System and method for transmitting auxiliary signal in a multiplex communication system

Abstract: In an auxiliary signal transmission system used in a multiplex communication system, a first auxiliary signal which is necessary in a transmitting terminal and a receiving terminal is transmitted directly without processing in an intermediate repeater station, and a second auxiliary signal which is necessary in at least one intermediate repeater station is processed in the intermediate repeater station, and thereafter, is transmitted to the receiving terminal. Therefore, transmission discontinuity in the system caused by a fault in the intermediate repeater station can be prevented.

Description: The present invention relates to a system for transmitting auxiliary signals used in a multiplex communication system which includes a transmitting terminal, at least one intermediate repeater station and a receiving terminal, said multiplex communication system transmitting a main signal together with said auxiliary signals using a plurality of channels, each comprising a plurality of time slots, for transmitting said auxiliary signals together with said main signal. Such a system is disclosed in GB-A-2145608, and may be used in a digital microwave multiplex radio communication system. To carry out the transmission of a digitalized order signal, low speed data or a system switching control signal (generically known as the auxiliary signal) between the terminal office and the intermediate repeater station, between the intermediate stations, and between the terminal offices, by using the digital microwave multiplex radio system, the system is used for inserting these signals into a main signal (sometimes known as a digital service channel and hereinafter referred to as DSC), and in the intermediate repeater station, a signal processing is carried out in a signal processing portion, to take out or repeat the order-wire signal or the low speed data from the received signal. In this case, desirably the auxiliary signal transmission system prevents problems in the system even if a problem occurs in the intermediate repeater station. In a digital microwave multiplex radio system which transmits the auxiliary signal between the terminal office and the intermediate repeater station, or between intermediate repeater stations, if the transmission capacity is small, a system which performs a shallow frequency modulation of a carrier wave by this signal, to carry out analog transmission (such a system is known as an analog service channel) is used. However, for example, when the transmission capacity is large, such as in a digital multi-value quadrature amplitude modulation system, the purity of the regenerated carrier wave should be maintained at high degree, to ensure that any deterioration of an error rate of the main signal is kept as small as possible, and therefore, the above-mentioned service channel can not be used. Accordingly, a DSC system in which all digitalized signals, including the order signal, are included in the main signal and are transmitted, is used. There are four kinds of signals that can be transmitted by the DSC, i.e., the DSC synchronizing signal, the system switching control signal, the order-wire signal, and low speed data. The order-wire signal and low speed data are necessary in both the intermediate repeater station and the terminal office, but the system switching control signal is necessary only in the terminal office. The system switching control signal is used to prevent problems in the main circuit and to maintain the quality of the main signal, and is the most important among the signals transmitted by the DSC. On the other hand, in the signal processing portion in the intermediate repeater station, as mentioned already, the order-wire signal and the low speed data are taken out only after all of the other DSC signals are taken out. Therefore, if a fault occurs in this portion, a problem arises in that the system switching control signal can not be repeated to the receiving terminal office, and thus problems arise in the operation of the main circuit. An object of the invention is to provide an auxiliary signal transmission system to be used in the multiplex communication system which can prevent problems in the system even if a problem arises in an intermediate repeater station. According to one aspect of the invention, the transmitting system initially defined is characterised by means for separating said auxiliary signals in the transmitting terminal into a first auxiliary signal required only in said transmitting and receiving terminals and a second auxiliary signal required in said at least one intermediate repeater station; means for inserting said first auxiliary signal, output by said separating means, separately from said second auxiliary signal into said main signal in said transmitting terminal; means for transmitting said first auxiliary signal without processing of said first auxiliary signal in said at least one intermediate repeater station; and means for processing said second auxiliary signal in said at least one intermediate repeater station, and after processing said second auxiliary signal, transmitting said second auxiliary signal from said at least one intermediate repeater station towards said receiving terminal. According to another aspect of the invention, there is provided