Performance evaluation of uplink power control algorithm over TDMA systems

Future PCS (personal communication system) cellular networks will mainly be driven by high link quality, high bandwidth utilization, low power consumption and efficient network management. Power control is one of the several major techniques which could help to achieve these goals. By exploiting power control techniques, co-channel interference could be reduced and as many links as possible could be obtained with satisfactory link quality. SIR-based (signal-to-interference ratio-based) power control was proposed as a technique for managing co-channel interference in cellular radio systems. Furthermore, new distributed autonomous feedback power control methods were introduced to achieve excellent performance without the difficult centralized control used in SIR-based methods. Unfortunately, the implementation of those power control algorithms is still challenging owing to the precision of SIR. The main aim of this paper is to investigate an uplink power control algorithm which depends indirectly on the signal-to-noise ratio in the TDMA (time division multiple access) cellular system. Simulation of the prototype hardware implementation of the receiver baseband signal processing based on the PACS (personal access communications system) specification is used as the main approach to explore the performance evaluation of this power control technique. According to simulation results, suitable values of those parameters used in this power control algorithm are derived, and the minimum frequency reuse factor under different propagation environments is also obtained for PACS under power control. © 1998 John Wiley & Sons, Ltd.     

TD-SCDMA中的二阶快速收敛功率控制

基于信号干扰比(SIR)测量的归一化功率控制在无线蜂窝系统中有着广泛的应用。论文提出TD-SCDMA系统中的基于SIR测量的二阶快速收敛分布式功率控制算法,使用当前功率和前次功率共同参与运算控制移动台发射功率。仿真结果表明,论文提出的二阶快速收敛DPC算法在相同的传播环境下比DPC和SOPC具有更快的收敛速度。     

Time delay compensation in power controlled cellular radio systems

Transmission power control is an important means to manage the radio resources in wireless communications. The performance, however may be reduced due to time delays as in any controlled system. Most controllers to date are designed without considering time delays, which may result in oscillatory or unstable systems. To overcome these problems, time delay compensation (TDC) is introduced. The main idea is to adjust the measurements [e.g., signal-to-interference ratio (SIR)] to include the effects of issued but not yet applied power control commands. TDC thereby improves the stability and performance of an arbitrary power control algorithm. The benefits are illustrated by simulations using some popular power control algorithms     

认知无线电技术在地空数据链系统中的应用浅析

将认知无线电思想引入到地空数据链组网系统中,提出了地空认知无线通信系统的概念,并重点探讨了地空认知无线通信系统的自适应功率控制应用。在自适应功率控制需求分析的基础上,明确了功率控制的典型应用场景,提出了自适应功率控制的总体实现方法,并以JTIDS数据链为对象分析了其关键技术的解决方案。     

Autonomous SIR-based power control for a TDMA radio system

Power control based on signal-to-interference ratio (SIR) has been proposed as a technique for managing cochannel interference due to frequency reuse in a time-division multiple-access (TDMA) radio system. Early studies have focused on SIR balancing approaches that require centralized control for global power adjustment and/or associated channel reassignment or call admission control. This paper investigates the achievable performance of an autonomous power control technique which relies only on a simple fixed-step feedback adjustment algorithm. Simulation results, assuming no adaptation to Rayleigh fading, indicate that this simple power control technique can perform nearly as well as ideal SIR balancing/call removal, yielding a possible increase in spectrum efficiency of at least three times compared to a system without power control. Tracking of Rayleigh fading is found to provide an additional improvement in SIR of 4 to 4.5 dB for the range of fading rates expected in the pedestrian wireless access environments. This work is targeted toward understanding the traffic capacity and deployment implications of wireless technology alternatives that could provide access to local exchange networks.     

