基于判决反馈的CPM信号定时相位联合估计算法

针对连续相位调制(CPM)信号同步问题,提出了一种基于数据辅助联合直接判决的同步算法。该算法基于CPM信号的PAM分解,利用最大似然函数推导出定时和相位误差函数,并迭代求解恢复出定时和相位信息。首先根据信号帧中独特码实现同步信息的快速捕获,然后运用直接判决后反馈迭代的方法进行定时和相位信息的跟踪。仿真结果表明,文中方法的性能逼近MCRB界,同时运算复杂度小,便于工程实现。     

基于星座图的QAM信号调制方式识别

给出了利用信号星座图的QAM信号调制方式识别技术。在对QAM信号进行分析的基础上。重点讨论了信号载频、码元速率盲估计方法以及信道盲均衡方法。仿真结果表明，利用这种方法，可以精确地估计QAM信号的载频和码元速率，成功地将信号星座图恢复出来，并通过信号星座图完成信号的识别。     

QAM接收机的定时误差估计算法的研究

定时恢复是全数字接收机中的一项关键技术。以Gardner定时误差检测算法为基础,从理论上对算法的计算复杂度、以及整个定时恢复环路实现的难易程度对其进行分析。以64QAM为例对整个环路进行了仿真验证,该算法对载波相位不敏感,并且简单易行,适用于QAM信号的定时恢复。     

Full constellation phase detector for carrier recovery in high-order QAM systems

A full constellation phase detector that improves carrier acquisition performance in high-order quadrature amplitude modulation (QAM) is proposed. The weighting function of the phase detector is mathematically derived, and simulated phase detector characteristics are presented for 256QAM. The results of an experimental evaluation are also reported, which show that the carrier recovery loop based on the proposed phase detector has a large frequency acquisition range and low phase tracking error in high-order QAM.     

Multilevel QAM Modulation Techniques for Digital Microwave Radios

A pilot carrier injection method is described together with feedback balance coding which reduces spectral power near the carrier. Robustness of carrier recovery using the pilot carrier injection method is theoretically estimated. The estimation suggests that recovered carrier SNR higher than 40 dB can be expected even under muitipath fading with notch depth of 45 dB located just at the carrier frequency. Signatures for multipath fading are estimated for a 64-QAM system with transversal equalizers as a countermeasure. Measured signatures agree reasonably well with the calculated ones. Dependences of signatures on modulation level, transversal equalizer tap number, and rolloff rate are also shown.     

Identification of the source of an interferer by comparison with known carriers using a single satellite

We describe a method for identifying the source of a satellite interferer using a single satellite. The technique relies on the fact that the strength of a carrier signal measured at the downlink station varies with time due to a number of factors, and we use a quantum‐inspired algorithm to compute a “signature” for a signal, which captures part of the pattern of variation that is a characteristic of the uplink antenna. We define a distance measure to numerically quantify the degree of similarity between two signatures, and by computing the distances between the signature for an interfering carrier and the signatures of the known carriers being relayed by the same satellite at the same time, we can identify the antenna that the interferer originated from, if a known carrier is being relayed from it. As a proof of concept, we evaluate the performance of the technique using a simple statistical model applied to measured carrier data.     

基于多门限极性判决的QAM载波恢复算法

正交幅度调制(QAM)是现代通信中最为常用的一种调制方法,其载波恢复是决定接收机性能的关键因素之一.从提高收敛速度和减小锁定误差的角度出发,提出了一种用于QAM解调的多门限极性判决载波恢复算法,该算法充分利用QAM星座图中对角线上锁定误差为零的信号点,增加了用于提取相位误差的符号集.分析和仿真表明,与传统的面向判决载波恢复算法相比,该算法不仅保留了极性判决载波恢复算法频偏搜索范围大的优点,且能进一步提高收敛速度.     

256 QAM Modem for Multicarrier 400 Mbit/s Digital Radio

This paper describes the performance of a 256 QAM modem with 400 Mbit / s transmission capacity. A variety of novel techniques are introduced as ways to achieve good performance. Key techniques include 1) an accurate 256 QAM modulator employing a new monolithic multiplier IC, 2) a carrier recovery circuit which satisfies such requirements: good phase jitter performance and no false lock phenomenon, 3) a highly stable high-level decision circuit, and 4) a forward error correcting code. As an overall modem performance, BER characteristics and signatures are presented. The equivalent CNR degradations of 1 dB(at BER of 10^-4) and 2 dB (at BER of 10^-9)are obtained using a single Lee-error correcting code and a seven-tap baseband transversal equalizer. The residual bit errors are decreased below the order of 10^-10. The performance of a 256 QAM multicarrier modem has given prospect for the development of 400 Mbit/s digital microwave radio system.     

