一种慢跳频系统频率跳变时刻同步算法

提出一种盲接收环境下的慢跳频（SFH）系统频率跳变时刻同步算法。该算法针对慢跳频系统中1跳数据包含多个调制符号的特征,通过非线性变换得到包含离散谱线的信号。利用跳频信号在每1跳内能量恒定的特性,将1跳信号均匀划分为2段,提取分段信号非线性变换后离散谱线能量差异,作为调整频率跳变时刻的判决量,通过反馈环路实现盲接收环境下频率跳变时刻的精确同步。对典型慢跳频DPSK（SFH/DPSK）系统在盲接收环境下的同步性能进行仿真,在Eb/N0大于16 dB时,算法同步性能接近10-3,验证了算法的有效性。     

一种全球定位系统弱信号捕获策略

信号捕获是目前广泛应用的数字全球定位系统(GPS)接收机的重要部分,弱信号条件下的信号捕获过程是目前GPS接收机算法研究的重点。本文分析和比较了2种经典捕获检测策略(TONG捕获策略及NM捕获策略)的性能,并针对弱信号条件下GPS信号捕获的特点,提出了一种适用于弱信号条件下的捕获检测策略—双门限搜索检测策略。理论分析和仿真说明该策略在弱信号条件下具有较好的性能。     

基于压缩感知的神经电信号测量方法设计

介绍了一种基于压缩感知的神经电信号采集方法,用于解决传统无线神经电信号采集系统面临的数据量及系统功耗的限制问题.鉴于压缩感知处理信号的稀疏性要求,该方法还可应用于其他生物电信号的采集、压缩,仿真验证压缩比可达10x,重建信号的信息损失较小.另外,由于以往神经电信号采集系统只截取动作电位中的一部分电位信息,因而存在信息损失现象;而本文方法可实现信号的连续采集.     

基于支持向量聚类改进的雷达信号分选方法

在复杂的电磁信号环境下,针对使用支持向量聚类算法进行信号分选时,聚类结果易受核函数参数和惩罚因子的影响,及计算复杂度高和准确率低的问题,提出了一种将支持向量聚类与集对分析相结合的雷达信号分选方法。该方法使用集对分析先对支持向量进行聚类,再用所得的聚类结果对剩余数据进行聚类。仿真结果表明该方法在含有一定数量的噪声信号环境下,能获得较好的分选效果,不仅耗时短,而且还具有较高识别率。     

基于遗忘因子RLS算法的自适应直达波对消技术

在以民用广播、电视及CDMA等信号为照射源的无源雷达系统中,由于发射信号为连续波信号,直达波和多径信号对雷达回波的干扰很强,影响了目标的检测。为此采用RLS自适应对消处理技术来抑制直达波干扰,针对RLS自适应算法的性能分析,提出了改进RLS自适应处理算法,收到了良好的滤波效果。最后在以广播信号为照射源的实验系统中,根据实际采集的数据进行仿真论证,验证了该方法的可行性。     

Variable sampling interval Shewhart control charts for monitoring the multivariate coefficient of variation

In many industrial manufacturing processes, the ratio of the variance to the mean of a quantity of interest is an important characteristic to ensure the quality of the processes. This ratio is called the coefficient of variation (CV). A lot of control charts have been designed for monitoring the CV of univariate quantity in the literature. However, the CV control charts for multivariate quantity have not received much attention yet. In this paper, we investigate a variable sampling interval (VSI) Shewhart control chart for monitoring multivariate CV. The time between two consecutive samples is allowed to vary according to the previous value of the multivariate CV, which will help the chart to detect the process shifts faster. The comparison with the fixed sampling interval Shewhart chart is implemented to highlight the advantage of the VSI method. Finally, an illustrative example is demonstrated on real data.     

