一种CDMA蜂窝通信系统中的功率控制算法

功率控制是CDMA蜂窝通信系统的关键技术.本文给出一种部分补偿信干比的功率控制算法,可以提高系统的容量,改善系统性能.     

大规模MIMO系统中基于用户分类的动态导频分配

针对大规模MIMO系统导频污染问题,提出一种基于用户分类的动态导频分配策略.根据目标小区用户信号强度的方差设置合理的用户信号强度临界值,将目标小区用户分为中心用户和边缘用户.中心用户采用最大载干比算法分配导频,以最大化中心用户总信道容量.边缘用户采用贪婪算法分配导频,以提高每个边缘用户的信干噪比.仿真结果表明,所提策略在提高边缘用户信干噪比的同时能够有效提高系统的信道容量.     

基于干扰和功率控制的多小区分布式波束成形

在多小区干扰信道中,基于分布式竞争设计,提出两种优化基站发射波束成形矩阵的设计,使每个小区的最差信干噪比最大.一种是基于干扰控制的设计,利用差异化的干扰系数,抑制小区间的干扰,提高系统性能.另一种是基于功率控制的设计,通过调整各基站的发射功率,提高系统性能.这两种设计,都能保持算法的分布式特性,又能有效地提高用户信干噪比.仿真分析表明,基于功率控制的设计在功率大的情况下,性能优于基于干扰控制的设计.     

DFP算法在CDMA移动通信上行链路功率控制中的应用研究

本文提出了一种基于DFP算法的功率控制方案。详细研究了该方案在CDMA移动通信中,进行融合基站分配的上行链路功率控制的应用理论。首先导出了最小发送功率控制模型。而后,提出了用DFP算法求解该模型的原理框图,并分析了用该方案进行最小发送功率控制的基本理论和实际性能,探讨了该方案中进行一维搜索的方法。最后用计算机仿真法模拟出该方案的运行性能。结果表明与最小功率控制算法相比,DFP功率控制算法可以提高基站接收信号的平均信扰比,降低信扰比的平均偏差,减小信扰比低于目标信扰比一定比例的用户数量,从而可以降低用户信号的中断概率、提高信道容量。     

蜂窝小区边缘同频嵌入垂直覆盖的网络性能

提出一种在蜂窝小区边缘同频嵌入垂直覆盖的新型混合小区网络结构,具有抑制小区间干扰和提高边缘信干比等优点。该网络结构是以不改变目前蜂窝网络“水平覆盖”结构的前提下,在小区边缘干扰区域同频嵌入天线波束为垂直向下的微小基站,称作“垂直覆盖”,因此易于实际操作和实现。首先分析了蜂窝小区水平覆盖的干扰深度,垂直覆盖基站的干扰特性,及各自的频谱效率。随后,针对提出的蜂窝小区边缘同频嵌入垂直覆盖的网络结构,分别研究了混合小区的水平覆盖中心区域和垂直覆盖小区边缘区域的频谱效率。结果表明,提出的新型混合小区网络结构,能有效抑制蜂窝小区间干扰,改善小区边缘性能,实现更高的频谱效率。     

基于Q-Learning算法的毫微微小区功率控制算法

该文研究macro-femto异构蜂窝网络中移动用户的功率控制问题,首先建立了以最小接收信号信干噪比为约束条件,最大化毫微微小区的总能效为目标的优化模型;然后提出了基于Q-Learning算法的毫微微小区集中式功率控制(PCQL)算法,该算法基于强化学习,能在没有准确信道状态信息的情况下,实现对小区内所有用户终端的发射功率统一调整。仿真结果表明该算法能实现对用户终端的功率有效控制,提升系统能效。     

一种采用混合平衡准则的新功率控制算法

功率控制算法按准则可以分为基于功率平衡准则和基于SIR平衡准则两大主流。基于信干比平衡的功率控制算法存在正反馈问题。基于功率平衡和信干比平衡混合准则的功率控制算法可以解决正反馈问题,但复杂度较高,实现比较困难。提出了一种基于功率平衡和信干比平衡混合准则的功率控制算法。本算法在每次迭代中通过测试接收信号功率和接收信干比,只需要一次判决产生下一周期的发射功率,因此具有易于实现的优点。分析和仿真表明本算法是有效的。     

大尺度信干比共享下的基站协作干扰协调

在基于正交频分多址接入(OFDMA)技术的蜂窝移动小区中,小区间的干扰是影响系统性能的主要因素。多点协调(CoMP)技术被视为能够协调小区间干扰的主要手段。在下行多点协作传输系统中,小区基站采用三向天线来对小区划分扇区,从而消除了相邻小区边缘处的干扰。各扇区分别计算扇区内用户的大尺度信干比(SIR),小区之间通过共享大尺度信干比信息,对各自服务的用户按照一定的规则进行匹配,对小区中心用户的SIR和边缘用户的SIR进行了折中,从而有效解决小区边缘用户由于小区间干扰带来的低信干噪比(SINR)问题。仿真结果表明,本文提出的用户匹配算法以较小的反馈开销,较大的提高了小区边缘用户的信干噪比和系统吞吐量。      