16 QAM Carrier Recovery PLL for Service-Channel Transmission Using FSK Additional Modulation

This paper describes the design and performance of the 16 QAM carrier recovery PLL for service-channel transmission using FSK additional modulation. When FSK additional modulation is applied, tracking phase error occurs and corrupts the 16 QAM signal. To reduce the phase error without widening the loop noise bandwidth is an important issue in the 16 QAM-FSK double modulation scheme. An analytical expression to estimate the peak phase error due to class 4 partial response FSK is established, By using the approximation formula, an optimization of the carrier recovery PLL is presented. Moreover, experiments and computer simulations are carried out for the 200 Mbit/s 16 QAM and 64 kbit/s SC double modulation system. As a result, it is demonstrated that a 0.1 dB 16 QAM equivalent power loss and an 8 dB frequency deviation margin of SC transmission performance can be obtained.     

相位噪声对多天线QAM性能影响分析

正交幅度调制系统(QAM)对载波的相位噪声非常敏感,多天线技术的使用可以提高通信系统的性能。对QAM系统在当今通信系统中的应用及相位噪声对QAM系统性能影响进行介绍,对多天线QAM系统受相位噪声影响进行了理论分析及仿真验证,并给出了闭式误差向量幅度(EVM)表达式。给出的理论公式及仿真结果对多天线QAM系统相位噪声指标的确定及系统性能分析具有参考意义。     

A Unified Approach to Pulse Design in Data Transmission

The problem of designing optimum pulseshapes for data transmission over randomly selected channels is examined using a meansquared error criterion. Earlier work has focused principally on SSB or VSB systems in the presence of timing and carrier phase jitter, but we extend the results here to any two-dimensional signaling scheme (including as special cases SSB, VSB, combined AM-PM, QAM, and staggered QAM) and to any type of channel dispersion. By imposing certain mild constraints on the transmitter and receiver filters, it is seen that one can solve for optimum pulses more easily than with earlier approaches, and yet the resulting system is still essentially optimum. These constraints leave design freedom only in the rolloff bands of the pulse spectra, and a major thurst of the work is to design for optimal utilization of whatever excess bandwidth is available. The approach used involves immunity to channel distortions: only the type of channel distortion to be encountered is known, and series expansions of mean-squared error are used to find sensitivity coefficients. These coefficients are then minimized by proper signal design. Closed form expressions are found for the optimum pulses, and these results are compared with previous work. A second approach, which uses as its criterion the mean-squared error averaged over all possible channel characteristics, is also discussed.     

基于软件无线电的MQAM信号调制识别

提出了一种软件无线电高阶QAM信号的识别算法。该算法直接从接收信号中估计出频偏和相偏并进行补偿,同时估计波特率和定时误差,并经过低通滤波、采样率变换、定时抽取等步骤,恢复出星座图,然后计算星座图实部信息的高阶累积量进行识别。实验结果表明,在SNR大于12dB,码元符号数为1000时,识别率可以达到96%。     

Timing jitter due to carrier linewidth of laser-diode pulse sourcesin ultra-high speed soliton transmission

We theoretically analyze the timing jitter due to both the carrier phase noise of laser-diode (LD) pulse sources and the Gordon-Haus effect in soliton transmission. A formula is derived for the timing jitter in terms of the carrier linewidth, one of the measurable parameters common to all types of LD pulse sources. The transmission distance restricted by the timing jitter is analyzed, and the carrier linewidths required for ultra-long distance and ultra-high speed soliton transmission are estimated as well. Recirculating loop experiments at 10 Gb/s are demonstrated using two pulse sources; a gain-switched DFB-LD and a sinusoidally driven monolithically integrated MQW-DFB-LD/MQW-EA modulator, which have different carrier linewidths due to their different pulse formation processes. The difference in the carrier linewidths of the two pulse sources is measured by the proposed technique which is based on the optical heterodyne method. The observed difference between the two pulse sources in terms of timing jitter accumulation and timing jitter reduction with optical bandpass filters for the two pulse sources well support the theoretical predictions     

Threshold Effect on Error Probability in QAM Systems

This paper considers the effect of the carrier phase error on the probability of error in a binary quadrature amplitude modulation (QAM) data transmission system in the presence of intersymbol interference and additive Gaussian noise. The analysis shows that there exists a threshold value of the carrier phase error such that the error probability remains almost unchanged as long as the carrier phase error is less than that threshold value, but increases rapidly once the threshold is exceeded. Good agreement between theory and computer simulations is obtained. Some practical implications of this threshold effect are discussed.     

