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。      

瑞利衰落信道下M-ary二维扩频系统的性能分析

本文基于广义二维扩频的方法,结合M-ary扩频方式,提出了一种M-ary广义二维扩频的方法,给出了该方法的发射机和接收机的工作原理.并在瑞利衰落信道中,分析了M-ary广义二维扩频解调的误比特率性能,得到了误比特率的理论分析结果,同时进行了计算机仿真.计算机仿真曲线与理论分析曲线相吻合,进一步验证了理论分析的正确性.     

Theory of optimum M-ary laser detection

An upper bound on the average error probability of all possible M-ary optical systems, using large-average photon statistics, has been derived. This bound clearly indicates the superiority of the M-ary system over the binary one in terms of allowable transmission rates below which the error rate decreases exponentially with code-block length. A probabilistic solution for the problem of efficient signal selection has been found and demonstrated with a simple illustration.     

Analytical study of FFH systems with square-law diversity combiningin the presence of multitone interference

An analytical study of the performance of fast frequency-hopped (FFH), M-ary orthogonal frequency-shift keyed noncoherent modulation with linear combining of square-law envelopes in the presence of multitone interference is presented. The multiple equal-power interference tones are assumed to correspond to some of the possible FFH/M-ary orthogonal signaling tones. It is also assumed that the channel fading characteristics of the signal and interference tones are independent. We evaluate the effect of the channel fading on the system's performance as a function of various parameters, such as the number of hops per symbol, the signal power to multitone interference power ratio, and the number of interference tones. Our numerical results indicate that by use of square-law time diversity combining, a large number of hops per symbol make the bit-error probability of the system more sensitive to the fading of multitone interference. Finally, the analysis has been proven valid by simulation     

Enhancement of tolerance to MAIs by the synergistic effect between M-ary PAM and the chip-level receiver for optical CDMA systems

In this paper, an M-ary pulse-amplitude modulation (PAM) coded optical code division multiple access (CDMA) system applying the chip-level receiver with M-level threshold detection is proposed. First, in order to increase the number of transmitted bits per pulse, the PAM coded system is considered. However, when the correlator is applied in the receiver, the multiple access interferences (MAIs) with high intensities deteriorate the system performance significantly even if the number of MAIs is small. Consequently, the chip-level receiver with M-level threshold detection instead of the correlator in the M-ary PAM-CDMA system is proposed. The proposed system can obtain the synergistic effect between the PAM and the chip-level receiver, in which the chip-level receiver reduces more MAIs compared with the correlator and the PAM has the larger number of transmitted bits per frame than ON-OFF keying (OOK). As a result, the proposed system can increase the code length and the number of weights, and achieves higher tolerance to MAIs than the OOK-CDMA system with the chip-level receiver under the condition in which the chip duration, the bit rate, and the number of subscribers are kept constant. It is shown that the proposed M-ary PAM-CDMA system with the chip-level receiver achieves better bit error probability (BEP) than the OOK-CDMA system with the chip-level receiver.     

正交循环码M进制扩频接收机的研究

该文提出了一种基于正交循环码的M进制扩频接收机方案,发端将一条原型扩频码循环移位构成M个扩频码,实现M进制扩频,接收端利用时频变换域正交匹配滤波器实现了非相干解扩解调。该方案不仅减少了需要的扩频码数目,而且有效地降低了接收机的计算复杂度。该文对所提出的系统在单用户和多用户条件下的误码性能进行了理论分析和仿真,并比较了3种M进制解扩方法的运算量。结果表明:正交循环码M进制扩频系统的计算复杂度和误码特性均优于传统的M进制系统。     

单光源全双工逆向调制的光通信技术研究

逆向调制光通信是自由空间光通信的一种特殊形式 ,它的系统包括两个不对称的终端:询问端和逆向调制端,询问端由光发送机和光接收机组成 ,逆向调制端由逆向调制装置组成。逆向调制光通信可实现逆向调制端对询问端的单向通信 ,它具有视场角大、功耗低、体积小等优点,适合于小平台工作环境。与 传统自由空间光(FSO)通信相比,逆向调制光通信系统无需复杂的跟瞄系统,但通常只能 完成逆向调制端对询 问端的单向通信。如果要实现逆向调制光通信的全双工通信,可以考虑从调制方式和系统设 计上进行研究。 本文从调制方式出发提出了一种单光源全双工逆向调制光通信方案,仿真分析了方案的信 号传输过程,实现了室内近距离逆向调制单光源全双工光通信实验,验证了方案的可行性 。     

