CDMA接入信道的容量分析

本文简要介绍了CDMA接入信道的特性,随后给出了接入信道容量的概念和计算方法,最后提出了优化接入信道容量的建议.     

Multi-user Fair Scheduling in the Downlink of CDMA Packet Systems

A fair scheduling algorithm is proposed to improve the system throughput while maintaining the fairness in the downlink of a code-division multiple access (CDMA) system employing AMC and multicodes. R. Kwan and C. Leung suggested an optimal scheduling to maximize the total throughput based on simultaneous transmissions strategy. In this letter, we extend the optimal scheduling so that some degree of fairness can be maintained. We formulate a mixed-integer nonlinear programming problem to assign the radio resources such as the transmit power and codes to several users effectively. The result shows that the proposed algorithm provides a significant throughput gain over PF scheduling with one-by-one transmission at the same level of fairness     

On the Capacity Degradation Due to Coexistence of WCDMA and CDMA2000 Systems

In this paper,we investigate the capacity degradation due to the coexistence of WCDMA and CDMA2000 net-works by system-level Monte Carlo simulation.Both systems are simulated according to the deployment of macro cells,andspeech service is considered.The capacity losses under different carrier spacing and different geographical offset are evalu-ated.Simulation results show that considerable capacity loss is seen when WCDMA is the victim system,while the influ-ence of WCDMA to CDMA2000 is slight.Increasing carrier-to-carrier spacing and decreasing geographical offset lead toless capacity loss and co-locating the base stations of both systems is a preferred solution.     

Performance Investigation of CDMA/PRMA with Imperfect Power Control in TDD Cellular Systems

This study investigates the performance of joint code-division multiple access/packet-reservation multiple access (CDMA/PRMA) with the consideration of imperfect power control in TDD-CDMA cellular systems, and compares with that of CDMA/PRMA with an assumption of perfect power control. Both voice and World Wide Web (WWW) Internet browsing traffic were considered. We have studied their performances in terms of packet loss probability, power outage probability and average access delay. The results show that the assumption of CDMA/PRMA with perfect power control is too optimistic and independent of cell radius. It might be valid when the cell radius is <500 m. In addition, the performance of CDMA/PRMA with imperfect power control is highly limited by the cell radius due to its constraint on transmission power levels. Therefore, careful study is required if CDMA/PRMA is used in TDD systems.     

PN短码在CDMA网络规划中的应用研究

PN(伪随机噪声)短码规划是CDMA(码分多址)网络设计中特有的问题,良好的PN码规划对于实现设计良好的网络至关重要。通过对同相偏干扰和邻相偏干扰这一对矛盾的分析和处理,介绍了PN码偏置规划的原理以及需要满足的基本条件,并提出了可行的规划方案。     

Performance of Multiuser Detection in Multirate CDMA Systems

Multiuser detectors for asynchronous multirate code-division multiple-access (CDMA) systems are considered. A multirate CDMA system model able to fit several system concepts in the same framework is presented. The performance of the multi-code (MC) system with one processing gain and the multiple processing gain (MPG) system is compared. Upper bounds for the expected value of the asymptotic multiuser efficiency of the decorrelating detector for a synchronous multirate CDMA system with three effective users are derived for a system with one and two processing gains. The numerical results show that the performance of the decorrelating detector for MC and MPG systems do not differ significantly. The bit error rates (BER) of the decorrelating, parallel interference canceler (PIC) and groupwise serial interference canceler (GSIC) with either PIC or decorrelator within the group are compared. The results show that the decorrelating and the GSIC detectors yield the best performance. For all interference cancellation schemes the BER saturates at high SNRs due to decision errors degrading the multiple-access interference (MAI) estimates.     

A Comparative Capacity/Coverage Analysis for CDMA Cell in Different Propagation Environments

In the design of cells in mobile communication systems, path loss prediction models play an important role and have been the subject of the study for some time (M.F. Ibrahim and J.D. Parsons, IEE Proceedings, Vol. 130, No. 5, 1983). This paper presents the analysis of two main factors that affect the capacity bounds in a UMTS cell for different propagation models. These are the (i) interference levels at Node B, which increases with the number of active users, and (ii) the limited sending power of the user equipment (UE) which may not be able to send signals with enough power to reach Node B with the required received power level due to path loss. The aim of this paper is to analyse the capacity/coverage of the uplink of UMTS system in different propagation environments (free space, suburban, urban, dense urban, rural) and derive the capacity bounds for the UMTS cell. The capacity bounds have been extracted based on the extended COST-231 Hata model (http://cost.cordis.lu/src/whatiscost.cfm). COST-231 Hata is an extension of the Okumura—Hata model which covers the higher frequencies (G.L. Stüber, “Principles of Mobile Communications,” Kluwer, 1996) necessary for WCDMA. The basic model describes the propagation loss in an urban environment, but a number of correction factors can be applied to extend its application to a broader range of environments. The analysis takes into account a number of capacity influencing factors such as the CDMA code non-orthogonality, the inter-cell interference, imperfect power control, and different service specific factors. The simulation results show the effect of different system and varying environmental parameters upon the system's capacity in different environments. The results clearly demonstrate that it is too optimistic to rely on studies based on free space assumptions.     

