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。     

Distributed power control in CDMA cellular systems

In wireless cellular communication, it is essential to find effective means for power control of signals received from randomly dispersed users within one cell. Effective power control will heavily impact the system capacity. Distributed power control (DPC) is a natural choice for such purposes, because, unlike centralized power control, DPC does not require extensive computational power. Distributed power control should be able to adjust the power levels of each transmitted signal using only local measurements, so that, in a reasonable time, all users will maintain the desired signal-to-interference ratio. In this paper, we review different approaches for power control, focusing on CDMA systems. We also introduce state-space methods and linear quadratic power control (LQPC) to solve the power-control problem. A simulation environment was developed to compare LQPC with earlier approaches. The results show that LQPC is more effective, and is capable of computing the desired transmission power of each mobile station in fewer iterations, as well as being able to accommodate more users in the system     

Macrodiversity power control in hierarchical CDMA cellular systems

Hierarchical code division multiple access (CDMA) cellular systems, consisting of macrocells with underlying microcells, are studied. We seek power control schemes which will allow both hierarchical layers to share the same spectrum. For the reverse link, hierarchical maximal ratio combining (HMRC) is applied where each mobile station (MSs) is received and coherently combined by base stations (BSs) in both layers. For the forward link, selective transmit diversity (STD) is applied where each BS provides multiple transmit paths for MSs to choose. We show that both HMRC and STD are effective in hierarchical CDMA architectures. We conclude that hierarchical architectures are a viable solution for improving CDMA cellular system capacity, and a significant performance gain can be achieved without assigning disjoint spectrum between the layers, by utilizing macrodiversity schemes such as HMRC and STD     

A feasible method to implement optimum CIR-balanced power control in CDMA cellular mobile systems

Power control is essential in the design of direct-sequence code-division multiple-access (DS-CDMA) techniques. Optimum power-control (OPC) methods with carrier-to-interference ratio (CIR) balancing have been formulated as eigenvalue problems for frequency-division/time-division multiple-access (FDMA/TDMA) cellular systems. For the CDMA cellular system, its OPC was also formulated as an eigenvalue problem based on a large link-gain matrix. The OPCs with CIR-balancing were realized by solving eigenvalue problems of link-gain matrices. We reformulate the CIR-balanced OPC in CDMA cellular systems by benefiting from the power constraints as an eigenvalue problem based on a novel link-gain matrix. For a feasible implementation, a two-level hierarchical power-control structure is proposed to carry out the eigendecomposition which is required for the CIR-balanced OPC. Shortages of unbalanced CIR and global outage are two common issues in CIR-balanced power control. To tackle these two problems, a simple linear prediction method and an adaptive on-off strategy are proposed. Furthermore, because of the capacity limitation of wireless communications, a differential pulse code modulation scheme is presented to reduce the number of bits required for the transmission of command words in the two-level hierarchical power-control structure.     

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.     

Open-loop power control error in cellular CDMA overlay systems

Adaptive power control has widely been used in DS/CDMA systems to overcome the so-called “near-far” problem. This paper studies the adaptive open-loop power control of a cellular CDMA system, which is overlaid in the downlink by a narrowband signal. The effects of downlink power allocation schemes to power control error in the presence of narrowband interference are analyzed. In order to get a minimum power control error in the CDMA overlay situations, an optimum downlink power allocation scheme is used, which works well for a wide range of signal to narrowband interference ratio     

Grey-based power control for DS-CDMA cellular mobile systems

The propagation channel of a mobile radio system exhibits severe signal shadowing and multipath fading, which results in wide variation of signal-to-interference ratio (SIR) at the receiver. To tackle this problem, power control is used to maintain the desired link quality and thus achieve higher capacity. In order to mitigate the channel variation effect precisely, a new application of grey theory to the power control strategy in the direct-sequence code-division multiple-access cellular mobile systems is introduced. This scheme aims to predict the SIR affected by the channel variation at the receiver and issue an appropriate control signal to the transmitter. The simulation results indicate that the grey-based scheme can offer less outage probability than the previous mechanisms     

Efficient distributed power control for cellular mobile systems

Various distributed carrier-to-interference (C/I) balancing procedures have been developed to cope with implementational drawbacks of centralized power-control schemes. However, it would be inevitable for these distributed schemes to lose some system performance compared to a centralized one since they control their power level based on only the local C/I measurements. An efficient distributed power-control (DPC) scheme is proposed to maximize the system performance. A distributed C/I balancing algorithm is suggested, which converges fast and is robust to C/I estimation errors. A simple instability detection rule is also suggested to accelerate the balancing phase of DPC schemes. Numerical results indicate that our algorithm achieves improvements in terms of the outage probability as well as the algorithm speed. Robustness to the C/I measurement errors is also explored     

Robust autoregressive predictive power control method for mobile CDMA systems

A closed-loop power control (CLPC) scheme with a multistep (indicating multiple prediction steps) linear autoregressive predictor is presented. The proposed CLPC relies on low-rate sample vector based autoregressive prediction. Compared to currently available predictive CLCP schemes, it demonstrates particularly robust performance in the presence of large loop delays and channel estimation errors.     

