The present invention relates to a radiotelephone system having a plurality of sub units for a main unit.
Recently, digital radiotelephone systems have been widely used because of their enhanced convenience and reasonable prices. Among them, especially cordless and radiotelephone systems having a main unit and plural sub units and a limited communication area for office or home use have been spread.
A conventional digital radiotelephone system will be described referring to drawings. FIG. 8 is a block diagram showing the structure of a conventional digital radiotelephone, and FIG. 9 shows a format of a calling signal of the conventional digital radiotelephone.
In FIG. 8, numeral 1 denotes a telephone line of public network, numeral 2 is a keyboard for inputting telephone numbers and extension numbers, numeral 3 is a dial section for outputting a dial number to the telephone line 1, 4 is a receiver which is an output part of sound signals, 5 is a transmitter which is an input part of sound signals, 6 is a sound decoder for decoding digital signals to sound signals, 7 is a sound encoding unit for encoding sound signals to digital signals, 8 is a radio section consisting of a transmission circuit for converting the digital signals, to radio signals and a reception circuit for the reverse conversion, 9 is an antenna which is a transmission and reception part for radio signals, 10 is a controller for controlling the signals between each of the sections from the keyboard 2 to the antenna 9, 11 is a main unit comprising from the keyboard 2 to the controller 10.
Numeral 12 is a sub-unit keyboard for inputting a telephone numbers and extension numbers, numeral 13 is a sub unit receiver which is an output part of sound signals, 14 is a sub unit transmitter which is an input part of sound signals, 15 is a sub unit sound decoder for decoding digital signals to sound signals, 16 is a sub unit sound encoder for encoding sound signals to digital signals, 17 is a sub unit radio section consisting of a transmitting circuit for converting the digital signals to radio signals and a reception circuit for the reverse conversion, 18 is a sub unit antenna which is a transmission and reception part for radio signals, 19 is a sub unit controller for controlling the signals between each of the sections from the sub unit keyboard 12 to the sub unit antenna 18, 20 is a first sub unit comprising from a sub unit keyboard 12 to a sub unit controller 19. Numeral 21 is a first radiowave between the main unit 11 and the first sub unit 20. 22 is a second sub unit having the same constitution as of the first sub unit, and 23 is a second radiowave between the main unit 11 and the second sub unit 22.
The operation of the conventional digital radiotelephone system constituted as shown above will be illustrated.
When the first sub unit 20 makes private line communication with a second sub unit through the main unit 11, as shown in FIG. 8, the user of the first sub unit 20 of a call out side inputs first the extension number of the second sub unit 22 (12 in this conventional example). The sub unit controller 19 of the first sub unit 20 sends the call out request signal for requesting calling from the input extension number to the main unit 11, to the sub unit radio section 17, and the signal converted into radio signal in the sub unit radio section 17 is then sent to the sub unit antenna 18, and transmitted to the main unit 11 as the first radiowave 21.
The main unit 11 receives the first radiowave 21 through the antenna 9, and the radiowave is decoded to the call-out request signal at the radio section 8, then the controller 10 reads the extension number of the second sub unit 22 included in the call out request signal and sets the calling signal for calling the second sub unit 22, and after converted to a radio signal at the radio section 8, the calling signal is transmitted as the second radiowave 23 from the antenna 9 to the sub unit 22 as shown in FIG. 8.
The second sub unit 22 receives the second radiowave 23 through the sub unit antenna of the second sub unit 22 (the same structure and function as the sub unit antenna 18), and the radiowave is decoded to the calling signal at the sub unit radio section of the second sub unit 22 (the same structure and function as the sub unit radio section 17), then the sub unit controller of the second sub unit 22 (the same structure and function as the sub unit controller 19) judges if the extension number of the second sub unit 22 is included in the calling signal, and if the calling signal is included, a calling accept signal indicating the private communication is possible is converted into radio signal at the sub unit radio Section of the second sub unit 22 and sent from the sub unit antenna of the second sub unit 22 to the first sub unit 20 through the main unit 11 as the second radiowave 23 to make the private communication.
However, in the conventional constitution above, when the system has plural sub units for one main unit, only one extension number to be called can be set in a calling signal for calling from the main unit to sub units. Accordingly, each of the extension numbers have to be set and transmitted respectively for the calling from the main unit to a plurality of sub units or from one sub unit to plural sub units through the main unit at the same time.