多进制正交扩频加卷积编码体制性能分析

介绍了多进制正交扩频加卷积编码体制的发射端和接收端的原理,给出了多进制正交扩频系统的理论误比特率性能,针对接收端需要对多路匹配滤波器输出信号进行最大值判决,以利于后级的信道译码,从对数似然比(LLR)出发,提出了一种适用于多进制正交扩频系统的次最优的软信息提取方法。对在AWGN信道中多进制正交扩频系统性能进行了MATLAB仿真。结果表明,多进制正交扩频加卷积编码体制不但能有效地解决带宽与处理增益之间的矛盾,还可以获得比直扩系统加卷积编码更高的增益。     

Optimum decoding of M-ary polarisation modulated laser signal

A decision rule has been derived for optimum decoding of an M-ary polarisation modulated signal in a laser communication system.     

全双工逆向调制回复空间光通信系统性能评价

基于逆向调制反射器(MRR)的空间光通信系统因其结构紧凑、可免去链路一端的捕跟(APT)系统、功耗低等优点,是空间光通信系统研究热点之一。提出采用双波长激光发射实现全双工逆向调制回复空间光通信结构,并基于该结构对强度调制解调模式,通信距离为300 km,通信速率为1 GHz下的地面站对近地小卫星全双工通信链路进行了链路计算及通信误码率的分析。当MRR端口径为0.1 m时,通信链路余量大于5 dB,通信误码率优于10-15,满足通信链路的要求。并进一步分析了仿真结果存在的缺陷。结果表明所提出的空间光通信结构在小卫星对地面站全双工激光通信是可行的,是未来空间光通信系统发展趋势之一。     

Essence and Advantages of FM-DCSK Versus Conventional Spread-Spectrum Communication Methods

Frequency-modulated differential chaos shift keying (FM-DCSK) is essentially a technique that combines modulation with a spread-spectrum property for communications. It is also an effective technique similar to recent multiantenna methodologies that can make use of multipath effects, thereby achieving an excellent anti-multipath fading capability. Through analysis and simulation, this paper reports some essential characteristics and advantages in the system performance of the newly proposed M-ary FM-DCSK technology. The basic design of the M-ary FM-DCSK-based chaotic spread-spectrum communication system and a comparison with its conventional equivalent are presented. It is shown that the former is not only robust in multipath fading environments and simple in implementation, but also flexible in adjusting system parameters and trading-off several effects among bandwidth efficiency, energy efficiency, data rate, and error performance. It is demonstrated that the FM-DCSK technique is promising for the next generation of wireless communication systems as an excellent modulation and spread-spectrum scheme candidate.     

相关衰落信道上MIMO系统中组合SC/MRC的性能分析

研究相关瑞利衰落信道上MIMO系统中组合发射机选择合并(SC)/接收机最大比合并(MRC)的天线分集系统性能.使用矩生成函数方法,推导相关瑞利衰落信道上采用组合SC/MRC天线分集争相干检测的M进制相移键控(MPSK),M进制正交幅度调制(MQAM),M进制脉冲幅度调制(MPAM)等几种M进制数字调制方式的误符号率精确表达式.数值计算结果阐明相关性和天线阵结构对采用组合SC/MRC天线分集的几种M进制数字调制方式的平均误符号率性能的影响.     

一种基于SAWTDL的次最优M元扩频接收机

针对最优M元扩频接收机复杂度高的问题,提出了一种低复杂度的次最优M元扩频接收机方案。它的发端使用修正的正交循环码进行M元扩频,降低了组合相关干扰。接收端只需要一个低位声表面波抽头延迟线(SAWTDL)器件就可实现M元解扩,避免了SAWTDL器件一致性问题的困扰。分析了频偏对系统性能的影响,结果显示,该系统的抗频偏能力要好于最优接收机。     

Generalized differential encoding: a nonlinear signal processingperspective

Incoherent detection based on differential encoding has been successfully applied to phase-shift-keying (PSK) signals because it eliminates the need for carrier phase acquisition and tracking at the receiver. This paper generalizes the idea of differential encoding by using a nonlinear transformation called multilag high-order instantaneous moment (ml-HIM). The ml-HIM decoder is capable of removing the effects of phase ambiguity, Dopper frequency, Doppler rate, and even higher order phase distortions. The degrees of freedom offered by the different lags are exploited to optimize system performance. In addition to the classical M-ary PSK, the generalized differential encoding idea is also applied to nonconstant modulus constellations, such as M-ary QAM and AM-PM     