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.     

Adaptive closed-loop power control algorithms for CDMA cellular communication systems

Power control has been widely studied and shown to be crucial for the capacity and performance of direct-sequence code-division multiple-access (DS-CDMA) systems. Practical implementations typically employ fast closed-loop power control, where transmitters adjust their transmit powers according to commands received in a feedback channel. The loop delay resulting from the measurements, processing, and transmission of the power control commands can result in oscillations of the transmission powers and lead to degradation in the system performance. In this paper we present new adaptive closed-loop power control algorithms that are able to alleviate the effect of the loop delay. The algorithms are based on self-tuning controllers designed for a log-linear model of the power control process. We carried out computational experiments on a DS-CDMA network using the distributed constrained power control (DCPC) as a reference algorithm. Practical versions of the algorithms are also provided and they were compared with the fixed-step power control (FSPC) algorithm employed in the IS-95 and WCDMA systems. The numerical results indicate that our algorithms can significantly improve the radio network capacity without any increase in power control signaling.     

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.     

CDMA cellular systems performance with fading, shadowing, andimperfect power control

This paper addresses capacity estimation for cellular code-division multiple-access (CDMA) systems, assuming the IS-95 standard as a reference. Extending a previous analytical method (Viterbi et al., 1994), we obtain a sequence of bounds on capacity, and then we introduce an accurate approximation to reduce computation complexity. The analysis accounts for interference internal and external to the reference cell, fading, shadowing, and imperfect power control. Outage probability is expressed in terms of the characteristic functions (cf's) of the interference and imperfect power control random variables (RV's). The interference contributions are computed on the basis of a Poisson distribution for the number of users in a lognormally shadowed channel. Results are provided for different channel conditions and are validated against Monte Carlo simulations. A comparison against previously published CDMA capacity estimates is carried out, aimed at clarifying some controversial issues. It is also confirmed that large system capacity is achievable under tight power control     

Implications of mobile cellular CDMA

The results of four extensive field tests of code division multiple access (CDMA) cellular technology performed between November 1991 and September 1992 are presented. These tests include: validation system field tests conducted in San Diego, California, operating over five cell sites, comprising a total of eight sectors, and involving up to 70 mobile units, plus simulated other user and other base station interference; tests in Munster, Germany, the configuration of which consisted of two cell sites and two mobiles plus 20 simulated other users operating in the 1700-MHz band; tests in Geneva, Switzerland, the same as in Munster, but operated in the 800-900-MHz band, with cells located at GSM base station sites; and a field test conducted in Washington, DC, operating on two-sectored cell sites involving seven mobile units, plus simulated other user and other base station interference     

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。     

Downlink power allocation and adjustment for CDMA cellular systems

This letter provides a downlink power control algorithm and its convergence for adjusting as well as allocating appropriate power levels according to the need of mobiles. The adjustment process and its property provide a distinct view for understanding existing CDMA downlink power control algorithms     

多业务类分层结构CDMA系统功率控制研究

针对不同QoS要求的多业务类提供支持的分层结构CDMA系统的功率控制进行了研究，给出了该系统的一种功率控制算法。通过对反向链路运用HMRC方法，得到了一种支持多业务类的分层结构CDMA系统中反向链路CIR的简单分析方案和系统容量分析方法。     

Simplified power control method for cellular mobile communication

The centralised power control (CPC) method measures the gain of the communication links between every mobile and every base station in the cochannel cells and determines optimal transmitter power to maximise the minimum carrier-to-interference ratio. The authors propose a simplified power control method which has nearly the same performance as the CPC method but which involves much smaller measurement overhead     

Centralized power control in cellular radio systems

This paper describes a centralized power control scheme for cellular mobile radio systems. The power for the mobiles in the proposed scheme is computed based on signal strength measurements. All the mobiles using the same channel in this scheme will attain a common carrier-to-interference ratio. The proposed scheme is analyzed and shown to have an optimal solution