INSTALLATION FOR CONNECTION OF CORDLESS TELEPHONE SETS TO A SUBSCRIBER'S TELEPHONE EXCHANGE

Abstract: An installation for connection of cordless telephones to a subscriber's exchange (1) thus to create a cordless telephone system comprises stationary base stations (2a-5b) which are wire-connected to the exchange (1), and portable handsets (10-13). The base stations (2a-5b) and the handsets (10-13) consist of short-range radio transmitters and receivers. The cordless telephone system comprises an interconnection unit (14) which is in wire communication with the exchange (1) and which is arranged to detect a calling signal in the exchange (1) and to transfer said signal to a control unit (15). The latter cooperates with the base stations (2a-5b) and orders the latter to search for the handset (10-13) for which the call is intended. The base station (2a-5b) that finds the handset (10-13) in question is arranged to inform the control unit (15) accordingly and to simultaneously emit a cordless call to the handset (10-13). When an answer is received, communication with the subscriber's exchange (1) is sought and the exchange is arranged to then establish call communication between the calling subscriber and said base station (2a-5b).

Description: INSTALLATION FOR CONNECTION OF CORDLESS TELEPHONE SETS TO A SUBSCRIBER'S TELEPHONE EXCHANGE The subject invention concerns an installation for connection of cordless telephone sets to a subscriber's telephone exchange in order thus to create a cordless telephone system. This installation comprises base stations consisting of short range radio transmitters and radio receivers which are stationary units, and portable handsets, likewise consisting of short range radio transmitters and radio receivers. The base stations are wire-connected to the subscriber's telephone exchange. Installations of this kind are previously known from SE 8502319-0. They are intended to be used within a comparatively small area, such as within the precinct of a hospital, a factory or an office building and the operative range of the radio transmitters in the base stations as well as in the handsets is very restricted, amounting to only some 20-40 meters. The prior-art installation comprises a radio exchange the purpose of which is to establish connection between the subscriber's exchange and the base station that detects the best quality signal emitted from a selected, wanted handset. However, owing to the short operative range of the radio transmitter it sometimes happens, when a handset is being moved during a call in progress, that the signal from the transmitting base station to the handset becomes too weak for the call to be continued. Under these conditions, the radio exchange transfers the call to the one of several adjacent base stations that has the strongest signal. Thanks to the function of the radio exchange the limitation that would otherwise have afflicted the radio transmitters having a short operative range, is eliminated. One disadvantage found in an installation of the kind described is, however, the complicated nature of the radio exchange. The subject invention provides an installation wherein the wide range of possibilities inherent in a modern subscriber's telephone exchange to establish connection is utilized, whereby it becomes possible to construct the rest of the installation in more simple manner than has hitherto been possible. The characterizing features of the invention appear from the appended claims. The invention will be described in closer detail in the following with reference to the accompanying drawing, schematically illustrating an installation comprising a subscriber's exchange to which eight base stations are connected. A subscriber's exchange 1 in accordance with the embodiment illustrated in the drawing, is in wire communication with eight base stations 2a, 2b, 3a, 3b, 4a, 4b and 5a, 5b. These are stationary units, each one of which is capable of operating on one of several available speech channels at a time. The base stations 2a-5b form radio cells 6, 7, 8 and 9, respectively, corresponding to the range of coverage of the base stations 2a-5b. The number of base stations for each cell 6-9 may be chosen according to need. For the sake of simplicity, only one handset 10, 11, 12 and 13, respectively, is shown in each one of the radio cells 6-9. The installation also comprises an interconnection unit 14 which is in wire communication with the subscriber's exchange 1, and a control unit 15 in the form of a computer of uncomplicated structure, the function of which is to coordinate the activities of the base stations 2a-5b. In the following is assumed that an incoming call is received from an external or internal telephone 16 and that the selected subscriber's handset is handset 12. This subscriber is temporarily transferred from the exchange to the interconnection unit 14 and the incoming call thus is transferred to the cordless system. This function is one commonly existing in subscriber's telephone exchanges, particularly when they are interconnected with paging systems. The information on the identity of the wanted handset is transferred to the control unit 15. The latter orders one base station 2a-5b in each cell 6-9 to search for the wanted subscriber. In the example given base station 4a or 4b will find the handset 12 since the latter is located within radio cell 8. Base station 4a, for example, informs the control unit 15 that it has found the wanted sub¬ scriber and is allowed to connect the call since this station is the one that at that instance has the strongest signal. The base station 4a then puts a (cordless) call onto the handset 12. When an answer is received, the base station 4a emits a coded signal representing a "meet-me"- answer to the exchange 1. The latter then interconnects the telephone 16 and the handset 12. Another example of utilizing the exchange 1 is to make use of its ability to "register" calls. Assuming, for instance, that while a call is in progress the subscriber, carrying the handset 12, moves outside the area of radio cell 8 and into that of radio cell 9. The strength of the signal between the handset 12 and the base station 4a then will be weakened. The base station informs the control unit 15 accordingly, with the result that the unit emits another search order in the manner described in the aforegoing to one base station 2a-5b in every one of cells 6-9. Either base station 5a or 5b is now able to establish contact with the handset 12. The control unit 15 therefore orders base station 4a to "transfer" the call to e.g. base station 5a and instructs the latter station to take over the call. Base station 5a then establishes call communication with the handset 12. Base station 4a then supplies the exchange 1 with a coded signal of call transfer to base station 5a and thereafter interrupts communication with the exchange 1 as well as with the handset 12. The exchange 1 emits a call to base station 5a. Upon receipt of an answer therefrom a switch-over is effected in the exchange 1, establishing call communication between the telephone 16 and the base station 5a, whereupon communication between the telephone 16 and the handset 12 is re-established. A call switch-over, or "hand over", can in the manner described be made for each handset 10-13 that is connected to the system as soon as the strength of the signal decreases below an acceptable value while a call is in progress. The invention has made it possible to utilize in an uncomplicated manner the possibilities offered by a modern subscriber's exchange 1 to transfer calls and form "meet-me" answers, thus also obviating the need for a radio exchange having a comparatively complicated structure. The installation is flexible in as much as it allows connection thereof to subscriber's exchanges of all dimensions. The system is not either limited to a pre¬ determined number of base stations or radio cells. The invention is not limited to the embodiment described and illustrated herein but a number of modifications are possible within the scope of the appended claims. Instead of temporary transferring a subscriber to the interconnection unit 14, the latter could be arranged to detect a ringing signal or other calling signal, for instance in the form of a digital cable (digital telephone). Also manually activated calls to the interconnection unit 14 may be made. The function of the control unit 15 could be integrated in the interconnection unit 14 or in one of the base stations 2a-5b.

