GB2128452A

GB2128452A - Cordless telephone subset

Info

Publication number: GB2128452A
Application number: GB08326162A
Authority: GB
Inventors: Gunter Hofgen
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1982-09-30
Filing date: 1983-09-29
Publication date: 1984-04-26
Also published as: GB8326162D0; AU1992183A; GB2128452B; NZ205661A; DE3236194A1

Abstract

The subset consists of a stationary part and a movable part (1, 2), with the latter containing all operating controls. Signal transmission between the parts is effected by alternately transmitted (TDM) pulse groups which modulate a carrier frequency (F, F<+>). The carrier frequency is additionally swept with a constant sweep width. The sweep frequency (fi) (e.g. sawtooth wave) is adjustable, so that several telephone subsets can be operated at the same carrier frequency but with different sweep frequencies, within the same range of effectiveness. The operating controls on the part 2 include a dialling keyboard 21. <IMAGE>

Description

SPECIFICATION Cordless telephone subset The invention relates to a cordless telephone subset of the type having a stationary part without operator controls and a movable part with operator controls between which transmission is effected by alternately transmitted pulse groups which modulate a carrier frequency. Such a telephone subset is known from the article by E.

Braun and S. Schön, entitled "Ein schnurloses Intrarot-Telefon" as published on pages 24 to 27 of telecom report 3 (1 980), No. 1. As the carrier frequency-for this telephone there is used infrared light which transmits the digitalized signals by way of pulse-position modulation. The two-way transmission between the subscriber station and the receiver is effected on a carrier frequency which, according to the time-division multiplex transmission principle, is utilized by both equipment units.

It is the object of the invention to provide a telephone subset of the type mentioned hereinbefore which operates on a single carrier frequency which can also be used by neighboring telephone subsets, and which has a constant transmission quality throughout its effective operating range.

According to the present invention there is provided a cordless telephone subset comprising a stationary part without operating controls and a movable part provided with all the operating controls, between which the signal transmission is effected by means of alternately transmitted pulse groups which modulate a carrier frequency, characterized in that the carrier frequency is swept with a constant sweep width having an adjustable sweep frequency the pulse groups of both parts being preceded by the same identification signals.

The cordless telephone subset operates on one single carrier frequency which can also be in neighbouring telephone subsets without any interferences occurring therebetween. Owing to the broadband transmission employed, no disturbing variations of field intensity are caused by multipath effects.

The invention will now be explained in greater detail with reference to an embodiment shown in Figs. 1 to 4 of the accompanying drawings, in which: Fig. 1 shows a block diagram of a telephone subset employing one stationary and one movable part; Fig. 2 shows the two-way transmission as a function of time between the stationary and the movable part as shown in Fig. 1; Fig. 3 shows a block diagram of the transmitting/receiving units of the telephone subset as shown in Fig. 1, and Fig. 4 shows a diagram of the frequencymodulated carrier frequencies in the transient state.

Fig. 1, by way of block diagram, shows a telephone subset comprising a stationary part 1 and a movable part 2. The further telephone subsets of this type in a telephone system are of the same design and, therefore, not shown.

To the subscriber's line 3 there is connected an adapter 4 in which those component parts are accommodated which are required for adapting the stationary part 1 to the subscriber's line, such as the hookswitch, the dial-pulse contacts, etc.

The adapter 4 is followed by a coder-de-coder 5 (CODEC) and by an interface 6 which are both in connection with a (master) control M. This control M is connected via three lines 7, 8, 9 to a transmitting/receiving unit S/E to which, in turn, there is connected an antenna 10. The control effects the reconditioning of the incoming and outgoing signals including the temporary storing and idenfication checking, and controls the operations.

The movable part 2 comprises a receiver 11 and a microphone 1 2 which, via a coder-decoder 1 3 (CODEC) are connected to a (slave) control S.

To this control S there is also connected a ringer 14 and an operating control 15 and, via three lines 16, 17, 1 8, it is in connection with a transmittingreceiving unit S/E to which, in turn, an antenna 19 is connected. The operation of the control S is similarto that of the control M.

