DE4210023A1 - Digital signal transmission system - divides transmitted signal into partial signals fed to two two=wire lines via phantom circuit - Google Patents

Abstract

The transmission systems uses electrically symmetrical two-wire lines (1, 3) for transmitting two signals (dA0, dB0) with the same bit frequency in opposite directions between two spaced stations. The latter have transceiver circuits (10), each dividing the signal to be transmitted (dA0) into partial signals fed along the four line wires of the two two-wire lines (1, 3) and combining the partial signals received from the opposite station via these line wires into a reception signal (dB0). The transceiver circuit (10) in each station uses a phantom circuit (2) for supplying the partial signals to the four line wires and receiving the partial signals from the latter. ADVANTAGE - Cost-effective digital transmission system with wide effective range.

Description

The invention relates to a system according to the preamble of Claim 1.

Such a system is known from ntz, volume 44 (1991) issue 11, Pages 790 to 795, where a technology intended for the USA for Transmission of a digital signal via conventional copper cables is mentioned. The technology is called HDSL (high rate Digital Subscriber Line). A digital signal is included the bit rate of 1.544 Mbit / s standardized in two in the USA Partial signals with 784 kbit / s each divided, which then each via Two-wire line are transmitted. This is done accordingly Transmission of a 1.544 Mbit / s digital signal in reverse Direction, over the same two-wire lines. It deals a four-wire double duplex system.

Such systems are intended in particular in the subscriber access area a telephone network equipped with conventional copper cables be used to transmit digital signals with To enable bit rate frequencies that are higher than those with  ISDN devices possible bit repetition frequencies without this Installation of an optical fiber transmission network required is.

As for the transmission of a digital signal with that in Europe standardized bit rate of 2.048 kHz concerns, is from public standardization discussions at ETSI, in particular from a presentation that took place on January 28, 1992 Ameritech, known as:

• - Split the 2.048 Mbit / s digital signal into two sub-signals 1.024 Mbit / s each and transmission as with HDSL technology. This Proposal was made with "European Dual Duplex at 1024 kb / s" designated.
• - Splitting the 2.048 Mbit / s digital signal into three sub-signals each with 784 kbit / s and their transmission via one Two-wire line to the remote transceiver. The same thing applies to transmission in the reverse direction, so that it is is a duplex transmission system. It is called such system as "European Triple Duplex at 784 kb / s".

Here, the bit rate is on each of the two-wire lines reduced and thereby the transmission range increased. The However, the proposal requires three two-wire lines in order to transmit a total of 2.048 Mbit / s digital signal.

On the other hand, it is known from EP-A2 0 112 716 that over two Two-wire lines don't just transmit two main digital signals can, but also a secondary digital signal in each of the two directions of transmission if you have a circuit for it used that leads over the two two-wire lines. Such a Circuit is commonly used in telecommunications as "Phantom circle" referred to, for example in the book  "Communication engineering - an introductory presentation" by K. Steinbuch and W. Rupprecht, Springer Verlag 1973, 2nd revised edition, Page 255. In the publication mentioned, the secondary ones Digital signals are not actual message signals like the two primary signals, but only z. B. control signals, Test or test signals to monitor the function of the for primary signals established transmission system.

It is the object of the invention to provide a system for the transmission of digital message signals to indicate that as inexpensively as possible is allowed and long ranges.

The object is achieved as indicated in the claim.

The invention will now be described with reference to the drawings Exemplary embodiments show, explained in more detail. Show it:

Fig. 1 is a block diagram for explaining the principle of the invention,

Fig. 2 shows a first embodiment in which the four-wire line consisting of the two two-wire lines is operated in four-wire simplex, and

Fig. 3 shows a second embodiment in which the four-wire line consisting of the two two-wire lines is operated in four-wire double duplex.

In Fig. 1 a transmit-receive device 10 is shown schematically, which is present in a station A. The same transceiver is present in a station B remote from station A. For example, station A is located at the subscriber of a telephone network and station B (not shown) at the local exchange of the telephone network. Shown is a part of the four-wire line running between station A and station B, which consists of two electrical symmetrical two-wire lines 1 and 3 , for. B. normal copper two-wire lines. The transceiver 10 of station A, the four-wire line and the transceiver of station B form a transmission system for transmitting a first digital signal d _A0 from station A to station B and a second digital signal d _B0 from Station B to station A. The bit repetition frequencies of the digital signals to be transmitted in the two directions are the same and fixed, z. B. 2.048 Mbit / s.