神经网络在CDMA移动通信上行链路功率控制中的应用研究

提出了一种神经网络功率控制方案，研究了该方案在码分多址(CDMA)移动通信中实现最小发送功率控制问题。首先导出了最小发送功率控制模型。而后，利用最陡下降方法得到了求解该模型的神经网络的原理框图，并分析了用该网络进行最小发送功率控制的基本理论和实际性能，探讨了该网络相关参数的确定方法。最后用计算机仿真法模拟出该方案的运行性能。仿真结果表明与最小功率分配算法相比，神经网络功率控制方案可以提高基站接收信号的平均信扰比，降低信扰比的平均偏差，提高信扰比达到目标信扰比90％以上的用户数量，从而可以降低用户信号的中断概率、提高信道容量。     

蜂窝网络下行链路单反馈干扰对齐算法研究

干扰是无线蜂窝网络面临的主要问题之一。蜂窝网络干扰对齐能消除干扰的影响从而提高系统信道容量。经典蜂窝网络下行链路干扰对齐算法仅优化单个用户自身信道容量,从而限制了蜂窝小区整体信道容量的提升。从提高蜂窝小区总信道容量出发,该文提出一种蜂窝网络下行链路单反馈干扰对齐算法。构建了蜂窝网络下行链路干扰对齐数学模型;在用户端以最大化用户SINR为目标构造接收矩阵;而在基站端以最大化小区总信道容量为目标构造预编码矩阵,并通过梯度投影算法来求解该优化问题。实验结果表明,相比于传统蜂窝小区下行链路干扰对齐算法,新算法可有效提高蜂窝网络下行链路信道容量。     

Reverse link capacity analysis of a CDMA cellular system with mixedcell sizes

The demands for mobile communication services are growing rapidly. In heavily populated areas, cell splits are unavoidable to increase the capacity of the cellular system. Cell splitting makes a cellular system have mixed cell sizes. For cell planning, it is necessary to analyze the reverse link capacity of a code-division multiple-access (CDMA) cellular system with mixed cell sizes. In this paper, we propose a method to calculate the reverse link capacity of a CDMA cellular system with mixed cell sizes. When a macro cell is split into three micro cells, as an example, we calculate the reverse link capacities for the three micro cells and the neighboring macro cells. The results show that as the radius of a micro cell decreases, the reverse link capacity of the micro cell increases, while those of the neighboring macro cells decrease     

Forward‐link analysis of a two‐tier CDMA system with imperfect power control

Power control is an effective technique to reduce cochannel interference and increase capacity for cellular radio systems. The purpose of forward‐link power control in a CDMA system is to reduce the amount of interference in neighbouring cells by reducing the total amount of power transmitted. In an underlaying two‐tier system, microcell's capacity is limited by the forward link due to the interference from macrocell's basestation. Therefore, forward‐link power control is required to enhance system capacity and reduce outage probability. In this paper, we study the effect of imperfect forward‐link power control due to the limitation of power transmitted by basestation. Performance measures including capacity, outage probability and service hole area are analysed. Copyright © 2002 John Wiley & Sons, Ltd.     

Link and System Level Performance of Multiuser Detection CDMA Uplink

The link level performance and the cellular systemcapacity in the uplink direction of a CDMA cellularsystem utilising multiuser detection base stationreceivers is analysed by simulation. In the receiver,parallel multistage multiuser detection is employedtogether with two-antenna diversity reception and fastclosed-loop power control. A system level simulator isbuilt to utilise the link level simulation results andto show the increase in cellular capacity obtained byusing multiuser detection. The capacity is studied inurban micro and macro-cell environments utilising thechannel models developed in the European CODITproject. The modelling of the environment specific andCDMA specific features is considered in the systemsimulator. The system level simulator is calibratedwith analytical capacity calculations.     

Capacity, throughput, and delay analysis of a cellular DS CDMAsystem with imperfect power control and imperfect sectorization

An analytical model is developed to evaluate the performance of a cellular slotted DS CDMA system in terms of user capacity, throughput, and delay for the reverse link, i.e., from mobile to base station, considering interference from both home cell and adjacent cells. The user capacity is studied for voice communications and the throughput and delay are investigated for data communications. The effect of both imperfect power control and imperfect sectorization on the performance is investigated. It is shown that the system is rather sensitive to small power control errors and that voice activity monitoring and sectorization are good methods to improve the performance of cellular DS CDMA systems     

Performance analysis of cellular CDMA networks overfrequency-selective fading channel

