Browse Prior Art Database

DIRECT MODE SUBSCRIBER CHANNEL SELECTION METHOD

IP.com Disclosure Number: IPCOM000009775D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-18
Document File: 6 page(s) / 270K

Publishing Venue

Motorola

Related People

Steve Valentine: AUTHOR [+2]

Abstract

A channel selection method for frequency simplex radios operating in direct mode, whereby the radio channel to be used for the communications is determined from the radio's current location with respect to a trunked radio system base site. The objective of the channel selection strategy is that a direct mode radio will choose a Direct Mode chan nel in the Trunked mobile receive band when the DM radio is in close proximity to the trunked radio system base site, and choose a Direct Mode channel in the base station receive band when the DM radio is some distance from the base site.

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MOTOROLA

Technical Developments

DIRECT MODE SUBSCRIBER CHANNEL SELECTION METHOD

by Steve Valentine and Chris Johnson

ABSTRACT

A channel selection method for frequency simplex radios operating in direct mode, whereby the radio channel to be used for the communications is determined from the radio's current location with respect to a trunked radio system base site. The objective of the channel selection strategy is that a direct mode radio will choose a Direct Mode chan nel in the Trunked mobile receive band when the DM radio is in close proximity to the trunked radio system base site, and choose a Direct Mode channel in the base station receive band when the DM radio is some distance from the base site.

INTRODUCTION

This paper describes a mobile station (MS) based channel selection method for frequency sim~ plex radios operating in direct mode or talk around, that minimizes the probability of direct mode communications impacting the coverage range of fixed land mobile trunked radio networks.

PROBLEM TO BE SOLVED

In TETRA trunked mode operation (TMO), radios shall usually operate in half duplex mode.

This employs a pair of 25 kHz radio frequency channels, as uplink and downlink, for communica~ tion. The uplink channel is used for mobile station transmit/base station receive operation, and the downlink for base station transmit/mobile station receive operation.

However, TETRA Direct Mode operation (DMO) employs frequency simplex operation and uses a single 25 kHz radio channel to support communications. Therefore a minimum of two Direct Mode radio channels can reside in a TMO pair i.e.

one DM channel in the mobile station transmit band and the other in the base station transmit band.

Motorola, Inc. 2000

Such a scheme maximizes the use of the DM channel capacity available. However, the allocation of DM channels in either the TMO BS receive band or BS transmit band does pose some potential interference problems. For example, a Trunked mobile station operating some distance away from its base station will be receiving the desired signal at a relatively low signal strength and will have a correspondingly low signal margin to cope with interference.

See appended Figure I.

If a nearby Direct Mode conversation starts up using a channel in the base station transmit/mobile station receive band then the level of interference due to DM MS TX wideband noise may reduce the Trunked radio 's signal to noise ratio below that .

required to receive acceptably.

Likewise, if a base station is receiving a signal from a remote Trunked mobile station and a direct mode conversation commences that is using a radio channel in the mobile station transmit/base station receive band, then the base station is likely to incur a reduction in signal to noise ration. See Figure 2.

To minimize the potential interference due to DM communication in these two scenarios, while at the same time maximizing the use of the available channels for DMO, we propose an MS based Direct Mode cha...