Telephone system comprising a satellite

(54) Title: Telephony system comprising a satellite

The invention relates to a telephony system comprising a satellite arranged to relay a number of one-way signaling channels and one-way voice transmission channels, which are later paired to two-way voice transmission channels, a number of ground stations each comprising a number of line equipment connected to each subscriber and each having an input a first output for signals indicating the state of the subscriber and a second output for outgoing voice signals and number information from the subscriber, a signaling equipment connected to said first output of said line equipment and arranged to send reports on the status of said subscribers and receiving commands for assignment of calling and called pages of said two-way voice transmission channels to calling and called subscribers, respectively, over said signaling channels, and a frequency converter equipment connected to said input and to said second output of said line equipment and arranged to connect said calling and calling subscribers to their assigned sides of said two-way voice transmission channels under the control of said commands; and a central control station in which other signaling equipment is arranged to receive said reports and send said commands and a control equipment is connected to said second signaling equipment and is arranged to generate said commands and address them to said ground stations.

In the publication INTELSAT / IEE Conference on Digital Satellite Communication,

No. 59, 1969, telephony systems are described which include a synchronous satellite and in which a number of ground stations are connected to wax · their transit stations and have been

7W5279-6 arranged its control computers to distribute a group of commonly used transmission channels between the ground stations in proportion to their changing needs for transmission capacity. The purpose of this so-called ΠΑ technology, where DA is an abbreviation of Demtmfl Assignment, is to provide efficient utilization of the synchronous satellite's limited number of transmission channels, whereby advantage can be gained, for example, of such traffic intensity variations between ground stations due to differences in local time. A number of transmission channels of so-called PA-type, where PA is short for Preassigned, are fixedly distributed between ground stations to provide them with the required transmission capacity for their average traffic so that the DA-type common-use transmission channels need only be utilized during traffic peaks.

An extension of a telephony system of the aforementioned kind to include also a number of simpler ground stations directly connected to subscribers offers a solution to the problem of providing telephone service to such sparsely populated areas where geographical conditions prevent the establishment of reliable ground connections.

The invention is primarily intended to enable a telephony system comprising a satellite and a number of ground stations connected directly to subscribers at a low total cost and, secondly, for the telephony system to behave from the subscribers seen as a conventional telephony system.

The invention, the features of which are set forth in the appended claims, will now be described in more detail with reference to the accompanying drawing, in which Fig. 1 shows the signaling and speech transmission paths in a telephone system according to the invention, Figs. 2 and 3 show signaling frames for signaling between a number of ground stations connected directly to subscribers. and a central control station of the telephony system of FIG. 1; and FIG. 4 and 5 shows block diagrams of the internal structure of the ground stations and control stations respectively.

FIG. 1 shows the signaling and voice transmission paths of a telephony system comprising a synchronous satellite not shown arranged to relay a number of one-way signal channels and one-way voice transmission channels which are later merged into two-way voice transmission channels, a number of low-traffic ground stations, each of which includes a number of terminals each comprising its subscriber and has an input for incoming voice signals, a first output for signals indicating the state of the subscriber and a second output for outgoing voice signals and number information from the subscriber, a signaling equipment connected to said first output of said line equipment and arranged to send reports on the status of said subscribers and to receive commands for assignment of calling and called pages of said two-way voice transmission channels to calling and called subscribers Over said signaling channels, and a frequency generating equipment connected to said, input and to said second output of said line equipment and arranged to connect said calling and calling subscribers to their assigned sides of said two-way voice transmission channels under the control of said commands, and a central control station 2 in which a second signal signals is in. 3 7405279-6 arranged to receive said reports and transmit said commands and a control equipment is connected to said second signaling equipment and is arranged to generate said commands and address them to said low traffic ground stations 1.

In the central control station 2 of Fig. 1, a number information decoding means is connected to a data input of said control equipment, and a frequency shelf equipment is arranged to connect the number information decoding means to said called sides of said two-way voice transmission channels.

In Fig. 1, furthermore, a small number of high-traffic ground stations 3 are connected to each of their transit stations in an extensive conventional telephone network and are connected to each other and to the central control station 2 partly via terrestrial connections and partly via the synchronous satellite. According to the example, the central control station 2 is also connected to a transit station in said telephone network. Among the synchronous satellite's two-way voice transmission channels, a first number whose transmission paths are symbolized by solid lines permanently distributed between ground stations 2 and 3 and a second number whose transmission paths are symbolized by dashed lines can be temporarily assigned to either of these ground stations the control station 2 in known manner as described, for example, in Swedish patent specification 354,557.