a method of transmitting auxiliary signals in a multiplex communication system which includes a transmitting terminal, at least one intermediate repeater station and a receiving terminal, said multiplex communication system transmitting a main signal together with said auxiliary signals using a plurality of channels, each comprising a plurality of time slots, for transmitting said auxiliary signals together with said main signal, characterised by separating said auxiliary signals in the transmitting terminal into a first auxiliary signal required only in said transmitting and receiving terminals and a second auxiliary signal required in said at least one intermediate repeater station; inserting said first auxiliary signal, output by said separating means, separately from said second auxiliary signal into said main signal in said transmitting terminal; transmitting said first auxiliary signal without processing of said first auxiliary signal in said at least one intermediate repeater station; and processing said second auxiliary signal in said at least one intermediate repeater station, and after processing said second auxiliary signal, transmitting said second auxiliary signal from said at least one intermediate repeater station towards said receiving terminal. Further features and advantages of the present invention will be apparent from the ensuing description with reference to the accompanying drawings to which, however, the scope of the invention is in no way limited, and in which: Figure 1 is a diagram showing a format used in a digitial multiplex modulation system; Fig. 2 is a diagram showing a construction of a conventional system; Figs. 3A, 3B and 3C are block diagrams showing the operation of the conventional system; Fig. 4 is a block diagram showing the principle of the system according to the present invention; Figs. 5A to 5D are diagrams showing one embodiment of a transmitting terminal of the present invention; Figs. 6A to 6C are diagrams showing one embodiment of an intermediate repeater station of the present invention; Figs. 7A and 7B are diagrams showing one embodiment of a receiving terminal of the present invention; Fig. 8 is a diagram showing a format of another embodiment of the present invention; Figs. 9A - 9C are diagrams showing examples of the conventional system; and, Figs. 10A - 10C are diagrams showing another embodiment of the system according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows an example of a frame format of a digital multi-value quadrature amplitude modulation system having 16 values (hereinafter referred to as 16 value QAM modulation system). In Fig. 1, F₁₁ ∼ F 1n , F₂₁ ∼ F 2n , F₃₁ ∼ F 3n , F₄₁ ∼ F 4n show main signal frame synchronizing signals, "M" shows a main signal sequence, "C" shows a stuff control signal, "P" shows a parity bit, and "D₁ ∼ D₃" show a DSC signal, respectively. In Fig. 1, the DSC signal or the stuff control signal or the parity bit and main signal sequences are inserted between the main signal frame synchronizing signals, which are repeated at a constant period. Note, in a 64 value QAM modulation system, 6 channels are used (hereinafter abbreviated as CH), and in a 256 value QAM modulation system 8CH are used. Figure 2 is a diagram showing an example of a construction of a conventional circuit. As shown in Fig. 2, when a terminal office transmitting portion and a terminal office receiving portion are provided at two ends and an intermediate repeater station is provided therebetween, the intermediate repeater portion extracts all of the DSC signals D₁ ∼ D₃ , in order to take out the order-wire signal and the low speed data included in the D₁ ∼ D₃ portion in the example of the frame format of Fig. 1, the order-wire signal and the low speed data signal are separated therefrom and these signals are again inserted to the main signal, as a repeat of the procedure. Figs. 3A ∼ 3C are block diagrams of an apparatus for carrying out the operation of the conventional system; wherein Fig. 3A shows a terminal office transmitting portion, Fig. 3B an intermediate repeater station, and Fig. 3C a terminal office receiving portion. Hereinafter, the operation of the conventional system will be explained, with reference to Figs. 3A ∼ 3C and on the assumption that the system has 4 channels. In Fig. 3A, a main signal whose transmission speed has been accelerated at a velocity converting portion (not shown in the drawing) and gaps provided therein, is input to a main circuit. Further, a frame synchronizing signal is added to a system switching control signal, an order-wire signal, and low speed data in a signal processing portion 3, converted into three parallel signals, output along three channels, and thereafter, inserted into the gaps in the main signal at an inserting portion 1, so to obtain a 4CH signal having the format shown in Fig. 1. This signal is supplied to a modulating portion 2, wherein the carrier wave is modulated, and the modulated waveform as a 16 value QAM is sent to a next office. A protecting circuit is also processed in the same way as the main circuit mentioned above, and the 16 value QAM modulated waveform is sent via an inserting portion 1′ and a modulating portion 2′ to the next office. Note, in this case a protecting circuit test signal is used instead of the main signal. In Fig. 3B, the 16 value QAM modulated waveform applied to