均衡技术是克服码间干扰(Inter-Symbol Interference,ISI)的有效措施,由于信道特性的随机性与时变性,实际中消除码间干扰最常用的是自适应均衡器。本文对基于最小均方(Least Mean Squares,LMS)算法和递推最小二乘(Recursive Least Squares,RLS)算法的自适应均衡器进行仿真研究,分析了信道特性与设计参数对自适应均衡器的收敛速度与稳态性能的影响。
盲多用户检测算法广泛应用于码分多址(Code-Division Multiple-Access,CDMA)系统中,能够有效克服多址干扰(Multiple Access Interference,MAI)与"远-近"效应(Near-Far effect)的影响,是CDMA技术中的研究热点。对基于卡尔曼(Kalman)滤波算法的盲多用户检测器进行了研究,在白高斯噪声信道与平坦瑞利衰落信道环境下仿真分析了多址干扰与"远-近"效应对系统性能的影响。仿真实验表明,基于Kalman滤波的盲多用户检测器在两种信道中误码率性能均优于基于最小均方(Least Mean Squares,LMS)算法和递推最小二乘(Recursive Least Squares,RLS)算法的盲多用户检测器,可以有效抵抗多址干扰与"远-近"效应的影响,对提高CDMA系统容量具有十分重要的应用价值。
Retired geosynchronous (GEO) communication satellites affect the GEO orbit environment in outer space. According to the new concept of modern design, the authors propose creatively a method of reusing retired GEO communication satellites, through adjusting retired GEO satellites to slightly inclined orbit geosynchronous (SIGSO) satellites. After these retired satellites are applied to the navigation and communication system, integrity of navigation system and positioning accuracy of the system is improved. Meanwhile, some transponders on these retired satellites can be used to establish a new satellite communication service, and initiate the study and utilization of the multi-life cycle for retired satellites. Experimental results show that this project has significant social value and can make remarkable economic benefit.
SHI HuLiAI GuoXiangHAN YanBenMA LiHuaCHEN JiBinGENG JianPing
Multiple Path Interference (MPI) and Multiple Access Interference (MAI) are important factors that affect the performance of Chinese Area Positioning System (CAPS). These problems can be solved by using spreading sequences with ideal properties and multi-user detectors. Chaotic sequences based on Chebyshev map are studied and the satellite communication system model is set up to investigate the application of chaotic sequences for CAPS in this paper. Simulation results show that chaotic sequences have desirable correlation properties and it is easy to generate a large number of chaotic sequences with good security. It has great practical value to apply chaotic sequences to CAPS together with multi-user detecting technology and the system performance can be improved greatly.
The positioning of the GPS or Chinese Area Positioning System (CAPS) software receiver was developed on a software receiver platform. The structure of the GPS/CAPS dual-mode software receiver was put forward after analyzing the differences in the satellite identification, ranging code, spread spectrum, coordinate system, time system, carrier band, and navigation data between GPS and CAPS. Based on Matlab software on a personal computer, baseband signal processing and positioning procedures were completed using real GPS and CAPS radio frequency signals received by two antennas. Three kinds of experiments including GPS positioning, CAPS positioning, and GPS/CAPS positioning were carried out. Stability and precision of the results were analyzed and compared. The experimental results show that the precision of CAPS is similar to that of GPS, while the positioning precision of the GPS/CAPS dual-mode software receiver is 1-2 m higher than that of CAPS or GPS. The smallest average variance of the positioning can be obtained by using the GPS/CAPS dual-mode software receiver.
The positioning precision of the transmitting Chinese Area Positioning System(CAPS) is reduced due to the non-ideal distribution of the satellite constellation.Positioning and navigation enhancement methods are able to improve the reliability and accuracy of the positioning system,especially for users in special regions and special applications.In this paper,a positioning enhanced scheme based on ultra-wide band(UWB) pseudolite is proposed for CAPS.It is demonstrated that the link budget of UWB pseudolite satisfies the FCC's emission mask requirements.The localization algorithm of the enhanced CAPS is presented.The simulations indicate that the positioning precision of the proposed enhanced scheme is improved greatly,and the feasibility of the enhanced scheme is thus proved.
