MOBILE CORDLESS TELEPHONE SYSTEMS

Abstract: In a mobile cordless telephone system of the kind in which a handset (4) is linked to a public switched network system (6) by a radio link via a local base station (3) connected to the network, each handset (4) has a unique calling code. The system includes a call diversion switch (1) in a line connection between a base station (3) and network (6), and in operation the set (4) of a handset user registers with the call diversion switch (1) the presence of the handset (4) to the most appropriate adjacent base station (3) by sending a signal over a first channel to the base station (3) announcing its presence and the base station (3) registers this information to the call diversion switch (1) which checks within the network (6) against the handset user's unique calling code, creates a personal identification and communicates this to the base station (3).

Description: MOBILE CORDLESS TELEPHONE SYSTEMS This invention relates to a mobile cordless telephone system of the kind in which a handset is linked to the public switched network system by radio link via a local base station. The local base station is connected to the network and each handset has a unique calling code. One particular form of mobile cordless telephone system is that known under the trade name "Telepoint" in which the base stations are located at various sites such as Railway Stations, Airports, Office and Housing blocks. Anybody with a personal handset within the range of a base station can then set up a call into the public network system and these people can also receive a call within that range. In order to be able to receive a call on the mobile handset it is necessary for the handset to advise the base, station of its presence. It has previously been proposed that this is done by the handset regularly emitting when it is switched on a location signal which is scanned over a number of channels and proposals have been made to select certain of these channels or to group the channels for scanning purposes. When a call is directed to a particular handset then the location of the handset is determined by picking up one of the channels from the handset which is free and making a connection over that channel. It is an object of the invention to provide a way of identifying the location of a handset and enabling the message to be transferred to it or from it as required. In accordance with the present invention there is provided a mobile cordless telephone system of the kind in which a handset is linked to a public switched network system by a radio link via a local base station connected to the network, and in which each handset has a unique calling code, which system includes call diversion switch means between a base station and the network and which in operation includes the set of a handset user, registering the presence of the handset to the most appropriate adjacent base station with the switch means by sending a signal from the handset over a first channel to the base station announcing its presence and the base station registering this information with the call diversion switch means which checks within the network against the handset users unique calling code and creates a personal identification code and communicates this to the base station. The call diversion switch means may include voice mail facilities which can transmit messages which are waiting to the handset user. In order that the invention may be fully understood the basic principles thereof will now be described by way of example only with reference to the two figures of the accompanying drawing in which Figure 1 is a schematic diagram showing the principle features of the invention and Figure 2 is a modification thereof. Referring first to Figure 1 this shows an example of the basic architecture of the invention using a separate switch for ease of explanation. Every handset user who subscribes to the two way service has a personal telephone number which normally routes calls to a call diversion switch 1 (CDS). This switch may have Voice Mail and/or paging services normally connected to the personal number. A key feature of this switch 1 is the ability to access it by inputting the subscriber's personal number and, after the exchange of suitable security passwords if required, input a new telephone number to which all subsequent calls will then be diverted. A Management System 2 (MS 2) is essentially the same as that used for existing 'Telepoint' systems. The significant addition is that each users personal telephone number in the CDS 1 will be recorded against their portable handset unique identification. A local Base Station 3 in this example will permit the registration of one Handset Unique Identification against each network line number at a time. In addition it will be capable of calling the CDS 1. Location registration will only be held for controlled periods whilst the handset is within range. A handset 4 connects with the Base Station 3 by a suitable radio link and a normal 'phone 5 is directly linked to the public network 6 and via that to the switch 1. In operation a handset user with handset 4 uses a manual location registration procedure to alert the Base Station 3 to his presence and desire to receive incoming calls. The Location Registration will cause the base station 3 to make a registration call to the MS 2 with an additional indication that this relates to Two Way calling. When the MS 2 provides the registration response to the Base Station 3 it will, from the record it holds against the portable handset unique identification, include the Handset user's Personal number and any password in the response. This may need to be subject to some form of security coding or it could alternatively be input as part of the location registration procedure at the base station 3. Once the registration call has been released the base station 3 will call the CDS 1 using the Personal number and password supplied by the MS 2. At this stage, if voice mail facilities are provided in the CDS 1, the handset user may be alerted to any waiting messages. The base station 3 will then use the network number of the line on which it is calling to invoke the call diversion service and then release the call. At this stage it should be noted that two calls have been used to invoke Location registration, these calls may be charged to the person invoking the two way service with Call Details created in the Base Station. A person using phone 5 wishing to reach a subscriber's handset 4 will dial the personal number of the handset 4. This will route the call via the Public Switched Telephone Network (PSTN) 6 to the CDS 1. The CDS 1 will on recognising an incoming call to a called number obtain the called number and activate a call diversion to a base station. If the handset location has been registered as above the CDS 1 will make an outgoing call to the base station 3 using the network line number that the base station provided on location registration. The CDS 1 does not need to answer the call at this stage. When the base station 3 receives the incoming call it will use the one handset unique identification registered against that line to call the relevant handset 4. Since no other information needs to pass between the CDS 1 and the Base Station 3 at this stage the call is not answered. When the Handset 4 user does answer the CDS 1 will also answer the original call from the calling party 5. This latter leg is now charged to the calling party 5 by the network as the calling party expects. The leg of the call from the CDS 1 will be charged to the CDS 1, however a call record may also be generated in the Base Station 3 for subsequent download to the Telepoint MS 2. Unsuccessful calls (e.g. No answer, unable to locate handset etc) may also be answered after a suitable time-out at the CDS 1 and the calls diverted to an announcement or voice messaging system. The leg of the call from the CDS 1 to the base station 3 will be cleared and no charge incurred by either party. De-registration of location at the Base Station 3 may occur due to one or more of the following:- i) Manual De-Registration of location. ii) Failure of a predetermined number of attempts by the base station to verify the presence of the handset by non-call related establishments. iii) Unable to alert handset on incoming call attempts(s). iv) Expiry of a timer in the Base Station. The handset user 4 may be altered and given the opportunity to re-register shortly before the expiry of iv). In the event of i) or ii) above a call will be made to the CDS 1 to de-activate the call diversion. The cost of this call would be included in the charge for activation of the Two Way service. Incoming callers would then revert to voice mail etc. To economise on the number of calls to the MS 2, the base station 3 will not overwrite the information against a network line unless it is required for another user. Lines are allocated in rotation. If the base station 3 already has the personal number associated with a handset unique identification it can re-invoke diversion at the CDS 1 without referring to the MS 2 again. De-registration of location (i.e. removal of the call diversion) at the CDS 1 may occur due to one or more of the following:- v) Receipt of a De-Registration message from the Base Station 3 as described above. vi) Unable to alert handset 4 on incoming call attempt(s). vii) Expiry of a time-out approximately the same value as iv) above. This will save the base station calling in to de-register. viii) A Location registration call being received from another base station. This acts as a new location registration. It should be noted that there is no need to inform the original base station in case viii) since no calls will reach it and the internal timer or failure to set up a registration will ensure de-registration. The basic principle described above is subject to a number of variations. Some of these are discussed below:- The proposal set out in relation to Figure 1 uses a separate CDS switch. If the network supported a call diversion service then no separate switch is required and the personal number could be, for example, the Handset users normal fixed network telephone number. In this case Location De-registration would be totally dependent on the Base Station since the Network would not provide the necessary covering timeouts. Alterations for a large site e.g. Shopping Mall, Marina, Exhibition Centre or a Business Park, the base station may take the form of a Switch with Telepoint facilities added. Access from the network to this type of base station would be using call diversion from the Network. Once again each handset registered at this location would be associated with a unique telephone number and therefore effectively with a network line number. This number would be used for diversion at the CDS 1 as before and the proposal is thus fully compatible. This demonstrates the principle that it is the network number of the base station line with which the Handset has its location registered that is used for diversion (equivalent to the roaming number in cellular networks) thus providing a flexible approach to the configuration of the Network. In this variation of the architecture it is possible for a Handset 4 to roam between base stations connected to the local switch without needing to re-register at the CDS. In call hand-over could also take place between individual base stations in such a group without affecting the network part of the call. This approach would also be valid for future generations of isolated Telepoint Base Stations incorporating call diversion thus permitting more handsets than the number of network lines to be registered at any one time. Where the CDS 1 comprises of an adjunct switch, or indeed several switches distributed in different locations depending on Traffic requirements, an alternative approach is to use data connected network links directly to the MS 2 as shown in Figure 2 to which reference is now made. The working of the System is now modified such that when the MS 2 receives the Authentication Request containing the Location Registration from the Base Station 3 it will communicate with the CDS 1 to establish the call diversion using the unique identification to personal number translation as before. When the MS 2 receives the acknowledgment from the CDS 1 it will then reply to the Base Station 3 to complete the registration sequence. Incoming calls then proceed as before. The advantages of this method are:- i) Only one network call required to establish location registration. ii) More secure communication and control of call diversion. iii) More economic CDS/MS communication. iv) Faster establishment of location registration as perceived by Handset user. The disadvantages are:- v) A new interface has to be defined between CDS and MS. vi) More development is required in MS and CDS. vii) The Application is not as universal as in Figure 1. viii) Collection of voice mail at location registration time requires an extra call. The system as described above uses manual location registration. It will work equally effectively with automatic methods. Such methods may employ a Beacon to indicate the location of a base station since unlike Cellular and DECT systems CT2 base stations used in 'Telepoint 1 only transmit when carrying traffic. Alternatively the Handset may "silently poll" for a base station. It will be seen from the above that the invention gives a cheap and effective way of registering the presence of a handset and enabling contact to be made swiftly with it without any particular development in the switch means being necessary. Existing voice mail systems can be used and no separate location register is necessary.