According to an example shown in Fig. 1, it is assumed that a. subscriber 4 raises a hand-held microphone from a telephone set equipped for tone dialing. The ground station 1 to which the subscriber 4 is connected transmits via a first signaling channel, whose transmission path is symbolized by a dotted line, a call state report, of the subscriber 4 to the central control station 2. This generates a command for assigning a currently available two-way voice transmission channel to the subscriber and transmits this command via a second signaling channel, whose transmission path is symbolized by a dash-dotted line, to the subscriber 4 ground station 1, whose frequency shelf equipment connects the subscriber 4 to a calling at the voice transmission channel one. At the same time, the central control station 2 frequency generating equipment connects said number information decoding means to a called side of the voice transmission channel to enable the transfer of number information of a called subscriber 5 from the subscriber 4 to the control station of the central control 2 via the signaling channel, whereby it is transmitted to the signal transfer channel.

The control equipment of the central control station 2 now designates, based on said number information, the ground station 1 to which the called subscriber is connected, generates a command for allocating said called side of the voice transmission channel to the called subscriber 5 and transmits this command via said audible signaling channel to the subscriber 5 ground station 1, whose frequency generating equipment connects subscriber 5 to said called side of the voice transmission channel. Thus, a call connection symbolized by a dashed line between the ahonants 4 and 5 is established which call connection will be monitored by the control equipment of the central control station 2 by periodically receiving reports.

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tt about the states of subscribers 4 and 5 broadcast from their respective ground stations 1.

It should be noted that the control station 2 only transits calls made over its own transit station. For example, a call connection established via the synchronous satellite between a calling subscriber having a grounded connection to a ground station 3 via a local station and a transit station and a called subscriber connected to a ground station 1, while the control station 2 is involved in the connection of the call connection but does not transit it.

Figures 2 and 3 show signaling frames for signaling between the ground stations 1 and the central control station 2 in Fig. I. According to the example, the · ground stations 1 are divided into 10 groups of the order of 100 ground stations each. In each group, the individual ground stations are assigned a common first signaling frame of 1000 ms in length and were their time slots within this according to line a in fig. 2 to transmit via a first 4 kHz signaling channel report word RW to the central control station 2 in the form of short pulse bursts. These pulse bursts contain, in an order shown on line b the same figure, information regarding carrier synchronization CR, bit synchronization BR, word synchronization UV, transmitting station T1, message type H and current message M, followed by a transmission-free interval G to prevent overlap between the pulse stations 1. minor errors in their time synchronization.

The division of ground stations 1 into groups assigned to each 1000 ms length signaling frames according to Fig. 2 means that an extension of the telephony system of Fig. 1 to include an increased number of ground stations 1 can be done simply by adding one or more similar signaling frames. according to the extent of the extension, whereby all signaling frames assigned to the ground stations 1 are transmitted within separate 4 kHz signaling channels.

The central control station 1 is assigned its own second signaling frame according to line a in Fig. 3 of the same length as said first signaling frame, 1000 ms, for transmitting via a second 4 kHz signaling channel both time and synchronization information in the form of a reference pulse burst RB and partly command CK as soon as they need to be generated to the ground stations 1. The control station 2 is further arranged to transmit in pauses arising between the command words CW a continuous synchronization information S, which is in the form of a bit pattern formed according to the example of alternating binary ones and zeros. When a command word CW is to be transmitted, the control station 2 is arranged to indicate this in advance through a temporary change S in the synchronization information S obtained most easily by a repetition of e.g. the number zero in said bit pattern.

The reference pulse cut RB contains, in a sequence shown in line b in Fig. 5, information regarding carrier synchronization CR, bit synchronization BR, word synchronization Ulf, transmitting station TI, addressed station ES, message type H and current message M. The information regarding addressed station ES can refer to all ground stations 1 as a selected group of them to enable the dispatch of a common command. The CW command word contains information about one

'.............' \ '......' 7405279-6 selectively addressed station ES, message type H and current message M.

The word synchronization information UW contains a word that is unique in the signaling frame of Fig. 3 and detected by the ground stations 1. A time signal is generated just when the detection is completed and utilized to cause the ground stations 1 and the pulse scours respectively to arrive at the transponders in the synchronous cell. the central control station within time slots whose time positions are fixed relative to the reference pulse burst time position.

The additional synchronization information S has the purpose of maintaining in the pauses between the reference pulse cut RB and the command word CW as accurate synchronization as possible in both the modem in the ground stations 1 and in the transponders of the synchronous satellite in the telephony system.

