基于FPGA的多模式通信信号解调及自适应位同步技术

通信信号的识别与解调是通信侦察的重要组成部分。本文在假设侦察识别过程已经完成,且调制模式主要为FM、FSK、BPSK和QPSK四种方式,码速率在一定范围内变化的前提条件下,讨论这四种不同模式通信信号的解调技术,在解调中引入自适应的位同步技术,保证解调结果的正确输出。整个系统各模块基于FPGA实现,便于编程、修改以及升级改进,利于移植。     

卫星通信中的OQPSK调制技术分析

卫星通信系统的通信质量很大程度上依赖于所采用的调制方式。偏移正交相移键控(OQPSK:Offset Quadrature Phase Shift Keying)是在QPSK的基础上提出的一种恒包络调制技术。本文在详细介绍OQPSK调制技术原理和特点的基础上,分析了OQPSK调制技术的频谱特性及其在卫星通信中的优势,结果表明:OQPSK调制技术有良好的频谱效率、功率效率和抗非线性特性,非常适合卫星通信信道。     

基于DDS的多载波水声通信信号发生器的实现

根据水下远程通信系统对信号发射的要求,设计并实现了由FPGA和DSP组成的水下声通信信号发生器。采用直接数字合成（DDS）方法,实现了多载波频移键控（MFSK）和正交频分复用（OFDM）2种水声远程通信复杂信号。实验结果表明,该系统性能稳定,能够满足水声通信系统对发射信号的实时发生要求。     

码宽对水声信号功率谱的影响分析

通信信号的功率谱分布情况影响着通信系统的传输效率,码宽对功率谱分布的影响较大。针对四相相移键控、二进制频移键控等典型水声通信信号,采用现代功率谱估计方法中基于参数模型的Burg算法,对其功率谱分布进行了估计。重点研究了不同码宽条件下,Burg算法估计信号功率谱的基本特征和分布规律,对码宽对功率谱的影响进行了归纳总结,为扩频通信和典型水声通信信号的设计提供了技术支持。     

超窄带通信调制技术研究

在分析超窄带通信中的关键技术一具有高频带利用率的双向编码调制方式:可变相移键控(VPSK),甚小频移键控(VMSK)的基础上重点讨论了1/2甚小频移键控(VMSK/2)调制方式的编解码原理,并给出了其频谱的数学表达式和计算机仿真频谱图.对VMSK/2信号的频谱利用率和误码率作出初步估计,给出了VMSK/2无线数字传输系统模型,并对近似零群时延滤波器进行了初步分析.     

PAPR Reduction in OFDM Systems with Large Number of Sub-Carriers by Carrier Interferometry Approaches

High Peak-to-Average Power Ratio(PAPR)is one of the major drawbacks of Orthogonal Frequency DivisionMultiplexing(OFDM)systems.This paper presents the structures of the particular bit sequences leading to the maximumPAPR(PAPR_(max))in Carrier-Interferometry OFDM(CI/OFDM)and Pseudo Orthogonal Carrier-Interferometry OFDM(PO-CI/OFDM)systems for Binary Phase Shift Keying(BPSK)modulation.Furthermore,the simulation and analysisof PAPR_(max) and PAPR cumulative distribution in CI/OFDM and PO-CI/OFDM systems with 2048 sub-carriers are pre-sented in this paper.The results show that the PAPR of OFDM system with large number of sub-carriers reduced evidentlyvia CI approaches.     

Bandwidth‐Efficient Precoding Scheme with Flicker Mitigation for OFDM‐Based Visible Light Communications

Recently, orthogonal frequency‐division multiplexing (OFDM) was applied to VLC systems owing to its high rate capability. On the other hand, a real‐valued unipolar OFDM signal for VLC significantly reduces bandwidth efficiency. For practical implementation, channel estimation is required for data demodulation, which causes a further decrease in spectral efficiency. In addition, the large fluctuation of an OFDM signal results in poor illumination quality, such as chromaticity changes. This paper proposes a spectrally efficient method based on a hidden‐pilot‐aided precoding technology for VLC with less flickering than a conventional OFDM‐based method. This approach can obtain channel information without any loss of bandwidth efficiency while ensuring illumination quality by reducing the flickering effect of an OFDM‐based VLC. The simulation results show that the proposed method provides a 6.4% gain in bandwidth efficiency with a 4% reduction in flicker compared to a conventional OFDM‐based method.     

