WO1992010913A1

WO1992010913A1 - Cordless telephone system

Info

Publication number: WO1992010913A1
Application number: PCT/GB1991/002155
Authority: WO
Inventors: Robert Joseph Gerard Macnamee
Original assignee: Hutchison Personal Communications Limited
Priority date: 1990-12-05
Filing date: 1991-12-05
Publication date: 1992-06-25
Also published as: GB9026493D0; GB2250660A

Abstract

Several different cordless telephone networks can cover an overall operating area. Each network has its own link identification code (LID) which when transmitted by a portable secondary station is recognised by the primary stations of one of the networks as being its home LID. In order to make better use of the overall system, one or more network operators may agree to handle call requests from one another, however preference is given to the home network. In order to do this, a primary station receiving a call request, checks the LID and, if it is not its home LID but that of a roamer, it waits a predetermined time or number of channel scans before accepting the call request which is processed by a host primary station in a way which is transparent to the secondary station that it is not its home primary station.

Description

CORDLESS TELEPHONE SYSTEM

TECHNICAL FIELD

The present invention relates to a cordless telephone system, to a secondary station for use in the system and to a method of operating the system. More particularly the present invention is concerned with intersystem roaming in a cordless telephone system. BACKGROUND ART

For convenience of description the present invention will be described with reference to a cordless telephone system which is becoming known in Europe as CT2 and which is disclosed in MPT1375 "Common Air Interface Specification" published by the Department of Trade and Industry (DTI), London. In CT2 there are 3 possible modes of operation, namely, domestic in which a primary (or base) station is connected to the PSTN and has radio transceiving means which can establish a radio link with radio transceiving means provided in a secondary (or portable) station; business in which the primary station is equivalent to a PABX and can communicate by way of a radio link with any in range secondary unit; and public access in which primary stations are disposed at different geographical locations, such as banks, petrol filling stations and railway stations, and users of authorised secondary stations can access the entire public switched telephone network by way of a primary station. In the public access mode only secondary stations can initiate a call at present.

In a system such as CT2, if there are two or more licensed network operators for the public access mode then each operator has its own geographically distributed primary stations some of which are in close proximity to the primary stations belonging to another network operator. Each network operator has at least one unique link identification code LID. All the primary stations belonging to a network are coupled to computers in one or more administration centres, which computers may carry out tasks such as authorisation and billing. The primary stations may also carry out authorisation checks. Secondary stations are supplied to users by network operators who also bill the user. Each network operator has its own identity code OPSIC. In order to identify a secondary unit for call authorisation purposes, the secondary unit is provided with a unique personal identification number (PIN) and an account number as well as an electronic serial number PID (portable identity unit). Thus when a secondary station wants to make a call it first searches to find a free channel and then it sends a request message which initially includes LID, OPSIC, PIN and Account Number. An in range primary station will examine this message and if the LID corresponds to its own system then it will authenticate and authorise the call locally or by reference to its administration centre. Assuming that these are satisfactory then the user keys in the called party's number and primary station attempts to establish a connection.

A network operator or its agent when supplying a secondary station has to write into a non-volatile store the LID, OPSIC, PIN and Account Number thus enabling the secondary station to use all the network operator's primary stations, for convenience of reference this network and its primary stations will be referred to as the "home network" and "home primary stations", respectively. If a user wishes also to be able to access the PSTN by way of another network operator, which will be termed a "host network", he has to write to the home network operator to obtain a roaming registration. If this is granted the home network operator provides a long codeword containing a LID, OPSIC, PIN and Account Number which has to be entered by a user into the non-volatile memory. Thus when using the secondary station, the user has to determine which of these two registrations he wishes to operate through allowing for the fact that the host network may be more costly to use than the home network. In certain situations the user may have to trade-off the prospect of extra cost against the fact that there are no home primary stations accessible because they are busy or not in range and furthermore he is able to access an overall network which may be twice the size of the respective home and host networks. However it is felt that the formalities of obtaining another registration from the home network operator, entering the long codeword in a secondary station and selecting one of the two (or more) registrations acts as a disincentive to obtaining a roaming registration which in turn means that the best use is not being made of the entire CT2 system. DISCLOSURE OF INVENTION

It is an object of the present invention to make cordless telephone systems more user friendly.

According to a first aspect of the present invention there is provided a method of operating a cordless telephone system comprising at least two network operators, each network operator controlling a network comprising a plurality of primary stations and at least one administration centre coupled to the primary stations, each network operator having a link identification code (LID), wherein each primary station comprises radio transceiving means enabling it to communicate with an in-range secondary station on any one of a plurality of channels, the secondary station when initiating a call request transmits a predetermined LID, characterised in that when a primary station, on scanning the available channels, receives a call request having a LID which it recognises as being that of a roaming secondary station delays responding to the call request until after a predetermined condition has been met.