基于感知无线电非合作博弈功率控制算法的研究

本文基于Goodman提出的非合作博弈功率控制模型改进了代价函数。针对感知无线电系统（CR）中各用户的通信需求,采用多载波码分多址（MC-CDMA）感知无线电系统,解决感知用户对主用户干扰和通信中断等问题,为实现感知频谱资源的有效分配,提出了一种新的感知无线电系统功率控制博弈算法。通过仿真表明,该算法同几种经典算法相比,既满足不同种类用户SIR要求,又提高了系统吞吐量,实现了对不同用户发射功率的有效控制,且系统性能明显提高。     

Application of convolutional error correcting codes in ultrawideband M-ary PPM signaling

The interference issues related to ultrawideband (UWB) radio pose tight restrictions on the maximum data rate of UWB radio telecommunication systems. A possible solution is to reduce the required signal to interference ratio (SIR) that gives satisfactory performance to the UWB system. In this letter, we propose coded M-ary UWB radio communication systems. Two classes of convolutional codes, namely, low-rate superorthogonal codes and high-rate punctured codes are considered for this purpose. Simulation results on the bit error rate of the proposed system indicates that the system is capable to work in lower SIR's and therefore supports higher data transmission rates in a real interference environment compared to the previously proposed UWB communication systems.     

A system plan for a 900-MHz portable radio telephone

The system concepts for a high capacity personal radio telephone system are described. Previous systems for mobile radio telephone service have been based on a rigid assignment of frequencies to specific small geographic areas within the total coverage area. This approach has led to conservative geographic frequency reuse constraints and the requirement for accurate location techniques in the system. Through the utilization of the power imbalance that exists in the proposed portable radio telephone system between base and portable unit transmitters these constraints are eliminated. It will be shown how this power imbalance allows the selection of the optimum signal for the portable unit and relaxed requirements on location and reuse of frequencies. The required signal-to-interference ratios must be obtained within a design reliability level over the coverage area. Computer simulation of the frequency reuse plan and the propagation variability over the area indicates the nominal repeat intervals necessary as a function of this reliability level. A reuse plan that obtains the required repeat intervals with a high degree of spectral efficiency, through the combined use of geographic and frequency separation, will be presented. This system called tertiary offset, achieves a significant increase in interference protection by splitting each channel into a group of three channels and utilizing each subgroup in a different pattern of reuse over the area. The improvement due to this plan will be shown.     

Capacity evaluation of a mixed-traffic WCDMA system in the presence of load control

This paper deals with the capacity analysis of a direct-sequence code-division multiple-access (DS-CDMA) cellular system in the presence of heterogeneous traffic. We consider a distributed resource allocation strategy that uses a closed-loop control scheme to manage the processing gain, the signal-to-interference ratio (SIR), and the system load. In particular, each base station aims at maintaining the uplink load to its allowable maximum value in order to achieve the maximum throughput. A typical urban cellular system is considered in which the path loss depends on the /spl alpha/th power of the distance, shadowing is log-normally distributed, and short-term fluctuations due to multipath fading are present. Besides, a radio resource-management scheme is considered, which is able to control transmission power and spreading gain values so as to maintain the total received power at the base stations at a maximum allowable level. In this scenario, this paper derives a novel analytical approach for the evaluation of system capacity of DS-CDMA systems in presence of different traffic sources. Bit-error-ratio (BER) and bit-rate requirements have been considered for the different traffic classes. Simulation results have permitted to validate the developed analytical framework on a very comprehensive range of cases. The proposed analysis is finally applied to universal mobile telecommunications system (UMTS)-like traffic classes in order to evaluate the system capacity.     

多输入多输出天线蜂窝系统中的分布式功率控制方法

在蜂窝无线通信系统设计中,基于信号干扰比(SIR)测量的功率控制方法得到广泛的应用。该文提出多输入多输出(MIMO)天线蜂窝系统中的基于SIR测量的分布式功率控制(DPC)方法。该方法通过控制移动台或者基站的发射功率可以达到以下两个目标的其中之一：(1)最小化所有基站或者移动台的平均接收SIR中断概率;(2)在满足目标SIR要求的前提下最小化平均发射功率。数值仿真结果显示,该文提出的DPC方法在低的计算复杂度下,可以达到降低SIR中断概率和减小发射功率的目的。     

A Unified Framework for Transmitter Power Control in Cellular Radio Systems

In earlier works on transmitter power control in cellular radio systems, the problem of whether a signal‐to‐interference ratio (SIR) threshold is achievable is determined by apparently different rules for homogeneous and heterogeneous SIR systems. In this paper, we present a unified and more universal framework for both cases. We also highlight the conditions under which a given SIR threshold vector for the heterogeneous SIR system is achievable, although so far there is no general solution to this problem.     