OFDM系统中基于三维星座旋转的物理层安全加密算法

传统无线通信的安全主要依赖于上层加密机制,无法保护物理层调制方式和调制信息的安全.本文针对正交频分复用（OFDM,Orthogonal Frequency Division Multiplexing）系统提出了一种物理层加密调制算法.该算法首先利用相位随机化的信号进行信道探测并提取出等效信道相位信息,然后对三维星座进行物理层调制加密,最后接收端进行解密解调.该方案充分利用了无线信道相位响应的随机性、互易性和位置敏感性,并将该特性用于增强物理层信号的安全性.理论分析和计算机仿真结果表明该算法具有较强的安全性,且相对于传统的QPSK（Quadrature Phase Shift Keying）调制,该算法的误码率性能提升约2.5dB.本文关注于物理层安全,旨在物理信号层提供新的安全保障,在未来5G通信和军事安全通信中有较广泛的应用前景.     

Analysis of the Effect of the I/Q Base-Band Filter Mismatch in an OFDM Modem

In digital communication modems in which a very high rate system clock is used, it is necessary to use analog base-band shaping filters in the inphase (I) and quadrature (Q) paths of the modulator. However, this type of implementation inherently produces a mismatch of the I and Q paths. In the present paper, results of the analysis of the transmitter (TX) I/Q mismatch in an Orthogonal Frequency Division Multiplexing (OFDM) system with Differential Coherent Quadrature Phase Shift Keying (DQPSK) modulation is presented. Theoretical analysis shows that the Signal-to-Noise (SNR) degradation due to the I/Q mismatch can be represented by a mismatch transfer function on the basis of which one can compute the maximum affordable amplitude and phase mismatch of the TX filters transfer functions.     

Compressed sensing channel estimation for STBC‐SM based hybrid MIMO‐OFDM system for visible light communication

This paper presents the idea of sparse channel estimation using compressed sensing (CS) method for space–time block coding (STBC), and spatially multiplexing (SM) derived hybrid multiple‐input multiple‐output (MIMO) Asymmetrically clipped optical‐orthogonal frequency division multiplexing (ACO‐OFDM) optical wireless communication system. This hybrid system accounts multiplexing gain of SM and diversity gain of STBC technique. We present a new variant of sparsity adaptive matching pursuit (SaMP) algorithm called dynamic step‐size SaMP (DSS‐SaMP) algorithm. It makes use of the inherent and implicit structure of SaMP, along with dynamic adaptivity of step‐size feature which is compatible with the energy of the input signal, thus the name dynamic step size. Existing CS‐based recovery algorithms like orthogonal matching pursuit, SaMP, adaptive step‐size SaMP, and proposed DSS‐SaMP were compared for hybrid MIMO‐ACO‐OFDM visible light communication system. The performance analysis is demonstrated through simulation results with respect to bit error rate, symbol error rate, mean square error, computational complexity, and peak‐to‐average power ratio. Simulation results show that the proposed technique gives improved performance and lesser computational complexity in comparison with conventional estimation algorithms.     

