Open-Loop Power Control Error in a Land Mobile Satellite System

In order to combat large scale shadowing and distance losses in a land mobile satellite system, an adaptive power control (APC) scheme is essential. Such a scheme, implemented on the uplink ensures that all users' signals arrive at the base station with equal average power as they move within the satellite spot beam-an important requirement in a CDMA system. Because of the lengthy round-trip delay on a satellite link, closed-loop power control systems are only of marginal benefit. Therefore, an open-loop APC scheme is proposed to counteract the effects of shadowing and distance loss. A fairly general channel model, consisting of log-normal shadowing and Rician fading, is assumed. This can be applied to a specific two-state land mobile satellite channel model, involving shadowed intervals with Rayleigh fading and unshadowed intervals with Rician fading. It is found that the power control error can be approximated by a log-normally distributed random variable. To quantify the performance of the APC, the standard deviation of the power control error in decibels is analyzed as a function of the specular power-to-scatter power ratio, the measurement time and the vehicle velocity. To illustrate the usefulness of the results, we analyze the effect of the power control error on the system capacity of a CDMA mobile satellite link. >

[1]  Andrew J. Viterbi,et al.  Convolutional Codes and Their Performance in Communication Systems , 1971 .

[2]  M. Gudmundson.  Correlation Model for Shadow Fading in Mobile Radio Systems , 1991 .

[3]  Branimir R. Vojcic,et al.  Power control versus capacity of a CDMA system operating over a low Earth orbiting satellite link , 1993, Proceedings of GLOBECOM '93. IEEE Global Telecommunications Conference.

[4]  Laurence B. Milstein,et al.  Performance of DS-CDMA with imperfect power control operating over a low earth orbiting satellite link , 1994, IEEE J. Sel. Areas Commun..

[5]  Andrea Goldsmith,et al.  Error statistics of real-time power measurements in cellular channels with multipath and shadowing , 1994 .

[6]  Jean Conan.  The Weight Spectra of Some Short Low-Rate Convolutional Codes , 1984, IEEE Trans. Commun..

[7]  L. B. Milstein,et al.  A CDMA cellular system in a mobile base station environment , 1993, Proceedings of GLOBECOM '93. IEEE Global Telecommunications Conference.

[8]  T. Aulin.  A modified model for the fading signal at a mobile radio channel , 1979, IEEE Transactions on Vehicular Technology.

[9]  Daniel Cygan,et al.  The land mobile satellite communication channel-recording, statistics, and channel model , 1991 .

[10]  Che-Ho Wei,et al.  On the performance of rate 1/2 convolutional codes with QPSK on Rician fading channels , 1990 .

[11]  John G. Proakis,et al.  Digital Communications , 1983 .

[12]  R. Clarke.  A statistical theory of mobile-radio reception , 1968 .

[13]  J. D. Parsons,et al.  Characterisation of mobile radio signals: model description , 1991 .