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。     

遥控副载波数字化解调器技术研究

介绍低码速率下的PSK遥控副载波实现快速可靠捕获并进行载波同步与位同步的数字化解调方法.给出了数字化解调原理、载波同步、位同步方法并给出仿真,结果具有一定的参考价值.     

自组织网络中前导信号设计及检测算法研究

初始化链路建立过程中前导信号的捕获和解调是自组织网络通信的关键.目前常规OFDM调制前导结构存在快速捕获与时频同步精度较难兼顾的问题,导致接收端定时同步误差较大,从而影响后续寻呼信息的解调性能.基于OFDM调制前导结构的性能分析,提出了异码级联和自循环级联两种前导信号设计和同步方案.仿真与分析表明,与已有方法相比,所提方案不仅能保证接收端较短的捕获时间和较高的频率同步准确性,同时也能显著提高定时估计性能.     

一种差分传输参考直扩超宽带系统的实现方案

文中提出了一种差分传输参考直扩超宽带系统的实现方案。该方案利用接收信号的前一个码元作为本地参考信号，解差分恢复出扩频序列，然后通过数字匹配滤波器完成PN码的相关匹配来实现同步捕获，而后采用类似方法解调实现信息恢复。通过对系统的同步性能及其误码率性能进行分析和仿真试验,结果表明该方案不仅可以实现快速的同步捕获，并且具有复杂度低、占用资源少等优点。     

一种适用于PAM-UWB系统的同步算法

本文提出了一种适合PAM-UWB系统的同步算法,该算法采用TDT同步算法与滑动相关相结合来实现同步捕获.具有复杂度低、速度快、精度高的优点.通过对系统同步性能的仿真分析以及采用差分解调实现信息恢复所得出的系统误码率特性,证明了该算法是可行的.     

M码卫星导航信号直接解调方法研究

针对新一代M码卫星导航信号解调分析问题,在比较两种捕获方法特点的基础上,本文从工程可实现的角度提出了一种M码导航信号直接捕获方法,采用扩频码同步、载波剥离和亚载波剥离等技术,直接对载波C/A码、P(Y)码和M码复用信号进行解调处理.仿真结果表明,本文方法可以有效地降低C/A码和P码信号对于M码信号接收的影响,能够准确地恢复出原始扩频序列.     

一种用于高速率QPSK信号的并行解调方法

为实现数据的高速解调,提出了一种QPSK并行解调模型,并对定时同步、载波同步、自动增益控制(AGC)和数据恢复等各个模块进行了Matlab仿真分析.重点提出并仿真实现了一种在并行解调中实现载波同步后的模糊统一和数据恢复的方法.     

基于频偏预校正匹配滤波的同步方法

针对突发通信同步,介绍了进行正交下变频和采样数字化后进行匹配滤波的方法,分析了频偏对匹配滤波的影响,提出了频偏预校的方法,进而分析了频偏未校正匹配滤波、频偏预校正匹配滤波和无频偏解调后同步的性能。对低信噪比条件下存在较大频偏时频偏预校正、频偏未校正及无频偏解调后同步3种情况下的同步性能进行了建模仿真分析。     

TD-SCDMA直放站下行同步算法性能研究

文章首先介绍了下行同步精度及稳定度在时分同步码分多址(TD-SCDMA)直放站应用中的重要作用,然后结合ADS(Advanced Design System)对特征窗捕获匹配和相关解调两种同步算法的仿真结果,从算法原理上比较了这两种同步算法的抗干扰性能.最后根据仿真统计结果结合直放站实际应用状况分析了两种同步算法的优缺点和适用环境,并根据实际应用中的问题提出了一些改良意见.     

基于DSTFT的FSK信号的解调

提出一种基于离散短时傅里叶变换在时域和频域解调2FSK信号的方法,介绍此方法的基本原理,给出解调的依据,并详细阐述一种新的码元同步算法,该同步算法分为粗同步和细同步两个步骤,从理论上分析采用该算法可以实现精确的码元同步,实验中采用Matlab工具进行仿真,仿真结果表明同步情况理想,解调效果良好。     

Multiple-dwell and sequential code acquisition with diversity forFFH/MFSK spread-spectrum systems under band multitone jamming

Pseudonoise code acquisition is investigated for constant hopping rate fast frequency-hopped (FFH)/M-ary frequency-shift keying systems under the effects of white Gaussian noise and band multitone jamming. In particular, serial search acquisition systems based on the traditional multiple-dwell test (up to three dwells) and three novel sequential tests are analyzed and compared. Analytical results show the following in a heavily jammed environment: (1) the inherent time diversity in an FFH system can significantly improve the acquisition performance of the multiple-dwell test and (2) the novel sequential tests can significantly outperform the multiple-dwell test. Our analytical results are verified by computer simulations     

基于多天线辅助估计的高精度UWB快速捕获算法研究

本文提出了一种基于多天线辅助估计的UWB(超宽带)快速捕获算法,利用UWB信号的循环平稳特性,将接收信号与它自身延迟一个信息位产生的模板相关,应用最大似然方法就可得到一个粗略的同步时间估计,在充分利用线性天线阵空间分集增益的情况下,这种估计相当准确。在此基础上继续进行精确同步,直到捕获任一符号位的第一帧第一个到达脉冲。文中采用流图法给出了本算法平均捕获时间的闭式解。理论分析和计算机模拟表明,该算法与同等硬件复杂程度和同等捕获精度的其他捕获方法相比可明显地缩短平均捕获时间。     