Fig. 4 shows a block diagram of the internal structure of one of the ground stations 1 in Fig. 1 and the connection to one subscriber 6 which according to the example has a telephone set equipped for tone dialing. A line equipment 7 having a two-wire connection to the subscriber 6 and comprising a fork connection of two matched transformers to provide a transition to a four-wire connection is provided with an input 8 for incoming voice signals, a first output 9 for signals indicating the subscriber 6 state, which information is obtained via a line relay in the line equipment 7, and a second output 10 for outgoing voice signals and number information from the subscriber 6. A transmitting signaling equipment 11 has an input 12 connected to said first output 9 of the line equipment 7 and is arranged to transmit said report word SW via a modem 13 and a receiving signaling equipment 14 is arranged to receive said command word CW via the same modem 13. In addition, a transmitting frequency interchange equipment 15 and a receiving frequency interchange equipment 16 are connected to said second output 10 and to said input 8 of the line equipment 7, respectively, and arranged to connect the subscriber 6 to the called or called sides of an assigned two-way voice transmission channel through the modem 13 via the modem CW.

A synchronization word detector 17 is connected to a first output 18 of the receiving signaling equipment 14 to detect the unique word Ulf in the signaling frame of Fig. 3 and generate said time signal in the form of a short pulse just when the detection is completed. The pulse is fed to an input of a flank triggered flip-flop 19 to adjust it, thereby activating an output gate 20 to feed high-frequency pulses from a crystal controlled pulse generator 21 to a counter 22.

The eu decoder 23 is connected to the counter 22 and is arranged to output an activation signal to an activation input 24 of the transmit signaling equipment 11 when the counter 22 has counted a suitable number of pulses from the pulse generator 21 to cause the reporter's RW pulse burst to arrive at the transponders the central control station 2 in FIG. 1 within a time slot whose time position is fixed relative to the time position of said reference pulse burst RB, taking into account also the transmission time from the current ground station 1. The activation signal from decoder 23 is also used to reset counter 22 and flip-flop 19.

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An off-circuit 25 * * in series' with an or-circuit 26 connected between two input registers 27 and 28 arranged for the transmitting frequency generating equipment 15 and the receiving frequency generating equipment 16, respectively, and a second output 29 of the receiving signaling equipment 14, the second output 29 being arranged for supplying a first control code to the input registers 27 and 28 obtained via said command word CW and indicating a called side of a two-way voice transmission channel assigned subscriber 6. An inhibition input of the and circuit 25 is connected to said first output 9 of the line equipment 7 to inhibit the frequency generating equipment 15 and 16 from being affected by said control code if the subscriber 6 is found to be busy, corresponding to a raised microphone state and a binary one signal on said inhiberingsingång. Through this arrangement, time is gained when connecting call intercepts, since ground station 1 reporting to the control station 2 about the state of the subscriber 6 can take place after the connection has been completed.

In addition, frequency generating equipments 15 and 16 input registers 27 and 28, respectively, are arranged to be supplied via the or circuit 26 and a third output 5θ is connected to the receiving signaling equipment 14 with a second control code obtained via said command word CW and indicating a calling side of a two-way voice transmission channel assigned. In this case, the command word CW is directly caused by the transmitting signaling equipment 11 having sensed via its input 12 which is connected to said first output 9 of the line equipment 7 that the subscriber 6 has switched from switched on to a lifting microphone state and then sent a message for call status for the subscriber 6 to the control station 2 via said report word EV.

The line equipment 7 is assigned to a control circuit 31 having a control input connected to said first output 9 of the line equipment 7 to be activated in the air-up state of the subscriber 6, a tone detector 52 having an input connected to said second output 10 of the line equipment 7 and a output arranged to output an output signal when said number information appears; a flank triggered flip-flop 55 having a one-position input connected to said third output 50 of the receiving signaling equipment 14 via and-circuit 51 and or-circuit 26 to be set by said second control code indicating a calling side of a two-way voice transmission channel assigned to the subscriber 6 and a zero-setting input connected to the output of the tone detector 32 to be reset by said number information, and a relay 34 having a control input connected to an output of the flip-flop 35 and arranged to connect a coupling tone voltage KT to said input 8 of the line equipment 7 when the flip-flop 35 is one-position. The arrangement has the purpose of breaking the dial tone to the subscriber 6 immediately when the number information occurs. If the switching of the number information would be known in a known way to its decoding which takes place in the control station 2, the switching tone would be broken only after a second.

The tone detector 52 contains two tone detecting circuits 55 and 56 which are tuned to. a first frequency band comprising 697-941 Hz and a second frequency band comprising 1209-1477 IIz, respectively, assigned said number information or connected in parallel between the input and output of the tone detector 52 via their respective threshold circuit₇ 7405279-6 and 38, respectively, and each input of one or circuit 39 · The output of the tone detector 32 is additionally connected to an actuation input 40 of the transmitting frequency converter equipment 15 to effect transmission from it only when said caller information or said output speech signals occur. Due to the fact that the tone detector 32 responds selectively to the number infoxmation and speech signals and is relatively insensitive to background noise, a saving in total instantaneous transmitter power on the voice transmission channels in the transponder frames of the synchronous satellite of the telephone system can be achieved.

