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BEACON CONTROL OF RADIO TRANSMITTERS TO REDUCE RADIO FREQUENCY INTERFERENCE

IP.com Disclosure Number: IPCOM000006564D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-15
Document File: 3 page(s) / 196K

Publishing Venue

Motorola

Related People

Timothy J. Klandrud: AUTHOR [+2]

Abstract

The out-of-band emanations f?om a mobile unit radio frequency (RF) transmitter may cause interference to sensitive receivers if ttie mobile unit is too close to the sensitive receiver. The mobile units used in the IRIDIUMM system may interfere with radio astronomy (RA) measurements if operated too close to a RA site. The RA site can be protected by physically controlling the area around the site. This is not generally practical since an area with a radius of 10 to 30 Km would need to be controlled. Alternatively, signs could be posted warning users not to turn on their mobile equipment within the protection zone radius. This may be unacceptable since the users may not see the signs or could avoid this control by simply ignoring the warnings.

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MOTOROLA INC. Technical Developments Volume 16 August 1992

BEACON CONTROL OF RADIO TRANSMITTERS TO REDUCE RADIO FREQUENCY INTERFERENCE

by Timothy J. Klandrud and John L. Nelson

  The out-of-band emanations f?om a mobile unit radio frequency (RF) transmitter may cause interference to sensitive receivers if ttie mobile unit is too close to the sensitive receiver. The mobile units used in the IRIDIUMM system may interfere with radio astronomy (RA) measurements if operated too close to a RA site. The RA site can be protected by physically controlling the area around the site. This is not generally practical since an area with a radius of 10 to 30 Km would need to be controlled. Alternatively, signs could be posted warning users not to turn on their mobile equipment within the protection zone radius. This may be unacceptable since the users may not see the signs or could avoid this control by simply ignoring the warnings.

  A warning beacon system can be used to restrict the use of the mobile transmitters so that the intertier- ence levels arc acceptable. The beacon(s) arc located near the RA site and transmit an RF signal which can be received by a mobile unit. If the power level is above a known threshold the mobile unit lowers its out-of- band emanations to an acceptable level. The emanations can be lowered by reducing the transmitter power, tum- ing off the transmitter, increasing the filtering used or by using some other form of out-of-band power control. Spoofing of the mobile unit can be avoided by sending scrambled information as part of the beacon message and through the use of special control functions implemented in a processor within the mobile unit. Any or all of the concepts described herein can be used to protect a receiver (stationary or mobile) from interfer- ing units (mobile or stationary).

  This description of the beacon protection assumes that the receiver to be protected is a radio astronomy receiver, the possible interfering transmitter is a small mobile unit. and the system control and general com- munications services are provided by a satellite base sta- tion. Figure 1 illustrates the use of beacons to protect a Radio Astronomy receiver 1 from mobile units 2,3. The mobile units communicate with a satellite 4. One or more beacon units 5.6 transmit RF warning signals 7,s to any mobile units that might be in the area. The effective

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isotopic radiated power (EIRP) of each of the warning signals is large enough so that any mobile unit which has a line-of-sight link with the beacon and is within the desired protection radius can receive the beacon warn- ing signal clearly The protection radius is a predetermined distance needed to protect the RA site from mobile unit interference. This distance can vary from site to site and can also vary for different types of mobile units. The beacons 5,6 are located far enough away from the RA site so that they do not cause interference with the FCA receiver.

  When the mobile un...