Transmitters U ₁ and U _{3 are} inserted in the two-wire lines 1 and 3 in the transceiver 10 . Lines 2 are connected to the center taps of the transmitter windings facing station B and are part of a phantom circuit leading over the lines of the four-wire line in a manner known per se. In this way it is ensured that for the transmission of the digital signal d _A0 from station A to station B and a corresponding digital signal d _B0 from station B to station A not only two transmission channels in the form of the two two-wire lines 1 and 3 , but three transmission channels are available. These three transmission channels are shown in the schematic representation according to FIG. 1 and denoted by d ₁ , d ₂ and d ₃ .

A multiplexer / demultiplexer 11 contains a demultiplexer part which somehow divides the input signal d _A0 into a plurality of sub-signals and a multiplexer part which composes the digital signal d _B0 from a plurality of sub-signals received by the four-wire line. The three channels d ₁ to d ₃ are available for transmitting the partial signals in the two transmission directions.

It is essential for the invention that one of the partial signals from d _{A0 is} transmitted via the phantom circuit, as well as one of the partial signals of the signal d _B0 to be transmitted in the opposite direction. The transceiver 10 thus contains means for transmitting one of the partial signals from d _A0 via the phantom circuit and means for receiving a partial signal d _B0 received from the phantom circuit.

This is indicated by the fact that the channel which connects the multiplexer / demultiplexer 11 to the phantom circuit 2 is identified by a double arrow. Like the entire phantom circuit, it is therefore used in the duplex process.

Devices are provided for transmitting and receiving the partial signal via the phantom circuit or from the phantom circuit, which are shown as a block and are designated by 12 . They also contain the devices required for sending and / or receiving via or from the two-wire lines 1 and 3 , such as, for. B. line coders / decoders, echo cancellers and other transmission units.

The principle of the invention shown in FIG. 1 is therefore: The formation of a phantom circuit from the four-wire line and transmission of a partial signal branched off from the digital signal to be transmitted via the phantom circuit. The bit rate of the partial signals, which must then be transmitted over one or both two-wire lines, is reduced by branching off a partial signal and transmitting it on the phantom circuit, so that the digital signal can be transmitted over a longer range.

In contrast, the proposal "European Triple Duplex at 784 kb / s" was Based on the opinion that a third two-wire line should be used, if you reduce the transmission bit rate and thus the Wants to increase transmission range.  

Two exemplary embodiments of the principle of the invention shown schematically in FIG. 1 will now be explained with reference to FIGS. 2 and 3. In FIG. 2, applied to the input digital signal is _A0 d by a demultiplexer 111 into two signals d _A1 and _A2 d divided. In the first channel d ₁ , which leads to the two-wire line 1 , the one partial signal d _{A1 is} transmitted. The partial signal d _A2 reaches a two-wire line 2 via a line and a hybrid circuit 14 , so that it is transmitted to the remote station via the phantom circuit.

In the transceiver device of station B, not shown, the digital signal d _B0 to be transmitted to station A is also divided into two digital signals d _B1 and d _B2 . d _B1 is transmitted to station A via the two-wire line 3 and arrives there via channel d ₃ to the input of a multiplexer 112 . d _B2 passes from the phantom circuit, ie the two-wire line 2 , via the hybrid circuit 14 and a line to a second input of the multiplexer 112 . This combines the digital signals d _B0 sent from station B to station A from the partial signals d _B2 and d _B1 . The hybrid circuit 14 is the means to send the partial signal d _A2 via the phantom circuit to the opposite station and to receive the partial signal d _B2 transmitted from there via the phantom circuit. The two two-wire lines present on the four-wire side of the hybrid circuit 14 here form the channel d ₂ symbolically shown in FIG. 1, which is operated in duplex. The two two-wire lines 1 and 3 are each only operated in one transmission direction. In the terminology which is explained by the publication "ntz..." Mentioned at the outset, it is a four-wire simplex system. According to the invention, a phantom circuit is set up in it, in which partial signals of digital signals to be transmitted are transmitted in duplex.

A block 13 indicates transmission technology devices, in particular an arrangement of echo cancellers. Each of them compensates the echo superimposed on a received signal from one of the transmitted partial signals, which undesirably adds to the received signal. Echo means the echo of a transmission signal that arises at the so-called "near end". Such echo cancellers are known.

A second exemplary embodiment of the system according to the invention will now be explained with reference to FIG. 3. The transceiver 10 here contains a demultiplexer 113 , which divides its digital input signal d _A0 into three sub-signals d _A1 , d _A2 and d _A3 . The sub-signals d _A1 and d _A3 each reach the two-wire line 1 and the two-wire line 3 via a line and a hybrid circuit 141 and 143, respectively, and are transmitted to the remote station B via these two two-wire lines. The partial signal d _A2 reaches the two-wire line 2 via a line and a hook-up circuit 142 and is thus transmitted to the station B via the phantom circuit.

