基于前导序列的突发通信载波同步算法

在突发通信中,载波同步技术是解调系统的核心和关键技术。给出了一种基于恒包络零自相关序列(CAZAC)作为前导的突发通信载波同步算法,该算法基于CAZAC序列零自相关特性,先用载波频差前向校正、载波相位前向校正进行载波初始同步捕捉,再用锁相环技术进行跟踪,能够在低信噪比下进行快速载波恢复。仿真结果表明,本算法的同步速度快,捕获的频率范围较宽。     

雷达通信一体化技术

雷达通信一体化设计是雷达系统和通信系统的有机结合及资源共享。一体化系统的设计包括传输体制设计、突发解调算法设计和高效纠错编译码技术。针对雷达天线孔径特点,设计了一种基于雷达脉冲体制特点的突发通信体制,符号速率达到150 Msps,提出基于数据辅助的信号快速检测、定时估计算法和基于数据辅助的载波恢复算法,完成解调方案设计,开展编码器校验矩阵构造设计及译码并行算法设计,译码速率超过150 MHz。各项技术进行了算法仿真、软件设计及平台验证,实现了突发速率150 Msps的通信系统收发,对利用雷达系统进行通信及数据传输提出了一种可行方案。     

多速率突发PSK信号全数字无前导字解调器

突发模式通信应用日益广泛,基于前导字的解调算法降低了系统的数据传输效率。提出了一种适于多速率突发信号的全数字无前导字解调方案,通过FIFO操作和采样率转换适应多种速率的要求,参数估计、定时同步和载波恢复均采用前向算法,可以在不损失任何数据符号的条件下完成解调,具有较高的数据传输效率。算法易于硬件实现,给出了仿真和硬件测试的结果,结果显示在中高信噪比条件下算法具有较好的性能,验证了算法的有效性和可靠性。     

遥控副载波信号的软件解调方法

介绍了一种适合于突发模式下的PSK信号遥控副载波解调方法,其目的是对于突发副载波信号接收时实现快速可靠的捕获,并进行载波同步和位定时同步。文中设计的解调器是有别于传统解调器的全数字接收解调器,利用软件无线电的思想用软件方法实现解调,介绍的Viterbi载波同步算法和Gardner位定时同步算法结构简单,易于利用数字硬件实现,仿真结果也验证了此解调算法的可行性和有效性。     

一种短突发航空超短波调制解调算法及实现

针对项目对超短波航空通信的实际需求,提出并实现了一种短突发航空超短波通信调制解调器。首先分析了超短波航空通信信道特性,根据信道特性设计了短突发的信号帧格式,提出了适合短突发信号的载波同步和位同步算法,实现了适合信道特性编码调制算法,给出了工作原理和实现过程,最后分析了误码率性能和试验结果。相比长周期通信方式,所提的短突发通信调制解调算法易于实现、计算量小且具有较强抗信道衰落特性,试验和工程使用表明了该算法能很好地满足超短波航空通信的性能需求。     

双伪码扩频通信的解调算法及其性能研究

传统的直接序列扩频通信系统中,载波解调硬件电路实现比较复杂,双伪码扩频通信解调简单,无需载波恢复,而且抗干扰能力更强。但是,当扩频码周期较短时,选择合适的解调算法对通信性能有着极大的影响,本文根据传统双伪码包络检波解调算法的不足,比较了各种长度的双伪码在不同解调算法上的性能,提出了一种新型解调算法,并通过Matlab对其性能进行了仿真,验证了其正确性和实用性。     

高动态短时突发通信系统的载波同步技术

载波同步是数据解调中的重要环节之一。由于高动态短时突发通信系统的通信时间极短,在算法观测时间内可认为频率无变化,因此可对载波频偏进行一次校频,使之快速落入锁相环快捕带内,然后利用锁相环进行跟踪以完成载波同步。实践表明:利用一种改进的FFT校频技术对载波频偏进行一次校频,能使载波频偏快速落入锁相环快捕带内。最后分别对改进的FFT校频技术及锁相环进行了仿真分析,结果表明该方法在低信噪比下仍具有良好的性能。     

