Telephonic communications – Having light wave or ultrasonic link for speech or paging... – Including fiber optic link within telephone network
Patent
1994-12-22
1997-10-21
Cumming, William
Telephonic communications
Having light wave or ultrasonic link for speech or paging...
Including fiber optic link within telephone network
H04Q 730
Patent
active
056804385
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a cordless telephone system.
2. Description of the Related Art
The basic cordless telephone system comprises a base unit which is hard wired to the public telephone (PSTN or ISDN) network together with one or more handsets which are linked to the base unit by means of a two-way radio link. To this end, each handset includes a transceiver and a keyboard with associated circuitry, and the base unit comprises one or more transceivers, at least one for each handset, together with control and interface circuitry.
In order to cater for larger systems installed in physically larger premises, it is known to provide a plurality of base units distributed around the premises and all hard wired to a central control and interface unit at which the connections to the external telephone network are made. The maximum capacity of each base unit in such a system is defined by the number of transceivers which are installed in that base unit.
SUMMARY OF THE INVENTION
The present invention is concerned primarily with the larger systems which would ordinarily require multiple base units, as described above. In the present invention, instead of a plurality of base units each having a number of transceivers, the system comprises just one base unit, which includes all the necessary transceivers, together with the usual control and interface circuitry, and is characterised by further comprising a plurality of RF input/output "heads" which communicate with the individual handsets on the system, and pass signals to and from the handsets by radio communication. The RF heads will be distributed about the premises in the same manner as the base units would have been, and are linked to each other and to the base unit by means of a hard-wired RF connection, such as coaxial cable.
Preferably the RF heads will be non-intelligent, and will simply convert signals from hard-wired form to radio form, probably with a change of frequency involved. In the preferred embodiment of the invention, each RF head comprises a respective transponder which acts as a wideband converter of signals to and from the RF connection. Preferably the incoming signal is converted to a different frequency unique to that particular transponder so that the signals from all the transponders may be carried simultaneously by the RF cable connection, separated by frequency. The exact frequencies involved vary but, as an example, the cordless telephone (CT) band in the UK is from 864.1 to 868.1 MHz, and forty channels are defined within this 4 MHz band. Preferably the transponders will have a bandwidth sufficient to cover this full 4 MHz and will normally downconvert the radio signals to an IF frequency suitable for transmission along the RF cable. This IF frequency will be unique to the transponder: for example a first transponder might downconvert to an IF band of 100 to 104 MHz, a second to an IF band of 105 to 109 MHz, a third to an IF band of 110 to 114 MHz, and so on. Note that 1MHz has been left between the IF bands to act as a guard band.
In the base unit itself, each of the transceivers is capable of receiving any single channel from any of the RF heads. The transceiver is tuned to the channel in any of the IF bands corresponding to an RF head. The transceiver may therefore select the reception of the same CT channel on different transponders to establish the best reception of a particular CT for example or may tune sequentially to all the CT channels on a particular transponder to establish the activity level in the CT band and repeat this on the other transponders. In this way a single transceiver can be made to scan all the channels on all the transponders. Normally this duty would be carried out by a plurality of transceivers to provide a reasonable service level and traffic capacity.
In an embodiment, the transceivers and/or transponders may be made frequency agile, able to change their tuned IF frequency, under the control of the control circuitry, according to the requirements
REFERENCES:
patent: 5133001 (1992-07-01), Bohm
patent: 5195127 (1993-03-01), Ichikawa et al.
patent: 5381459 (1995-01-01), Lappington
AT & T Wireless Communications Products, Ltd.
Cumming William
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