码分多址星形卫星数据网的功率控制研究

码分多址卫星通信系统的网络容量较小,而功率控制不理想使其容量进一步降低。本文给出了功率下的中断概率公式,由此计算功率控制误差对系统容量的影响。     

一种FDMA-DAMA卫星通信网功率控制方案

卫星通信系统中对系统功率的控制非常重要,这直接关系到系统的可用性程度,并且随着系统工作频率的提高尤为显著。针对资源按需分配频分多址(FDMA-DAMA)体制卫星通信系统功率控制问题,分析了传统方案的局限性和不足,在工程实际经验基础上,通过理论推导提出了一种新的功率控制方案,并给出了具体的功率参考值测试方法。通过与实际系统链路发射功率参考值测试数据比对,验证了新功率控制方案的发射功率参考值测试以及计算方法的正确性。     

CDMA卫星通信系统功率控制研究

文章从卫星通信系统的功率控制原理入手,提出了一种适合CDMA卫星通信系统的功率控制方法;给出了精准的功率控制时的系统容量,通过推导给出的中断概率公式和例举的CDMA卫星通信系统实际数据,将功率控制误差对于系统容量的影响进行了仿真.仿真结果表明,当标准方差不断增大,系统的中断概率增大,系统容量随之显著减小;而采用精准的功率控制技术,可以有效改善系统性能.     

Efficient Detection Algorithms for MIMO Communication Systems

In this paper, two new efficient detection algorithms, Type 1 (T1) with better complexity-performance tradeoff and Type 2 (T2) with lower complexity, are derived from one generalized framework for multiple-input multiple-output (MIMO) communication systems. The proposed generalized detection framework constructed by parallel interference cancellation (PIC), group, and iteration techniques provides three parameters and three sub-algorithms to generate two efficient detection algorithms and conventional BLAST-ordered decision feedback (BODF), grouped, iterative, and B-Chase detection algorithms. Since the group interference suppression (GIS) technique is applied to the proposed detection algorithms, the complexities of the preprocessing (PP) and tree search (TS) can be reduced. In (8,8) system with uncoded 16-QAM inputs, one example of the T1 algorithm can save complexity by 21.2% at the penalty of 0.6 dB loss compared with the B-Chase detector. The T2 algorithm not only reduces complexity by 21.9% but also outperforms the BODF algorithm by 3.1 dB.     

K波段卫星通信系统的抗衰落对策

本文概述了Ｋ波段卫星通信系统发展的优越性和巨大潜力。简单介绍了该波段卫星通信系统的衰落影响因素，提出了三各抗衰落对策，位置分集、自适应资源共享技术、自适应调制技术，并加以重点讨论。同时也分析了各种抗衰落技术的优势及存在问题。     

卫星通信系统中的多址接入协议

简述了卫星通信中多址协议的分类和影响多址协议性能的因素,重点介绍了三种预约多址协议PRMA-HS、PRMA/CDMA和Butst Reservation CDMA,并分析了它们的性能.     

卫星通信系统调制方式的研究

本文从卫星通信的特性出发 ,针对其带限和非线性的信道特性 ,提出了各种PSK调制方式 ,这类调制方式是利用已调信号包络恒定、频谱占有率低以及经由非线性信道而产生的频谱扩展和频率失真小等特点 ,使卫星通信的已调信号和特殊信道达到良好的匹配。本文还对相干载波提取中的锁相环提出了一种改进方法。     

卫星重叠通信系统功率控制策略研究

针对卫星重叠通信系统中扩频信号与原业务信号相互干扰的问题,提出了一种功率控制的策略。该策略分析了原业务信号对扩频信号的影响,给出了一种预测原业务信号功率的方法,来计算单用户的发射功率;并且推导出扩频信号总的发射功率与原业务性能恶化的关系,来限制扩频信号的发射功率。在上述理论分析的基础上,对一种典型的卫星重叠通信系统进行分析,评估出在原业务信号允许的恶化量为1 d B时,可接入用户数为22个。     

一种适用于卫星移动通信系统的功率控制技术

针对卫星通信系统中传播时延大,信道条件复杂的特点,提出了一种适用于卫星移动通信系统的功率控制技术。在开环功率控制过程中,功率控制端调整发射功率时,不仅考虑了本次接收信号的即时信息,还考虑了对端需求的历史信息,以及对链路质量不断修正的结果。在闭环功率控制过程中,采用块内多次平均,块间相关修正的方式来加快闭环功率控制的速率,提高其收敛性。仿真了所提的功率控制算法的平均接入时间,仿真结果验证了其性能。     

Admission Control Algorithms for Cellular Systems

This paper evaluates call admission control algorithms for a cellular or microcellular system. Algorithms are evaluated based on two Quality of Service (QoS) metrics: the new call blocking probability, which is the probability that a new call is denied access to the system, and the forced-termination probability, which is the probability that a call that has been admitted will be terminated prior to the call's completion. Three novel algorithms are presented: the Weighted Sum Scheme, the Probability Index Scheme, and the Hybrid Control Scheme. The weighted sum scheme uses the weighted sum of the number of calls underway in various cells when making the admission decision. The probability index scheme computes a probability index, which reflects the forced-termination probability of a new call arrival, and admits those calls with low probability indexes. The hybrid control scheme combines these two approaches. These novel algorithms are compared with three known algorithms: the Reservation Scheme in which a specific number of channels are reserved in each cell for handoffs, the Linear Weighting Scheme in which the admission decision depends on the total number of calls underway in a group of cells, and the Distributed Admission Control Scheme in which the admission decision depends on the projected overload probabilities in the cell at which the new call arrives and adjacent cells. We show that the Hybrid Control Scheme yields the best performance, particularly during periods when load differs from the expected level. We also show that the simple Reservation Scheme performs remarkably well, often superior to more complex schemes that have been proposed.     

