Analytical performance evaluation of downlink beamforming with power control by transmit power limited channel inversion

We investigate the transmission performance of a downlink BPSK transmission system which uses beamforming combined with cross-polarised antenna arrays and power control in a Rayleigh fading environment to fulfil QoS requirements of real time services. A power control method termed “power control by transmit power limited channel inversion” is applied in the system. Power limitation in the downlink and the effect on the bit error rate performance is especially interesting for mobile stations at the cell borders of a cellular communication system. For this non-linear transmit model we derive analytical formulas for the average transmit power and the bit error rate performance. The exact validity of the results is verified by Monte-Carlo simulations. We also show the interaction of power control and beamforming, and the dependency of the gain in transmit power from the SNR, an effect that is not visible without transmit power limited power control.     

基于不确定非线性智能电网感知网络控制系统方法研究

针对传统的不确定时滞的鲁棒控制系统不能满足现代电力系统发展的需求,提出一种基于不确定非线性智能电网感知云网络化控制识别方法。使用传统的数据值和基于电力网络到网络系统模型作为电力感知网络到网络模型的电力云网络,控制数据优化使用电源感知网络,而不是利用控制节点的预测值,突破了鲁棒控制的不确定时滞系统的控制效果。运用感知模型中的正向云算法修正加权系数,仿真实验证明,该识别方法能够很好地优化传统的不确定时滞鲁棒控制电力系统,具有良好的适应性和鲁棒控制性,进一步提高了智能电网传感云网络控制的各项性能指标。     

Analysis of an up/down power control algorithm for the CDMA reverselink under fading

We analyze the performance of a code division multiple access (CDMA) reverse link a with an up/down power control algorithm in the presence of fading. We derive a stochastic nonlinear feedback control system model for the power controlled reverse link, and study the power control performance based on the nonlinear model using the technique of statistical linearization. We provide a general analysis framework that allows us to study the effect of mobile speed, power control step size, and fading channel parameters such as correlation coefficient and rate of fading on power control errors. Numerical results show excellent accuracy of our analysis, which can be used to design and optimize the system parameters without going through lengthy simulations. For example, in the presence of shadow fading, it is seen that a power control step size in the range of 0.5-1.3 dB is sufficient to keep power control errors near a minimum. In the case of Rayleigh fading, the standard deviation of power control errors grows quickly even at moderate mobile speeds     

Effect of imperfect power control on acquisition performance in aDS/CDMA system

The effect of imperfect power control on acquisition performance is considered for a DS/CDMA system. The imperfect power control increases mean acquisition time substantially when the standard deviation of received power is above 1 dB     

WCDMA的功率控制参数对系统设计的影响研究

介绍了WCDMA系统的功率控制机制；分析了功控调整步长、TPC差错、TPC时延和SIR估计等参数对系统性能的影响；给出了WCDMA系统中功率控制的实现模型；得出了在不同的运动速度下，功率控制参数与系统设计的关系。     

Markov chain model for performance analysis of transmitter power control in contention based wireless MAC protocol

We have developed a three-state discrete-time Markov-chain model for the performance evaluation of contention-based medium access control (MAC) protocol. The proposed Markov-chain model is then used to analyze the carrier sense multiple access (CSMA) type MAC protocol for its delay and throughput characteristics with and without transmitter power control. Using simulations, the conditional capture probability (p _cap ), which gives a measure of the effectiveness of transmitter power control due to the capture effect, is quantified and experiments are performed to validate these simulated data for the p _cap . To analyze the effect of transmitter power variation, the Markov-chain model is modified by incorporating the p _cap . Numerical results show significant throughput as well as delay performance improvement using transmitter power control.     

DS-CDMA with power control error using weighted despreadingsequences over a multipath Rayleigh fading channel

Closed-form solutions for the average bit error rate (BER) performance of a direct-sequence code division multiple-access system with imperfect power control are derived for both coherent and noncoherent reception operating over a multipath Rayleigh fading channel. The RAKE structure receivers under consideration employ despreading sequences weighted by adjustable exponential chip waveforms optimized for multiple-access interference rejection. The chip-weighting waveforms employed are determined only by one parameter γ which leads to easy tuning of the waveforms in practice to achieve the best performance. The results indicate that the number of active users supported at a given BER for the case of γ tuned to maximize the average signal to interference plus noise ratio Hˆ is much larger than the case of γ=0 (fixed or rectangular despreading sequence). It is shown that imperfect power control affects the irreducible BER for the case of γ=0. On the other hand, the effect of imperfect power control on the BER performance for the case of γ tuned to maximize Hˆ is equivalent to a reduction in the average signal-to-noise ratio, and, hence, system performance can be compensated by increasing the transmitter power. It is further shown that the effect due to imperfect power control on BER performance is significant while that on the maximum value of Hˆ obtained by tuning γ is rather insignificant     