Encoding true-color images with a limited palette via soft vector clustering as an instance of dithering multidimensional signals

One of the classic problems of digital image processing is to encode true-color images for the optimal viewing on displays with a limited set of colors. A major manifestation of optimal viewing in this regard is to maximally remove parasitic artifacts in the degraded encoded images such as the contouring effect. Several robust attempts have been made to solve this problem over the past 50 years, and the first contribution of this paper is to introduce a simple – yet effective – novel solution that is based on soft vector clustering.The other contribution of this paper is to propose the application of the soft clustering methodology deployed in our color-encoding solution for the dithering of multidimensional signals. Dithering essentially adds controlled noise to the analog signal upon its digitization so that the resulting quantization noise is dispersed over a much wider band of the frequency domain and is therefore less perceptible in the digitized signal. This comes of course at the price of more overall quantization noise. Dithering is a vital operation that is performed via well-known simple schemes upon the analog-to-digital conversion of one-dimensional signals; however, the published literature is still missing a general neat scheme for the dithering of multidimensional signals that is able to handle arbitrary dimensionality, arbitrary number and distribution of quantization centroids, and with computable and controllable noise power. This gap is also filled by this paper.     

All-optical OFDM network coding scheme for all-optical virtual private communication in PON

A novel optical orthogonal frequency division multiplexing (OFDM) network coding scheme is proposed over passive optical network (PON) system. The proposed scheme for all-optical virtual private network (VPN) does not only improve transmission efficiency, but also realize full-duplex communication mode in a single fiber. Compared with the traditional all-optical VPN architectures, the all-optical OFDM network coding scheme can support higher speed, more flexible bandwidth allocation, and higher spectrum efficiency. In order to reduce the difficulty of alignment for encoding operation between inter-communication traffic, the width of OFDM subcarrier pulse is stretched in our proposed scheme. The feasibility of all-optical OFDM network coding scheme for VPN is verified, and the relevant simulation results show that the full-duplex inter-communication traffic stream can be transmitted successfully. Furthermore, the tolerance of misalignment existing in inter-ONUs traffic is investigated and analyzed for all-optical encoding operation, and the difficulty of pulse alignment is proved to be lower.     

Pilot-aided sampling frequency offset estimation and compensation using DSP technique in DD-OOFDM systems

To improve the outage performance of an optical orthogonal frequency-division multiplexing (OFDM) system under the frequency offset between the sampling clocks in the transmitter and receiver, a pilot-aided sampling frequency offset (SFO) estimation and compensation scheme for the optical OFDM system with intensity-modulation and direct-detection (DD-OOFDM) is experimentally demonstrated. The experimental and simulated results show that the scheme can work effectively even with large sampling frequency offsets. In addition, it can achieve a good bit error rate (BER) performance without the sampling clock frequency synchronization in the receiver.     

Resource allocation for OFDM relay systems with statistical QoS guarantees

By integrating the concept of effective capacity, we propose the resource allocation schemes for subcarrier‐pair based OFDM decode‐and‐forward and amplify‐and‐forward relay systems for quality‐of‐service (QoS) guarantees. The objective is to maximize the system throughput subject to a given statistical delay QoS constraint. First, we pair the subcarriers over the source‐relay channel and the relay‐destination channel by the descending order of the subcarriers' channel gains. Second, by making use of the derived equivalent end‐to‐end channel gains of the subcarrier pairs, we apply joint water‐filling power allocation over the subcarrier pairs and then partition the power of the subcarrier pairs between the source and the relay. We prove that as the equivalent end‐to‐end channel gains of the subcarrier pairs are given, the combination of sorted subcarrier pairing and joint water‐filling power allocation is jointly optimal to maximize the effective capacity. The simulation results show that our proposed schemes achieve the highest effective capacity for OFDM decode‐and‐forward and amplify‐and‐forward relay systems as compared with other existing schemes. The results also verify that our proposed schemes can efficiently provide different levels of delay QoS guarantees, even if under the stringent delay QoS constraints. Copyright © 2012 John Wiley & Sons, Ltd.