demodulating portions 4, 4' via a main circuit and a protecting circuit is demodulated and a signal having a format shown in Fig. 1 is obtained and applied to a selecting and separating portion 5, so that the D₁ ∼ D₃ portions transmitted by the main circuit and the protecting circuit are taken out and an order-wire signal and low speed data signal having a good S/N ratio are obtained. Then, the taken out order signal and low speed data are processed together with the system switching signal in the signal processing portion 6, in the same way as mentioned above, and are inserted in the inserting portion 7 and 7' into the portions D₁ ∼ D₃ shown in Fig. 1. Thereafter, the carrier wave is modulated in the modulating portions 8 and 8', and the 16 value QAM modulated waveform is sent to a next office. In Fig. 3C, the 16 value QAM modulated waveform from the intermediate repeater station is demodulated in the demodulating portions 9 and 9', to obtain a signal having the format shown in Fig. 1. This signal is separated in the separating portions 10 and 10' into the main signal, the protecting circuit test signal, and the portions D₁ ∼ D₃ , and thereafter, as in Fig. 3B, the portions D₁ ∼ D₃ having a good S/N ratio are selected in a selecting and separating portion 11, and the system switching control signal, the order-wire signal, and the low speed data signal are obtained therefrom. In the example as shown above, the signal transmitted by using the DSC is formed by 4 kinds of signals, i.e., the DSC synchronizing signal, the system switching control signal, the order-wire signal, and the low speed data signal. The order-wire signal and the low speed data signal are necessary in both the intermediate repeater station and the terminal offices, but the system switching control signal is necessary only in the terminal offices. The system switching control signal is used to prevent problems in the main circuit, and to maintain the quality of the main signal, and is the most important among the signals transmitted by the DSC. In the signal processing portion in the intermediate repeater station, as mentioned above, the order-wire signal and the low speed data signal are taken out only after all of the DSC signals are taken out. Therefore, if a fault occurs in this portion, a problem arises in that the system switching control signal can not be repeated to the terminal office, and therefore, problems in the main circuit can not be prevented. The above-mentioned problem can be solved by providing an auxiliary signal transmission system in which, as shown in Fig. 4, in the transmitting portion, a digital service channel synchronizing signal is added to the system switching control signal in a signal processing portion 14, and to the order-wire signal and the low speed data in a signal processing portion 15, respectively, and thereafter, is inserted via inserting portion 12, 13 into a main signal having a specified channel (CH₁) 16 or another channel (CH₃ , CH₄) 17, to be output, and in an intermediate repeater station, the signal of the specified channel (CH₁) 16 is directly repeated without signal processing, and the order-wire signal and the low speed data signal in the other channel (CH₃ , CH₄) 17 are taken out by signal processing in a signal processing means 21, or after a repeated signal process processing, are inserted via the inserting portion 20 into the main signal of the other (CH₃ , CH₄) channel 17, to be repeated. As shown in Fig. 4 of the present invention, a DSC synchronizing signal and a system switching control signal are inserted via an inserting portion 12 into a main signal of a specified channel 16, and the DSC synchronizing signal, and an order-wire signal and a low speed data signal are inserted via an inserting portion 13 into a main signal of another (CH₃ , CH₄) channel 17. In the intermediate repeater station, the signal of the specified channel 16 is repeated without processing, and only the order-wire signal and the low speed data signal of the other (CH₃ , CH₄) channel 17 are processed and taken out in a signal processing means 21, or again processed and inserted via an inserting portion 20 into this channel 17, to be repeated. That is, since the system switching control signal is not processed in the intermediate repeater station, if an obstacle arises in the signal processing portion, the system switching control signal is transmitted to a terminal receiving portion, and thus the occurrence of a fault in the system can be prevented. Figures 5A ∼ 5D, 6A ∼ 6C, and 7A ∼ 7B are block diagrams of the apparatus for carrying out the present invention, wherein Figs. 5A ∼ 5D are block diagrams of a terminal transmitting portion; Figs. 6A ∼ 6C are block diagrams of an intermediate repeater station; and Figs. 7A and 7B are block diagrams of a terminal receiving portion. Note, throughout the drawings the same symbols designate the same elements. Hereinafter, assuming that the number n of the channels is 4, the operation of Figs. 5A ∼ 5D, 6A ∼ 6C, and 7A, 7B will be explained with reference also to Fig. 1. In Fig. 5A, a synchronizing signal is added in a signal processing portion 14 to the system switching control signal input from an external source, and the system switching control signal is inserted into a specified channel, for example, the portion D₁ of channel 1 in Fig. 1. Further, the order-wire signal and the