Browse Prior Art Database

INFRASTRUCTURELESS RADIO NETTING PROCEDURE

IP.com Disclosure Number: IPCOM000007033D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-20
Document File: 4 page(s) / 168K

Publishing Venue

Motorola

Related People

Mark A. Gannon: AUTHOR

Abstract

The FCC's recent Notice for Proposed Rule Mak- ing to replace Part 90 by Part 88 which would man- date the usage of 5 and 6.25 kHz channelization in the private land mobile radio spectrum at VHF and UHF is an outgrowth ofthe need for better spectral utilization in these bands and the realization that narrowband FDM channel access is one way to achieve that goal.

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MOTOROLA INC. Technical Developments Volume 20 October 1993

INFRASTRUCTURELESS RADIO NETTING PROCEDURE

by Mark A. Gannon

  The FCC's recent Notice for Proposed Rule Mak- ing to replace Part 90 by Part 88 which would man- date the usage of 5 and 6.25 kHz channelization in the private land mobile radio spectrum at VHF and UHF is an outgrowth ofthe need for better spectral utilization in these bands and the realization that narrowband FDM channel access is one way to achieve that goal.

  Most of the present day land mobile radios employ synthesized RF hequency sources whose fre- quency base is derived horn the radio's reference oscillator. Tight reference oscillator stability require- ments exist for narrowband radio systems (e.g. 5,
6.25,12.5 kHz channel spacings) to improve receive sensitivity and to minimize adjacent channel splat- ter. For example, a frequency offset of 500 Hz leads to a sensitivity degradation of 1 dB and 4 dB of extra splatter into an adjacent channel for some 12.5 kHz radio systems. Figure 1 depicts how a Frequency offset can lead to extra adjacent channel splatter.

  One technique to maximize sensitivity and to minimize splatter is to employ highly stable refer- ence oscillators in the subscriber radios. For exam- ple, better than 1 ppm stability is required for less than 500 Hz offset at an RF frequency of 500 MHz. This burdens those units with a substantial cost pen- alty relative to the 5 ppm reference typically employed by 25 kHz channelization radios operating at VHF and UHF

  Another technique is for a subscriber with a less expensive reference oscillator to 'net' onto a stable base station reference, as is done in some present day systems. This technique involves the deploy- ment of base station units with highly stable refer- ence oscillators (commonly done), the monitoring of the base transmit signal by the subscriber unit before subscriber unit operation, the measurement of the difference between where the subscriber expects the base station transmit frequency to be and where the base station transmit frequency really

0 Motorola. 1°C. 1993

is, and the correction of the subscriber's reference oscillator based on this measured frequency error. Figure 22 shows this pictorially. This technique works very well for systems like trunked systems where base station transmitters are always present, but is not practical in systems that do not employ base units.

  This invention, an infrastructureless radio net- ting procedure, does not require an installation of a base unit, does not require an expensive highly sta- ble subscriber frequency reference, and will enable a cost effective implementation of highly stable subscriber reference oscillators. This invention allows subscriber units to correct their frequency reference when operating in systems with exclusively or pri- marily subscriber to subscriber operation, which is common in radio systems operating at VHF or UHF This invention also provides for reference freque...