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Browse Prior Art Database

CELL RE-SELECTION FOR AIR-TO-GROUND MOBILE

IP.com Disclosure Number: IPCOM000009579D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Sep-04
Document File: 4 page(s) / 210K

Publishing Venue

Motorola

Related People

Matt Bridle: AUTHOR

Abstract

Many land mobile radio systems have a require- ment to also integrate some form of air-to-ground communications. It is not usually feasible to use the same radio frequencies for air-to-ground communi- cation as those used for land mobile communication. Therefore, an air-to-ground network using separate frequencies must be used which can lead to difftcul- ties in cell selection. The problems are described further in this article cell together with a special air- to-ground mobile as a proposed solution. The arti- cle describes a TETRA radio system, but is equally applicable to other technologies.

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Page 1 of 4

Developments Technical 0 M MOTOROLA

CELL RE-SELECTION FOR AIR-TO-GROUND MOBILE

by Matt Bridle

INTRODUCTION

  Many land mobile radio systems have a require- ment to also integrate some form of air-to-ground communications. It is not usually feasible to use the same radio frequencies for air-to-ground communi- cation as those used for land mobile communication. Therefore, an air-to-ground network using separate frequencies must be used which can lead to difftcul- ties in cell selection. The problems are described further in this article cell together with a special air- to-ground mobile as a proposed solution. The arti- cle describes a TETRA radio system, but is equally applicable to other technologies.

17dBC/I@10,0cOA.

PROBLEM TO BE SOLVED

  The radio channel between a base station (BS) and a mobile station (MS) in an aircraft, which is above local obstructions, is essentially line-to-sight and the propagation loss is consequently much less than that between a BS and a ground based MS at the same radial distance. The result is that the fre- quencies used for aircraft communications cannot be used within the terrestrial network because of the interference that an aircraft mobile would cause to (and receive from) the terrestrial network. The problem is illustrated in Figure 1.

Fig. 1 C/l for an aircraft at 10,000 ft

B Motomla. 1°C. ,999 291 September 1999

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Page 2 of 4

Developments Technical 0 M MO-LA

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%i Mommla. 1°C. ,999 292 September 1999

  In order to maintain at 17dB Carrier/Inter- ference (C/I) ratio (which is required for good com- munication), any frequencies used for air-to-ground communication could not be re-used within 2OOkm. Therefore, a separate network of base stations is required using air-to-ground frequencies.

  Since the propagation loss is much lower between a BS and an aircraft MS, cell sizes can be much larger for an air-to-ground network than for a terrestrial network. Using a 3 Watt MS, cell radii of around 50 km can be achieved for aircraft above about 1OOm. The number of cells required to pro- vide area coverage for aircraft is therefore much less than that required to provide area coverage for ter- restrial mobiles. For example, to provide radio cov- erage for the whole of the UK would only require around 50 cells. This compares with around 2000 cells likely to be used in the terrestrial network. Therefore, on average, a single cell in the air-to- ground network will cover an area corresponding to the area covered by approximately 40 cells in the terrestrial network.

  However, when an aircraft is on the ground its communications range is no greater than a terrestrial mobile. Therefore in order to obtain radio coverage when on the ground the aircraft mobile must be able to use the terrestrial cells when it is not able to obtain service from one of the air-to-ground cells.

  Radio communications is often most important when an aircraft is ascending or descending...