同步CDMA系统中的MMSE检测器研究

分析了基于实域估计的最小均方误差(MMSE)检测器及其在同步CDMA系统的应用。首先对同步CDMA系统进行了描述,并在此基础上对这种新的MMSE检测器在同步CDMA系统中的设计和近似实现方法进行了探讨。     

Other-Cell-Interference Factor Distribution Model in Downlink WCDMA Systems

Interference performance is among the most important issues especially in WCDMA cellular networks planning coverage and capacity. F-factor has been introduced in previous works to model the interference in WCDMA downlink dimensioning process. In this paper, we establish its PDF expression assuming one interferer in the serving cell both with and without correlated shadowing effect. Uniform and non-uniform traffic situations are distinguished through the study of both uniform and non-uniform traffic load cases. Then, we generalize the expression for multiple interfering cell tiers. We show the impact of this evaluation on the design process in order to increase the capacity of a network. Anis Masmoudi received his Engineering diploma in 1999 from Sup'Com (Ecole Supérieure des Communications de Tunis: High Communication School of Tunis) then graduated in 2001 with Master of Science from Ecole Nationale d'Ingénieurs de Tunis (ENIT). He worked in 2000–03 as a research engineer in Centre d'Etudes et de Recherches des Télécommunications (CERT), then he is recruited in 2003 by Institut National des Sciences et de Technologie (INSAT) as a teacher assistant. His PHD research work is focused on mobile cellular networks planning, WCDMA / HSDPA dimensioning processes and 3G networks optimisation in cooperation with Institut National des Télécommunications d'Evry -France (INT). Sami Tabbane is Professor at Ecole Supérieure des Communications de Tunis (Sup'Com). He has graduated from Ecole des Mines de Paris in 1988 and got a PhD of Ecole Nationale Supérieure des Télécommunications de Paris (ENST) in 1991. He started his carreer at Centre National d'Etudes des Télécommunications (CNET) in Issy les Moulineaux in 1992–94 and was recruited by Sup'Com in 1994. His main research areas are: mobility management (handover and location management), cellular networks planning and service implementation and optimization in 3G networks. He is the co-author of “Réseaux GSM” (Hermes, 1995) and “Ingénierie des Services de Télécommunications” (Hermes-Lavoisier, 2005). He is the author of “Réseaux Mobiles” (Hermes, 1997), “Handbook of Mobile Networks” (Artech House, 2000), “Ingénierie des Réseaux Cellulaires” (Hermes-Lavoisier, 2002).     

多小区下行链路协同算法应用研究

干扰是影响网络指标的重要因素,也是影响客户感知的一个重要因素,尤其是在CDMA系统中,同频干扰是一个不可避免的问题。在CDMA系统中采用了单小区的联合检测、智能天线等技术来消除干扰。文章介绍针对高负荷网络下出现的同频干扰问题的多小区下行链路协同算法(MDIC)的实现以及在现网中的验证。     

Capacity and SER Analysis of MIMO MRC Systems in an Interference-Limited Environment

The effect of co-channel interference (CCI) is considered in multiple-input multiple-output (MIMO) systems employing maximal ratio combining (MRC) under independent and identically distributed Rayleigh fading. Closed-form capacity and symbol error rate expressions are presented to evaluate the performance without any numerical integrations or statistical simulations. The analytical results are compared with Monte Carlo simulations and the good agreement is obtained.