一种实用的MPSK/TDMA突发信号盲解调方案

针对时分多址(TDMA)目标的信号参数完全未知的情况,提出了一种MPSK/TDMA突发信号盲解调方案。该方案采用基于独特字的信号盲检测算法对突发信号进行了正确检测,采用改进修正协方差法来精确估计载波,采用基于非线性变换方法来精确估计MPSK信号的符号速率。设计了一种前馈法的载波同步和码元同步算法,实现了MPSK/TDMA突发信号的盲解调。理论分析和仿真试验表明,该方案具有良好的工程应用性能。     

一种短时突发PSK信号的自适应解调方法

短时突发相移键控（PSK）通信具有隐蔽性好、信道利用率高的特点，得到广泛应用。将已调信号非线性放大、限幅处理，使其幅度稳定在一定范围，基于锁相原理得到与已调信号同步的本地载波，是PSK信号解调相干载波恢复的常用方法。然而接收信号的非线性处理，会使PSK信号信噪比急剧下降，影响载波相位跟踪精度，给帧同步信号生成和码元抽取带来不确定性，导致误码率升高。针对常规方法存在的问题，提出了基于Hilbert变换的短时PSK信号自适应解调算法，通过信号归一化，在不降低解调信号信噪比情况下，确保载波恢复运算不受数据信号幅度的影响，具有恢复速度快、跟踪精度高、帧同步信号解调可靠、码元采样时间准确的特点。     

一种2FSK非相干盲解调系统设计

针对复杂电磁环境下通信侦察接收机侦收的通信信号难以被准确解调的问题,在传统差分解调算法的基础上设计出一种2FSK信号非相干盲解调算法。该算法利用估计的载波频率将信号下变频到准基带,通过差分解调算法解调出基带信号,利用基于码元跳变点的定时同步算法完成实时解调处理。仿真结果表明,该算法抗噪声与载频估计误差性能好,当SNR≥4 d B时,解调算法的误码率(BER)小于1%。     

A novel frequency offset estimation method for OFDM systems with large estimation range

In this paper, we proposed a novel frequency synchronization method which has larger estimation range than conventional method proposed by Tufvesson. A two steps frequency offset estimation method is performed in the new method. In the first step the received signal is correlated with local training sequence to eliminate the influence of training sequence which makes the estimation range of frequency offset is independent of period of the repeated data in the training sequence. The received signal is correlated with its delay in the second step to obtain the fine estimation of frequency offset. Precise estimation can be achieved in the proposed method than Tufvesson's method. The period of the repeated data in the training sequence determines the estimation range of the frequency offset in the conventional method, while in the new method they are irrelevant. Tens of subcarriers spacing can be estimated by the new method. The new method can be used in other cases as long as a known sequence is transmitted, which will introduce valuable flexibility in training sequence design. The validity of the algorithm is verified in AWGN channel and multipath fading channel.     

一种基于控制点偏移修正的纵向塞曼稳频方法与系统

针对目前普遍采用的功率平衡法实现热稳频的纵向塞曼激光器存在的稳频控制点偏移问题,建立了左右旋圆偏振光光功率差调谐曲线零点与稳频控制点之间频率偏移量的数学模型,提出了稳频控制点偏移的修正方法。该方法通过对左右旋圆偏振光的精确偏振分光和对称功率检测来抑制稳频控制点偏移的随机扰动分量,同时补偿其相对稳定偏置分量,可有效降低稳频控制点偏移引起的激光频率漂移。实验表明,基于稳频点偏移修正方法构建的纵向塞曼热稳频系统,在2h40min内输出光频率相对变化小于4×10-9,阿伦方差频率稳定度为1.9×10-10(采样时间1000s),在24h的重复实验中系统输出光中心频率漂移小于1.3×10-9。故该方法可有效抑制激光器稳频控制点漂移,提高激光频率稳定度。     

一种改进的基于DS/CDMA信号共轭周期平稳特性的载波频偏盲估计方法

在DS／CDMA系统中,我们可以利用接收信号的共轭周期平稳特性估计载波频偏,但是用于估计频偏的样本个数的有限性降低了这类方法估计结果的准确性和稳定性。为此本文在这类方法的基础上提出了一种改进的载波频偏盲估计方法,该方法通过对接收信号预置一个已知的载波频偏,有效的消除了有限的样本个数对估计性能造成的影响。同时它是一种盲估计算法,不需要专门的训练序列,不会降低无线带宽利用率。仿真结果表明该方法能够很好的利用有限长度的样本数据快速准确的估计出系统载波频偏,它的估计性能较改进前的方法有明显的提高。     

