基于模糊规则的低轨卫星信道自适应估计算法

低轨卫星通信功率控制需要有对信道增益及时的估计,而由于低轨系统链路增益的时变特性使传统的信道估计方法性能受到限制.基于模糊滤波理论,提出一种在功率控制中使用的自适应LMS信道估计算法,根据分析模型和经验数据建立信道增益及其滑动均值大小的模糊集,利用LMS算法调整模糊隶属函数的参数,使算法具有对信道时变特性一定的适应性.仿真结果表明了算法的有效性.     

一种在无线衰落信道上支持实时业务的分组调度算法

无线分组调度算法能为蜂窝网络中的移动用户提供服务质量的保证。在此问题上,以前的研究工作中一个经典的假设是基站与用户之间的信道条件变化为一平稳随机过程。但在实际情况中,这样的平稳假设并非总是合理的。研究表明基于平稳假设的调度算法,如流行的M-LWDF和EXP-rule算法,在非平稳信道上的性能下降明显。在CDMA蜂窝通信系统中,为在时变衰落信道上支持实时数据业务,该文提出一种基于模糊逻辑控制的分组调度算法,简称FROS。它能在保证用户QoS要求的同时,考虑到无线信道的快衰落特性而充分利用多用户分集(Multiuser diversity)所带来的增益,从而提高系统容量。系统级仿真证明,FROS算法能在优化系统分组时延性能和优化系统吞吐量性能之间保持良好的平衡和折衷,在平稳信道和非平稳信道的条件下都能获得比M-LWDF和EXP-rule算法更好的性能。     

社会科学与管理科学

Y2000-62074-1126 0007204无线电资源管理=Session S29:radio rGSOHECe manage-ment[会,英]//1999 IEEE International Conference onCommunications,Vol.2 of 3.—1126～1166(H)本部分8篇论文的内容有:基于 IS-95的 CDMA系统的正向功率分配,多媒体 DS-CDMA 系统反向线路的最佳功率分配,非均匀通信量多单元 DS/CDMA系统的功率分配最佳化,宽带蜂窝通信网中动态信道分配,蜂窝网络中信道分配的最佳算法,TDD/FDD-CDMA 混合蜂窝网络频率选择策略,无线/移动网络的多速率资源控制方法,干扰和通信负载对干扰自适应动态信道分配的 TDMA/FDMA 系统性能的影响。     

CDMA蜂窝集群前向功率控制技术的研究

本文对基于CDMA的集群通信系统的功率控制进行了初步的研究。针对集群通信的特点，本文提出了CDMA共享信道的概念和集中式前向功率控制技术，并进行相应的仿真。结果表明，该技术很好地解决了在CDMA蜂窝通信中实现集群功能的功率控制问题，大大增加了系统的容量。     

多速率CDMA系统中基于信道增益的功率控制

CDMA系统中,功率控制对于降低系统干扰,提高系统容量和性能具有重要作用。介绍了一种基于信道增益向量的功率控制方案,并通过仿真验证了该功率控制方案的性能。仿真结果表明,该功率控制方案相对于基于数据速率的功率控制方案具有额外的4～6dB的增益。     

扩频通信与扩频调制技术

Y99-61517-38 9915633码分多址系统的算法和性能(含7篇文章)=Session2:algorithms and performance CDMA systems[会,英]//1998 IEEE International Coanference on Comnmni—cations,Vol.1 of 3.—38～71(MaG)本部分共收入7篇文章,讨论了可供选择的宽带CDMA 系统的性能比较,基于宽带 CDMA 的 WLL(无线用户环路)系统的基站收发信机的实现,新用户对盲目自适应同步多用户直接序列(DS)CDMA 检测的影响,频率非选择性衰落信道上自举多用户 CDMA 检测器的性能,无线通信中最低中断率的最佳功率控制,基于信号干扰比的功率控制的 CDMA 蜂窝系统的多小区模拟结果,在 CDMA 系统中的快速前向链路功率控制。     

CDMA2000 1X系统反向功率控制性能分析

本文主要分析了CDMA2000 1X蜂窝系统反向链路的功率控制性能，在分析过程中假设无线信道为独立的瑞利衰落信道，分别从功率调节步长、移动台移动速度、功控比特的BER以及信道参数几个功控参数来加以分析研究，并由此得出提高功率控制性能的一些方法。     

