A new carrier recovery circuit for land mobile satellitecommunication

A DCF (dual carrier filter) reverse-modulation-type carrier recovery circuit is proposed to achieve a low carrier skipping rate and satisfactory phase tracking performance for coherent detection of PSK (phase shift keying) signals in fast Rician fading channels. The proposed scheme employs both narrow and wide bandwidth carrier filters simultaneously for the reverse-modulation-type carrier recovery circuit. It is clarified by computer simulation that the Pe performance of a QPSK (quadriphase shift keying) modem employing the proposed scheme shows an improvement of 1.5 dB in required E_s/N_O at Pe=10⁴ (after Viterbi decoding (R=7/8, K=7), C/M (direct-to-multipath signal power ratio)=10 dB, interleaving size=64×64), compared with conventional coherent detection employing the reverse modulation tank-limiter scheme or the Costas loop scheme     

MPSK信号载频盲估计

研究了相位编码信号（MPSK）的载频盲估计算法。在没有接收信号先验知识的情况下，首先对MPSK信号载频进行粗估计，然后进行相关运算把信号，接着估计码速率，得到载频和码速率的估计值，就把载频估计问题转化为频偏估计问题。利用基带MPSK信号的相位函数是分段线性函数且每一段直线的斜率均正比于频偏的性质，对接收信号的相位函数进行处理，把分段直线变成一条直线，最后运用最小二乘拟合法得到直线的斜率从而得到频偏估计。仿真表明本算法在没有先验知识的情况下可以对MPSK信号载频进行精确估计。     

Low-Complexity Compensation of SOA Nonlinearity for Single-Channel PSK and OOK

Carrier density fluctuations in semiconductor optical amplifiers (SOAs) impose penalties on phase-shift keying (PSK) signals due to nonlinear phase noise (NLPN), and on-off keying (OOK) signals due to self-gain modulation. In this paper, we propose a simple scheme to equalize the impairments induced by SOA nonlinearities, derived from the small signal analysis of carrier density fluctuations. We demonstrate via simulation almost complete cancelation of the NLPN added by a saturated SOA on a differential PSK signal. We demonstrate via both simulations and experiment the effectiveness of the method for mitigation of nonlinear distortions imposed by SOAs on an OOK signal.      

fso中一种光载波外差dpsk系统的设计

介绍了自由空间光通信中的相干通信系统,通过对相干光通信中振幅键控(ASK),频移键控(FSK),相移键控(PSK),差分相移键控(DPSK)四种光载波相干调制方式性能的分析和比较,仿真结果得出PSK调制误码性能更好,提出了一种光载波外差差分相移键控(DPSK)系统.     

Approximate maximum likelihood coherent detection of M-ary PSKsignals using Viterbi algorithm

Reduced complexity coherent detection based on maximum likelihood sequence estimation using the Viterbi algorithm is proposed for the reception of uncoded M-ary PSK signals with unknown carrier phase. The computer-simulated bit error rate performance of 4PSK is reported     

卫星测控侦察中相位编码信号的调制识别

针对卫星测控链路中常用的数字调相信号BPSK、QPSK、OQPSK（偏移QPSK）和UQPSK（非平衡QPSK）的调制识别问题，提出了基于二阶矩和相位差统计特性的分类算法。该方法首先以二倍码速率对复基带信号进行采样，然后利用能量归一化的二阶矩的模和相邻样点相位差绝对值的统计特性，分两个等级实现对这四种信号的分类。分析了载频偏移、相位误差以及成形脉冲对分类算法性能的影响，并通过计算机仿真验证了算法的有效性。     

Performance of M-ary PSK signals in slow Rayleigh fading channels

The error rate performance of M-ary coherent phase shift keyed signals and M-ary differential phase shift keyed signals in slow Rayleigh fading channels is analysed. Closed-form expressions for the symbol error rate are presented. The coherent PSK signals are 3 dB stronger than the differential PSK signals at high SNR for given M in a Rayleigh fading environment.<>     

Trellis-coded 8PSK with embedded QPSK

A coded eight-phase-shift-keying (C8PSK) method is described that is characterized by a quaternary phase-shift-keyed signal embedded in the modulated sequence. This method is a double-trellis-coded modification of the well-known C8PSK and is referred to as MC8PSK. Five coded bits are generated from four user bits in a single coding step and then mapped to an 8PSK symbol followed by a QPSK symbol. Given comparable decoder or receiver complexity, the coding gains of C8PSK and MC8PSK are comparable. Advantages of MC8PSK concern carrier synchronization. With C8PSK, problems with carrier phase tracking are encountered. With MC8PSK, these can be avoided, since carrier phase control can be based on the embedded QPSK. For some codes, error-free decoding is achievable in any locking condition of a QPSK-dependent PLL (phase locked loop), making synchronization and decoding especially simple. The partitioning of the channel symbol set, the associated bit mapping, and the code design are treated in order to describe MC8PSK. Aspects of receiver synchronization are discussed for C8PSK and for MC8PSK, focusing on QPSK phase-detection principles. The implementation of a four-state MC8PSK modem for an information rate of 2.048 Mb/s is described, and experimental results demonstrating the very robust carrier synchronization are presented     