The ringing signal for establishing a connection with a telephone subset comprising the stationary part 1 and the movable part 2, as coming in on the subscriber's line 3 is forwarded by the adapter 3, via a line R, to the interface 6, by which this ringing signal is converted into a digital ringing signal which, from there, is adapted via the control M and the line 7 to the transmitting/receiving unit S/E. This transmitting/receiving unit S/E is modulated accordingly, and the resulting signal is radiated by the antenna 1 0. The antenna 1 9 picks up this signal and the transmitting/receiving unit S/E reconverts this signal and transmits it, via the line 18, to the control S which then actuates the ringer 14.

In substituting for the functioning of the hookswitch upon lifting the receiver, the user may now actuate a button 20 in the operating panel 1 5. Upon depressing the button 20, a corresponding signal (message) is transmitted to the stationary part 1 where it is received and fowarded by the control M to the interface 6, and from there, via a line 6, to the adapter 4, so that now the telephone connection is established between the calling subscriber and the user of the telephone subset.

Speech is now applied from the adapter 4 to the coder-decoder 5 where it is digitalized by employing a 32 kbit/s adaptive deltamodulation.

Via the control M and the line 7, the digitalized speech is applied to the transmitting/receiving unit S/E from where a corresponding signal is radiated via the antenna 10. The movable part 2 receives this signal with its antenna 19 and forwards it via the transmitting/receiving unit S/E and the line 18, to the control S and further to the coder-decoder 13, where the digitalized speech is reconverted into its analog form for being reproduced in the receiver 11.

The speech as received by the microphone 12 is transmitted in the opposite way to the subscriber's line 3 and then to the calling subscriber. At the end of the call, the user again actuates the button 20 in substituting for the hookswitch function when replacing the handset, so that finally, by the interface 6, via the line B, the adapter 4 is caused to effect the clearing of the subscriber's line 3.

The user of the telephone subset comprising the stationary part 1 and the movable part 2, when wishing to call another subscriber within the telephone system, has to actuate the button 20 and thereafter the corresponding keys of a dialling keyboard 21 as provided for in the operating panel 15. The further operations are then the same as those described hereinbefore, with the dialling signals being transmitted via a line W from the interface 6 to the adapter 4.

In order to achieve a two-way transmission on one carrier frequency, an alternating transmission according to the time-division multiplex transmission principle is provided for between the stationary part 1 and the movable part 2. For this purpose, the control M of the stationary part 1 includes a (not shown) clock generator with the aid of which there is formed the necessary data frame and the bit timing. The control S in the movable part 2 synchronizes itself to this data frame and the bit timing.

The alternating time slots of the time-division multiplex transmission are shown in Fig. 2. In the upper part above the time axzis t, there is shown the alternating transmission and receiving of the stationary part 1, designated S1 and El, and in the lower part there is shown the transmitting and receiving of the movable part 2, designated by S2 and E2 respectively. In each partial transmitting time slot S1 or S2 there is transmitted a data message consisting of 20 bits for the synchronization S, 20 bits for the identification K, 10 bits for the preamble P and 206 bits for the information content N. There is provided a protective period of time or guard space of 10 percent.In the case of the intended digitalization with 32 kbit/s there will then result for the data frame a period of time of 6.4 ms. This results in a transmission speed of 90 kbit/s between the stationary part 1 and the movable part 2. In the ready-to-operate state, the transmitting/receiving units S/E of the stationary part 1 and of the movable part 2 are only actuated for a short period of time in order to test the quality of the radio connection, so that in this way the current consumption can be reduced to a considerable extent. For this purpose, the stationary part 1, at intervals of 128 data frames = 81 9.2 ms, transmits a test message which is set up in the same way as a data message and, instead of the information content, contains a test code.In the case of a proper functioning of the movable part 2, the latter retransmits an acknowledge message which is set up in the same way as the test message and, instead of the information content, contains an acknowledge code. On the movable part, the ready-to-operate state can be indicated optically (not shown).

The mode of operation upon the first switching on or in the case of interferences will be explained hereinafter.

Fig. 3 shows block diagrams relating to the transmitting/receiving units S/E of the stationary part 1 and of the movable part 2. Both transmitting/receiving units are of identical design, so that only one is described herein. The following description applied to the case in which the stationary part is transmitting and the movable part is receiving.

In the transmitting unit there is contained a microwave oscillator 23 whose carrier frequency F amounts to 37 GHz, as well as an oscillator 24 for a sweep frequency fi ranging between 1 and 10 GHz and having a sawtooth shaped waveform.