BPSK‒QPSK和QPSK‒16QAM的光调制格式转换

信号在调制方式不同的系统之间传输时,需要对信号调制格式进行转换,而调制格式转换通常在电信号上进行,要将光信号恢复成电信号。在电信号上进行调制格式转换后,再经电光调制器变换成光信号发射。频繁的光电或电光转换通常会增加系统成本,针对该问题,提出了利用相干叠加在光域上实现二进制相移键控(BPSK)到正交相移键控(QPSK)以及QPSK到正交幅度调制(16QAM)的调制格式转换的方法。实验通过Optisystem软件对转换模型进行仿真,采用10 Gpbs伪随机信号作为测试信源,通过星座图观测出信号成功转换为QPSK和16QAM;并在不同光信噪比、光源线宽和信号功率下对转换模型与直接QPSK、16QAM传输模型进行误码分析对比,在相同条件下转换模型和直接传输的误码率高度保持一致,表明这种调制格式转换方法具有较高的稳定性和准确性,能够适用于不同系统间的信号传输。     

40Gbit/s DP-QPSK Transponder模块技术分析

文章介绍了40 Gbit/s DP-QPSK(双极化四相相移键控)模块的调制技术、相干接收技术和总体方案设计以及在模块中需要解决的关键问题.利用DP-QPSK调制技术和相干接收技术,实现了40 Gbit/s光系统的长距离传输.40 Gbit/s DP-QPSK具有很高的光谱效率以及较大的色散和偏振模色散容限,可以更好地...     

一种新的CDMA系统信干比估计方法

本文根据CDMA系统中解扩后基带信号的特点和基带信号模型,分析了基于QPSK调制的基带信号信噪比估计方法,提出了一种新的适用于CDMA解扩后基带信号的信干比估计方法.计算机仿真结果表明,在低信干比情况下该方法较其他方法,有较高的可信度.     

太赫兹频段OFDM一体化波形的雷达探测性能分析

传统的正交频分复用(OFDM)信号在太赫兹通信系统中通常会面临峰均功率比(PAPR)过高的问题,严重降低功率放大器的效率,恶化太赫兹链路的非线性效应。恒模雷达-通信一体化波形可以抑制PAPR的影响。本文采用模糊函数作为评价标准,从距离和速度两方面分析和比较了太赫兹频段正交频分复用-16阶正交幅相调制-线调频(OFDM-16QAM-LFM)、正交频分复用-二进制相移键控-线调频(OFDM-BPSK-LFM)、正交频分复用-最小相移键控-线调频(OFDM-MSK-LFM)3种OFDM一体化波形的雷达探测性能。数值仿真结果表明,OFDM-16QAM-LFM波形在太赫兹频段的距离和速度探测性能良好,但PAPR过高;OFDM-BPSK-LFM、OFDM-MSK-LFM波形采用相位调制代替幅度-相位调制,保持恒定包络特性;OFDM-BPSK-LFM一体化波形的距离分辨力不会随着子载波数量增加而恶化,但速度分辨力随着子载波数量的增加而受到很大影响,不适宜用于高速运动状态下多目标的速度检测;OFDM-MSK-LFM波形可承载更多的子载波,适应复杂场景下的多载波雷达探测需求。本文方法为不同应用场景的一体化波形选择提供了参考。     

基于一阶统计矩的数字通信信号调制方式的自动识别

数字通信信号调制方式的自动识别在军用和民用方面都具有十分重要的意义。为了能自动识别MASK、MFSK、MPSK和MQAM四类信号,本文基于截获信号的一阶统计矩,提出七个特征参数,它们均可利用常规信号处理技术得到,与基于二阶或高阶矩的其它特征参数相比,这些参数提取过程具有计算量小、提取方便的优点。给出四类信号调制方式自动识别算法的实现流程,该识别算法以判决理论为基础,不要求实现码元同步。仿真结果证明,在信噪比≥7dB时,识别算法的平均识别成功率＞97%,性能明显优于同类算法,有望用于实际的非协作通信系统中信号的检测和快速识别。      