Cramer-Rao lower bounds for QAM phase and frequency estimation

In this paper, we present the true Cramer-Rao lower bounds (CRLBs) for the estimation of phase offset for common quadrature amplitude modulation (QAM), PSK, and PAM signals in AWGN channels. It is shown that the same analysis also applies to the QAM, FSK, and PAM CRLBs for frequency offset estimation. The ratio of the modulated to the unmodulated CRLBs is derived for all QAM, PSK, and PAM signals and calculated for specific cases of interest. This is useful to determine the limiting performance of synchronization circuits for coherent receivers without the need to simulate particular algorithms. The hounds are compared to the existing true CRLBs for an unmodulated carrier wave (CW), BPSK, and QPSK. We investigated new and existing QAM phase estimation algorithms in order to verify the new phase CRLB. This showed that new minimum distance estimator performs close to the QAM bound and provides a large improvement over the power law estimator at moderate to high signal-to-noise ratios     

多种调制格式微波信号的光学产生方案

提出了一种基于偏振调制器（PolM）和Sagnac环级联的多调制格式微波信号的光学产生方案。理论分析了PolM在基带编码信号的驱动下产生偏振键控（PolSK）信号的基本原理,Sagnac环中嵌有两个马赫增德尔调制器（MZM）,分别对顺时针和逆时针传输的PolSK信号进行独立调制。通过合理调整两个MZM的驱动信号,实现了幅移键控（ASK）、频移键控（FSK）和相移键控（PSK）微波信号的产生。在仿真实验中,产生了比特率为2 Gbit/s的40 GHz ASK信号、20/40 GHz FSK信号和20 GHz PSK信号,同时验证了比特率和载波频率的宽带可调谐性。Sagnac环结构提升了系统的稳定性,并且针对每种调制格式的微波信号,在不改变链路结构的情况下其比特率和载波频率都可以通过控制基带编码信号和MZM的射频驱动来进行独立且灵活的调谐。     

脉内相位编码信号的识别与码序恢复

为了提高低信噪比(SNR)下对雷达脉内相位编码(PSK)信号的处理能力,对传统的相位差分法进行了改进,并利用该方法对PSK信号进行了识别与码元序列的恢复。根据PSK信号的特性,结合滤波、数字变频和高阶差分来减小噪声对相位的影响,提高了相位差分法的抗噪性。对相位差分序列归一化后,先进行码元宽度的精确估计,再由码元关系去除伪跳变点。最后通过一系列的特征提取,实现了PSK信号的综合处理。仿真结果表明,所提算法在低信噪比下性能良好,具有很高的工程应用价值。     

A Novel Ternary CDMA Code for TPSK Modulation Scheme

In code division multiple access (CDMA), two or more chips are grouped together to form symbols and each symbol is transmitted during the symbol period. The phase shift keying (PSK) modulation techniques map the digital baseband data into two or more possible signals by varying the phase of a radio frequency (RF) carrier. The recently proposed PSK scheme called ternary PSK (TPSK) scheme can convey three possible symbols. In this paper, a novel ternary based CDMA sequence so-called large area synchronous even ternary (LAS-ET) sequence is introduced to increase spectrum efficiency in TPSK scheme. Its sequence duty ratio and cross-correlation are analyzed. The performance analysis of this sequence is compared with the large area synchronous (LAS) sequence in term of symbol error rate and chip error rate (CER) over various channel models. It is shown that TPSK scheme in LAS-ET sequence outperforms LAS sequence in terms of CER evaluation. At the same time, the spectrum efficiency is doubled when a pair of chips in LAS-ET sequence is mapped into one symbol.     

Carrier detection of PSK signals

This paper reports on a theoretical study of the detection of the 2f and 4f carrier components of phase-shift keying (PSK) signals produced by passing signal and noise through a nonlinear device. Unbalanced quadrature PSK (QPSK) signals, i.e., QPSK signals with unequal power in the two channels, are studied. The complete range of channel power ratio is covered, with equal emphasis on the general unbalanced case and the two limiting cases of binary PSK and (balanced) QPSK. Analytic expressions are derived for the detected SNR of carrier harmonics 2f and 4f as a function of SNR, channel power ratio, and normalized input bandwidth. The results apply equally well to PSK data signals and direct-sequence spread-spectrum signals. Measurements confirm every aspect of the theory. The least detectable signal type is balanced QPSK, which is detectable (at 4f) at a threshold SNR ranging from -2 to -13 dB as the detection process gain (chip or data rate/detection bandwidth) is varied from 40 to 80 dB     

低信噪比下相位编码信号载频估计新方法

研究了电子侦察中相位编码信号的载频估计问题, 提出一种低信噪比下载频估计新方法.该方法首先将相位编码信号划分为等长度的交叠区间, 并计算各个区间内信号频谱的聚集性测度, 然后采用网格密度聚类算法对聚集性测度进行分类, 以聚类结果作为载频估计的特征类, 最后叠加特征类频谱并提取峰值得出信号载频估计值.实验结果表明, 该方法无需先验知识, 对编码形式不敏感, 且能够在较低信噪比下完成相位编码信号的载频估计, 适合于电子侦察场合.     

