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MOBILE POWER CONTROL BY THE BASE STATION

IP.com Disclosure Number: IPCOM000005705D
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2001-Oct-29
Document File: 3 page(s) / 153K

Publishing Venue

Motorola

Related People

Ronald H. Chapman: AUTHOR

Abstract

As the frequency spectrum becomes more crowded, there is a need for greater spectral efficient radios and communications systems. As these are developed it is apparent that system margins are reduced. One of the areas that this is apparent is in the area of adjacent channel splatter performance and the associated frequency tolerances. Another area where this is seen is in the attempt to provide enhanced channel usage by the technique of frequency reuse. In both of these areas, the dynamic range of the signal strength as seen at the base station receiver plays a pivotal role in the performance of the system.

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Page 1 of 3

@ MOTOROLA

Technical Developments Volume 8 October 1988

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MOBILE POWER CONTROL BY THE BASE STATION

by Ronald H. Chapman

   As the frequency spectrum becomes more crowded, there is a need for greater spectral efficient radios and communications systems. As these are developed it is apparent that system margins are reduced. One of the areas that this is apparent is in the area of adjacent channel splatter performance and the associated frequency tolerances. Another area where this is seen is in the attempt to provide enhanced channel usage by the technique of frequency reuse. In both of these areas, the dynamic range of the signal strength as seen at the base station receiver plays a pivotal role in the performance of the system.

   In the majority of the present systems, the dynamic range is determined by the difference between the system sensitivity (usually in the range of -113dBm.) and the value of the signal strength achieved when the mobile is nearto the base station antenna, or the value obtained from a fixed control station that is transmitting too much power.

   One way to reduce the dynamic range of the signals received at the base station is to vary the power of the transmitting mobile. In the present Cellular Radio systems the level of the received signal strength is measured on a periodic basis, and the mobile is told to adjust its transmitted power accordingly. The rate at which the correction is made is in the order of 10 sec. intervals. In many situations this is not often enough to compensate for log-normal variations of the signal strength.

   To overcome this difficulty, an approach was developed that allowed a real time control of the mobile tran- mist power. It is necessary to have aduplex radio to perform the function, because of the need to tell the mobile what to do while it is transmitting.

   The approach used was to place the mobile power control into a negative feedback loop, where the signal strength decision is made at the base station receiver. To maintain a stable feedback system it is necessary to maintain a static operating point. This means that the DC component of the feedback signal must be transmit- ted from the base station to the mobile. The initial approach was to send a DC level signal to indicate if the power was to be increased or decreased. This approach did not work!

   The approach that worked with great success used the received signal strength to adjust the duty cycle of an oscillator. This oscillator signal was transmitted to the mobile and the signal was fed into an integrator circuit. If the duty cycle was greater than 50% the value of the signal out of the integrator would try to increase. If the duty cycle was less than 50% the value of the signal out of the integrator would try to decrease. If the duty cycle varied about the 50% point, the integrator would remain at its last value. Thus it was possible to provide a feedback signal that contained a DC component without requiring the transmission p...