The station B, not shown, sends its digital signal d _B0 by also dividing it into three sub-signals d _B1 , d _B2 and d _B3 and d _B1 via the two-wire line 1 , d _B3 via the two-wire line 3 and d _B2 via the Phantom circle sends. The hybrid circuits 141 to 143 serve to receive the partial signal which is transmitted via the two-wire line, which is connected to its two-wire side, from the opposite station and via two-wire lines which lead to inputs of a multiplexer 114 . The multiplexer 114 composes the digital signal d _B0 from the three received partial signals.

In the exemplary embodiment in FIG. 3, the two two-wire lines, which are connected to the four-wire side of the hybrid circuit 141 , form the channel d ₁ indicated in FIG. ₁ , via which the first partial signals d _A1 , d _{B1 are} transmitted in the two transmission directions . Two two-wire lines, which are connected to the four-wire side of the hybrid circuit 142 , form the channel d ₂ indicated in FIG. 1, via which second partial signals d _A2 , d _B2 are transmitted in duplex, and two-wire lines, which are connected to the Four-wire side of the hybrid circuit 143 are connected to form the channel d ₃ indicated in FIG. 1, via which third partial signals d _A3 , d _B3 are transmitted in duplex.

According to the terminology given in the above-mentioned publication "ntz ...", this is a four-wire double duplex system. According to the invention, it has a phantom circuit via which partial signals of the digital signals to be transmitted are transmitted in duplex. A block 13 also indicates echo cancellers and other transmission technology devices, as in FIG. 2.

Some examples of a suitable division of the signal to be transmitted into partial signals are given below. The bit repetition frequencies of the partial signals are designated with the same letters and indices as the channels shown in FIGS. 1 to 3, in which they are transmitted.

To the principle of the invention according to FIG. 1

Bit rate d ₁ = bit rate d ₃ = 2 × bit rate d ₂ . The partial signal to be transmitted via the phantom circuit should therefore have half the bit rate as the partial signals transmitted via the two-wire lines 1 and 3 .

Example of Fig. 2

d ₁ = d ₃ = 2 × d ₂ as in FIG. 1. This means here that the digital signal d ₀ (the index A or B is omitted here) is divided into d ₁ with 2/3 of the original bit rate and d ₂ with 1/3 of the original bit rate. If d _{0 is} 2.048 Mbit / s, then d ₁ = 1365.3 kbit / s and d ₂ = 682.7 kbit / s.

Example of FIG. 3

d ₁ = d ₃ = 2/5 × d ₀
d ₂ = 1/5 × d ₀ .

With a digital signal d ₀ with 2.048 Mbit / s, then d ₁ and d ₃ would have 819.2 kbit / s and d ₂ 409.6 kbit / s.

As an alternative to this, the bit repetition frequencies of the three partial signals can be the same, that is to say equal to 1/3 of the original bit repetition frequency, which means with a digital signal d ₀ with 2.048 Mbit / s: 682.7 kbit / s. A 2B / IQ coding can result in a transmission speed of 341.3 kbaud.

Claims (1)

System for transmitting a first digital signal (d _A0 ), the bit repetition rate of which is predetermined, from a first station (A) to a second station and a second digital signal (d _B0 ) with the same bit repetition frequency in the opposite direction via one of two electrical symmetrical two-wire Lines ( 1 , 3 ) existing four-wire line, in which a transceiver ( 10 ) is present in each station,

• - Which divides the digital signal (d _A0 ) to be transmitted from the station into partial signals (d _A1 , d _A2 ; d _A1 , d _A2 , d _A3 ) and sends them out via the four-wire line ( 1 , 3 ) and
• - The digital signal (d _B0 ) of the received partial signals (d _B1 , d _B2 ; d _B1 , d _B2 , d _B3 ) of the digital signal to be transmitted from the other station (d _B0 ), characterized in that in the transceiver each station means (U ₁ , U ₃ , 2 , 14 , 142 ) are present, which form a phantom circuit ( 2 ) from the four-wire line ( 1 , 3 ) and one of the partial signals (d _A2 ) of the digital signal to be transmitted (i.e. _A0 ) via the phantom circuit ( 2 ) to the other station and receive a partial signal (d _B2 ) which the other station transmits via the phantom circuit ( 2 ).