Analysis of DS-CDMA system supporting heterogeneous traffic with decorrelating detector

Single-cell and multiple-cell direct-sequence code-division multiple-access (DS-CDMA) systems supporting heterogeneous traffic are investigated when decorrelating detector is used at receiver. Theoretical analyses and numerical examples are presented to study the effect of imperfect power control on the system performance of the reverse link. As to the forward link, the system performance is analyzed and the power allocation problem at base stations is formulated as a constrained optimization problem. Two algorithms, namely, the optimal algorithm and the unit transmission power allocation (UTXPA) algorithm, are proposed to solve this optimization problem. Computer simulations are presented to compare the performance of the proposed algorithms.     

Performance considerations of code division multiple-access systems

The performance of code division multiple-access (CDMA) systems is determined using direct-sequence spectral spreading. Asynchronous users are assumed so that there is no network control. Under relatively ideal conditions, the degradation in system performance as a function of the number of users is shown to have a threshold effect. This basic limitation in the number of users of the system is further limited if the powers are unequal. For two users, system performance as a function of their power ratios also has a threshold effect. System performance as a function of the amount of spectral spreading is determined. The performance of both coded and uncoded systems is predicted.     

Turbo Coding with Equalization in WCDMA Downlink

In this paper, the performance of turbo coding in WCDMA downlink is considered in conjunction with receivers using two adaptive channel equalizers. Bit error and frame error rates are compared to the performance of the conventional Rake receiver. Special consideration is given to the cases with two receive antennas, the efficiency of the channel interleaver, the number of iterations in decoding, the performance with various numbers of users, the influence of mobile receiver velocity as well as to the effect of power control. The simulation results show that turbo coding, combined with power control and channel equalizers is a very efficient way to implement reliable data transmissions in WCDMA downlink. The results in the paper also verify that the adaptive channel equalizers is a very promising technique to improve the receiver performance and increase the user capacity.     

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.     

WCDMA功率控制技术的研究与实现

介绍了功率控制技术的作用和分类,以及宽带码分多址(WCDMA)系统反向闭环功率控制的技术标准和组成部分,分析得出了WCDMA系统反向功率控制实现的定时限制条件.讨论了影响功率控制技术性能的几个关键因素:信扰比(SIR)估计精度、步长选择、功控比特传输错误及功控时延等,并给出了仿真曲线和结果分析.最后给出了WCDMA系统前、反向功率控制技术基于FPGA的实现结构框图和测试结果.     

Combined power control and error-control coding in multicarrier DS-CDMA systems

We propose truncating the transmission power (allocating no power) for symbols with low channel gain, and tagging erasures on the corresponding symbols at the receiver. The motivation is that symbols with low channel gain are highly likely to be in error and yet, if transmitted, consume the energy resource and generate interference to other users. Truncating the power for those symbols has the effect of reducing the interference to other users and allocating more power on symbols with high channel gain (thereby reducing the error probability). Since block codes can correct twice as many erasures as errors, the coded performance can be improved by properly combining the power control with the error-control coding. In this letter, we analyze the performance of the Reed-Solomon-coded multicarrier direct-sequence code-division multiple-access systems with two power-control schemes. We show that the probability of incorrect decoding can be significantly improved by properly combining the power control with the error control coding.     

Neural Network Based Receiver for Multiuser Detection in MC-CDMA Systems

In this paper, we present a multiuser detection technique based on artificial neural network (NN) for synchronous multicarrier code division multiple access systems over Rayleigh fading channels. To test the robustness of the proposed receiver, also the effect of power control problem is studied with a comparative manner. Bit error rate (BER) performance of the NN based receiver is compared with the single user bound and conventional receivers. Although the BER performance of the conventional receiver degrades as the number of the users and power level differences among the users increase, as a decision structure, neural network based receiver gives closer BER performance to the single user bound.     

