Joint Transmit Beamforming and Power Control for CDMA System

1　Introduction　Power control and beamforming are two main methods toreduce interference in CDMA cellular communication sys tem. In power control, the transmitters powers are constant ly adjusted when the instantaneous SIR is not equal to targetSIR, so that the quality of weak links is improved. Base sta tion equipped with antenna arrays may adjust their beam pat terns so that they have maximum gain towards the directionsof target mobiles and minimum gain towards the other direc tio…     

The Effect of On-Off Scheduling to the Required Transmit Power in Systems with Fast Power Control

Physical layer channel-aware scheduling may significantly improve coverage and throughput of IP based services in wireless cellular networks, and the feasibility of such schedulers is actively studied within 3G and 4G systems. A channel-aware scheduler requires access to instantaneous channel state information in order to direct transmission to users with favorable channel conditions. In frequency division duplex (FDD) systems, this requires a fast feedback channel between mobile and base stations, and the overhead of the feedback control channel should be kept as low as possible.In this paper, we study the effect of control channel overhead to on-off scheduling (OOS) when fast transmit power control is applied in data and control channels. On-off scheduling is a simple channel-aware scheduling algorithm, where transmission to a user is suspended if the transmit power exceeds a given threshold. On-off scheduling is applied on the data channel while control channel is always on so that the scheduler is able to obtain channel state information from active users. The gain of OOS strongly depends on the power ratio between control and data channels, and increased interference due to control signaling and decreased interference due to channel-aware scheduling should be jointly considered in system design. Gains in the required transmit power are translated into gains in coverage and capacity assuming WCDMA parameters, and the results can be applied, e.g., when designing scheduling algorithms and corresponding signaling formats for WCDMA uplink.     

CDMA系统中的反向功率控制技术分析

对CDMA系统的反向功率控制技术进行了分析。根据系统和信道模型,导出了基站参考SNR设置的上限。只有参考信噪比(SNR)的设置低于上限时,基站才可以通过发送功率控制命令给移动台,使接收SNR达到参考SNR。否则,移动台有限的发射功率并不能使接收功率达到参考SNR,这时的CDMA系统是不稳定的。     

CDMA系统中上行链路发射功率控制理论的研究

综述了CDMA系统上行链路发射功率控制研究的一些基本理论。首先从控制系统的角度出发,将反向闭环功控问题抽象为标准的控制过程,其中的输入输出量可看作控制系统的各个分量。在此基础上综述了现有的控制策略,阐述了功率控制器的设计,重点是控制步长的设计。最后讨论了需要进一步研究的问题。     

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。     

Power Allocation and Control in Multimedia CDMA Wireless Systems

This paper proposes an analysis of outage performance of a Direct Sequence-Code Division Multiple Access (DS-CDMA) wireless system with heterogeneous traffic. Imperfections in closed-loop power control and the activity characteristics of any traffic source in the system are taken into account. For given requirements of signal-to-(noise + interference) ratio and outage probability of every user in the system, the system capacity is derived in terms of the maximum number of users of each class that can be accomodated. The optimization problem is explicitly solved for a system consisting of a single cell and an approach is outlined for solving the optimization problem in a multi-cell system. The analysis is carried out by resorting to various approximations of Multiple Access Interference (MAI), that require different methods for solving the optimization problem and yield different degrees of accuracy. From numerical results it is seen that optimal power allocation is essential to limit the effects of power control imperfections, mainly in the case of non uniform amplitudes of residual power fluctuations. In the second part of the paper, a performance study of fixed step closed-loop power control algorithms is presented. A detailed simulation of the power control loop evidences that fast fading phenomena can not be easily tracked, even at moderate Doppler spread. Statistics of residual power fluctuations are estimated and can be used to support the assumptions in the first part of the paper. Furthermore, second order statistics of the controlled channel are estimated, and second order outage statistics (average rate and duration of outage events) are derived as a quantitative measure of residual channel burstiness.     

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.     

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。     

Sector Transmit Power Pooling on Real CDMA Networks

This paper uses logfile data from commercial code division multiple access networks to quantify the base station power amplifier (PA) size reduction achieved with sector transmit power pooling. Sector transmit power pooling in a base station involves sharing the transmit power load of several sectors across the same bank of amplifiers. This transmit power trunking results in a reduction in required PA size. The logfile analysis used to estimate this reduction is augmented with simulated short-term power variations. A new constrained Poisson call arrival model is used to ensure that the simulated power variations accurately reflect actual network operating conditions. A Gamma random variable approximation is also used to improve simulation efficiency. The results of this analysis indicate that sector power pooling can significantly reduce required PA size for realistic network operating conditions     

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.

Robust Transmit Power Control for Cognitive Radio

A cognitive radio network is a multiuser system, in which different users compete for limited resources in an opportunistic manner, interacting with each other for access to the available resources. The fact that both users and spectrum holes (i.e., unused spectrum subbands) can come and go makes a cognitive radio network a highly dynamic and challenging wireless environment. Therefore, finding robust resource-allocation algorithms, which are capable of achieving reasonably good solutions fast enough in order to guarantee an acceptable level of performance under worst case interference conditions, is crucial in such environment. The focus of this paper is the transmit-power control in cognitive radio networks, considering a noncooperative framework. Moreover, tools from control theory are used to study both the equilibrium and transient behaviors of the network under dynamically varying conditions.      

