无线弱实时多媒体业务传输模型分析

提出了无线“弱实时多媒体业务”的概念。利用RTP协议的体系框架,结合自适应的ARQ重传算法,实现了新的传输模型。仿真结果显示,该传输模型很好地解决了无线“弱实时多媒体业务”传输在时延、吞吐量抖动和差错概率之间的均衡问题。

多径环境下脉冲超宽带系统的传输性能分析

为分析多径环境下脉冲超宽带跳时多址系统的传输性能,通过研究IEEE 802.15.3a工作组给出的多径信道参考模型,提出了一个同时存在符号间干扰、符号内多径干扰和多用户干扰的跳时超宽带系统相干解调的性能分析模型,分别得到了符号内多径干扰、符号间干扰和多用户干扰的方差,且推导得到了系统的误比特率计算公式,并用计算机仿真验证了公式的有效性。通过计算相邻多径的平均间隔,论证了符号内脉冲自身多径的干扰是不可忽略的。在不同的信道环境下,以一定误码率要求作为衡量标准,比较了单用户系统中仅考虑符号间干扰和同时考虑符号内多径干扰及符号间干扰的用户最高传输速率,并分析了多用户系统中接入不同用户数时对应的平均传输速率的上限。

Study on Dynamic Response of the “Dualistic” Structure Rock Slope with Seismic Wave Theory

Currently, scant attention has been paid to the theoretical analysis on dynamic response mechanism of the ＂Dualistic＂ structure roek slope. The analysis presented here provides insight into the dynamic response of the ＂Dualistie＂ structure rock slope. By investigating the principle of energy distribution, it is shown that the effect of a joint plays a significant role in slope stability analysis. A dynamic reflection and transmission model （RTM） for the ＂Dualistic＂ structure rock slope and explicit dynamic equations are established to analyze the dynamic response of a slope, based on the theory of elastic mechanics and the principle of seismic wave propagation. The theoretical simulation solutions show that the dynamic response of the ＂Dualistic＂ structure rock slope （soft-hard） model is greater than that of the ＂Dualistic＂ strueture rock slope （hard-soft） model, especially in the slope crest. The magnifying effect of rigid foundation on the dynamic response is more obvious than that of soft foundation. With the amplitude increasing, the cracks could be found in the right slope （soft-hard） crest. The crest failure is firstly observed in the right slope （soft-hard） during the experimental process. The reliability of theoretical model is also investigated by experiment analysis. The conclusions derived in this paper could also be used in future evaluations of Multi-layer rock slopes.

Sensitivity analysis of key input parameters in conditional cell transmission model for oversaturated arterials

A novel conditional cell transmission model （CCTM） is a potential simulation tool because it accommodates all traffic conditions from light condition to oversaturated condition. To test the performance of the CCTM, a series of experiments for sensitivity analysis were designed and performed for a multilane, two-way, three-signal sample network. Experiment 1 shows that the model is performed in a logical and expected manner with variations in traffic demand with time and direction. Experiment 2 shows when the possibility of the occurrence of a useful gap increases to 60% and 100%, the delays in left rams decrease by 5% and 15%, respectively. In Experiment 3, comparing the possibility of a conditional cell of 0 with 100%, delay of left turn and delay of the entire network were underestimated by 58% and 11%, respectively. Hence, sensitivity analysis demonstrates that by reflecting local drivers＇ behaviors properly, the CCTM provides an accurate representation of traffic flow in simulating oversaturated traffic conditions.

IMPACTS OF ATOVS DATA ASSIMILATION ON PREDICTION OF A RAINSTORM OVER SOUTHEAST CHINA

Using the Advanced Research WRF (ARW WRF) model and the Gridpoint Statistical Interpolation (GSI) three-dimensional variational analysis (3DVAR) system,the impact of assimilating ATOVS (Advanced TIROS Operational Vertical Sounder) radiance through the prototype Community Radiative Transfer Model (pCRTM) is evaluated on the forecasting of a heavy rainstorm occurring over the central Guangdong province in the southeast of China on 20-21 June 2005. A pair of comparison experiments (NODA and DA) for this case is conducted with multiple configurations,including nesting domains with 4-km and 12-km grid distances. The results showed that by changing the initial condition through data assimilation,a modified divergence and moisture field with the structure of dipoles has been added to the axis of the rainband with a southwest-northeast orientation. When more moisture carried by a southwesterly low level jet (LLJ) was converged into the northeast portion of the rainband around the observatory station of Longmen,the amplitude of moisture static energy (MSE) increased substantially at low levels much more than at middle levels,resulting in the enlarging of differences in MSE between 500 hPa and 850 hPa; the atmosphere became more unstable. Consequently,the convective rainfall increased in the northeast part of the province around the Longmen station,which was consistent with the observed distribution of rainfall.

Transmission Capacity Analysis for Linear VANET under Physical Model

In this study, the transmission capacity of VANETs in a highway scenario is analysed on the basis of a 1D line model and the carrier sense multiple access with collision avoidance(CSMA/CA) protocol. We describe the CSMA/CA protocol used in IEEE802.11 p from the perspective of the geometric relationship amongst simultaneous transmitters. The desired channel and interfering channels are assumed to experience the same amount of path-loss and Rayleigh fading. On the basis of the proposed model, we analyse the attempted transmission probability of each road segment and the maximum intensity of active transmitters, including their theoretical values. Then, we employ the physical model to obtain the outage probability and derive the upper bound of the transmission capacity of a VANET, which is defined as the average spatial density of successful transmissions in the network. Simulation results indicate that the theoretical value offers a good bound on network capacity.

The impact of media coverage with a piecewise transmission rate in the spread of diseases

A three-dimensional compartmental model with media coverage is proposed to describe the real characteristics of its impact in the spread of infectious diseases in a given region. A piecewise continuous transmission rate is introduced to describe that media coverage exhibits its effect only when the number of the infected exceeds a certain critical level. Further, it is assumed that the impact of media coverage on the contact transmission is described by an exponential decreasing factor. Stability analysis of the model shows that the disease-free equilibrium is globally asymptotically stable if the basic reproduction number is less than unity. On the other hand, when the basic reproduction number is greater than unity and media coverage impact is sufficiently small, a unique endemic equilibrium exists, which is globally asymptotically stable.

Characteristic difference analysis and transfer parameter determination for different satellites to detect NDVI values

Here we propose a new method of NDVI difference analysis and NDVI difference correction for multi-sensors to detect NDVI.This method integrate PROSPECT model,SAIL model and MODTRAN atmospheric radioactive transfer model to simulate the remote sensing signals of different satellites for both NDVI difference analysis and correction without using real satellite images.The effects of both the sensors' spectral responses and atmospheric condition are simulated,and the differences among NDVI values derived from thirty different satellites are analyzed quantitatively.Focusing on the conversions of NDVI values among different satellites,through linear regression analysis,we estimate the transfer parameters between any two different satellite NDVI values,and present the lookup tables of transfer parameters under the atmospheric conditions of three surface visibility range values (10,23 and 50 km).The proposed method is useful for NDVI applications and analyses for multi-sensors.