Browse Prior Art Database

SPACE DIVERSITY HOPPER FOR DIGITAL DATA TRANSMISSION

IP.com Disclosure Number: IPCOM000005877D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-13
Document File: 2 page(s) / 96K

Publishing Venue

Motorola

Related People

Daniel R. Tayloe: AUTHOR

Abstract

A digital TDMA system such as GSM is capable of full duplex transmission of speech and voice. Field tests per- formed in England, France and Italy show that 50% of the received signals experience delay spreads of less than 20 - 30% of the coherence bandwidth. This means that flat (nonfrequency selective) fading of such channels is a normal occurrence. To reduce the effect of this problem, the use of frequency hopping was proposed.

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MOlOROLA Technical Developments Volume 10 March 1990

SPACE DIVERSITY HOPPER FOR DIGITAL DATA TRANSMISSION

by Daniel R. Tayloe

   A digital TDMA system such as GSM is capable of full duplex transmission of speech and voice. Field tests per- formed in England, France and Italy show that 50% of the received signals experience delay spreads of less than 20 - 30% of the coherence bandwidth. This means that flat (nonfrequency selective) fading of such channels is a normal occurrence. To reduce the effect of this problem, the use of frequency hopping was proposed.

   The basic premise behind frequency hopping is to move a mobile unit out of fading by changing its frequency, thereby obtaining additional uncorrelated samples that hopefully will not be in the fade. Unfortunately, there are several problems associated with this approach. First, initial start up systems must comprise cells having a large number of transmitters in order for frequency hopping to be effective. Since most systems at their infancy do not require this addi- tional capacity, the initial investment for start up systems can be rather high. In certain suburban and rural systems, use may never warrant this additional capacity, thereby making TDMA systems less attractive in these areas. Further- more, in most TDMA environments, the time slot used to broadcast paying, system, and call specific information does not hop, thereby exposing the system to slow fading disruptions.

   In order to overcome these shortcomings, this article suggests the implementation of space diversity hopping as an alternative to frequency hopping. The basic premise behind space diversity hopping is to obtain additional uncor- related samples that are not in the fade, by switching between two or more antennae at the base site.

   For an omni cell, one implementation suggests using six omni antennas capable of being independently accessed on a frame by frame basis. While six is an arbitrary number use only for instruction, it is obvious that any plurality of antennae will suffice, as long as they are accessible on both the transmit and receive paths...