密集多径信道下IR-UWB信号同步捕获方法

超宽带(UWB)信号的快速同步捕获是UWB通信系统中的关键问题.本文提出一种分步同步捕获方法,首先采用两种次最优的最大似然估计算法进行粗搜索,然后在粗搜索获得的有限范围内利用最大值阈值检测进行精估计.该方法提高了密集多径信道下极窄脉冲形式UWB信号(IRUWB)的捕获性能,并有效降低了计算复杂度和处理时间.文中还根据IRUWB信号接收特点,从捕获能量的角度定义了捕获概率.通过仿真评估了捕获能量对系统性能的影响,并对算法性能和参数选择进行了分析.     

密集多径信道下IR—UWB信号同步捕获方法

超宽带(UWB)信号的快速同步捕获是UWB通信系统中的关键问题．本文提出一种分步同步捕获方法，首先采用两种次最优的最大似然估计算法进行粗搜索，然后在粗搜索获得的有限范围内利用最大值／阈值检测进行精估计．该方法提高了密集多径信道下极窄脉冲形式UWB信号(IR-UWB)的捕获性能，并有效降低了计算复杂度和处理时间．文中还根据IR-UWB信号接收特点，从捕获能量的角度定义了捕获概率．通过仿真评估了捕获能量对系统性能的影响，并对算法性能和参数选择进行了分析．     

一种适合PPM-UWB信号的时移TDT同步捕获算法

指出TDT(timingwithadirtytemplate)盲同步捕获算法只适于PAM调制(脉冲幅度调制)UWB系统,而不能在PPM调制(脉冲相位调制)UWB系统中应用。提出了一种TS-TDT(time-shift-TDT)盲同步捕获算法,解决了PPM调制UWB系统快速同步捕获问题。该算法通过两条相关支路分别计算接收信号的延迟互相关值而获得同步信息,无需训练序列。理论分析和仿真实验结果表明,该算法结构简单,同步精度灵活可变,性能良好。     

基于能量检测的UWB数据包联合捕获方法

针对非相干UWB系统的数据包捕获问题,提出了一种联合信号捕获、误码率性能优化与包同步字检测的捕获方案.在信号捕获后发送导频序列实时估计信噪比,并搜索积分窗口长度,以获得最低误码率.给出了数据包捕获模型的合适性能指标,分别采用串行搜索与跳K步搜索策略,结合7位与13位巴克码为包同步字进行数据包捕获,仿真结果表明,三者联合的方案能够在保持一定包捕获性能的同时获得较好的误码率性能.     

基于TDT的Hermite脉冲超宽带同步算法

同步捕获是超宽带（UWB）通信面临的主要难题之一。＂脏模板＂（TDT）同步捕获算法十分适合UWB系统,在数据辅助（DA）模式下它具有低复杂度和快速捕获的特点。但是,在无数据辅助（NDA）的模式下,它的性能就要取决于系统随机信号的干扰。因此,分析利用正交Hermite脉冲的方法来解决这个问题。算法采用一串交替的正交Hermite脉冲来调制要发送的信号,并对原TDT算法进行了相应的修改来实现同步。该方法无需训练序列,在NDA模式下能够达到良好的性能。理论分析仿真结果表明,算法在均方误差（MSE）上跟传统TDT算法相比有较好改善。     

低速非相干扩频信号的快速同步方法研究

为了降低低速非相干扩频信号的同步时间,提出了一种分阶段的同步方法。该方法将整个同步过程分为伪码搜索与捕获、频率细估计、伪码跟踪、定时和载波相位跟踪几个阶段。其中前2个阶段采取了并行处理方法,在降低处理时间的同时提高了可接收的信号动态范围;后续各个阶段的处理充分利用了前面处理已经获知的同步信息,进一步减少了信号的同步时间。仿真和FPGA实测结果表明,该同步方法可实现低速非相干扩频信号的快速同步,与传统同步方法相比,同步速度可提高一个数量级。     

卫星入路由通信的定时和载波同步算法

在卫星通信中,需要快速、高效地对接收信号的位定时和载波初始相位信息进行估计.针对MC-S-ALOHA卫星入路由信号的特点,给出了一种基于前导序列的定时同步和载波同步算法,该算法仅需要一个训练符号,既用于定时恢复,也用于载波频率捕获,额外开销量小,因此,该算法适合于突发模式的MC-S-ALOHA网络传输系统.仿真结果表明,该算法也能快速地实现定时和频率捕获,捕获的频率范围较宽, 而且实现结构简单.     