Via the line 8, the oscillator 24 is capable of being adjusted by the control M, to different values. The sweep frequency fi modulates the carrier frequency F in its freqency with a sweep width of 1 50 GHz, thus producing the expanded carrier frequency to be transmitted which is modulated by the digitalized signals, that is, by the speech, the calls, etc. The output of the microwave oscillator 23 is connected to a terminal a of a switch 25, by which it, in the transmitting state, is connected to the antenna 10 connected to the terminal d thereof.

The aforementioned switch 25 comprises four terminals a to d between which, for example, diodes are arranged. By the control, these diodes are positioned in such a way that, in the transmitting state, the terminals ad and bc and, in the receiving state, the terminals ab and cd are each connected to one another. The switch 25 may alternatively consist of a magic-T.

The digitalized signals to be transmitted are applied, via the line 7, to the switch 25, thus controlling the connection between the terminals ad in such a way that an amplitude shift keying of the expanded carrier frequency F is effected.

Modulation may also be effected by frequency shift keying. In the course of this, the oscillator 24 is switched, by the digitalized signals to be transmitted, between two values of the sweep frequency, which effect the expansion of the carrier frequency. In the receiving unit there will then have to be provided a corresponding detector circuit for recovering the transmitted signals.

In the receiving section, a mixer M is connected with its one input to the terminal c and with its other input for the mixer oscillator, to the terminal b. In this way, the receiving state, the antenna 10 is connected to the one input and the microwave oscillator connected to the one input and the microwave oscillator 24 acting as the mixer oscillator, is connected to the other input of the mixture M. The intermediate frequency ZF as produced by the mixer M, is applied via a bandpass filter 26 and amplifier 27, to a demodulator 28 by which the demodulated signal is applied to the line 1 8.

The bandpass filter 26 has a centre frequency which corresponds to the sweep width of the frequency modulation of the carrier frequency, and accordingly, amounts to 1 50 MHz. The bandwidth ranges about 10 and 1 5 MHz. The correlation of the carrier frequency F+ as produced in the microwave oscillator 23, and which is used as the mixer frequency, with the carrier frequency F as received from the stationary part 1, requires a frequency locked loop. This frequency locked loop consists of a discriminator 29 and of a controller Ri having an integral behaviour.The discriminator 29 is connected to the output of the amplifier 27 and, in the event of a deviation from the centre frequency of the carrier, transmits a corresponding signal to the subsequently arranged controller Ri which controls the oscillator 24 in such a way as to effect a correlation between the carrier frequencies F and F+ and, in the transient state, a time shift of half a period. Relative thereto, the frequency difference between the carrier frequencies F and F+ equals the sweep width, hence amounts to 1 50 MHz. The frequency locked loop is so simple and reliable in operation, because the sweep frequency fi has a sawtooth shaped waveform.

In the transmitting/receiving unit S/E of the movable part 2, owing to the same type of construction, identical parts are indicated by the same references; merely the carrier frequency is designated F+. The transmitting/receiving unit of the stationary part 1 is shown to be in the transmitting state, and the transmitting/receiving unit of the movable part 2 is shown to be in the receiving state.

Fig. 4 shows the frequency-modulated carrier frequencies F and F+ as a function of time in the transient state of the frequency locked loop. From the half a period time shift between the carrier frequencies F and F+ as adjusted by the controller Ri, there results the difference of 1 50 MHz which is equal to the sweep width of the frequency modulation. From this it also results that the intermediate frequency ZF as provided by the mixer M, equals 1 50 MHz.

In the respective stationary part and the associated movable part, for expanding the employed carrier frequency F or F+, there is respectively always used the same sweep frequency fi. In the case of neighbouring telephone subsets, there are used different sweep frequencies fi, so that simultaneous operation in the case of overlaping supply areas is possible without any mutuai interference, with the areas being separated from one another. The respective sweep frequency fi is adjusted by the control M or S, via a corresponding instruction transmitted over the line 8 or 1 7 to the respective oscillator 24.

At the first switching on of the telephone subset comprising the stationary part 1 and the movable part 2, it may happen that the sweep frequencies fi thereof are not in agreement.

