WO1999013659A1

WO1999013659A1 - Interface for connecting standard telephone set to radiotelephone system

Info

Publication number: WO1999013659A1
Application number: PCT/GB1998/002646
Authority: WO
Inventors: Edward P. Morton; Helen Marlow
Original assignee: Telefonaktiebolaget L M Ericsson
Priority date: 1997-09-05
Filing date: 1998-09-03
Publication date: 1999-03-18
Also published as: GB2329095A; CN1269948A; AU8878998A; GB9718938D0

Abstract

An interface unit is described, allowing a standard DTMF telephone set to be connected to a cellular or satellite radiotelephone system. The unit is able to monitor the duration of each DTMF tone sent thereto, and a call is initiated when the duration of one tone exceeds a predetermined duration.

Description

INTERFACE FOR CONNECTING STANDARD TELEPHONE SET TO RADIOTELEPHONE SYSTEM

TECHNICAL FIELD OF THE INVENTION

This invention relates to a telecommunications device, and in particular to a device which allows a fixed subscriber to gain access to a cellular or satellite telephone system. More specifically, the invention relates to an interface unit for a satellite or cellular radio telephone system, which allows for the connection thereto of a standard telephone set. DESCRIPTION OF RELATED ART

US Patent No. 4,775,997 describes a system which allows a standard telephone set to be connected to a cellular-type transceiver, which can be used as a fixed station communicating with a network by wireless transmission. This has the advantage that it avoids the need to establish a fixed link to the transceiver from the network.

In order to make the provision of this service as transparent as possible to the user, the interfacing system of US Patent No. 4,775,997 allows for the connection thereto of a standard touch-tone or DTMF phone. A difficulty with this approach is that, to gain access to the network, a cellular transceiver must transmit the digits dialled by the user, together with a "SEND" signal. When the cellular transceiver is a dedicated mobile phone, this is achieved by pressing a dedicated "SEND" button on the phone. However, when the user has a standard telephone set, connected to a cellular transceiver through an interface system of the type described in US Patent No. 4,775,997, there is no such "SEND" button. Moreover, as mentioned above, it is desirable for the service to be as transparent as possible, and so it is desirable for the actions to be taken by the user to initiate the call to be as close as possible to the actions required when initiating a call through any other telephone system. In such a system, therefore, it is necessary to provide a mechanism for detecting when the user has finished dialling the number of the party which he wishes to call. In US Patent No. 4,775,997, this is done either by analyzing the first few digits of the dialled number to determine how many digits are expected, and then transmitting a "SEND" code after the requisite number of digits, or by transmitting the "SEND" code when a predetermined time elapses after the dialling of one digit.

However, this has the disadvantage that the predetermined time must be relatively long, since the normal interval between digits can be quite long, and so it introduces a delay into the process of initiating a call, while the predetermined time elapses.

W096/32824 describes another system of this general type, in which a "SEND" signal is transmitted when the user dials the "#" character.

However, this has the disadvantage that requires the user to dial a specific additional character, thus reducing the transparency of the system. SUMMARY OF THE INVENTION

This invention relates to an interface unit, which allows the standard telephone set to be connected to a radio telephone transceiver, and which allows the end of dialling to be detected in a way which minimises inconvenience to the user.

Specifically, the system is able to detect DTMF tones generated by a standard telephone set when a user dials the digits of the number to be called. The end of dialling is detected when the duration of one of the tones exceeds a predetermined time. This predetermined time may be relatively short, since the normal duration of a tone is short . This allows the act of placing a call using the system in accordance with the invention to be as close as possible to the act of placing a call using a telephone connected to an exchange through a fixed link.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a block schematic diagram of an interface unit in accordance with the invention.

Figure 2 is a flowchart showing a mode of operation of a unit in accordance with the invention. Figure 3 is a flowchart showing a second mode of operation of a unit in accordance with another aspect of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a telephone system including an interface unit 2 in accordance with the invention. The unit 2 includes a radio transceiver 4 which communicates with a network, such as a cellular or satellite radio telephone network, via an appropriate antenna 6. The transceiver is under the control of a micro controller and associated memory 8. The unit 2 further includes a subscriber line interface circuit

(SLIC) 10, which is also under the control of the micro controller 8, and to which a standard DTMF phone 12, or other DTMF generator, may be connected. A DTMF detector 14 monitors signals output from the SLIC 10 in response to dialled tones received thereby, and is connected to the micro controller 8. A tone generator 16, acting under the control of the micro controller 8, generates ringing and other tones for supply to the SLIC 10, for transmission to a user. The SLIC 10 is also connected to the radio transceiver 4 for audio communication.

