DE29914706U1 - Line termination device for a subscriber line - Google Patents

Description

GR 99 G 2626

Description

Line termination device for a subscriber line
5

The invention relates to a line termination device for a subscriber line according to the preamble of claim 1.

Voice transmission is carried out analogously via an analog subscriber connection in the telephone network. While in conventional voice transmission, the so-called POTS (Plain Old Telephone System), only a relatively narrow frequency band, the so-called voice band, could be used for voice transmission, in newer ISDN systems voice transmission takes place over a relatively wide frequency band.

With the xDSL transmission methods (xDSL = x-digital subscriber line), the frequency ranges 0 above the voice band are also used in the telephone network for broadband data transmission. xDSL transmission methods include HDSL (High Bit Rate Digital Subscriber Line), ADSL (Symmetry digital Subscriber Line) and VDSL (Very High Speed Digital Subscriber Line). The xDSL transmission methods are referred to as broadband network access and include all transmission methods over the telephone network that enable a higher data transmission rate between a subscriber and the exchange than the data transmission rate achievable with voice band modems. For this purpose, with the xDSL transmission methods, a so-called xDSL data signal, which is a digital signal coded for the xDSL transmission method, is transmitted in a higher frequency band separate from the voice band. The xDSL transmission methods can theoretically use the entire bandwidth of the copper pair available above the voice band and achieve data transmission rates in the Mbps range.

GR 99 G 2626

Despite the separate transmission of voice and data in different frequency ranges in xDSL transmission methods, secondary frequencies can pass from the voice band into the data band and vice versa. In particular, control signals in the voice range, such as ringing signals or charge pulses, can cause interference in the data band and interrupt or completely stop data transmission. To avoid such interference, the voice band and the data band must be separated before further processing.

The present invention relates in particular to the transmission-side merging and the reception-side separation of two or more signal streams of different transmission methods, in particular ADSL and ISDN, located in separate frequency ranges, for transmission on the same transmission medium, for example a subscriber line.

In current line termination lines for subscriber lines, the individual signal streams are each treated in their own transceiver units. The signal streams are combined or separated by so-called splitter circuits, which terminate the subscriber lines on both sides and provide an interface for the signal streams of the individual transmission methods. State-of-the-art splitter circuits of this type are designed as passive analog filters. Ideally, these splitter modules are transparent to the transceivers that generate and receive the signal streams. In reality, however, these splitter modules significantly impair the transmission behavior of the individual services or transmission methods, since the filter frequency responses can never be realized with an ideal frequency and phase response, i.e. the frequency ranges cannot be separated completely without feedback. When ADSL and ISDN are operated together, this typically results in a

GR 99 G 2626

Reduction in ISDN range, whereas the ADSL service achieves a lower data rate with the same line length. The comparison should be seen here with the exclusive operation of the respective service on a subscriber line.

Based on this prior art, the present invention is therefore based on the technical object of providing a generic line termination device for a subscriber line, which offers a simple solution for separating the voice and data bands, which can be adapted to specification changes, in particular for ISDN voice transmission and ADSL data transmission.

According to the invention, this object is achieved by a line termination device for a subscriber line with the features of claim 1.

Accordingly, there is provided a line termination device for a subscriber line which transmits and receives broadband signals via only one subscriber line, wherein a broadband signal is composed of a broadband low-frequency voice signal (ISDN) and a broadband low-frequency data signal (ADSL) and the frequency bands of the voice signal and the data signal do not overlap and wherein a digital crossover is provided which separates the low-frequency voice signal and the higher-frequency data signal from one another and wherein the digital crossover is arranged in the digital part of the line termination device.

An advantageous embodiment of the invention results from the sole subclaim.

The particular advantage of the invention is therefore the shifting of the splitter functionality from the analogue area to the digital area. This is achieved by a clock-synchronous

GR 99 G 2626

operation of the individual transmission methods that share the subscriber line is possible. Furthermore, the different impedance requirements are implemented over the entire relevant frequency range by means of suitable frequency-dependent external circuitry of the analog front end. Another possibility for implementing the required impedance curve of the line interface is the use of impedance synthesis loops in the analog front end.

Due to the shift in splitter functionality from the analog to the digital area of the transceiver, the transceiver circuits of the individual transmission methods are no longer completely independent of one another. Among other things, they use a common analog front end. The common transmit/receive signal is combined or separated in terms of frequency in a digital splitter module using digital filter algorithms. It should be noted that the sample rates of the individual streams must be the same at the summation point or when separated. This is achieved by sample rate adaptation stages and a clock synchronization unit in the digital splitter modules.

A digital splitter module can be used in the systems on both sides of the subscriber line, i.e. both on the subscriber side and on the network side.

The line termination device according to the invention with separation of data and voice bands in the digital part achieves the following advantages:

• The invention allows the analog splitter module to be replaced by a digital splitter module. The digital splitter module can be implemented in a single integrated circuit (IC) - simultaneously for several channels per chip. The structure of a passive analog

GR 99 G 2626

Splitters, on the other hand, require a considerable amount of space, as coils and capacitors must be used, some of which have high requirements for dielectric strength and component tolerance. The costs vary several times depending on the design, to the detriment of the analog solution.