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     

Handover algorithm to counteract corner effects in microcellularmobile networks

A new handover algorithm suitable for implementation in modern cellular mobile radio systems, such as GSM or UMTS, is proposed and its performance assessed. The algorithm is based on the gradient of measured power values. Both the uplink and the downlink measurements are considered. The simulation results show a performance improvement with respect to traditional algorithms     

Traffic channel SIR estimation based on reverse pilot channel in cdma2000

Signal-to-Interference Ratio(SIR) is a very important metric of communication link quality. For wireless cellular systems, several control mechanisms, such as power control mechanisms, rate control mechanisms, and allocation of radio resource, are based on SIR estimation.In previous researches, most of researchers concentrated on WCDMA systems, in which pilot symbol is time-multiplexed with data symbol; the method developed in this case is not feasible for cdma2000 systems where pilot symbol is code-multiplexed with data symbol. This paper first develops the SIR estimators based on the reverse pilot channel and then derives the approximate analytic expression for its Mean Squared Error (MSE) function, the accuracy of which is validated through simulation. It is shown that the MSE of the new SIR estimator is significantly smaller than that of other widely used SIR estimators, especially in low SIR case. Finally, the estimate quality of the proposed method is further improved by long-termly averaging the sample interference.     

Downlink joint rate and power allocation in cellular multirate WCDMA systems

This paper proposes a novel dynamic joint rate and power control procedure for downlink data transmission in a multicell variable spreading factor wideband code-division multiple-access (WCDMA) system where the different users have similar quality-of-service requirements in terms of the signal-to-interference ratio (SIR). Two variations of the dynamic joint rate and power allocation procedure, namely, Algorithm-1 and Algorithm-2, are presented. The performances of these two schemes are compared to the performance of the optimal dynamic link adaptation for which the rate and power allocation is found by an exhaustive search. The optimality criterion is the maximization of the total radio link level capacity (or sum-rate capacity) in terms of the average number of radio link level frame transmitted per adaptation interval under constrained SIR and power limit in the base station transmitter. The proposed schemes have linear time complexity as compared to the exponential time complexity of the optimal scheme and achieve better radio link level throughput fairness compared to the optimal link adaptation scheme with a moderate loss in total throughput. Performance evaluation is carried out under random and directional micromobility models with uncorrelated and correlated long-term fading, respectively, in a cellular WCDMA environment for both the homogeneous (or uniform) and the nonhomogeneous (or nonuniform) traffic load scenarios.     

认知无线电系统中一种新的自适应功率控制算法

本文针对认知无线电系统中的远近不公平性,提出将信道增益因子引入到基于信干比（SIR）的分布式非合作博弈功率控制算法中,并证明了其纳什均衡的存在性及唯一性。同时在此算法的基础上,针对部分用户的SIR不能满足下限阀值的情况,设计了一种新的自适应加权系数以控制发射功率,满足不同用户的输出SIR需求。仿真结果表明,与其它的分布式功率控制算法相比,该算法不仅有效地解决了远近不公平现象,满足了认知用户公平共享频谱资源的需求,同时使认知用户的SIR能同时满足上下限阀值的要求,且具有快速收敛的特性。      

Performance of the π/4-DQPSK, GMSK, and QAM modulation schemesin mobile radio with multipath fading and nonlinearities

