Effective Power Control Research Articles

Performance of closed-loop power control in DS-CDMA cellular systems

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.

DS‐CDMA outage performance over a mobile satellite channel

AbstractA DS CDMA satellite uplink with power control error is considered. CDMA system performance is normally interference limited, and, in an additive, white, Gaussian noise channel, with many users, sufficient processing gain, and effective power control, individual users typically experience the average performance over all users. In this case, the other users appear as the equivalent of additional Gaussian noise and each user experiences the same environment. An alternative measure of performance under fading conditions is the probability of outage. For coded signals, the fading must be averaged over all the symbols in the code word. For properly interleaved signals and i.i.d. Rayleigh fade statistics, the average must be performed over a chi‐squared variate. The probability of outage, defined as the probability that the decoded bit error rate exceeds a specified threshold, is monotonic with the probability that the chi‐squared variate is less than a specified threshold. We derive upper and lower bounds on the outage probability for soft decision decoding.

A model for voltage and reactive power control

An analytical model is developed to allow effective reactive power control in critically loaded power transmission systems. Representation of the transmission network, tap-changing transformers, and nonlinear loads is incorporated. The model has application in computer control and monitoring of transmission voltage performance.

Towards effective control of undue market power

Towards effective control of undue market power

Error Performance for Adaptive Transmission on Fading Channels

A communication system is analyzed in which the transmission power and/or rate are adjusted to the observed state (attenuation) of a slowly fading channel. The optimum control of power and rate with channel attenuation is determined. Some suboptimum control rules are also investigated. The average probability of error is evaluated for various types of adaptive transmission, imposing different constraints on power, rate, and bandwidth. It is shown that rate control is superior to power control and that simultaneous power and rate control further improves the performance. The most effective power and rate control presupposes a high peakpower-average-power ratio and a high peak-rate-peak-rate-average-rate ratio; with no peak power and bandwidth limitation, arbitrary small error probability is attainable for a given power and average rate.

Technical and economic aspects of the supply of reactive power in England and Wales

The paper discusses some problems of supplying reactive power in the transmission and distribution systems of England and Wales.The overall reactive-power requirements of the inductive loads of consumers and the shunt and series inductances of the system are reviewed and their effect on generator characteristics is examined. Consideration is given to the problems of supplying the demand for reactive power by means of the generators, system capacitance and compensating devices, and a scheme is outlined for the effective control of reactive power and voltage. An example is given relating to the possible conditions when the system load reaches 30 GW, and it is shown that the kVAr/kW ratio at bulk supply points for the optimum loading of the generators postulated is about 0.4 (0.93 lagging power factor) at times of peak load.Estimates are made of the extra cost of providing and operating a power-supply system to transmit reactive power as well as active power. Consideration is given to various forms of tariff adjustment for reactive-power supply, leading to a preference for separate charges for active and reactive power demands.The advantages and disadvantages of generating reactive power at or near the load, by the consumer or by the supply authority, are discussed. It is concluded that present methods of tariff adjustment are generally effective in inducing consumers to limit their demands for reactive power to an extent which would make uneconomic the provision of additional sources of reactive power on distribution systems.