基于Costas环的通用数字信号载波恢复及FPGA实现

BPSK、QPSK、OQPSK、8PSK 和 16QAM 在数字通信中应用广泛。针对非合作接收机解调数字通信信号的需求，研究了基于 Costas 环的通用数字信号载波恢复技术。仅需通过调整环路滤波参数和改变 Costas 环中鉴相器的鉴相方式，即可实现 BPSK、QPSK、OQPSK、8PSK 和 16QAM 等数字信号的载波恢复。对算法进行了仿真验证，并在 FPGA 上完成了硬件实现。     

相位噪声对QAM性能影响分析

多电平 QAM调制对载波的相位噪声非常敏感。该文研究了慢速相位噪声对 QAM性能的影响 ,推导了相位噪声影响的 1 6QAM误符号概率的理论公式 ,给出了载波相位噪声对1 6QAM误符号率影响的计算机仿真结果。论文得到的理论公式和仿真结果 ,对 QAM调制的单载波通信系统的本振源相位噪声指标确定和系统性能的优化具有重要意义     

适用于多速率高阶QAM的定时同步改进算法

针对速率可变的高阶正交幅度调制(QAM)信号定时同步问题,提出了一种基于Gardner理论的定时同步改进算法.新算法改原有滤波器结构为两级插值级联优化结构来实现多速率信号的定时同步,可独立于载波同步单独使用,比传统结构具有更强的普遍适用性.仿真结果表明,该算法可以准确地对速率可变的128QAM信号进行同步.     

Performance of Reduced-Bandwidth 16 QAM with Decision-Feedback Equalization

This paper presents and investigates the performance of a reduced-bandwidth 16 QAM (RB-16 QAM) signaling technique which employs severe narrow-band filtering and decision-feedback equalization in the receiver to compensate for the resulting intersymbol interference. The overall filtering is designed so as to provide the spectral efficiency of 64 QAM. RB-16 QAM is compared to 64 QAM in terms of its performance on additive white Gaussian noise channels, in multipath fading environment, as well as in terms of its sensitivity to modem imperfections including carrier and timing phase errors, filter imperfections, nonlinear distortion and sinusoidal interference. The results show that depending on the spectral shaping filters and the equalizer used, RB16 QAM can be significantly more advantageous than 64 QAM. A most interesting finding is that while RB-16 QAM is comparable to 64 QAM in terms of its spectral efficiency, its robustness against system imperfections is very much like that of conventional 16 QAM.     

A fully digital noncoherent and coherent GMSK receiver architecturewith joint symbol timing error and frequency offset estimation

We propose a fully digital noncoherent and coherent Gaussian minimum shift keying (GMSK) receiver architecture with joint frequency offset compensation and symbol timing recovery. Carrier phase offset can be estimated if the coherent demodulation mode is adopted. The converted base-band complex signal is first frequency discriminated and then passed through a digital filter which performs a fast Fourier transform (FFT). The frequency offset can be estimated from the DC component of the FFT, and the symbol timing error can be estimated from the phase angle of the FFT at a specified frequency which is equal to an integral multiple of half the bit rate. These two estimated parameters are then used for frequency offset compensation and symbol timing recovery during a preamble period. Coarse carrier phase can be estimated by averaging sampled in-phase and quadrature-phase signals and finding its phase angle within the preamble period after carrier frequency offset is estimated and compensated. The bit error rate (BER) performance of this GMSK receiver architecture is assessed for an additive white Gaussian noise (AWGN) channel by computer simulation     

Error probabilities for QAM systems on partially coherent channelswith intersymbol interference and crosstalk

We describe an efficient procedure to calculate the probability of error P_e for a quadrature amplitude modulation (QAM) communications system operating over a channel that introduces distortion, interference, and noise. The method is an extension of the saddlepoint integration technique introduced by Helstrom (1986) to efficiently evaluate P_e for one-dimensional pulse-amplitude modulation (PAM) systems with intersymbol interference (ISI) and crosstalk. We consider the effects of noise, random carrier phase offset, ISI, and crosstalk between the I and Q channels. The error probability is written as a double Laplace inversion integral and can be easily applied to any rectangular constellation. This integral is calculated by extending the saddlepoint integration technique to two complex dimensions. Results are presented for QAM systems with 16, 64, and 256 symbols. The technique can be directly extended to environments with cochannel interference consisting of other QAM signals