Matched-Filter Bounds for Multicarrier Communications Systems With Transmit Diversity

In this paper, we consider wireless multicarrier communications systems applying different transmit-antenna diversity techniques. Whereas the transmitter has available multiple antennas, we assume a single antenna at the receiver. Thus, we consider multiple-input single-output multicarrier transmission systems which are of special interest for downlink mobile radio applications. For these systems, we investigate the matched-filter bounds (MFBs) which represent the performance in an environment free of any interference and, thus, are lower bounds on the achievable performance. Especially, we focus on the analytical determination of the MFBs for selection diversity (SD), since this transmit-antenna diversity technique requires the least amount of preprocessing at the transmitter. Based on the derived MFBs, SD is investigated in detail, and compared with other transmit-antenna diversity techniques which are based on the maximum-ratio and the equal-gain transmission principles, respectively.     

Blind-Channel Estimation for MIMO Systems With Structured Transmit Delay Scheme

This paper considers blind-channel estimation for multiple-input multiple-output (MIMO) systems with structured transmitter design. First, a structured transmit delay (STD) scheme is proposed for MIMO systems. Unlike existing transmit diversity approaches, in which different antennas transmit delayed, zero padded, or time-reversed versions of the same signal, in the proposed scheme, each antenna transmits an independent data stream, therefore promises higher data rate and more flexibility to transmitter design. Second, second-order statistics based blind-channel estimation algorithms are developed for MIMO systems with STD scheme. Channel identifiability is addressed for both correlation-based and subspace-based approaches. The proposed approaches involve no pre-equalization, have no limitations on channel zero locations, and do not rely on nonconstant modulus precoding. Third, when channel coding is employed, estimation accuracy can be further enhanced through “postprocessing”, in which channel estimation is refined by taking the tentative decisions from the channel decoder as pseudo-training symbols. Simulation examples are provided to demonstrate the robustness and effectiveness of the proposed approaches.      

Combined Fuzzy-based Rate Management and Selective Power Control for Multimedia CDMA Cellular Systems

Power control mechanisms are essential for CDMA wireless communication systems to enhance user capacity. In this paper, we propose a novel power control scheme which combines transmission rate management with power adjustments for multimedia CDMA cellular systems. In the proposed scheme, a fuzzy logic controller (FLC) is first used to dynamically infer a suitable transmission rate for each service. Then a selective power control (SPC) scheme is used to adjust the transmission power for each service in order to maintain an acceptable signal-to-interference ratio (SIR). Numerical results show that the proposed scheme outperforms the original SPC and the Lagrangian relaxation technique and power control (LRPC) methods in outage probability, average transmission rate, probability of unsuccessful transmission, and probability of changes in transmission rates.

A Low Power Correlator for CDMA Wireless Systems

The complex valued matched filter correlators consume maximum power in the DS/SS CDMA receivers. These correlators accumulate 1024 samples lying in the range –7 to +7. This accumulation needs 3 data bits, 1 sign bit and 10 extra bits for overflow. Hence, the correlator can be implemented as a cascade of 4-bit full adder and a 10-bit incrementer. As a ripple carry adder (RCA) consumes the least power among all the existing adder architectures, we have implemented the 4-bit adder as a RCA. Previous incrementers were implemented as ripple counters. In this paper we propose a novel incrementer which is faster than a ripple counter based incrementer. Hence, it can be operated at a reduced voltage resulting in considerable power reduction. The incrementer is implemented using multiplexers, AND gates and TSPC registers. The ripple-counter correlator and the proposed incrementer correlator were laid out in MAGIC using 0.5 CMOS technology followed by power estimation using HSPICE. It is shown that the proposed architecture requires 50% less power than a ripple counter based design.     

CDMA2000中的发送分集技术

在第三代移动通信系统中,发送分集技术被用来提高前向链路的接收性能,因而介绍了在CDMA2000系统中使用的分集传送方式0TD和STS,分析了分集的原理和合并的方法,并给出了在三种典型信道下采用不同分集技术时系统性能的仿真结果.     

分布式残余频偏信道中STBC-OFDM的发射功率优化

在分布式残余频偏信道中,考虑多径瑞利衰落,针对采用判决反馈检测的两发射天线STBC-OFDM链路,提出了一种发射功率优化方法:根据平均信道功率增益、残余频偏方差以及噪声方差的大小,以最小化平均误比特率下界为目标,设置两分布发射天线的发射功率,仿真结果表明:相比于传统的各天线满功率发射方法,所提方法能够在节省发射功率的同...     

CDMA系统中一种新的基于MMSE多用户检测的自适应功率控制算法

功率控制技术是CDMA通信系统中克服“远一近效应”，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。在本文提出CDMA系统中一种新的白适应功率控制和MMSE多用户检测的联合优化的算法，仿真结果表明，这种新的联合优化算法对提高系统容量，改善系统性能有很大的作用。     

Dynamic Call Admission Control for Centralized CDMA Systems

Spectral efficiency of WCDMA based spread spectrum 3G/4G air interface technology is highly influenced by the common channel interference, hence the applied Call Admission Control method has great importance because it determines the number of active users admitted to the network. In this paper we present a dynamic air interface CAC algorithm which provides efficient usage of radio resources and allows real-time adaptation to the always changing network parameters. Required CAC parameters are derived for generalized multiplicative fading and generalized memory-less traffic sources. In order to validate its capabilities our proposed CAC method was investigated with ON/OFF traffic sources and lognormal fading channels.     

TD-SCDMA系统下行联合波束功控技术

TD-SCDMA系统最重要技术特征是智能天线技术。本文基于时延和角度扩散空间信道模型,提出了一种下行基站联合优化波束和发射功率的智能天线技术。