# US 5,347,562 A · Synchronizing groups of base stations in time division duplex communication systems

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- Number: US 5,347,562 A
- Document ID: US5347562A
- Status: Granted
- Kind: A
- Application number: 08/071,862
- Filed: 1993-06-02
- Granted: 1994-09-13
- Earliest claimed: 1989-08-18
- Assignees: Hutchinson Personal Communications Limited
- Inventors: Edwin R. Candy
- Web page: https://patentgrep.com/patent/US5347562A

## CPC

- H04B 7/24: for communication between two or more posts (wireless communication networks H04W)
- H04B 7/2693: {Centralised synchronisation, i.e. using external universal time reference, e.g. by using a global positioning system [GPS] or by distributing time reference over the wireline network}
- H04M 1/733: with a plurality of base stations connected to a plurality of lines {(for selection in cordless PBX H04W84/16)}
- H04B: TRANSMISSION
- H04M: TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08)

## Abstract

A telephone system in which communication between fixedly sited primary stations and transportable secondary stations is by way of respective time division duplex (TDD) radio links, particularly single frequency TDD links. In order to reduce radio interference between closely sited primary stations, their transmit periods are frame synchronized by using an externally produced radio signal. Conveniently a broadcast television field synchronization signal can be used.

## Claims

### Claim 1

A primary station for use in a cordless telephone system, in which communication between the primary station and a transportable secondary station is by way of a time division duplex radio link, said primary station comprising:
radio transceiving means for communicating with a secondary station,
means for receiving a radio signal which is broadcast by a source which is external to the cordless telephone system,
means for deriving a characteristic from the received radio signal, which characteristic is present in the received radio signal for a reason other than synchronizing stations in the cordless telephone system,
a clock generator for controlling the switching of the radio transceiving means between successive transmit and receive periods, and
means responsive to the derived characteristic for adjusting the clock generator so that the transmit period of the radio transceiving means is synchronized with those of at least one other primary station.

### Claim 2 (depends on 1)

The primary station of claim 1, wherein
the means for receiving the radio signal comprises a television signal receiving means; and
the means for deriving the characteristic comprises a television field synchronizing signal separator.

### Claim 3 (depends on 2)

A primary station as claimed in claim 2, wherein a divider is connected to the field synchronizing signal separator for dividing down the period between successive field synchronization signals, said divider having an output connected to said clock generator.

### Claim 4

A method of operating a cordless telephone system including fixed site primary stations and moveable secondary stations, each having radio transceiving means, the method comprising the steps of:
establishing a time division duplex radio link between a primary station and a secondary station of the cordless telephone system; and
synchronizing at least two primary stations of the cordless telephone system using a characteristic of a radio signal, which radio signal is broadcast by a source external to the cordless telephone system and which characteristic used to synchronize the primary stations is present in the received signal for a reason other than synchronizing stations in the cordless telephone system.

### Claim 5 (depends on 4)

A method as claimed in claim 4, in which the characteristic is a television field synchronization signal.

### Claim 6 (depends on 5)

A method as claimed in claim 5, further comprising sub-dividing the period of the television field synchronization signal.

### Claim 7

A method of operating a cordless telephone system including fixed site primary stations and moveable secondary stations, each having radio transceiving means, the method comprising the steps of:
establishing a time division duplex radio link between a primary station and a secondary station of the cordless telephone system; and
synchronizing at least two primary stations of the cordless telephone system using a characteristic of a radio signal, which radio signal is broadcast by a source external to the cordless telephone system for a reason other than synchronizing stations in the cordless telephone system, and the radio signal is not broadcast in a modified state to synchronize stations in the cordless telephone system.

### Claim 8 (depends on 7)

A method as claimed in claim 7, in which the characteristic is a television field synchronization signal.

### Claim 9 (depends on 8)

A method as claimed in claim 8, further comprising the step of sub-dividing the period of the television field synchronization signal.