The line equipment 7 is also assigned to a flip-flop 41 having a one-stall input connected to a fourth output 42 of the receiving signaling equipment 14 arranged to output a one-position signal to the flip-flop 41 obtained by said command word CW and representing the information that a subscriber called by the subscriber 6 is call, which information the control station 2 has received through said report word RW from the ground station 1 to which the called subscriber / -. is connected. A relay 43 has one. control input connected to an output of flip-flop 41 and arranged to connect a ringtone voltage RT to said input 8 of line equipment 7 when flip-flop 41 is one-position. A reset input of the flip-flop 41 is connected to a fifth output 44 of the receiving signaling equipment 14 arranged to output a reset signal to the flip-flop 41 obtained by the command word CW in response to the control station 2 having received a report from the ground station 1 to which the called subscriber is connected that he has responded.

A sixth output 45 of the receiving signaling equipment 14 supplies a flip-flop 46 with a one-position signal when said command word CW indicates that the control station 2 has received a report that the called subscriber is busy, a relay 47 having a control input connected to an output of flip-flop 46 supplies a busy tone voltage OUT to said input 8 of line equipment 7. When the subscriber 6 puts on his microphone, a binary zero signal is obtained on said first inlet 9 of the line equipment 7 which is inverted by an inversion circuit 48 to form a reset signal which is fed to a reset input of the flip-flop 46.

In addition, the one-position signal supplied to the flip-flop 46 from the sixth output 45 of the receiving signaling equipment 14 is supplied via an or-circuit 49 as a zero-setting signal to zero-inputs of the input registers 27 and 28 provided for the transmitting and receiving frequency image equipment 15, respectively. In addition, reset signal to the same input registers 27 and 28 is obtained from a seventh output 50 of the receiving signaling equipment 14, depending on said command word CW indicating that a call has ended. This command word CW is then directly caused by the transmitting signaling equipment 11 sensing that the calling subscriber 6 has applied to its microphone via its connection 12 to said preliminary output 9 of the line equipment 7 and then sent a report thereto to the control station 2.

If, instead, the subscriber 6 should be called and assigned to a called side of a two-way voice transmission channel via the control code from the second output 29 of the

7405279-6 receiving the signaling equipment 14, the same control code is used to set a flip-flop 51 via a control circuit 52 having a control input connected to said inverting circuit 48. A relay 53 having a control input connected to an output of flip-flop 51 supplies a ring voltage ES to said input 8 of the line equipment 7 because the flip-flop 51 is one-position. This has a reset input connected to the first output 9 of the line equipment 7 and is accordingly reset when the subscriber 6 raises his microphone.

Fig. 5 shows a block diagram of the internal structure of the control station of Fig. 1. This includes a modem 54, a transmitting signaling equipment 55 arranged to transmit the reference pulse burst EB, synchronization information S and command word CW via the modem 54, a receiving signaling equipment 56 arranged to receive said report word RW via the same modem 54, and a control equipment 57 containing a central unit CE , a program memory PM and a data memory DM and are connected to the transmitting and receiving signaling equipment 55 and 56, respectively, and are x-. arranged to generate the command word CW and selectively address them to the ground stations. 1st

In the control station 2, a telephone operator 58 at a switchboard 59 and a decoder 60 for said tone-coded number information are respectively connected to data input 6l and 62 of the control equipment 57. The decoder 60 is additionally connected to the switchboard 59 to provide a visual presentation of the telephone operator 58 there. decoded the number information. A receiving frequency forming equipment 65 is arranged to connect the telephone operator 58 at the switchboard 59 and the decoder 60 to called sides of two-way voice transmission channels assigned to calling subscribers in the telephony system.

The receiving frequency generating equipment 65 is hereby controlled by a control code inscribed in an input register 64 of the control equipment 57. This, through the described arrangement, obtains number information received in verbal or tone coded form from the users. calling subscribers via their assigned voice transmission channels.

A transmitting frequency forming equipment 65 is arranged to provide the telephone operator 58 at the switchboard 59 with a two-way connection to the calling subscribers under the control of a second control code inscribed in a second input register 66 of the control equipment 57. In addition, the telephone 58 at the switchboard 59 has a two-way connection 67 to the control equipment 57 to be able to actively participate in the connection of call connections between the subscribers in the telephony system. This, in combination with the ability of the telephone operator 58 to talk with calling subscribers, makes the telephony system of Fig. 1 extremely flexible and provides the capacity to serve illiterate persons.

&lt;It should be noted that if the number information is output from the calling subscribers in the form of finger disk pulses, these can be easily converted into a tone code for transmission via the voice transmission channels assigned to the subscribers by keying a tone voltage by means of a relay arranged in the line equipment 7 in Fig. 4. The tone code to which the decoder 60 in Fig. 5 is to decode is obtained

7405279-6 in this case in the form of a plurality of tones corresponding to the number of finger pulse rates.