CDMA移动通信系统中的联合功率控制与多用户检测

功率控制和多用户检测是CDMA移动通信系统中克服远近效应、抑制多址干扰(MAI)的两项关键技术。这里简要介绍了CDMA移动通信系统中功率控制与多用户检测技术,阐述了联合功率控制与多用户检测技术的基本概念,重点综述了联合功率控制与线性多用户检测技术以及联合功率控制与非线性多用户检测技术的研究进展,并对今后的研究方向进行了概括性的描述。     

Rayleigh信道下的多小区下行链路性能分析

针对存在来自相邻蜂窝小区的同信道、不同功率信道干扰的单用户下行链路场景,分析了基站和用户均为单天线时的系统性能.系统模型为两个基站、两个用户,基站与用户均为单天线.在期望信号和干扰信号均为Rayleigh分布时,运用基于概率密度函数性能分析法推导了系统中断概率;基于瞬时信干噪比(SINR)的推导,并对瞬时误符号率(SER)取平均的方法推导了平均误符号率(ASER)的闭合表达式和用户的接收SINR的n阶矩;根据用户接收平均SINR的n阶矩表达式,推导并分析了用户接收平均SINR的衰落量(AF)性能.计算机仿真了在不同干扰功率下多小区系统的中断概率、ASER的性能以及AF性能.仿真结果表明:单小区和多小区系统的中断概率、ASER和AF的解析曲线均与数值仿真结果一致.系统性能随着干扰基站功率的降低而提升,系统性能随发送功率的增加增益明显.     

The Other-Cell Interference Calculation of Forward Link Channel in Multicode CDMA Systems

This paper analyzes the other-cell interference of forward link channel in multicode CDMA system supporting a voice and data service. In this system, voice communication can be served by a basic code and data service can be supported by multiple codes. Using this analysis, we can get the approximated capacity of forward link. We describe the effect of data user activity and received power level ratio between a data service and a voice service. Also, this paper describes the forward link capacity and the power ratio of data power to voice power according to the change of FER threshold for data service.     

IS—95CDMA系统的容量分析

容量的需求是推动ＣＤＭＡ数字蜂窝移动通信开发的主要动力。系统的容量受许多因素的影响，本文针对ＩＳ－９５ＣＤＭＡ系统在采用了功率控制、话音激活和扇区划分技术的情况下，对系统的容量进行了分析，同时也分析了功率控制精度对容量的影响。     

The Capacity Analysis of the CDMA Cellular System

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Linear Interference Cancellation of Asynchronous CDMA Systems by Preconditioned CG Method

It is well known that the iterative method is used for solving a set of linear equations corresponding to linear interference cancellation structures. An ideal computation of the decorrelating or the linear minimum mean-squared-error (LMMSE) detector requires order K ³ flops, where K is the number of users. To alleviate the computational complexity, iterative decorrelating and the LMMSE detectors are proposed. In this paper, the symmetric successive over relaxation (SSOR) preconditioning scheme is applied to the conjugate gradient (CG) method. The performance of the detectors is investigated and it is found that the SSOR preconditioned CG (PCG) method can provide significantly faster convergence than CG method.     

Use of Adaptive Sectorisation for Capacity Enhancement in CDMA Cellular Systems with Non-Uniform Traffic

This paper discusses the application of adaptive sectorisation in the capacity enhancement of a CDMA cellular system dealing with non-uniform traffic. It considers the particular case where the traffic distribution consists of isolated areas of congested traffic called Hot Spots (HS). It is envisaged that the traffic density inside a HS is many more times that outside the HS. A more even traffic distribution among sectors is attempted by re-adjustment of sector boundaries using finite antenna beam switching. System capacity is estimated on the basis of tolerable interference in a sector taking into account of both intrasector and intersector interference in a multicell environment. Interference is evaluated under the assumption of perfect power control in the uplink. Normal propagation environment is assumed in the cell that allows path losses and shadowing losses in the mobile radio signal. Variation in the antenna gain is also accommodated by taking appropriate radiation pattern into account. It is shown that successive sector adjustment with increasing HS traffic intensity can deter call blocking in the HS sector. It is also shown that a significant improvement in system capacity could be obtained with adaptive sectorisation particularly when the HS user density is several orders of magnitude higher than that outside the HS.     

波束成形下DMIMO系统下行小区平均遍历容量分析

主要对波束成形下分布式MIMO系统下行小区平均遍历容量展开分析。首先建立了包含快衰落、阴影衰落和路径损耗的复合衰落信道模型。然后,在分布式基站功率受限条件下,推导各基站权重向量即最优波束;并基于ST-MRT传输策略,推导特定移动台位置条件下,小区下行点对点遍历容量表达式。最后,考虑移动台在小区内任意分布的特征,进一步推导出波束成形下小区平均遍历容量理论近似表达式。结果表明所推导的理论近似表达式可很好地反应系统的实际性能。     

CDMA系统中类解相关多用户检测器的研究

综合了近年来发展起来的线性类解相关多址干扰消除技术,对各种线性类解多址干扰技术的性能进行了分析,对其实现进行了一定程度的探讨,并得出了实际系统的误码率表达式。分析表明,该类算法能够较好地克服边缘效应,具有很好的应用前景。