In such a case, the stationary part 1 in response to its transmitted test message, receives no acknowledge message, and the receiving unit of the movable part 2 remains continuously switched on, because the time position of the arrival of messages from the stationary part 1 is still unknown. In the stationary part 1, the absence of acknowledge messages causes an automatic stepping on to another sweep frequency fi. Then again a test message is transmitted. This searching process is continued until there is found the sweep frequency fi which is in agreement with that of the movable part 2. After that, both the stationary part 1 and the movable part 2 assume the ready-to-operate state already described hereinbefore.

When a movable part is entered into the range of effectiveness of another stationary part and, by chance, is also adjusted to the sweep frequency thereof, it can erroneously synchronize itself to this particular sweep frequency. The control thereof, however, recognises that the identification code is not in agreement with its own identification code, so that stepping on to another sweep frequency fi is initiated. The movable part remains at this sweep frequency.

Since now the stationary part associated with the movable part no longer receives an acknowledge message it must, in turn, again search for the sweep frequencyfi of the movable part. This is effected by the functions described under "first switching on" hereinbefore.

It may also happen that the stationary part is disturbed by a movable part which belongs to another stationary part and is adjusted to the same sweep frequency. In such a case it transmits an instruction to its movable part for switching over to another sweep frequency, and is adjusted thereafter to this new sweep frequency.

in cases where the movable part is moved too far out of the range of effectiveness of its stationary part, the connection is interrupted and a corresponding signal (not shown) is displayed on the movable part. The stationary part now searches the sweep frequencies fi one at a time in turn. After a certain number of search processes have been carried out, the stationary part disconnects itself for a predetermined period of time. After the lapse of this period of time, the search process is repeated.

This cycle is repeated until the connection with the movable part can be re-established.

In the operating panel 1 5 there is provided a button 22 (Fig. 1), upon actuation of which the movable part is switched to a different sweep frequency. In the associated stationary part, this switching effects the automatic readjustment to the new sweep frequency. This function has been provided for in order to be able to improve the quality of the connection in the case of a deteriorating connection, by selecting a new sweep frequency.

The receiver rest and the power supply are not shown in the drawings. For these, there are various ways of realization, which, however, are not germane to the subject matter of the invention.

Claims

1. A cordless telephone subset comprising a stationary part without operating controls and a movable part provided with all the operating controls, between which the signal transmission is effected by means of alternately transmitted pulse groups which modulate a carrier frequency, characterized in that the carrier frequency is swept with a constant sweep width having an adjustable sweep frequency the pulse groups of both parts being preceded by the same identification signals.

2. A telephone subset as claimed in claim 1, in which said sweep frequency is the same in both said stationary and said movable parts.

3. A telephone subset as claimed in claim 1 or 2, in which said swept carrier frequency is amplitude keyed by said pulse groups.

4. A telephone subset as claimed in claim 1 or 2, in which two sweep frequencies are provided, between which switching is effected by said pulse groups.

5. A telephone subset as claimed in any preceding claim, in which said sweep frequency has a sawtooth shaped waveform.

6. A telephone subset as claimed in claim 2, in which in both said stationary and said movable parts the receivers operate on the superheterodyne principle, and in which the respective receivers are each provided with a frequency locked loop consisting of a discriminator and of a controller having an integrating behaviour.

7. A telephone subset as claimed in claim 6, in which the difference frequency between the received and the locally generated carrier frequency, in the transient state of the frequency locked loop, is equal to the sweep width, and the intermediate frequency is generated in the receiver has the same value.

8. A telephone subset as claimed in any preceding claims, in which said sweep frequency of said stationary part automatically adjusts itself to the sweep frequency of said movable part.

9. A telephone subset as claimed in any preceding claim, in which in said movable part, upon reception of a signal having an extraneous identification, there is automatically effected a switching over to another sweep frequency.

10. A telephone subset as claimed in any one of claims 1-8 in which said movable part switching over to another sweep frequency is capable of being carried out manually.

11. A telephone subset as claimed in any one of the preceding claims, in which in the ready-tooperate state, for the purpose of reducing the current consumption, the osciliators for the carrier frequencies are repeatedly only switched on for short periods of time, in the course of which a test signal is transmitted by said stationary part and, as a reply, an acknowledge signal is transmitted by said movable part.

12. A telephone subset as claimed in any one of the preceding claims, in which said carrier frequency is in the microwave range at approximately 37 GHz.

13. A telephone subset substantially as described with reference to the accompanying drawings.