As mobile communications have become so indispensable, every possible effort should be spent to achieve the optimum operating conditions. In addition to the normal impairments associated with wireless communications, in general, the mobile channel suffers from particular limitations that confine the performance of a mobile radio system. Among those impairments are the bandwidth limitation, interference, and multipath fading. With the strong motivation toward portable radio and personal communication systems, power limitation has manifest itself in the picture, and, consequently, nonlinear operation of the amplifiers involved (hence, the channel) will have to be dealt with. Constant envelope modulation schemes have been used in digital mobile radio systems recently installed. The Gaussian minimum shift keying (GMSK) is employed in the Global System for Mobile (GSM) communications installed in Europe, while in the North American IS-54 system, the modulation scheme used is the π/4-DQPSK. As the quest for higher data rates has kept on increasing, multilevel modulation schemes have been proposed with their performance over nonlinear channels having been overlooked. The paper provides a comparative study, based on simulation, and tests the performance of various modulation schemes operating over a wide variety of mobile radio channel conditions. The effective throughput of all systems is also considered     

Fast stochastic power control algorithms for nonlinear multiuser receivers

Uplink communication in a cellular radio network is considered where the base station in each cell employs linear or nonlinear (decision feedback) multiuser receivers. For any such receiver, the problem of interest is that of minimizing the total transmit power under the constraint that all the users of the network achieve their quality-of-service objective in terms of signal-to-interference ratio (SIR). When the solution is feasible for the desired SIR requirements, the optimum powers are computed with a distributed iterative power control strategy suitable for implementation at each base station. While the deterministic algorithm requires both in-cell and out-of-cell user information, the stochastic algorithm proposed in this paper can be implemented at the base stations in a truly distributed manner requiring knowledge of only in-cell parameters. Such an algorithm was proposed previously for the case where base stations use linear (single user) matched filter (MF) receivers. However, the feasibility region in terms of attainable SIRs for a well-designed multiuser receiver, particularly for a nonlinear receiver that employs decision feedback, is generally much larger than it is for the linear MF receiver. The stochastic power control algorithm in this paper, for linear or nonlinear multiuser receivers, converges in the mean-square sense to the minimal powers when the target SIRs are feasible. The second major focus of this paper is to improve the convergence properties of the conventional stochastic approximation based power control strategy by using the more recent results on averaging. Convergence issues of both the "nonaveraged" and "averaged" algorithms are investigated, and numerical examples are presented to demonstrate the performance improvement due to averaging.     

认知无线电中基于多次博弈的功率控制算法

基于博弈论对认知无线电网络中的功率控制问题进行了建模分析,提出了一种基于多次博弈的功率控制算法,证明了该算法中纳什均衡的存在性和惟一性。仿真结果表明,基于该博弈模型的功率控制算法收敛性比传统算法好,经过7次左右迭代即可收敛,满足系统实时性要求,同时又能够以较低的功率水平满足不同用户对信干比的要求,实现了对不同用户发射功率的有效控制,系统性能明显提高。     

A high performance hardware architecture for portable,low-power retinal vessel segmentation

The retina of the human eye and more particularly the retinal blood vasculature can be used in several medical and biometric applications. The use of retinal images in such applications however, is computationally intensive, due to the high complexity of the algorithms used to extract the vessels from the retina. In addition, the emergence of portable biometric authentication applications, as well as onsite biomedical diagnostics raises the need for real-time, power-efficient implementations of such algorithms that can also satisfy the performance and accuracy requirements of portable systems that use retinal images. In an attempt to meet those requirements, this work presents a VLSI implementation of a retina vessel segmentation system while exploring various parameters that affect the power consumption, the accuracy and performance of the system. The proposed design implements an unsupervised vessel segmentation algorithm which utilizes matched filtering with signed integers to enhance the difference between the blood vessels and the rest of the retina. The design accelerates the process of obtaining a binary map of the vessels tree by using parallel processing and efficient resource sharing, achieving real-time performance. The design has been verified on a commercial FPGA platform and exhibits significant performance improvements (up to 90×) when compared to other existing hardware and software implementations, with an overall accuracy of 92.4%. Furthermore, the low power consumption of the proposed VLSI implementation enables the proposed architecture to be used in portable systems, as it achieves an efficient balance between performance, power consumption and accuracy.