low speed data signal input to the signal processing portion 15 are added to a frame synchronizing signal, further converted into parallel signals for two channels, and thereafter, inserted into portions D₂ , D₃ of CH₃ , CH₄ in Fig. 1. The 4CH signals are then modulated as a carrier wave in a modulation portion 2, and a 16 value QAM modulation waveform is output to a next office. Similarly, in a protecting circuit, the order-wire signal and the low speed data signal are inserted via an inserting portion 12′, 13′ into the same position in the frame format. In Fig. 5A, the main signals in CH₁ and CH₂ ∼ CH₄ are applied to the inserting portions 12 and 13 via a frequency converter (not shown in the drawing) in which gaps are provided in the main signal. In Fig. 5B, reference numeral 16 denotes a signal applied to the inserting portion 12 or 13, and reference numeral 16a denotes a signal applied to the frequency converter mentioned above. Figure 5C is a detailed block diagram of the signal processing portion 14, in which a sync. signal generator 14a generates a sync. signal F′, and the system switching control signal is combined with the sync. signal F′ in a multiplexer 14b which is controlled by a controller 14C. The output of the multiplexer 14b is supplied to the gap corresponding to the portion D₁. Figure 5D is a detailed block diagram of the signal processing portion 15. The function of the circuit shown in Fig. 5D is very similar to that of the circuit shown in Fig. 5C. That is, the order-wire signal and the low speed data signal are added the sync signal generated in a sync. signal generator 15a in a multiplexer 15b under the control of the controller 15c, and the output of the multiplexer 15b is supplied to the gap corresponding to the portions D₂ , D₃ in CH₃ and CH₄. Next, in Fig. 6A, the 16 value QAM modulation waveform transmitted via the circuit is demodulated in demodulating portions 4, 4′, and a signal having a format shown in Fig. 1 is taken out. Note, the CH₁ signal is directly input to modulating portions 8, 8′. The CH₂ ∼ ₄ signals in the other channel 17 are applied to a selection/separation portion 18 in the signal processing means 21 and portions D₂ or D₃ having a good S/N ratio are selected, and thereafter, the signal is separated into the order-wire signal and the low speed data signal, to be output. Further, the order-wire signal or the low speed data signal which were taken out or sent from the intermediate repeater station, are added to the DSC synchronizing signal in the signal processing portion 19, as in the terminal office, and thereafter, inserted into portions D₂ , D₃ of the frame format shown in Fig. 1 in the inserting portion 20, 20′, to be applied to the modulating portions 8, 8′. The 16 value QAM modulation waveform is then repeated. Figure 6B is a block diagram of one example of the selection/separation portion 18 in Fig. 6A. In Fig. 6B, CH₃ and CH₄ input signals are supplied to a circuit 18a in which the frame sync. signals are extracted and the extracted sync. signal is supplied together with the input signals to latch circuits 18b and 18c and further supplied to the signal processing portion 19. The outputs of the latch circuits 18b and 18c are supplied to the F′ frame sync. separating circuit 18d, in which the frame signal F′ is removed and supplied to an external circuit such as a telephone circuit or a data circuit. Figure 6C is a block diagram of one example of the signal processing circuit 19 shown in Fig. 6A. As shown in Fig. 6C, the external signals, that is, the order-wire signal and the low speed data signals, are multiplexed in a multiplexer 19a with a sync. signal generated in a sync. generated 19b, under the control of the control circuit 19c controlled by the output of the circuit 18a, and supplied to the inserting portion 20. Next, in Fig. 7A, the signal having a frame format shown in Fig. 1 demodulated in the demodulating portion 22, 22′ taken out, and the CH₁ signal is supplied to a separation selection portion 23 so that a system switching control signal is taken out. Further, the CH₂ ∼ CH₄ signals are added to the selection separation portion 24 so that the order-wire signal and the low speed data are taken out. The outputs, including the main signal, of separating circuits 25, 26, 25′, 26′ are supplied respectively to a frequency converter (not shown in the drawings) and the insertion gaps are removed. In Fig. 7B, reference numeral 30 denotes the output signal of the separating portion and reference signal 30a denotes the output of the frequency converter explained above. By performing the signal processing shown in Fig. 5A to Fig. 7B, if a fault occurs in the signal processing means 21 of the intermediate repeater station, problems in the system can be prevented without affect on the switching control signal. Figure 8 is another example of a frame format of a digital multi-value quadrature amplitude modulation system in the case of the 16 value QAM system. In Fig. 8, "F" is a main signal frame synchronizing signal and "D₁ ∼ D₃" are DSC signals, respectively. The difference between Fig. 8 and Fig. 1 is that the DSC signals are all inserted in the same channel, as shown in Fig. 8. The system using the format shown in Fig. 8 was conventionally performed as shown in Figs. 9A ∼ 9C. Figures 9A ∼ 9C are block diagrams of a conventional signal transmission system. In