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     

MFSK/FFH系统多用户能力分析与仿真

MFSK/FFH系统特指采用快速跳频（FFH）技术和多进制频移键控（MFSK）非相干解调技术的系统,主要研究MFSK/FFH通信系统的多用户能力,并把它与差分跳频技术DFH的组网能力进行对比分析。通过分析MFSK/FFH通信系统的性能,给出了MFSK/FFH通信系统和差分跳频系统的比特差错率公式,为了公平对比MFSK/FFH网络和差分跳频网的组网能力,采用多用户频带利用率这个参数,理论和仿真表明,采用特定的检测方法,MFSK/FFH系统的多用户能力比差分跳频系统的好。     

SINR analysis of FFH/OFDM over frequency selective Rayleigh fading channel

Fast frequency hopping/orthogonal frequency division multiplexing (FFH/OFDM) has been previously proposed to achieve frequency diversity over frequency selective channels. However, the performances of the FFH/OFDM scheme have been usually calculated using simulations over empirical channel models in earlier works. The main aim of this paper is to theoretically expose the diversity of the FFH/OFDM signal over statistical models, specifically Rayleigh distributed, for frequency selective fading channels. In order to achieve this aim, we first derive the decision variables and the signal‐to‐interference noise ratios of the FFH/OFDM signal at the output of minimum mean square error and zero forcing receivers. For various levels of quadrature amplitude modulation used in FFH/OFDM, the performances are calculated and validated via simulations. The results show that FFH/OFDM in case of zero forcing equalization does not provide any diversity gain even over a frequency selective channel. However, in case of minimum mean square error equalization, it brings significant diversity gain at high signal‐to‐noise ratio (SNR) values with the rise of number of sub‐carriers. Moreover, the FFH/OFDM with four quadrature amplitude modulation scheme provides better performance than that of the conventional OFDM even at low SNR values, as well as a significant diversity gain at high SNR values. Copyright © 2016 John Wiley & Sons, Ltd.     

Channel capacity per user in a power and rate adaptive hybrid DS/FFH‐CDMA cellular system over Rayleigh fading channels

The theoretically achievable average channel capacity (in the Shannon sense) per user of a hybrid cellular direct sequence/fast frequency hopping code‐division multiple‐access (DS/FFH‐CDMA) system, operating in a Rayleigh fading environment, was examined. The analysis covers the downlink transmission and leads to the derivation of a novel expression between the average channel capacity available to each system's user under simultaneous optimal power and rate adaptation and the system's parameters, providing an optimistic upper bound, useful for practical modulation and coding schemes. The final derived closed‐form expression can be useful for the design of the DS/FFH‐CDMA system because it provides a theoretical tool for the initial quantitative analysis. Finally, avoiding the application of complex theoretical algorithm or lengthy simulation, we theoretically derived numerical results to illustrate the presented analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

相位搜索法扩频码捕获的仿真实现

扩频码同步是扩频通信系统中特别关键的技术,相位搜索法捕获是扩频码捕获中最基本的方法,硬件实现最简单,在短PN码捕获时有很大的优势.文中在MATLAB平台研究该捕获方法的实现,给出了整个同步过程的仿真模型,各部分的详细参数设置和关键部分的仿真结果.选择长度为31的PN码进行仿真,用5级移位寄存器产生本地PN码序列,不断调整其相位,直到本地PN码与接收的PN码序列初步对齐.仿真结果表明,该模型能够实现31位PN码的正确捕获.捕获时间与本地PN码和接收PN码之间的相位差有关.     

On the optimum processing gain for a hybrid DS/FFH‐CDMA cellular system over Rayleigh fading channels

The optimization between the processing gain and the theoretically achievable average channel capacity per user (in the Shannon sense) of a constant total system's allocated bandwidth hybrid direct sequence/fast frequency hopping code‐division multiple‐access (DS/FFH‐CDMA) cellular system, when operating in a Rayleigh fading environment, is presented. Then, the spectral efficiency, expressed in (bits/s/Hz), is estimated in terms of the achievable average channel capacity per user, during the operation over a broadcast cellular time‐varying link, and leads to a simple theoretical novel‐closed‐form expression for the optimal processing gain value based on the maximization of the achieved spectral efficiency. The final expression derived can be useful for the practical design of a DS/FFH‐CDMA cellular system and for an initial quantitative analysis since it relates to the optimal processing gain applied and all system's parameters. Finally, numerical results are presented to illustrate and prove the validity of the presented analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance Study of an FFH/BFSK Self-Normalizing Receiver with Multitone Jamming's Frequency Offsets

This study investigates how frequency offsets of multitone jamming affect the fast frequency-hopped binary frequency shift keying (FFH/BFSK)self-normalizing (SNZ) receiver under additive white Gaussian noise (AWGN). The average bit-error-rate (BER) expressions of the FFH/BFSK SNZ receiver and the average BER expressions of an FFH/BFSK spread-spectrum (SS) communication system with frequency offsets of multitone jamming for the sake of understanding the simulation results better. Simulation results show that BER performance of the FFH/BFSK SNZ receiver with diversity under the worst casemultitone jamming (MTJ) and AWGN suffers from multitone jamming's frequency offsets when the jamming power is moderate, which is validated by several simulations with different frequency offsets configured in multitone jamming. Therefore, an FFH/BFSK SNZ receiver under multitone jamming can be combated with the help of frequency offsets of multitone jamming.     

Interference rejection in FFH systems using least squaresestimation techniques

A fast frequency-hopped (FFH) receiver which uses a prewhitening filter to reject narrowband interference is described. By using an appropriate fractional tap spacing, it is shown that interference can be estimated independently of the desired signal. Bit error rate results are presented for the receiver for linear square-law combining. The results compare favorably to those obtained by a near-optimal automatic gain-control (AGC) combining technique. The performance of the prewhitening filter interference rejection method is shown to be superior to that of a nonparametric self-normalizing receiver. Finally, simulation results for an FFH receiver using the complex least mean-square (LMS) algorithm to update the prewhitening filter coefficients are presented