A Novel Joint Detection of Frequency Offset and MAI for MC-CDMA Systems

While multicarrier CDMA techniques are used to reduce interference and improve the performance of the system in fading channel, carrier frequency offset and multiple access interference remain major obstacles for a multicarrier CDMA system's performance. In this article we propose a novel joint detection method called modified maximum likelihood multistage parallel interference canceller (M-ML-MPIC) to eliminate the frequency offset and MAI simultaneously. The main idea of our approach is to combine PIC multiuser detection and frequency offset estimation based on a maximum likelihood function with guard interval. We discuss our scheme and report on its performance using a set of simulation experiments.     

Blind Sequential Monte Carlo Joint Tracking of Channel State and Frequency Offset in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation scheme, which has been adopted for several wireless standards. In order to fully exploit the benefits of an OFDM system, estimation of the channel state information must be performed. Moreover a well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. This frequency offset introduces inter-carrier interference in the OFDM signal. In this paper we address the problem of jointly tracking the channel and frequency offset based on a Sequential Monte Carlo filtering approach. The proposed algorithm works in a decision-directed way, thus does not require the use of pilot symbols, providing a worth-mentioned increase in the useful data rate. Through simulations we demonstrate the efficiency of this approach against a similar approach where the Extended Kalman Filter is used. Moreover our method is compared with two recently proposed pilot-based methods.     

Sequence Design for Data-Aided Estimation of Synchronization Parameters

In this letter, we propose a systematic technique for optimum data-sequence design for data-aided (DA) estimation of synchronization parameters. It is assumed that the system operates in burst mode, transmitting a linearly modulated information signal over an additive white Gaussian noise channel. The method is based on the minimization of the corresponding Crameacuter-Rao lower bound subject to a power constraint and is applied in four practical receiver synchronization contexts: estimation of the symbol timing with known carrier frequency offset and either known or unknown carrier phase, joint estimation of the symbol timing and carrier phase with known carrier frequency offset, and joint estimation of the carrier phase and carrier frequency offset with known symbol timing     

Compensation of quadrature imbalance in an optical coherent OQPSK receiver in presence of frequency offset

In this paper,we describe the impact of quadrature imbalance (QI) in the presence of frequency offset in an optical coherent offset quadrature phase shift keying (OQPSK) receiver.Arbitrary conjugate misalignment was realized in a 2×4 90° optical hybrid,and the ellipse correction (EC) method of quadrature imbalance was applied in our simulation.In the case of transmission,the EC method can significantly improve the system performance.     

光子探测PPM阵列信号的频偏和相偏预测方法

对于基于脉冲位置调制（PPM）的光子探测阵列接收的深空光通信系统,提出了一种直接预测频偏和初始相偏的PPM时隙同步方法。该方法首先测量每个支路各个光子的到达时间,进而得到每个光子到达时间相对于PPM时隙位置的偏移量,统计得到不同偏移量处的光子分布。然后利用前、后半帧数据光子分布峰值点对应时隙位置差值即半帧数据频偏累积值的原理对频偏进行估计;根据频率估计值修正光子达到时间数据后,再根据修正后一帧数据光子分布统计图峰值位置相对于理想同步位置的偏移量大小估计出初始相偏。仿真结果表明,在计数时钟频率大于等于四倍时隙时钟频率情况下,该方法均能实现时隙同步。     

A Novel Bit Error Rate Analysis and Improved ICI Reduction Method in OFDM Communication Systems

In this paper, we have proposed a novel method for the bit error rate (BER) analysis with frequency offset and improved inter-carrier-interference (ICI) reduction in the OFDM digital communication system. We also analyze the sub-carrier index before and after cancellation of the frequency offset and discuss the carrier-to-interference ratio (CIR). The results of the present analysis are compared with the others reported literatures.     

Revisiting the timing and frequency offset estimation based on cyclostationarity with new improved method

Timing and frequency offset estimation based on the second order cyclostationarity have been explored in many literatures [1]- [9]. In this article, we revisit the class of these estimators and propose for both single carrier and OFDM systems, a new method for timing and frequency offset estimation. Different from the previous methods, here, the estimation of timing and frequency offset process are independent of each other. Thus it does not introduce propagation error which is inherent in most of the estimators proposed so far and has an improved performance. Monte Carlo simulations are performed to verify the results.