Performance of closed-loop power control in DS-CDMA cellularsystems

In situations where the round-trip delay between the mobile and the base stations is smaller than the correlation time of the channel, power control schemes using feedback from the base station can effectively compensate for the fast fading due to multipath. We study several closed-loop power control (CLPC) algorithms by analysis and detailed simulation. We introduce a new loglinear model for analyzing the received power correlation statistics of a CLPC scheme. The model provides analytical expressions for the temporal correlation of the power controlled channel parameterized by the update rate, loop delay, and vehicle speed. The received power correlation statistics quantify the ability of closed-loop power control to compensate for the time-varying channel. To study more complex update strategies, detailed simulations that estimate the channel bit-error performance are carried out. Simulation results are combined with coding bounds to obtain quasi-analytic estimates of the reverse link capacity in a direct-sequence code-division multiple-access (DS-CDMA) cellular system. The quasi-analytic approach quantifies the performance improvements due to effective power control in both single-cell and multicell DS-CDMA systems operating over both frequency-nonselective and frequency-selective fading channels. The effect of nonstationary base stations on the system performance is also presented     

Performance of optimum transmitter power control in cellular radiosystems

Most cellular radio systems provide for the use of transmitter power control to reduce cochannel interference for a given channel allocation. Efficient interference management aims at achieving acceptable carrier-to-interference ratios in all active communication links in the system. Such schemes for the control of cochannel interference are investigated. The effect of adjacent channel interference is neglected. As a performance measure, the interference (outage) probability is used, i.e., the probability that a randomly chosen link is subject to excessive interference. In order to derive upper performance bounds for transmitter power control schemes, algorithms that are optimum in the sense that the interference probability is minimized are suggested. Numerical results indicate that these upper bounds exceed the performance of conventional systems by an order of magnitude regarding interference suppression and by a factor of 3 to 4 regarding the system capacity. The structure of the optimum algorithm shows that efficient power control and dynamic channel assignment algorithms are closely related     

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     

Steady-State Performance and Stability Analysis of Mixed Pole Machines With Electromechanical Torque and Rotor Electric Power to a Shaft-Mounted Electrical Load

This paper presents the steady-state model, performance, and stability analysis of a mixed pole machine with a new operational mode which provides a rotor torque and an n -phase rotor electrical output power to a shaft-mounted rotating electrical load. The machine operated under this mode can be used in applications that require contactless power, such as in robotics, or applications that require independent control of both rotor torque and rotor electric power, such as for contactless rotational antennas and turret systems. The performance assessment includes electromagnetic torque, electrical efficiency, mechanical efficiency, and total efficiency based on both simulation and experimentation. The effect of electrical loading and stator voltage on both rotor torque and rotor electric power is also considered. The machine steady-state stability is introduced by plotting the machine operating characteristics that determine all stable operating regions of the machine under the proposed mode of operation.     

Master–Slave Current-Sharing Control of a Parallel DC–DC Converter System Over an RF Communication Interface

Using analog wireless communication, we demonstrate a master-slave load-sharing control of a parallel dc-dc buck converter system, thereby eliminating the need for physical connection to distribute the control signal among the converter modules. The current reference for the slave modules is provided by the master module using radio-frequency (RF) transmission, thereby ensuring even sharing of the load current. The effect of delay due to RF transmission on system stability and performance is analyzed, and regions of operation for a stable as well as satisfactory performance are determined. We experimentally demonstrate a satisfactory performance of the master-slave converter at 20-kHz switching frequency under steady state as well as transient conditions in the presence of a transmission delay. The proposed control concept, which can potentially attain redundancy that is achievable using a droop method, may lead to more robust and reconfigurable control implementation of distributed converters and power systems. It may also be used as a (fault-tolerant) backup for wire-based control of parallel/distributed converters.     

Uplink power control for TDMA portable radio channels

Power control based on signal-to-interference ratio (SIR) has been proposed as a technique for managing co-channel interference in frequency reuse radio systems. Recently, new autonomous power control methods were introduced to achieve near-optimum performance without difficult centralized control proposed earlier. The achievable performance from preliminary studies appears promising for providing significant increase in spectrum efficiency. However, the implementation of the SIR-based power control algorithms remains challenging. In this paper, implementation of power control that indirectly depends on SIR is discussed. As an example, a simple closed-loop power control algorithm for the portable transmitter is introduced for TDMA portable radio systems. While it may appear specific for the system considered, the underlying principle and parameters required (i.e., error indicator, received power level, and signal quality indicator) are common to the implementation of digital demodulation circuitry. Computer simulations indicate that SIR level is maintained at a level suitable for sustaining desirable performance. Furthermore, when the power-control updating period is short, as in the specific system considered, moderate-rate short-term fading can be tracked and mitigated