According to a second aspect of the present invention there is provided a cordless telephone system comprising at least two network operators, each network operator controlling a network comprising a plurality of primary stations and at least one administration centre coupled to the primary stations, each network operator having a link identification code (LID), each primary station comprising radio transceiving means enabling it to communicate with an in-range secondary station on any one of a plurality of channels, the secondary station when initiating a call request transmits a predetermined LID, characterised in that a primary station includes control means which, in response to the primary station receiving a LID which it recognises as being that of a roaming secondary station, delays responding to the call request until after a predetermined condition has been met.

The predetermined conditions may be a predetermined time delay or detection of a predetermined number of call requests on one or more channels.

By means of the method and system in accordance with the present invention, the cordless telephone system becomes more user friendly. This is because a user wishing to make a call does not have himself to pre-register with one or more host systems because the network operators have pre-arranged to handle call requests from each other's networks although the bias is for the home network to handle the call request by causing the host network's primary stations to wait before responding.

The pre-arrangements may include an agreement to share authorisation procedures but if this is not done then it may be necessary for a host primary station to contact its host administration centre which in turn would have to contact the home administration centre which carries out the authentication and authorisation. In the case of sharing authorisations then this may be

the host primary station or administration centre, which process is much quicker than referring to the home administration centre or primary station.

Optionally the respective network operators may agree on LIDS which are recognised by two or more network operators as surrogate home LIDs.

According to a third aspect of the present invention there is provided a secondary station for use in a cordless telephone system in accordance with the second aspect of the present invention, the secondary station comprising storage means for storing a link identification code (LID) which is recognisable by a host network operator as a surrogate home LID. BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, wherein

Figure 1 is a block schematic diagram of a cordless telephone system comprising two networks,

Figure 2 is a flow chart for implementing the method in accordance with the present invention, and

Figure 3 is a block schematic diagram of a secondary station. MODE FOR CARRYING OUT THE INVENTION

The illustrated cordless telephone system comprises two networks each of which comprises an administration centre AD1, AD2, respectively, coupled by links, for example land line links, to fixedly sited primary stations PS1A,PS1B and PS2A,PS2B, respectively. Each primary station comprises radio transceiving means enabling it to communicate with secondary stations SS which also contain radio transceiving means and also a connection to the PSTN. Six secondary stations are illustrated and for convenience of description it will be assumed that the stations SS1A,SS1B and SSIC are registered with the network operator based on administration centre AD1 and the stations SS2A,SS2B and SS2C are registered with the network operator based on administration centre AD2.

As mentioned in t tr-preamble, a secondary station wishing to initiate a call seeks a channel and if successful it then transmits a codeword containing LID, OPSIC, PIN and its Account Number. If a secondary station, such as SS1A, is within range, that is typically within 100 and 200m, of its home primary station PS1A, then the request will be handled by way of that primary station. However if a secondary station such as SSIB has roamed out of range of its home primary stations PS1A and PS1B, then when it initiates a call request it does not receive a response from its home system. However the request is picked-up by primary station PS2B but because the LID does not correspond to that used by its network, it refrains from replying immediately. However, in accordance with the present invention, it will wait for a specified time or specified number of channel scans and if the call request is still being repeated the primary station PS2B is enabled to compare the LID with one or more other LIDs. If it corresponds to a LID of a network which by prearrangement the operators have agreed to handle calls from secondary stations registered with each others networks, then the call request is authorised by one or other of the following methods: firstly in the host primary station which in this example will be PS2B, secondly in the host administration centre AD2 or thirdly in the home administration centre AD1. Whichever method is used is dependent on the arrangements between the operators. However an increasing time penalty is incurred the greater the number of stages which are involved. Assuming that the secondary station's details are acceptable then the remainder of the call set up procedure is completed by way of the primary station PS2B which is acting as a host primary station. As far as the user is concerned he is unaware of the fact that his call is being routed through a host primary station because the transaction is transparent to him.

The operations described are summarised by the flow chart shown in Figure 2. Block 10 indicates receiving a call request on one of the channels allocated for cordless telephony. Decision block 12 checks whether the LID is that of the home network. If it is a home LID (Y) then the call request is processed as normal, block 14. If the answer is negative (N), a decision block 16 asks whether or not the LID is that of pre-arranged roamer. If the answer is negative (N) then the flow chart reverts to the block 10. If the LID is a pre-arranged roamer" (Y) then the primary station waits for a predetermined time or number of channel scans, block 18, and then checks if the call request is still present, decision block 20. If the answer is negative (N) then the flow chart reverts to the block 10. If the answer is yes (Y), then the call request is processed in the same manner as if it had a home LID, block 14. Such processing is transparent to the user.

Optionally if an additional call charge is involved then the host primary station can relay this to the calling secondary station and obtain confirmation that the call can still go ahead.

The method by which an authorisation check is made is confidential to the network operator. However in order to enable a primary station to act efficiently as a host, the host primary station and/or administration centre may be provided with details of how the other network operator carries out its own authorisation check. The alternative, which will take up time is for the host administration centre to relay details of the secondary station to its home administration centre for verification. In the case of a home and a host primary station being next to each other, the time delay incurred before the host primary station responds should enable the home primary station to handle the call request.