For all transmission methods that share a subscriber line, only a single common analog front end is advantageously required, whereas with current solutions an analog front end must be included in each transceiver. This results in a significant reduction in costs.

· The characteristics of digital filters can meet much stricter requirements in terms of edge steepness and minimal group delay distortion. A system with a digital splitter can therefore be optimized in such a way that it suffers less loss of performance than a comparable system with an analog splitter. Furthermore, the circuit also proves to be more advantageous with regard to EMC radiation caused by excessively steep clock edges.

Crosstalk between the individual transmission methods due to insufficient outer band attenuation can be significantly reduced by using echo canceller modules in digital splitter modules. This leads to a further reduction in the performance losses that can occur when several transmission methods are operated together on the same subscriber line.

Due to the clock synchronization according to the invention, additional services, such as the so-called "Voice over IP" in the ADSL service ^, can be carried out without further clock synchronization.

· ■

GR 99 G 2626

·

·

The invention is explained in more detail below with reference to the embodiments shown in the figures of the drawing. It shows:

Figure 1

Figure 2

the basic circuit of the line termination device according to the invention with a digital splitter for ISDN and ADSL;

the architecture of an advantageous embodiment of a digital ISDN splitter.

Figure 1 shows the basic circuit of a line termination device for a subscriber line with a digital splitter, which is particularly suitable for separating the ISDN voice band and the ADSL data band.

The line termination device is connected to the telephone network 1 via two copper wires a, b. Voice and data signals are coupled into the line termination device via an ISDN/ADSL transformer 2 via these copper pairs of the POTS (Plain Old Telephone System). This transformer 2 is connected to a digital ISDN splitter circuit 5 (DISC = Digital ISDN Splitter Circuit) via a line driver circuit 3 and a codec 4. The ISDN/ADSL transformer 2, the line driver circuit 3 and the codec 4 form the common front-end interface 6 of the line termination device. The ISDN splitter circuit 5 contains means for separating the ADSL data and the ISDN voice data.

For this purpose, a high-pass filter 6 is provided in the ADSL path 7 and a low-pass filter 8 in the ISDN path 9. Furthermore, an ADSL transceiver module 10 is arranged between the ISDN splitter circuit 5 and the ADSL data interface 11. In addition, an ISDN transceiver module 12 is provided between the ISDN splitter circuit 5 and the PCM interface 13.

GR 99 G 2626

Figure 2 shows the architecture of the inventive ISDN splitter circuit corresponding to Figure 1.

The interface of the analog front end 20 is connected to the ADSL interface 21 via an upstream signal path 22 and a downstream signal path 23. At least one ADSL high-pass filter 24, 25, 26 is connected in each of these signal paths. In addition, a so-called echo canceller 27 is provided between the two ADSL signal paths.

Furthermore, the two ADSL signal paths 22, 23 are each connected to the ISDN interface 30 via a low-pass filter 28, 29. The low-pass filter 28, which is arranged between the ISDN interface 30 and the ADSL upstream signal path 22, is provided with a sampling rate decimator for reducing the pulse frequency. Conversely, the low-pass filter 29, which is arranged between the ISDN interface 30 and the ADSL downstream signal path 23, is provided with a sampling rate interpolator.

In addition, the ISDN splitter circuit 5 according to the invention also has an interface 31 for clock coupling and an interface 32 for control signal coupling.

The present invention is particularly suitable for line termination devices that are suitable for implementing ADSL over ISDN services, as offered by various network operators such as Deutsche Telekom.

GR 99 G 2626

it '&eeacgr;

&idiag; t • ·

List of reference symbols

a, b copper wires

1 telephone network

2 ISDN/ADSL transformers

3 Line driver circuit

4 Codec

5 Digital ISDN splitter circuit, crossover

6 high-pass filters

7 ADSL signal path

8 low-pass filters

9 ISDN signal path

10 ADSL transceiver module

11 ADSL data interface

12 ISDN transceiver module

13 PCM interface

14 analog frontend

15 ADSL interface

16 Upstream signal path

17 Downstream signal path 24, 25, 26 ADSL high-pass filter 27 Echo channeller

28, 29 Low-pass filter

30 ISDN interface

31 Interface for clock coupling

32 Interface for control signal coupling

Claims (2)

1. Line termination device for a subscriber line which sends and receives broadband signals via only one subscriber line, wherein a broadband signal is composed of a broadband low-frequency voice signal (ISDN) and a broadband higher-frequency data signal (ADSL) and the frequency bands of the voice signal and the data signal do not overlap, characterized in that a digital frequency divider is provided which separates the low-frequency voice signal and the higher-frequency data signal from one another, and that the digital frequency divider is arranged in the digital part of the line termination device. 2. Line termination device for a subscriber line according to claim 1, characterized in that the broadband low-frequency voice signal is an ISDN voice signal and the broadband higher-frequency data signal is an ADSL data signal.