transmitting station shown in Fig. 9A, a bipolar/unipolar converting (hereinafter called B/U conversion) portion 41 converts an input bipolar signal IN to a unipolar signal, inserted codes such as an error correcting code and a digital service channel (DSC) signal are processed in a transmitting code processing portion 42, multi-value quadrature modulation (hereinafter called multi-value QAM) is carried out in a modulating portion 43, and the output of the modulating portion 43 is transmitted from a transmitting portion 44. Further, a DSC multiplexing portion 45 controls a switch 46, and multiplies a system control signal from the switch control portion 47 switching a main circuit and a protecting circuit and an order-wire signal used between specified stations so as to form one signal. A repeater station shown in Fig. 9B receives in a receiving portion 51 the signal from an upstream station, and in a modulating portion 52, demodulates the multi-value QAM signal into a two value digital signal and demodulates ASC signal which FM modulates a carrier wave. Next, in an SC signal processing portion 53, the repeater station branches and inserts a DSC signal, and in a modulating portion 54, the two value digital signal is modulated together with the ASC signal and sent to a transmitting portion 55. Further, a DSC demultiplexing portion 56 demultiplexes and separates only the order signal between specified stations allocated to the station, among the multiplexed DSC signals. A receiving terminal station shown in Fig. 9C receives, in a receiving portion 61, the digital signal and the ASC signal demodulated in a demodulating portion 62, a receiving signal processing portion 63, and code processes such as a separation of an error correction or DSC signal are carried out, and a U/B converting portion 64 carries out a U/B conversion, and outputs the result. Further, a DSC separating portion 65 separates the order signal between the specified stations and the system control signal, and a switch control portion 66 controls the switch 67 by the system control signal to switch the main circuit and the protecting circuit. Here, the order-wire signal for all stations is used as ASC signal, and, the DSC signal, is formed by multiplying a plurality of order-wire signals between specified stations having different combinations of the stations to be used, and the system control signal used only between a transmitting terminal station and a receiving terminal station in which the system is switched. In Figs. 9A ∼ 9C, DSC signals are branched and inserted in each station, and thus the reliability thereof is decreased at each station. Therefore, the reliability of the system control signal multiplied in the DSC signal is also decreased, so that a problem of a higher probability of an error occurring in the system control is increased. To solve the above-mentioned problem, in the present invention, a first auxiliary signal which is required only in the transmitting station and the receiving station, such as used in the system control signal, and a second auxiliary signal required in the intermediate station, are separate in different time slot, and in the intermediate station, only the second auxiliary signal is branched and inserted. That is, the intermediate station does not branch or insert the first auxiliary signal, and thus the first auxiliary signal inserted in the time slot can be transmitted without any decrease in reliability. Figures 10A ∼ 10B are block diagrams of an auxiliary signal transmission system of another embodiment of the present invention. In Figs. 10A ∼ 10C, a B/U conversion portion 71, sending portions 74, 75, switches 76, 97, switch control portions 77, 96, and receiving portions 81, 91 have the same function as shown in Figs. 9A ∼ 9C, and therefore, the explanation thereof is omitted. The difference between Figs. 9A ∼ 9C and Figs. 10A ∼ 10C lies in the following. In a transmitting code processing portion 72 and a receiving code processing portion 93, a system control signal as a first auxiliary signal and a DSC signal as a second auxiliary signal are treated as different signals, and are inserted or branched by using different time slots. In a DSC multiplexing portion 75, a DSC demultiplexing portion 86, and a DSC separating portion 95, instead of a system control signal, a digital order signal for all stations is multiplexed and demultiplexed with an order signal for a specified station. Further, an ASC signal is not modulated and demodulated in modulating portions 73, 74 and demodulating portions 82, 83. Because, the system control signal is not separated or inserted in the intermediate station shown in Fig. 10B, the reliability is not decreased. Further, instead of the system control signal, the order signal for all stations is multiplexed as a DSC signal, and therefore, it is not necessary to FM modulate the carrier wave due to the ASC signal, as in the prior art. Accordingly, a precise carrier wave regeneration can be carried out so that the receiving error rate is reduced. As mentioned above, according to the present invention, the auxiliary signal which is necessary in the transmitting station and the receiving station can be transmitted without decreasing the reliability of the operation, and the error probability in the system control decreased, and thus the reliability of the whole system is improved.