Claims: CLAIMS 1. A mobile cordless telephone system of the kind in which a handset is linked to a public switched network system by a radio link via a local base station connected to the network, and in which each handset has a unique calling code, which system includes call diversion switch means between a base station and the network and which in operation includes the set of a handset user, registering the presence of the handset to the most appropriate adjacent base station with the switch means by sending a signal from the handset over a first channel to the base station announcing its presence and the base station registering this information with the call division switch means, which checks within the network against the handset users unique calling code and creates a personal identification code and communicates this to the base station. 2. A system as claimed in Claim 1 wherein the call diversion switch means includes voice mail facilities which can transmit messages which are waiting to the handset user. 3. A system as claimed in Claim 1 or 2, wherein registration is retained for a predetermined period. 4. A system as claimed in any preceding claim wherein a call is established from a calling subscriber by routing the call to the call diversion switch, diverting the call to the appropriate base station and directing the call to the relevant handset.

Inventors: CRISP GRAHAM, RUSSEL-JONES PETER, STOWELL DAVID FREDERICK, CRISP, GRAHAM, RUSSEL-JONES, PETER, STOWELL, DAVID, FREDERICK
Applicants: CRISP GRAHAM, PLESSEY TELECOMM, RUSSEL JONES PETER, STOWELL DAVID FREDERICK, GPT LIMITED
Application year: 1993
Main classification: H04Q7
IPC codes: H04W4, H04W60