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     

Converged delivery of WiMAX and wireline services over an extended reach passive optical access network

In this paper we present long-reach fiber access links supporting transmission of Worldwide Interoperability for Microwave Access (WiMAX) compliant signals. We present bi-directional full-duplex transmission of 256-state quadrature amplitude modulation (256-QAM) modulated WiMAX-compliant signals on a 2.4-GHz RF carrier over an 80-km long-reach access link at 100 Mb/s (down) and 64 Mb/s (up). Transmission of 64-QAM and 256-QAM-modulated signals on a 5.8-GHz RF carrier over a 118.8-km access link converged with four baseband differential quadrature phase shift keying (DQPSK) modulated wireline channels, along with ultra-wide band (UWB) and phase shift keying (PSK) radio-over-fiber (RoF) wireless signals over a deployed optical fiber link is also presented.     

A Digital Demodulator for PSK Signals

This paper describes a digital demodulator for phase-shift-keyed (PSK) signals in which the phase difference between the received signal and a carrier reference is found by measuring digitally the time interval between the zero crossings of the signal and the reference. In the case of coherent detection the reference is locked to one of theMpossible phases of the signal. The advantage of this demodulator is that bulky low-pass filters and delay lines as well as critical threshold devices can be dispensed with. On the other hand, digital measurement of the phase and the use of a finite-width sampling window lead to degradation of the error performance. This degradation is theoretically analyzed for both coherent and phase-comparison detection. The quantizing error proves to be small enough when the phase difference is coded into a 6-b binary number, and the theoretical results are in good agreement with measurements taken from an experimental phase-comparison demodulator for fourand eight-level PSK signals. The experimental demodulator is also described in the paper.     

GaAs MESFET Regenerator for Phase-Shift Keying Signals at the Carrier Frequency

This paper describes a GaAs metal-semiconductor FET (GaAs MESFET) phase regenerator for biphase phase-shift keying (PSK) signals at the carrier frequency. By using this regenerator, decision and reshaping of the signals can be made without detection, thus repeaters can be simplified. This paper shows that phase regeneration is characterized by the symbol m, which denotes the ratio of the normal signal to the phase-inverted signal. Ideal phase regeneration is obtained for m = 1. An analysis of the ratio m for the MESFET regenerator is presented, and it is shown that, if the gate bias or the local-oscillator power level are selected at a slightly higher point than that minimizing the conversion loss, then m = 1.03 is obtained at an excess loss of 3 dB. To verify this analysis, the ratio m was measured experimentally and it was found to agree with the analysis. Static and dynamic characteristics were also measured, and it is shown that the MESFET regenerator has decision and reshaping ability.     

Analysis of equal-gain diversity with partially coherent fadingsignals

An analytical technique based on Gram-Charlier series expansion is presented for the computation of the error probability of equal-gain combiner (EGC) with partially coherent fading signals. Imperfect carrier recovery is attributed to the random noise present in the carrier recovery loops. The resulting noisy phase references are assumed to satisfy Tikhonov distribution. The fades on the diversity branches are assumed to be slowly varying and statistically independent with Rayleigh-distributed envelopes. The error-rate performance of coherent and differentially coherent phase-shift keying (PSK) systems are compared and the phase precision requirement for a reliable coherent detection is computed. Detection loss caused by carrier phase errors is computed for several signal-to-noise ratio (SNR) reliability and bit error probability levels. It is demonstrated that the effect of carrier phase errors on the mean SNR is negligible compared to their effect on deep fades or small bit error probabilities. It is also shown that the carrier phase precision requirement can be reduced through signal combination     

卫星通信中的一种小参量跳频BPSK/DPSK相位估计算法

军事卫星通信系统中很多情况下采用跳频通信,这就导致PSK的相干检测比较困难,通常使用增加参考符号来对接收信号的相位进行估计.因此很多系统采用差分相位调制,比如DPSK调制方式就不需要相位信息,但DPSK比PSK的功率效率要低.本文提出一种新的相位估计算法,该算法利用小数据量的参考信号对相位调制信号的相干检测来提高功率效率,而且在同一编码块(同一跳)中实现相位估计.本文在3种通信信道环境下进行模拟试验(蒙特卡罗仿真),最后以输出的误码率来验证算法的先进性.