Browse Prior Art Database

PORTABLE ANTENNA DIVERSITY UTILIZING A PUBLIC SAFETY MICROPHONE

IP.com Disclosure Number: IPCOM000008611D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-26
Document File: 2 page(s) / 106K

Publishing Venue

Motorola

Related People

Matt Bridle: AUTHOR

Abstract

Antenna diversity is a technique used to improve the performance of mobile radio systems. This paper describes a possible way of implementing antenna diversity for handportable radios.

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MOTOROLA Technical Developments

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PORTABLE ANTENNA DIVERSITY UTILIZING A PUBLIC SAFETY MICROPHONE

by Matt Bridle

INTRODUCTION

  Antenna diversity is a technique used to improve the performance of mobile radio systems. This paper describes a possible way of implementing antenna diversity for handportable radios.

PROBLEM TO BE SOLVED

  Mobile radios travelling through a typical multi- path radio channel experience fading of the received signal. The consequence of this is that the signal received by a mobile radio in a typical mobile channel has to be higher than that received by the same radio in a "static" (non-fading) channel in order to obtain the same audio quality. This difference between the static and faded sensitivity is often termed the "fading margin." The fading margin depends on many factors including the mod- ulation scheme, the performance of the receiver, the required quality level and the radio channel. However a typical value would be around 10 dB. Reduction in the required fading margin can result in increased range or a reduction in mobile radio infrastructure.

  Antenna diversity is a well-known technique for reducing the required fading margin. The technique relies on using two or more antennas and switching, selecting or combing the signals from these antennas. If the signals received on these antennas are sufli- ciently de-correlated, when the signal from one antenna is experiencing a deep fade there will be a high probability that the signal(s) from the other antenna(s) are not in such a deep fade.

  De-correlation of the signals on the different antennas is most easily achieved by physically sep- arating the antennas. Lee [Mobile Communications Engineering, McGraw-Hill 1982, Page 2761 reports that a separation of 0.5 wavelengths is sufficient to achieve signals which are essentially de-correlated

(r < 0.2). This separation can be achieved with mobile radios for vehicular applications at frequencies above about 150 MHz (required spacing is 1 metre).

  For handportable radio applications, achieving the required physical separation becomes more dif- ficult. At 900 MHz portable radios with dual diver- sity antennas have been implemented. For example, handheld radios for the Japanese MCSL2 system in the 870-940 MHz b...