Thus far, the form of the unit 2 is generally conventional, being known, for example, from US Patent No. 5,117,450 or W096/32824. Figure 2 is a flowchart which schematically represents a first method of operation of the unit in accordance with the invention, directed by the micro controller 8. The process starts in step 30, for example when it is detected that the user's phone has been taken off-hook. In step 31, signals received at the SLIC 10 are monitored, to determine whether a DTMF tone has been received. When the start of a tone is received, then, in step 32, the DTMF digit is recognised and, immediately, the end of dialling timer is started in step 33. The signal is then monitored in step 34, until the tone representing the digit ends. When the end of the digit is detected, the process passes to step 35, where it is determined whether the end of dialling timer has expired before the digit ended. If not, that is, if the DTMF tone lasted for a time shorter than a predetermined duration, the process passes to step 36, in which the end of dialling timer is stopped and reset, and then to step 37, in which the detected digit is stored in the memory associated with the micro controller 8, before returning to step 31. If, however, it is determined in step 35 that the end of dialling timer had expired before the DTMF tone ended, that is, the tone lasted for longer than the predetermined duration, the process passes to step 38, in which it is detected that dialling is deemed to have ended, and then, in step 39, a call is placed on the basis of the previously stored digits.

Thus, the micro controller sets a predetermined duration, which may, for example, be in the region of 1 second. If any key is held down for longer than this time, it is determined that dialling has ended, and the call is initiatec¹. Note that, in this example, the final digit, namely the digit whose tone lasted for longer than the predetermined duration, is not stored and does not form part of the dialled number. Figure 3 represents an alternative process, in which steps 30-39 correspond to those described above with reference to Figure 3. However, the process includes an additional step, step 40, in which, following the detection that dialling has ended in step 38, the finally detected digit is stored. The result is that the finally detected digit is amongst the digits used to initiate the call, and so forms part of the dialled number.

It will be apparent that this principle may be applied in ways other than those specifically described. For example, the state of the end of dialling timer may be monitored continuously so that, if a tone lasts for longer than the predetermined duration, the call can be initiated (either using or not using the finally detected digit) as soon as the timer expires, without waiting for the last tone to end. Moreover, although the invention is described herein with reference to its use in initiating a call, other alternative uses are possible. For example, while holding down one specified key for longer than the predetermined duration may initiate a call, as described above, holding down other specified keys for longer than the predetermined duration might perhaps access other services or functions, such as switching between speech and fax modes, number storage, or cnanging the ring configuration.

There is thus described a unit, and a method of operation thereof, which allows a subscriber to gain access to a satellite or cellular system from a standard DTMF telephone set in a way in which minimises the difference between such use and use of a standard telephone connected to a fixed network.

Claims

1. An interface unit, comprising means for connecting a telephone set thereto, and a radio transceiver, and further comprising means for detecting DTMF tones sent thereto and means for initiating a call when the end of dialling is detected, characterised in that the unit further comprises means for detecting a duration of each detected DTMF tone, and means for detecting the end of dialling when a detected DTMF tone has a duration exceeding a predetermined time.

2. An interface unit as claimed in claim 1, comprising means for storing digits corresponding to the detected DTMF tones, and means for initiating a call to a number defined by the stored digits when the end of dialling is detected.

3. An interface unit as claimed in claim 2, wherein the digit corresponding to the detected DTMF tone having a duration exceeding the predetermined time forms part of the dialled number.

4. An interface unit as claimed in claim 2, wherein the digit corresponding to the detected DTMF tone having a duration exceeding the predetermined time does not form part of the dialled number.

5. An interface unit, comprising means for connecting a telephone set thereto, and a radio transceiver, and further comprising means for detecting DTMF tones sent thereto, characterised in that the unit further comprises means for detecting a duration of each detected DTMF tone.

6. An interface unit as claimed in claim 5, comprising means for accessing a service when a detected DTMF tone has a duration exceeding a predetermined time.

7. An interface unit as claimed in claim 5, wherein a detected DTMF tone having a duration exceeding a predetermined time is used to access a particular function.

8. An interface unit as claimed in claim 7, wherein the predetermined time is approximately one second.

9. An interface unit as claimed in claim 7, wherein the function which is accessed depends on the DTMF tone which is detected.

10. A method of connecting a telephone call to a wireless network, the method comprising: detecting each digit dialled by a user on a DTMF telephone; storing each dialled digit; monitoring the duration of each dialled digit; and sending the stored dialled digits to the network when the duration of one dialled digit exceeds a predetermined time limit.

11. A method of accessing a telephony function in a wireless network, the method comprising: connecting a DTMF telephone to an interface unit; detecting in the interface unit keys pressed by a user; and accessing a service when it is detected that a key has been pressed for a time exceeding a predetermined time limit.

12. A method as claimed in claim 11, comprising monitoring the durations of DTMF tones received by the interface unit .