Claims: CLAIMS 1. An installation for connection of cordless telephone sets to a subscriber's exchange (1) in order thus to create a cordless telephone system comprising base sta¬ tions (2a-5b) consisting of short range radio transmitters and radio receivers which are stationary units, and portable handsets (10-13), likewise consisting of short range radio transmitters and radio receivers, said base stations (2a - 5b) being in wire communication with the subscriber's telephone exchange (1), c h a r a c t e r ¬ i z e d in that the cordless telephone system comprises an interconnection unit (14) being in wire communication with the subscriber's exchange (1) and arranged to detect a calling signal in the subscriber's exchange (1) and to transfer said signal to a control unit (15), the latter being connected to the base stations (2a-5b) and arranged to cooperate with said stations in order to locate the handset (10-13) for which said call is intended, and in that the base station (2a-5b) that locates the wanted handset (10-13) is arranged to inform the control unit (15) accordingly and to simultaneously provide a cordless call in the handset (10-13) and, after having received an answer therefrom, to establish communication with the subscriber's exchange (1), the latter being arranged to then establish communication between the calling subscriber and said base station (2a-5b). 2. An installation as claimed in claim 1, c h a r a c¬ t e r i z e d in that each one of the base stations (2a- 5b) is arranged, upon deteriorated contact with a handset (10-13) during the duration of a call, to inform the control unit (15) accordingly, which unit is arranged to give a search order to all the other base stations (2a- 5b), and in that the station or stations of said base stations (2a-5b) that receives better contact with said handset (10-13) are arranged to inform said control unit (15) accordingly, said unit being arranged to then both order the first-mentioned base station (2a-5b) having the deteriorated contact to transfer the call and order the latter base station (2a-5b) having the best contact with the handset (10-13) to take over the call, and in that the base station (2a-5b) having the deteriorated contact is arranged to inform the exchange (1) of transfer of call and thereafter to interrupt its contact with the handset (10-13) as well as with the exchange (1), said exchange being arranged to then call said base station (2a-5b) having the best contact and upon receipt of an answer to effect the required switch of connection.

Inventors: WIKSTROEM RAGNAR, WIKSTROEM, RAGNAR
Applicants: TATECO AB
Application year: 1991
Main classification: H04Q7
IPC codes: H04W84