多元位置随机极性CP-EBPSK调制解调器研究

为改善随机极性的连续相位扩展二元相移键控(Extended Binary Phase Shift Keying with Continuous Phase,CP-EBPSK)调制信号的频谱利用率,提出了一种多元位置随机极性CP-EBPSK调制方式。阐述了多元位置随机极性CP-EBPSK调制原理。在数字冲击滤波器的基础上,分别给出了基于多路判决方式、贪婪判决方式和合理判决方式的解调器,并通过仿真对比和分析了CP-EBPSK调制、随机极性CP-EBPSK调制和多元位置随机极性CP-EBPSK调制的功率谱、-60dB带宽、频谱利用率和解调性能。仿真结果表明:1)在频谱结构不变的条件下,新的调制方式可使信息传输速率和频谱利用率成倍提高;2) 若以bps/Hz/SNR(dB)为综合指标,CP-EBPSK系统为1.18*10-3,随机极性CP-EBPSK系统为7.01,而新的调制解调系统为13.8。      

可见光通信单极性非对称限幅光OFDM技术研究

为了提升非对称限幅光正交频分复用(ACO-OFDM )的频谱效率,提出了一种单极性非对称限幅 光OFDM(UACO-OFDM)调制技术。UACO-OFDM是由ACO-OFDM和单极性OFDM(U-OFDM)两种 光OFDM信号组成,不同长度的信号在发送端按照一定规则进行叠加。然后通过发光二极管(LED)进行 传输,在接收端只用1个光电检测器(PD)接收光信号,采用干扰消除方法依次对不同信号 进行解调。当 调制阶数相同时,UACO-OFDM的频谱效率要高于ACO-OFDM。在频谱效率相等的情况下,对 UACO-OFDM和其他传统光OFDM调制方式的误比特率(BER)和峰均比(PAPR) 性能进行对比分析。 仿真结果表明,UACO-OFDM的BER性能更优。与频 谱能量有效OFDM(SEE-OFDM)相比,当子载波 数为64时,两者的PAPR性能比较接近;当子载波数为256024时,UACO-OFDM比SEE-OFDM的PAPR分别低2dB和5dB以上。     

Combination of PAPR reduction and linearization for the OFDM communication system

Orthogonal frequency division multiplexing (OFDM) has been widely used in many kinds of communication systems. However, OFDM signal has serious problem of high peak‐to‐average‐power ratio (PAPR) due to so many sub‐carriers. So, OFDM signal has very wide dynamic range. Therefore, the bit error rate (BER) performance may be degraded because of the nonlinear devices like the high power amplifier (HPA). Even if the linearization and large back‐off are used to compensate for the HPA nonlinearity, the power efficiency of the HPA is still very low since the PAPR is very high. Therefore, the PAPR reduction of the OFDM signal before the linearization would be more reasonable to improve the power efficiency and nonlinear compensation at the same time. In this paper, we propose a new combined method of SPW (sub‐block phase weighting) for PAPR reduction and linearization technique for the improvement of the power efficiency and for the nonlinear compensation of HPA. An updated SPW method is proposed to use a novel weighting factor multiplication of the complementary sequence characteristic and PAPR threshold technique. From the simulation results, it can be confirmed that BER performance is significantly improved and out‐of‐band spectrum radiations are much mitigated. Power efficiency of HPA can be enhanced since we can set small IBO (input back‐off) due to the PAPR reduction. The proposed system shows about 3 and 1 dB performance improvement than the LCP (linearized constant peak‐power)‐OFDM and LCP‐OFDM plus SPW at BER = 10⁻⁴. Copyright © 2010 John Wiley & Sons, Ltd.     

三种载波抑制归零码光调制格式性能

首先分析了基于载波抑制归零码的光载波抑制归零-开关键控(CSRZ-OOK)、载波抑制归零-差分相移键控(CSRZ-DPSK)和载波抑制归零-差分正交相移键控(CSRZ-DQPSK) 三种光调制格式的时域和频域特性,并数字仿真了其在40 Gbit/s单信道光纤系统中的传输性能.以Q值、眼图和误码率(BER)作为性能评价指标,研究了这三种调制格式对色散(CD)、偏振模色散(PMD)和非线性效应的抑制作用.结果表明:CSRZ-DQPSK相对于CSRZ-OOK、CSRZ-DPSK对色散、偏振模色散和非线性效应有非常好的容忍能力.