多媒体CDMA蜂窝网络上行顽健功率控制算法

研究了同时承载带宽保障业务和尽力而为业务的多媒体CDMA蜂窝网络上行链路顽健功率控制问题.考虑业务突发性、链路增益估计误差以及小区间干扰等因素,通过推导中断概率提出了一种非线性迭代算法.在给定尽力而为业务数据率分配方案的情况下,该非线性迭代算法能够判断是否可以通过功率控制有效地保证带宽保障业务和尽力而为业务的服务质量.在此基础上,分别为支持离散数据率和连续数据率的两类多媒体CDMA蜂窝网络设计了相应的上行链路功率控制算法.最后,通过仿真验证了所提出非线性迭代算法的收敛性,并通过与一种次优功率控制算法进行比较说明了所提出功率控制算法的性能优势.     

低轨卫星信道自适应模糊估计算法

针对功率控制,提出一种利用模糊规则的自适应LMS信道估计算法,通过将信道增益大小和前后变化值的大小划分为若干模糊集,建立将自适应算法和经验值相结合的自适应滤波器,使算法具有对低轨信道时变特性一定的适应性。仿真结果表明了算法的有效性。     

两跳中继CDMA蜂窝系统的上行链路容量分析

首先在两跳中继CDMA蜂窝系统的基础上,提出了2种使用带外信道提高传统CDMA蜂窝系统上行链路容量的中继方法;然后通过分析传统无中继CDMA蜂窝系统的干扰功率,分别得到这2种中继方法对当前小区和邻居小区总的干扰功率;最后在一种对称小区模型的基础上,通过数值计算对两跳中继CDMA蜂窝系统的上行链路容量进行分析,并讨论了2种中继方法对系统性能所产生的影响.     

多业务CDMA蜂窝移动通信系统的功率控制

本文提出了多业务CDMA蜂窝移动通信系统的一种下行链路功率控制策略，系统的最优功率分配可以归结为求解归一化链路增益矩阵在有约束条件下的最大实特征值。在对系统的最优功率分配进行理论分析的基础上，给予了相应的仿真结果，并针对实际系统负载过重的情形，提出了按照业务优先级别逐步去除小区用户的功率控制策略。     

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 Adaptive Power Control in the Uplink of CDMA Systems

In this paper, we propose an adaptive power control algorithm using optimal control theory for CDMA cellular systems. With linear quadratic control, each mobile transmits to achieve a desired SIR under the fast varying environment of practical CDMA cellular systems. We apply Kalman filter theory to estimate a channel variation which is vulnerable to nonconstant link gain, mutual interference and uncertain noise. Through simulation comparison with DCPC algorithm, the suggested power control algorithm shows an increased uplink channel capacity.

CDMA蜂窝系统中基于模糊神经网络的反向链路功率控制

CDMA是一个干扰受限系统,反向链路功率控制对于克服“远近效应”和增加系统容量是非常重要的.本文提出了一种基于模糊神经网络(FNN)的自适应闭环功率控制算法,该算法动态地调整功率控制增量,使基站接收到的每个用户的发射功率相等.仿真结果表明,由于模糊神经网络能够较好地识别反向链路的时变特性,FNN功率控制算法比传统的固定步长功率控制方法取得了更好的控制性能和更大的系统容量.而且,FNN能够通过神经网络训练自动地调整隶属度函数和模糊规则,从而适合于实现在线系统识别和自适应控制.     

Decentralized dynamic power control for cellular CDMA systems

The control of transmit power has been recognized as an essential requirement in the design of cellular code-division multiple-access (CDMA) systems. Indeed, power control allows for mobile users to share radio resources equitably and efficiently in a multicell environment. Much of the work on power control for CDMA systems found in the literature assumes a quasi-static channel model, i.e., the channel gains of the users are assumed to be constant over a sufficiently long period of time for the control algorithm to converge. In this paper, the design of dynamic power control algorithms for CDMA systems is considered without the quasi-static channel restriction. The design problem is posed as a tradeoff between the desire for users to maximize their individual quality of service and the need to minimize interference to other users. The dynamic nature of the wireless channel for mobile users is incorporated in the problem definition. Based on a cost minimization framework, an optimal multiuser solution is derived. The multiuser solution is shown to decouple, and effectively converge, to a single-user solution in the large system asymptote, where the number of users and the spreading factor both go to infinity with their ratio kept constant. In a numerical study, the performance of a simple threshold policy is shown to be near that of the optimal single-user policy. This offers support to the threshold decision rules that are employed in current cellular CDMA systems.     