An effect of multipath fading on the performance of a cellular code-division multiple-access (CDMA) system is analyzed in this paper. A wide-sense stationary uncorrelated scattering (WSSUS) channel model and the coherent binary phase-shift keying (BPSK) with asynchronous direct-sequence (DS) spreading signal are assumed in the analysis. The average error probability for both the forward link and reverse link of a cellular CDMA system over a frequency-selective fading channel using a conventional correlation-type receiver and RAKE receiver are derived. The impact of imperfect power control and channel capacity of a cellular CDMA system is also investigated. The closed forms of average error probability derived in the paper can save a lot of computation time to analyze the performance and channel capacity of a cellular CDMA system. The analytical results show that the performance and maximum transmission rate of cellular CDMA systems degrade with an increase in the number of simultaneous users and the number of interfering cells. The signal-to-interface ratio (SIR) for the reverse link derived in this paper can directly describe the interrelationships among a number of paths, number of users, number of interfering cells, fading factors, and maximum variation of a received unfaded signal     

分布式虚拟小区网络及其反向链路容量分析

本文提出了一种新的无线系统结构:基于分布式天线的分布式虚拟小区网络.在新型无线系统结构里,虚拟小区可自主移动与改变面积,这有益于容量提高,给无线资源管理带来诸多方便;其次,在不考虑阴影效应和多径衰落的情况下,对虚拟小区的反向容量进行了理论计算分析,并与分布式天线系统进行了对比.理论分析证明,虚拟小区可以降低用户发射功率,从而减少多用户干扰,提高系统容量.     

Adaptive channel assignment for different types of traffic in DS‐CDMA cellular systems

The link capacity of DS‐CDMA cellular systems is limited by the interference contained in the link. This link interference is affected by many environment factors and thus the link capacity varies with the environment. Since link capacity changes with the varying interference and different traffic types mutually interfere with each other, it is difficult to use link capacity efficiently. Static channel assignment (SCA) based on fixed link capacity is inefficient for DS‐CDMA cellular systems. To improve system capacity, channel assignments need to be adapted to variations in interference. In this paper, we propose an adaptive channel assignment (ACA) for different types of traffic. The proposed ACA is based on the reverse link power received at the base station and is adaptable to dynamically varying environments. It consists of two schemes: nonprioritized and prioritized. In the nonprioritized scheme, there is no difference in channel assignments between calls. In the prioritized scheme, however, the number of nonpriority calls acceptable is limited. In both schemes, a channel is assigned if the link power after assigning the channel is less than the power allowed in the link. The performance is evaluated in terms of link capacity and service grade. Utilizing the proposed algorithm yields more link capacity than using SCA in such environment changes as nonhomogeneous traffic load or varying path loss. Service grade is also improved by properly limiting the number of nonpriority channels. This revised version was published online in August 2006 with corrections to the Cover Date.     

衰落余量对cdma2000 1x前向链路发射功率和容量的影响

衰落余量决定链路可靠性并影响信道发射功率和用户容量的数值。本就衰落余量对cdma2000lx系统前向链路发射功率和渐近容量的影响进行了深入分析，首先介绍衰落余量概念，提出了cdma2000lx系统前向链路的发射功率和渐近容量表达式，然后通过仿真实验和数值计算给出一定条件下cdma2000lx系统前向链路的业务与导频SNR之间存在的对应关系，最后利用公式与仿真数据研究了衰落余量对前向总发射功率和渐近容量的影响。研究结果表明，cdma2000lx系统的前向总发射功率和渐近容量对衰落余量的大小十分敏感，衰落余量每增加ldB，都会引起总发射功率大幅上升，而渐近容量则迅速下降。     

MIMO系统中的交叉优化调度算法

多入多出(MIMO)系统中在多用户环境下可以在链路级利用空间复用或者在系统级利用多用户调度来提高系统容量。但是仅仅是分别优化MIMO系统链路级性能或是仅仅单纯在系统级进行调度是不够的,将两者联合起来进行优化可以获得更大的系统容量。为此,该文提出了一种新的交叉优化调度算法(Cross Optimization Scheduling Algorithm, COSA),将系统级的调度策略和链路级的物理层优化相结合,并且采用注水算法动态调整各天线的功率分配。仿真结果表明COSA算法不但在系统级为每个用户提供了公平的接入信道机会,而且在链路级中充分利用MIMO系统的空间复用特点以及动态的功率分配,提高了系统的容量。     

Forward Link Power Control Strategy and its Optimum Issue in CDMA Cellular Networks

In this paper, we propose a theoretical method in order to estimate the forward link outage probability and user capacity of a cellular system which are based on IS-95 CDMA standard, especialy impact of power control strategy and voice activity monitoring in the system under long-term fading effects, in which the light and heavy fadings are considered. According to the numerical results obtained in this paper, the power control strategy leads to approximately the threefold user capacity in contrast to the situation without power control strategy. The reults are compared with Interference-to-Signal Ratio (ISR) driven power control scheme[6][9] which can be used only for simulation of the system. The power control strategy not only improves the desired signal to the interference ratio in the reference user's receiver, but also offers uniform service to the user wherever it is located in the cell.