Claims: A system for transmitting auxiliary signals used in a multiplex communication system which includes a transmitting terminal, at least one intermediate repeater station and a receiving terminal, said multiplex communication system transmitting a main signal together with said auxiliary signals using a plurality of channels, each comprising a plurality of time slots, for transmitting said auxiliary signals together with said main signal, characterised by: means for separating said auxiliary signals in the transmitting terminal into a first auxiliary signal required only in said transmitting and receiving terminals and a second auxiliary signal required in said at least one intermediate repeater station; means for inserting said first auxiliary signal, output by said separating means, separately from said second auxiliary signal into said main signal in said transmitting terminal; means for transmitting said first auxiliary signal without processing of said first auxiliary signal in said at least one intermediate repeater station; and means for processing said second auxiliary signal in said at least one intermediate repeater station, and after processing said second auxiliary signal, transmitting said second auxiliary signal from said at least one intermediate repeater station towards said receiving terminal. A system for transmitting auxiliary signals used in a multiplex communication system according to claim 1, wherein said inserting means inserts first auxiliary signal into one of said channels and said second auxiliary signal is inserted into a different one of said channels. A system for transmitting auxiliary signals used in a multiplex communication system according to claim 1, wherein said inserting means comprises: means for inserting said first auxiliary signal into said main signal in a first one of the channels, and said second auxiliary signal into said main signal in third and fourth channels; first and second signal processing portions for adding a digital service channel synchronizing signal to said first auxiliary signal and to said second auxiliary signal, respectively; and means for inserting said first and second auxiliary signals into the main signal in said first channel and said third and fourth channels to be output respectively; and further comprising in said at least one intermediate repeater station: repeating means for repeating said first auxiliary signal without signal processing; signal processing means for extracting and processing said second auxiliary signal from the third and fourth channels; and an inserting portion for inserting said second auxiliary signal into said main signal in said third and fourth channels. A system for transmitting auxiliary signals used in a multiplex communication system according to claim 1, wherein said first auxiliary signal is sent by using a first time slot in one channel and said second auxiliary signal is sent by using second time slots different from said first time slot, and further comprises means in said intermediate repeater station for branching and inserting only said second auxiliary signal in said second time slots. A method of transmitting auxiliary signals in a multiplex communication system which includes a transmitting terminal, at least one intermediate repeater station and a receiving terminal, said multiplex communication system transmitting a main signal together with said auxiliary signals using a plurality of channels, each comprising a plurality of time slots, for transmitting said auxiliary signals together with said main signal, characterised by: separating said auxiliary signals in the transmitting terminal into a first auxiliary signal required only in said transmitting and receiving terminals and a second auxiliary signal required in said at least one intermediate repeater station; inserting said first auxiliary signal, output by said separating means, separately from said second auxiliary signal into said main signal in said transmitting terminal; transmitting said first auxiliary signal without processing of said first auxiliary signal in said at least one intermediate repeater station; and processing said second auxiliary signal in said at least one intermediate repeater station, and after processing said second auxiliary signal, transmitting said second auxiliary signal from said at least one intermediate repeater station towards said receiving terminal. A method according to claim 5, wherein said first auxiliary signal is inserted into one of said channels and said second auxiliary signal is inserted into a different one of said channels. A method according to claim 5 wherein said inserting step comprises: inserting said first auxiliary signal into said main signal in a first one of the channels, and said second auxiliary signal into said main signal in third and fourth channels; adding a digital service channel synchronizing signal to said first auxiliary signal and to said second auxiliary signal, respectively; and inserting said first and second auxiliary signals into the main signal in said first channel and said third and fourth channels to be output respectively; and wherein said at least one intermediate repeater station performs the following functions: repeating said first auxiliary signal without signal processing; extracting and processing said second auxiliary signal from the third and fourth channels; and inserting said second auxiliary signal into said main signal in said third and fourth channels. A method according to claim 5 wherein said first auxiliary signal is sent by using a first time slot in one channel and said second auxiliary signal is sent by using second time slots different from said first time slot, and said intermediate repeater station branches and inserts only said second auxiliary signal in said second time slots.

Inventors: ITOH HIDEAKI, OZAKI TAKAYUKI, ITOH, HIDEAKI, OZAKI, TAKAYUKI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1987
Main classification: H04J3
IPC codes: H04J3, H04B17