Speech and data communications over 942 MHz TAB and TTIB single sideband mobile radio systems incorporating feed-forward signal regeneration

The transmission of speech and data over 942 MHz pilot tone single sideband (SSB) mobile radio links is the main concern of this paper. It has been found that the use of feedforward signal regeneration enables a speech quality to be obtained in the Rayleigh fading environment which is superior to that achieved by a 25 kHz Advanced Mobile Phone Service (AMPS) type FM system and markedly superior to that obtained with a 12.5 kHz FM system. A new optimized form of SSB, phase-locked transparent tone-in-band (TTIB), is shown to be capable of achieving coherent data transmission such as M-ary phase shift keying (PSK) in the presence of Rayleigh fading without the usual "high-level" irreducible error rates. The signal processing described has wide application from line to satellite communications.     

M-ary nonlinear continuous phase frequency shift keying

The authors present a new approach for designing a continuous phase frequency shift keying (CPFSK) system which is a nonlinear mapping of the M-ary symbols into the N-ary CPFSK. Using this approach they have designed an M-ary nonlinear CPFSK (NCPFSK) system of simple structure. The proposed M-ary NCPFSK system is a modification of the multi-h CPM (MHCPM) scheme. The proposed modulation gives improved performance over conventional modulation schemes     

New chaos M-ary modulation method and its application in communications

At present,chaotic communications have been widely studied.However,these researches mainly focus on the binary systems while the researches of M-ary chaotic communications are not extensive.To change the situation,a chaos M-ary modulation method based on phase plane partition of Hamilton map is proposed.Firstly,the chaotic model of Hamilton map and its phase plane features are described,and then the way of creating the chaos M-ary modulation is discussed.Next,to evaluate the proposed method,the system simulation results and analysis are given.Finally,the chaos M-ary modulation method is applied to communications.     

Performance of orthogonal frequency division multiplexing based M-ary quadrature amplitude modulation in asymmetrical dual-hop mixed RF-FSO transmission system

This paper investigates the performance of a dual-hop mixed relay system with radio frequency (RF) and free-space optics (FSO) communication under the effect of pointing error (PE) and atmospheric turbulence (AT). This paper considers a system where RF and FSO links are cascaded. The RF link is modeled by Nakagami-m fading, and the FSO link is modeled as gamma–gamma (G-G) fading channel. Both the channel models use orthogonal frequency division multiplexing (OFDM) with M-ary quadrature amplitude modulation (QAM). The expressions for probability density function, cumulative distribution function, signal-to-noise ratio, and ergodic capacity are derived. The moment generating function (MGF) of fading and the bit error rate (BER) of the OFDM-based M-ary QAM scheme is derived in terms of Meijer's G-function. It has been observed that, in fixed gain relay systems, the modulation scheme's BER is dominated by the SNR of the RF link. While in a variable gain relay system, the turbulence conditions of the FSO system affect the SNR and the BER of the modulation method. The feasibility of heterodyne detection and intensity modulation direct detection (IM/DD) is analyzed in terms of outage probability and ergodic capacity. The results can be used to choose the optimal modulation order and relay system for QAM-OFDM-based optical wireless systems.     

一种基于单片SAWTDL的M元接收机性能分析

提出了一种基于单片声表面波抽头延迟线(SAWTDL)器件实现的M元扩频接收机,它只需一个SAWTDL器件就可实现M元解扩,从而大大降低了M元扩频接收机的复杂度,避免了SAWTDL器件一致性问题的困扰,同时也降低了M元扩频的选码难度。在扩频码长远远大于M的前提下,这种新接收机的性能与理想M元扩频接收机十分接近。     

高阶调制解调下的低复杂度软信息求解

现代通信系统中,软译码可有效提升译码性能,高阶调制如MQAM和MPSK能够在不增加带宽的同时获得高的传输速率。但高阶调制解调模式下软信息的精确求解过于复杂,目前已有的近似算法性能损失过大。针对软输入技术,结合16QAM和32PSK 2种高阶调制方式,对软信息计算作进一步分析,提出了采用数值逼近的方法对16QAM的最小距离软信息计算公式进行修正和采用旋转坐标转换软信息量度方案的方法对32PSK的软信息计算公式进行修正的2种算法。结合LDPC码的仿真结果表明,算法在不增加计算复杂度的前提下,其性能仍能进一步逼近理论算法。