率鉴频方法和它们的优缺点。     

Frequency offset estimation in the intermediate frequency for satellite-based AIS signals

In this paper, an accurate frequency offset estimator is investigated in the intermediate frequency for the satellite-based automatic identification system (AIS) signals. Using Gaussian minimum shift keying (GMSK) modulation for transmission, the AIS signal is shown to be a plane wave with the modulated phase information and carrier frequency resulting from the Doppler effects. Hence, the phase information can be eliminated with a re-modulated signal, and the frequency offset can be estimated by the ratio of the maximum spectral amplitude and its neighbor spectral amplitude based on the fast Fourier transformation (FFT) interpolation. The estimator has low complexity, and it is easy to implement. Computer simulations are used to assess the performance of the estimator.     

Differential detection of DPSK with frequency offset compensation

A baseband differential-detection receiver for DPSK, incorporating a planar extended Kalman filter for Doppler frequency offset estimation and compensation, is presented. Simulations show that its performance is close to the ideal case of no frequency offset. It is ideal for digital implementation and finds applications in mobile radio communications     

Multiuser detection of asynchronous CDMA with frequency offset

This article presents a near-far resistant detection scheme for asynchronous code-division multiple access with frequency offset. Based on a one-shot technique and Taylor expansion, a zeroth-order and a first-order one-shot linear decorrelating detector (LDD) are proposed. The zeroth-order LDD has simple architecture but suffers performance degradation for large frequency offset. The first-order one-shot LDD, with increased complexity, has very good near-far resistant property even for large frequency offset. Two versions of the first-order one-shot LDD are investigated according to different Taylor expansion approaches. The feasibility of the proposed detectors is demonstrated by computer simulations     

An approximation for the phase offset sensitivity of Viterbidetected continuous phase modulation signals

An approximation is presented for the loss in performance when the Viterbi algorithm receiver for CPM (continuous phase modulation) signals is subject to a phase offset. Pairs of symmetric error events are used to derive a closed-form result that approaches the asymptotic expression, based solely on minimum distance, as E_s/ N₀ approaches infinity. The improved accuracy of the approximation is demonstrated by comparison with a Monte Carlo simulation