Telecommunications system

Details Telecommunications system Telecommunications system

1998-01-30

2001-03-06

Kizou, Hassan (Department: 2738)

Multiplex communications

Communication over free space

Combining or distributing information via time channels

C370S324000, C370S510000, C370S514000

Reexamination Certificate

active

06198736

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to a telecommunications system, and in particular to a network comprising a base station with a control unit and a plurality of remote radio transceivers and to a method of establishing air frame synchronisation between the remote radio transceivers.
DESCRIPTION OF RELATED ART
A conventional digital cellular telephone base station includes a large number of radio transceivers, typically controlled from a central unit. Transmissions from the radio transceivers are divided into frames, and each frame contains a plurality of time slots, which typically contain transmissions to different mobile transceivers. A time division multiplex (TDM) link is used for carrying control and traffic signals between the control unit and the remote radio transceivers.
It is known to synchronise the radio transceivers, so that each radio transceiver begins transmission of a new frame at the same moment. In a conventional network, air frame synchronisation between the radio transceivers is established by means of a central timing unit, which is connected to all of the radio transceivers via a local bus cable network, and transmits a signal at 25 Hz, which is the air frame rate, to the radio transceivers.
However, this method of distributing the air frame synchronisation signals is disadvantageous when the radio transceivers are at a significant distance, for example up to 1,000 m, from the central timing unit, since then the propagation delays along the cable mean that true synchronisation can be lost and a separate cable is necessary for the air frame synchronisation signal.
SUMMARY OF THE INVENTION
The present invention seeks to provide a method of distributing air frame synchronisation between widely spaced radio transceivers, without requiring additional infrastructure.
In preferred aspects of the present invention, the air frame synchronisation signal is transmitted to the remote radio transceivers on the TDM link which carries the traffic and control signals. Preferably, data relating to the air frame synchronisation signal is encoded and transmitted in a time slot on the TDM link, and each remote radio transceiver includes circuitry for regenerating the air frame signal from the transmitted data.
Preferably, also, the remote radio transceiver includes circuitry for compensating for any delays on the transmission link.


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