多模终端待机低功耗设计

如今的移动通信网络是由多种制式及多个频段融合而成的多模网络,对于商用终端而言,多种难题交织在一起,其中待机时长是必须要解决的一个关键问题.为此,不同于传统增大电池容量的方法,采用降低待机功耗的策略:时域的时隙控制、频域的电流控制、睡眠和唤醒的电源门控制、低频时钟高频化,其中高频时钟校准低频时钟是降低睡眠态功耗的关键措施.这一系列方案的实施,使得终端在多模实际网络环境下的待机电流小于5 mA,终端的待机低功耗达到了有竞争力的商用水平.     

基于ADS-B的高精度站间同步方法

自动相关监视(ADS-B)可用于多站定位系统中实现时间同步,但直接同步的精度不足以满足工程应用的需要.为了提高同步精度,首先推导了利用ADS-B实现站间同步的机理模型,在实测数据的基础上仿真了直接同步方法的精度水平;其次分析了ADS-B位置误差的类型和来源,得到了不同误差类型的分布特征;最后根据不同误差类型的特点,提出了一种降低ADS-B误差影响的高精度多站同步的方法.该方法可有效降低ADS-B系统延时误差和定位误差对同步精度的影响,以实测数据为基础的仿真结果表明该方法可实现纳秒级的站间同步精度,具有良好的工程应用价值.     

基于前向结构的高动态突发信号载波同步算法

为实现高动态突发通信系统载波快速同步,提出了一种新的基于前向结构的突发信号载波同步算法,采用多级处理方案分级实现多普勒变化率、多普勒频偏及载波相位的估计及恢复.理论分析及数值仿真表明,在高动态低信噪比条件下,新算法的载波同步信噪比损失小于1 dB,且对多普勒变化率及信号电平参数不敏感,实现复杂度低,能够满足高实时性应用需求.     

The performance of MIMO system using MRT scheme in vehicular systems

In this paper an inter‐vehicle multiple‐input multiple‐output system using maximal ratio transmission (MRT) scheme is proposed, and its performance is investigated where the proposed system uses multiple antennas for transmission and reception. It has the advantage of increasing effectively the diversity order without changing the receiver. As far as we know, MRT has not been employed in vehicular systems to improve system performance. Specifically, error performance of the MRT with different number of antennas at the transmitting and receiving stations has been examined, ie, MRT (2, 1) and MRT (2, 2) in a vehicular system in which cascaded Nakagami‐m fading distribution used. First, we derive expressions of probability distribution function and then moment generating function of end‐to‐end signal‐to‐noise ratio. Based on these expressions, we obtain the symbol error rate expression on account of examining the performance of the considered system. Then, the upper bounds for the symbol error rate expressions for high enough signal‐to‐noise ratio values have been calculated. Finally, we validate the confirmation of obtained theoretical results through simulation results and furthermore show that the multiple‐input multiple‐output system using MRT scheme can provide the full diversity.      

On Least Squares Weighted Recursive Estimation of Clock Skew and Offset in Wireless Sensor Networks

Three clock synchronization algorithms for Wireless sensor networks (WSNs) in Pairwise broadcast synchronization (PBS) mechanism are derived.They include the joint Least squares estimator (LS),joint Least squares weighted estimator (LSW) and joint Least squares weighted Recursive estimator (R-LSW).For these estimators,the corresponding algorithms are derived and described by assuming a Gaussian random delay model.Unlike PBS,these estimators can achieve the Cramer-Rao lower bound (CPLB) for both listening node and active node without knowledge of the deterministic delay.The purpose of considering R-LSW is to reduce the use of storage space with the method of estimating while observing.Simulation and analytical results verify that the estimators are efficient.     

Chaos synchronization using the Fourier series expansion with application to secure communications

In this paper, a new method for secure communication based on chaos synchronization is proposed. It is consisted of a state feedback controller and a robust control term using the Fourier series expansion for compensation of uncertainties. In comparison with other uncertainty estimators such as neural networks and fuzzy systems, Fourier series are more efficient, since they have fewer tuning. Thus, their tuning process is simpler. Similar to the parameters of fuzzy systems, Fourier series coefficients are estimated online using the adaptation rule obtained from stability analysis. The case study is the Duffing–Holmes oscillator. Also, observer-based secure communication using the Fourier series expansion has been proposed. Simulation results and comparisons, reveal the superiority of the proposed approach.     

An approximate analysis for a class of assembly-like queues

Assembly-like queues model assembly operations where separate input processes deliver different types of component (customer) and the service station assembles (serves) these input requests only when the correct mix of components (customers) is present at the input. In this work, we develop an effective approximate analytical solution for an assembly-like queueing system withN(N 2) classes of customers formingN independent Poisson arrival streams with rates {_i=1,...,N} The arrival of a class of customers is turned off whenever the number of customers of that class in the system exceeds the number for any of the other classes by a certain amount. The approximation is based on the decomposition of the originalN input stream stage into a cascade ofN-1 two-input stream stages. This allows one to refer to the theory of paired customer systems as a foundation of the analysis, and makes the problem computationally tractable. Performance measures such as server utilization, throughput, average delays, etc., can then be easily computed. For illustrative purposes, the theory and techniques presented are applied to the approximate analysis of a system withN = 3. Numerical examples show that the approximation is very accurate over a wide range of parameters of interest.     

利用Henon系统实现混沌保密通信

本文针对Henon混沌系统对称性特征提出了一种新的混沌保密通信方法并计算研究了该方法的可行性和具体实施中的影响因素及其作用。     

Synchronization of chaos in simultaneous time-frequency domain

Synchronization of chaos presents many challenges for controller design. The novel notion of exerting concurrent control in the joint time-frequency domain is applied to formulate a chaos synchronization scheme that requires no linearization or heuristic trial-and-errors for nonlinear controller design. The concept is conceived through recognizing the basic attributes inherent of all chaotic systems, including the simultaneous deterioration of dynamics in both the time and frequency domains when bifurcates, nonstationarity, and sensitivity to initial conditions. Having its philosophical bases established in simultaneous time-frequency control, on-line system identification, and adaptive control, the chaos synchronization scheme incorporates multiresolution analysis, adaptive filters, and filtered-x Least Mean Square algorithm as its physical features. Without A priori knowledge of the driven system parameters, synchronization is invariably achieved regardless of the initial and forcing conditions the response system is subjected to. In addition, driving and driven trajectories are seen robustly synchronized with negligible errors in spite of the infliction of high frequency noise.     

Generalized solution to symbol error probability integral containing over different fading models

This paper presents a generalized solution to the symbol error probability (SEP) integral containing the product of two Gaussian Q‐functions . Numerical integration technique is first used to approximate the polar form of as a sum of exponentials. This approximation is then used to derive a closed‐form solution to the related SEP integral. Due to the exponential nature of the approximation, solution to the integral is expressed in terms of moment generating function (MGF) of a fading distribution. Therefore, the solution to integral exists for all fading distributions which have well‐defined MGF. The mathematical complexity of the proposed solution is directly proportional to the complexity of MGF expression. For most of the fading models, the corresponding MGF involves power or exponential functions, which guarantees algebraic simplicity of the proposed solution. Further, this generalized solution is used to evaluate the SEP of various modulation schemes over different fading channels. Various computer simulations run in MATLAB for wide range of scenarios confirm the accuracy of the proposed approximation and solution.