Adaptive S-ALOHA CDMA as an alternative way of integrating servicesin mobile environments

Code-division multiple-access (CDMA) schemes appear to be very promising access techniques for coping with the requirements of third-generation mobile systems, mainly because of their flexibility. This paper proposes an adaptive S-ALOHA DS-CDMA access scheme as a method for integrating nonreal-time (i.e., Internet applications) and real-time (i.e., voice) services in a multicell scenario by exploiting the potentials of CDMA under time-varying channel load conditions. The adaptive component makes data terminals autonomously change their transmission rate according to the total (voice+data) channel occupancy, so that the minimum possible data delay, which can be analytically obtained by defining a birth-death process, is almost always achieved. Moreover, by means of a simplified cellular model, the proposed algorithm revealed the same behavior, i.e., it tries to select the most suitable transmission rate at any time slot, when it is affected by intercell interference and even by power control imperfections. Finally, in order to gain more insight into the potentials of such an access strategy, the adaptive S-ALOHA CDMA scheme is then compared to a reservation time-division multiple-access (TDMA)-based protocol (PRMA++), showing the benefits of the CDMA-based solution in terms of capacity, flexibility, and data delay performance     

Robust power control of CDMA cellular radio systems with time-varying delays

Power control is an important factor to increase communication link quality and system capacity in the direct-sequence code-division multiple access (DS-CDMA) cellular radio systems. The Smith prediction filter can achieve the unbiased asymptotic tracking about a desired target signal to interference noise ratio (SINR) under the fixed round-trip delay. However, it is sensitive to the variation of round-trip delay. In order to track the desired SINR with the time-varying round-trip delay, a multiple-mode Smith prediction filter, which combines the multiple Smith predictors with a likelihood function, is proposed for the power control of CDMA systems. The proposed scheme can compensate for the unknown time-varying round-trip delay. Simulation results show that the performance of the proposed multiple-mode power control method is robust to time-varying round-trip delay in the CDMA cellular radio systems.     

Distributed Power Balancing with Linear Prediction and Adaptive On-Off Strategies for CDMA Cellular Mobile Systems

Several distributed balance (DB) power control algorithms that can achieve SIRbalance have already been proposed for cellular mobile systems [1–3].In the present paper, two simple strategies, namely linear prediction andadaptive on-off strategies, are further applied to forward link distributedbalance (DB) power control in DS/CDMA cellular mobile systems. The linearprediction is used to track the variance of the short-term fading andcompensate it in advance, and the adaptive on-off strategy is applied to solvethe problem that the received SIR of all the communication links less than theminimum required SIR. Simulation results indicate that DB power control withthese two strategies can achieve much better performance than the original DBpower control.     

CDMA系统中的功率控制

功率控制是CDMA移动通信系统中最为重要的核心技术之一。该文主要介绍CDMA系统反向链路和前向链路的各种功率控制技术。首先介绍功率控制对于CDMA系统的重要性及功率控制的分类，然后分别介绍CDMA系统反向链路和前向链路的功率控制算法。     

Power control for an asynchronous multirate decorrelator

For code-division multiple-access (CDMA) wireless systems employing multiuser detection, the varied bit-error rate (BER) requirements of multimedia traffic dictate the use of transmitted power control. Using a decorrelator in an asynchronous multirate direct-sequence CDMA system, it may be necessary for different users to combat the noise enhancement and the propagation losses to varying degrees depending on individual requirements. In this context, we propose a power control algorithm for a multirate decorrelator that is suitable for a class of BER-based link quality objectives. If the uplink channel gain of the desired user is known, then it is straightforward for each user to choose the transmitted power needed to meet its target BER objective. In practice, however, the uplink channel gain is often difficult to measure. To avoid this measurement, we employ stochastic approximation methods to develop a simple iterative power control algorithm. In this algorithm, each mobile uses the output of its own decorrelator to update its transmitted power in order to achieve its BER objective. We show that when a user's bits have nonzero asymptotic efficiencies, the power control algorithm converges quickly in the mean square sense to the minimum power at which a user achieves its quality-of-service objective