Figure 3 is a block schematic diagram of a secondary station SS suitable for use in the method and system in accordance with the present invention. The secondary station SS comprises a transmitter ^"24 connected to an antenna 26 which is also connected to a receiver 28. A demultiplexer 30 is included in the received signal circuit to separate a digitised speech signal from other data signals.

A microphone 31 is connected to a CODEC 32 which includes storage for the digitised speech. The CODEC 32 operates in accordance with CCITT recommendation G721 (1988) for 32 Kbit ADPCM (Adaptive Differential Pulse Code Modulation) . The CODEC 32 is connected to a data compressor/expander 34 which compresses the digitised speech into bursts suitable for transmission over a time division duplex channel. A control element 35 is provided which controls the operation and internal organisation of the secondary station and which has a store 36 connected to it for storing amongst other things its LID(s), OPSIC, PIN, Account Number and details of the usage and quality of all the time ,. division duplex channels. At the occurrence of a reverse time slot or physical channel in the best available duplex voice channel, a burst of compressed digitised speech is relayed by way of a change-over switch 33 to the transmitter 24 whose frequency channel has been predetermined by the control element 35 applying

10 control signals to a local oscillator 25.

Received digitised speech in a forward time slot or physical channel is relayed by way of a change-over switch 37 to the data compressor/ex ander 34 in which it is expanded to digitised speech having the required data rate and passed to the CODEC 5 32, the analogue speech is then relayed to a loudspeaker or other audio transducer 38.

A keypad 40 is connected to the control element 35, for keying-in data such as a called party's telephone number. The control element 35 causes the keyed-in data to be displayed on a o display device 42. The control element 35 also adds the necessary signalling to the keyed-in data which is conveyed by way of a change-over switch 44 to the transmitter 24.

The switches 33, 37 and 44 are controlled by the control element 35. If a secondary station SS wishes to "converse" with a primary station the control element 35 causes a data message to be generated and be sent to a MODEM 46 by way of a switch 44. A modulated output from the MODEM 46 is supplied to the transmitter 24 by way of the switch 33. The transmitter 24 transmits the signal on the reverse physical channel of a duplex voice chan el. A response from a primary station is routed to the control element 35 by way of the receiver 28 and demultiplexer 30.

The remainder of the message exchange takes place under the direction of the control element 35. Although the present invention has been described with reference to CT2, it can be applied to any other suitable cordless telephone systems such as DECT or cellular telephone systems such as GSM.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the design, manufacture and use of cordless telephone systems and devices and component parts thereof and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom. INDUSTRIAL APPLICABILITY ^'

The present invention is applicable to cordless and cellular telephone systems and secondary stations therefor.

Claims

1. A method of operating a cordless telephone system comprising at least two network operators, each network operator controlling a network comprising a plurality of primary stations and at least one administration centre coupled to the primary b stations, each network operator having a link identification code (LID), wherein each primary station comprises radio transceiving means enabling it to communicate with an in—range secondary station on any one of a plurality of channels, the secondary 0 station when initiating a call request transmits a predetermined LID, characterised in that when a primary station, on scanning the available channels, receives a call request having a LID which it recognises as being that of a roaming secondary station delays responding to the call request until after a predetermined condition has been met.

2. A method as claimed in claim 1, characterised in that a primary station and/or an administration centre is able to verify the authorisation of a secondary station having a LID belonging to a roaming secondary station.

3. A method as claimed in claim 1, characterised in that a secondary station has at least two LIDs, one of said two LIDs being that of the home network operator and the other of the two LIDs being recognisable by a host network operator as a surrogate home LID.

4. A method as claimed in claim 1, characterised in that the predetermined condition is a predetermined time delay or a predetermined number of call requests on one or more channels.

5. A cordless telephone system comprising at least two network operators, each network operator controlling a network comprising a plurality of primary stations and at least one administration centre coupled to the primary stations, each network operator having a link identification code (LID), each primary station comprising radio transceiving means enabling it to communicate with an in—range secondary station on any one of a plurality of channels, the secondary station when initiating a call request transmits a predetermined LID, characterised in that a primary station includes control means which, in response to the primary station receiving a LID which it recognises as being that of a roaming secondary station, delays responding to the call request until after a predetermined condition has been met.

6. A system as claimed in claim 5, characterised in that a base station and/or an administration centre comprises means for verifying the authorisation of a secondary station having a LID belonging to a roaming secondary station.

7. A system as claimed in claim 5, characterised in that at least one secondary station has storage means for storing at least two LIDs, in that one of the two LIDs is that of the home network operator and in that the other of the two LIDs is recognisable by a host network operator as a surrogate home LID.

8. A secondary station for use in a cordless telephone system as claimed in claim 5, comprising storage means for storing a link identification code (LID) which is recognisable by a host network operator as a surrogate home LID.

9. A secondary station as claimed in claim 8, characterised in that the storage means stores its own identity code (OPSIC), personal identification number (PIN) and Account Number.

10. A secondary station as claimed in claim 8, characterised in that there is provided transceiving means and control means for controlling the operation of the transceiving means and in that the storage means is coupled to or incorporated into the control means.