突发模式PSK信号的联合载波位时钟恢复算法

快速载波和位时钟恢复是突发模式传送系统的一个关键因素。本文提出了适用于突发模式PSK信号捕获阶段的一种快速联合载波位时钟恢复算法。算法基于一个特定图案的前导字,采用前向结构直接、同时估计各个同步参数。可估计的载波频差范围是大的,约为符号率的,并且算法所需的计算负载非常低,适合数字硬件实现。仿真结果验证了算法的可行性和有效性。     

基于遗传算法的UWB信号非相干捕获方法

 本文针对动态信噪比环境超宽带（UWB, Ultra WideBand）信号的非相干捕获,提出了一种基于遗传算法的信号捕获方案.以遗传算法结合在线估计接收信噪比,搜索积分窗口长度与定时位置的参数组合,实现系统要求的比特错误概率.该方法解决了传统捕获方案在未知信噪比条件下积分长度无法择优选取以及捕获门限难于设定的问题.仿真结果表明,基于遗传算法的二维参数捕获方法与传统Look and Jump by K steps算法相比有效的提高了未知信噪比条件下的系统捕获性能,拓展了UWB非相干系统的应用范围.     

一种用于OQPSK调制测试的快速载波同步方法

OQPSK调制信号测试中传统基于科斯塔斯环的载波同步方法具有载波捕获时间长与入锁慢特点,不能满足实时分析测试的处理需求。针对该问题,该文采用基于离散傅里叶变换的载波频偏预估计与简化载波同步环路相结合的改进方法,实现OQPSK调制信号测试中载波相位的快速精确跟踪。研究表明,所提算法可以有效的减小捕获时间且估计性能稳定,可以满足矢量信号分析测试的快速处理要求。     

Frequency acquisition synchronization for multiple antenna systems

In this paper, we consider the problem of frequency acquisition synchronization by using multiple antennas over wireless fading channels. We introduce frequency synchronization with different combining schemes including space diversity and time diversity. Their performance is estimated for a Rayleigh fading channel with an analysis both theoretically and by simulation. We investigate the relationship between the mean squared error (MSE) and the average signal‐to‐noise ratio (SNR) for combining of different blocks and antennas. Both the carrier frequency offset and the sampling frequency offset are estimated when multiple antennas are utilized for signal transmission. The estimation with maximum ratio combining (MRC) scheme is presented in detail, and the estimation with selection combining scheme and equal gain combining scheme are introduced briefly. The simulation results explicitly show that the performance of the frequency acquisition synchronization with MRC scheme is better than that of others and that the MSE at low SNR is not very close to the Cramér–Rao low bound in multiblock combining frequency synchronization. Furthermore, the results address that in order to improve the performance, the total number of receive antennas will be increased exponentially. Copyright © 2013 John Wiley & Sons, Ltd.     

Frequency Offset Estimation by Multi-Band Averaging Method: A New Approach for MB-OFDM Based Ultra-Wideband Communication System

In this literature, we present a new method for estimating the coarse frequency offset in multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wideband (UWB) communication systems. The proposed training based coarse frequency offset (CFO) estimator performs an averaging of initial estimate over the multiple bands of transmission during estimation process. The proposed multi-band averaging provides an improved estimation of approximately three times for band group 1 (BG1) compared to our earlier proposed scheme. To prove the efficiency of the proposed scheme, the Cramer Rao lower bound (CRLB) of the estimation error is calculated and compared with the simulation results. We illustrate the performance of MB-OFDM system in terms of bit-error rate (BER) with multi-band averaged frequency synchronization (MBAFS) and compare with earlier reported results for 100,000 noisy realizations in UWB channel model 2 (CM2).     

An interference suppression scheme for UWB Signals using multiple receive antennas

In this letter a simple narrow band interference (NBI) mitigation scheme for ultra-wide bandwidth (UWB) signals using multiple receive antennas is examined. The low spatial fading characteristic of UWB signals is exploited to provide "interference diversity" by selecting the signal with the lowest received power among multiple antennas. The resulting distribution of the signal-to-interference ratio (SIR) at the receiver is derived and compared with results based on measurement data. The performance improvement of the scheme in mitigating NBI is also examined through BER simulations.     