低轨卫星移动通信系统接入方案

在低轨卫星移动通信系统中,由于卫星和移动用户间的相对运动使得呼叫切换频繁发生.为了降低星间切换请求到达率,减小系统切换开销,本文在距离优先接入方案基础上进一步提出了两种接入策略:覆盖时间优先方案和仰角加权的覆盖时间优先方案.构造了非均匀分布全球话务密度模型.并参照某实际系统参数,对不同接入方案准则下的全球话务服务进行了系统仿真,得到了相应的系统性能参数.     

TD-SCDMA系统的外环功率控制算法研究

在3GPP协议规范中对外环功率控制算法没有定义,由各设备生产和制造商决定。TD-SCDMA系统每时隙下服务用户数较WCDMA系统每帧下服务用户数明显减少;另外,采用了自适应的智能天线技术,适合WCDMA的外环功率控制算法不能直接适用于TD-SCDMA,提出了一种先进的自适应功率调整步长的外环功率控制算法。由于外环功率控制参数对系统性能影响较大,基于自适应智能天线技术,给出了不同参数下外环功率控制算法的性能,可用于TD-SCDMA网络的规划优化。     

基于LDPC的MIMO卫星扩频通信系统

MIMO即多输入多输出通信技术,因其可以增大信道容量,而被广泛应用于各类通信系统中。在卫星通信系统中应用MIMO技术,主要面临同道干扰和噪声两个问题。文中介绍了克服同道干扰的MIMO卫星通信线性检测系统,并为解决上述问题,在输入端引入扩频技术和接近香农极限的LDPC编码,而在输出端进行解扩和译码,既减小了同道干扰,又明显削弱了噪声,从而实现了良好的性能。     

CDMA蜂窝移动通信系统中的联合功率控制

功率控制技术是CDMA系统克服“远-近效应”,降低多址干扰、增大系统容量的一项关键技术.第三代移动通信系统对功率控制提出了新的研究课题.本文简要介绍了联合功率控制技术的基本概念,重点阐述了目前在多媒体CDMA系统中,联合功率控制与速率控制技术,与多用户检测技术,以及与自适应天线阵列处理技术的研究进展,并分析了目前研究中仍然存在的问题,最后指出了未来的研究方向.     

Channel Estimation Algorithms for MLSD in Optical Communication Systems

Maximum likelihood sequence detection represents the most efficient technique in the electrical domain to combat fiber impairments such as polarization-mode dispersion and group-velocity dispersion. In order to successfully apply this technique, it is mandatory to estimate some key channel parameters needed by the Viterbi processor. We propose a simple and effective solution based on the least-mean-square algorithm to perform such an estimation.     

小卫星通信系统射频前端设计

阐述了小卫星的发展背景、工作模式及技术上的优点,介绍了小卫星采用的射频前端系统结构。为了系统的合理设计,以满足星间通信的要求,对系统中低噪放电路、锁相环电路、自动增益控制电路的工作原理和重要指标进行了分析,采用ADS,ADIsimPLL软件仿真,得出适合要求的电路结构。最终制作出系统电路板并调试实现预期指标。     

非对称PCMA卫星信号的截获方法

近年来PCMA等卫星通信新技术的应用对卫星通信信号的截获提出了更高的要求,通过分析PCMA卫星通信系统的工作原理,借鉴多用户检测技术中串行干扰抵消的基本思想,提出一种针对非对称PCMA信号的截获方法,并进行了性能仿真。仿真结果表明,在没有任何先验信息的情况下,可以实现对非对称PCMA信号中双方信号的截获和解调。     

Algorithms for Wireless Communication Systems: A Power-Efficiency Perspective

Within the last five years, there has been a cultural shift from wired landlocked connectivity to pervasive wireless information access. Most emerging mobile devices are now equipped with some form of embedded wireless radio. The expectations of high data rates and increased battery longevity have put tremendous pressure on all aspects of wireless system design.The goal of our projects at the Center for Multimedia Communication at Rice is to develop powerefficient wireless enabled mobile devices. In this paper, we will consider the control and coding issues to increase active access time of mobile communication devices. In particular, we develop scheduling algorithms which adaptively change the transmission power and rate, based on both the transmission queue backlog and the channel conditions. Thepacket level control algorithms exploit burstiness of data streams and channel variations to trade packet queuing delay with the average transmit power. The wide range of data rates dictated by the scheduler and our power efficiency objective is effectively met by a multi-antenna transceiver. We design non-coherent space-time codes for high mobile speeds, and space-time feedback strategies for low mobility applications. This paper highlights some of the proposed methods and presents some preliminary results. This revised version was published online in August 2006 with corrections to the Cover Date.     

Improving SINR via Joint Beam and Power Management for GEO and LEO Spectrum-Sharing Satellite Communication Systems

In this paper, we investigate a geosynchronous earth orbit(GEO) and low earth orbit(LEO)coexisting satellite communication system. To decrease the interference imposed on the GEO user caused by LEO satellites, we propose a joint beammanagement and power-allocation(JBMPA) scheme to maximize signal-to-interference plus noise ratio(SINR) at the GEO user, whilst maintaining the ongoing wireless links spanning from LEO satellites to their corresponding users. Specifically, we first analyze the overla...     

卫星移动通信系统及其进展

本文概述了卫星移动通信的特点，介绍了卫星移动通信系统的进展，结合典型的系统讨论了卫星移动通信系统的关键技术。