Acquisition for DS/CDMA systems with multiple antennas in frequency-selective fading channels

A generalized code acquisition scheme for direct-sequence code-division multiple-access systems with multiple antennas is proposed over frequency-selective fading channels. The proposed scheme is developed on the framework of a generalized configuration of multiple antennas and correlators. The nonconsecutive search method is generalized and extended to multiple antenna systems to exploit multipath signals in improving acquisition performance over frequency-selective fading channels. The proposed scheme also adopts a hybrid decision strategy to make effective decisions on acquisition. The mean acquisition time performance of the proposed acquisition scheme is analyzed and evaluated in frequency-selective Rayleigh-fading channels with general multipath delay profiles and spatial-fading correlations. The effects of nonconsecutive search on mean acquisition time are investigated for various channel environments, and the optimal choice of decision strategy is discussed. Furthermore, effects of various configurations of multiple antennas and correlators, decision thresholds, and correlation interval on the performance are also investigated.     

Coarse Acquisition Performance of Spectral-Encoded UWB Communication Systems in the Presence of Narrow-Band Interference

It is known that a major practical implementation challenge of ultra-wideband (UWB) receivers is the design of the coarse acquisition stage. Due to the fine time resolution of UWB signals, the acquisition stage has to acquire a large number of low-energy multipath components, with no or little knowledge of the state of the channel. In addition, the complexity further increases with the presence of narrowband interference due to the proposed spectral overlay. Our goal in this paper is to evaluate the affects of the lack of a priori knowledge of the channel state and the presence of narrowband interference during acquisition. Maximum-likelihood and maximum a posteriori procedures for estimation in the presence of narrowband interference are formulated, and two different interference mitigation techniques are evaluated. In particular, this paper considers UWB communication systems that use spectral encoding as both the multiple access scheme and the interference suppression technique. The qualitative results are, however, believed to be valid for any UWB system implementation. It is shown that the acquisition performance strongly depends on the amount of a priori knowledge of the channel state at the receiver, and on whether or not interference suppression is employed.      

基于一阶统计量信道盲估计空时分集TH-PPM UWB系统

首先利用一种空时分集结构提出一种多入多出超宽带系统收发信机模型,并给出相应的信号检测方法.然后,利用脉位调制信号结构导致的接收信号一阶统计量循环平稳特性,提出一种适用于系统且没有估计模糊度问题的低复杂度盲信道估计方法.仿真结果表明,提出的盲信道估计方法由于复杂度低且没有估计模糊度,给接收机的信号检测提供了准确的信道状态...     

Spectral-estimation-based acquisition for frequency-hoppingspread-spectrum communications in a nonfading or Rayleigh-fading channel

Acquisition of frequency-hopping spread-spectrum (FH/SS) signals based on autoregressive spectral estimation is addressed for nonfading and Rayleigh-fading channels. The hopped frequency is synthesized using a linear feedback shift register (LFSR). The most significant bit (MSB) of the frequency estimate is loaded into the LFSR. A new acquisition logic is devised for the acquisition scheme that employs the autoregressive spectral-estimation acquisition technique (ASEAT). To characterize the statistical distributions of the frequency estimation error, the truncated Gaussian and uniform distributions are considered. The probability of the MSB error and the mean acquisition time of the acquisition logic are derived. For the ASEAT with the acquisition logic, the acquisition scheme that uses multiple antennas is also addressed. Numerical results for the probability of the MSB error and the corresponding mean acquisition time are illustrated for the performance evaluation of both cases     

New focusing scheme for DOA estimation of multipath clusters in WiMedia UWB systems without coarse estimation of angle of arrival

Ultra wideband (UWB) systems are expected to coexist with narrowband systems as well as other UWB systems. By estimating the direction of arrival of the multipaths, one would be able to limit the transmission to these directions and limit the interference to other systems. The focussing of subspaces is used to improve the resolution performance in direction of arrival estimation of wideband signals. The focussing matrix is calculated based on initial coarse estimation of DOA. The error in initial estimation results in an irreducible bias in final estimated DOA. By making use of the known pilot signals in Wimedia systems, a new focussing scheme is proposed in this paper that does not require coarse estimation. Computer simulation experiments validating this scheme are also presented. The bias in final estimation is drastically reduced.     

分布式MIMO-OFDM系统的同步捕获算法

该文提出了一种分布式多输入多输出正交频分复用(MIMO-OFDM)系统初始信号检测和同步捕获算法。该算法设计了导频符号,采用谱分析方法实现可靠的初始信号检测、粗定时和粗频偏估计,并在快速傅里叶变换(FFT)之后进行精确地频偏和定时估计。仿真结果表明,该算法在低信噪比多径瑞利信道条件下具有很好的性能。