DE19624928C2 - Remote crosstalk compensation method - Google Patents

Description

Hybrid fiber / copper twin-wire system architectures (Hybrid Fiber Twisted Pair, HFTP) enable readiness development of symmetrical or asymmetrical participants conclude with data rates of 6.25 to 50 Mbit / s over existing copper double wire connection cable. When transferring over the copper twisted pairs occur, for example, the following Interference on: echoes, crosstalk, influence by Amateur radio systems (Radio Frequency Interference (RFI)), Impulse noise and white noise. Which of these disorders dominates and thus limits the system depends on the chose transmission methods.

With ISDN and HDSL (High Bitrate Digital Subscriber Line) are preferably frequency and simultaneous transmission applied with echo cancellation. With increasing transmission however, the near-end crosstalk transmission radio becomes bandwidth tion to a system-limiting factor. For high bit rates Copper transmission systems are time separated (TDM) Division Multiplex) and Frequency Separation (FDM - Frequency Division multiplex) method preferred. At TDM Proximity crosstalkers and echoes due to the temporal separation the data stream to the subscriber (downstream transmission) and of the data stream from the subscriber (upstream transmission) the, while in FDM systems this is due to the transmission in different frequency bands is reached. The ranges TDM and FDM systems are limited by remote control crosstalk from other systems, such as that Very high bitrate digital subscriber line VDSL system, in same cable caused. While with TDM systems the Realization effort, apart from the equalization, is decisive Lich through the synchronization of the different transmitters on Cable distributor (KVz) and by a necessary buffering of the  Data is determined, the effort is with FDM systems especially in the digital and analog separation filters. FDM systems are caused by long distance crosstalk (FEXT) or white noise (AWGN) limited. Which type of disorder dominates is determined by the Number of stages of the modulation method (e.g. QAM), the Cable length and the permissible transmission power given. Crucial system requirements for HFTP systems are Robustness, the guarantee of high availability and the Cost of the entire system. Because of a restricted Transmission quality for cable transmissions at high Internationally, frequencies are required to have an upper Cut-off frequency of 13-15 MHz of HFTP systems does not exceed is taken.

With previous approaches for hybrid glass fiber / copper double vein system architectures are the individual transmission systems viewed as independent of each other. At z. B. 25 HFTP systems in a cable results in a Gaussian, colored noise. At the lower transmission band one Frequency separation method (FDM system) enforces this the white noise (AWGN) embossed limitation due to the relatively low cable loss only with long cable lengths <1 km for a 16-step quadrature amplitude modulation (16- QAM). As a result of the slow increase in a relative Interference power due to remote crosstalk with the cable length can be large in a FEXT-dominated interference environment Achieve ranges. With symmetrical data transmission is one for the upper of the two transmission channels Modulation methods with low bandwidth efficiency (e.g. 4-QAM) advantageous if there is no strict bandwidth limitation consists. With a reduction in the available bandwidth and the associated bandwidth-efficient data transmission remote crosstalk attenuation (FEXT) is due the lower carrier frequency increases, the increase of a Minimum signal / noise ratio (SNR) of approx. 6 dB leads to a relative increase in FEXT noise level and one corresponding reduction in range.  

In a contribution by M. Pollakowski, H.-W. Wellhausen are "Properties of symmetrical local connection cables in the Frequency range ", in particular chapter 2.2 in the telecommunications Ingenieur, 49th year, issues 9 and 10, 1995.

The object of the invention is to provide a filter architecture Avoiding distant crosstalk for a communication network to be specified with a hybrid fiber / copper twin-wire system.

The object is achieved by the features of patent claim 1 solved.

The process has the advantage of being independent on the topology of the transmitter / receiver on the participant side and the use of different transmit power allowed from the switching node to the subscriber, which for Example of a reduction in the maximum spectral Power density in the area of amateur radio (RFI) frequency tapes for short lines can be used.

The method has the further advantage that regardless of the length of the respective connection paths Far crosstalk is suppressed and the signal-to-noise ratio is significantly increased.

By increasing the signal-to-noise ratio, there is an increase of the product based on bandwidth and cable length bar and a greater tolerance when hiring a Upstream transmission power possible.

Further advantageous embodiments of the invention are in the Subclaims specified.

Further special features of the invention will become apparent from the following Explanation of an embodiment based on Drawings can be seen.

Show it:  

Fig. 1 Near and far crosstalk in transmission systems and

Fig. 2 shows a system architecture for the transmitter side compensation of long-distance crosstalk.

In contrast to systems with echo cancellation (ISDN, HDSL) the performance of frequency separation Procedure for hybrid glass fiber / copper two-wire systems primarily not by NEXT near crosstalk, but by distance crosstalk FEXT limited. With long cable lengths the system is limited by white noise AWGN.

Fig. 1 shows the influence of crosstalk disorders which are divided into near crosstalk (NEXT) and long distance crosstalk (FEXT). These crosstalk disorders essentially arise from the coupling of transmission energy to other lines routed in the branch cable.

Fig. 2 shows a portion of a communications network KN. In this, transmitter S1 and receiver units E1 on the subscriber side Tn and transmitter and receiver units S1, ..., Sn; E1, ..., En arranged on the side of the cable distributor KVz. Cable distributors KVz and subscriber terminals Tn are connected by a data transmission channel Nkn. A hybrid circuit G in each case forms the connection unit between the transmission channel Nkn, Sending-Sn and receiving direction En. The interference by remote crosstalk FEXT takes place on the transmission link (see also FIG. 1). The data between the communication terminals is transmitted using the frequency separation method. The upper frequency band is used for a transmission from the subscriber Tn to the exchange and the lower frequency band is used for data transmission from the exchange to the subscriber Tn.

In the circuit arrangement shown, the signal is transmitted supply from the switching node VST via the cable distributor KVz to subscriber Tn shown (downstream transmission).

In this circuit arrangement, pre-distortion is used FEXT was eliminated. The transmission signal  of the interferer from the switching node to the subscriber carry (downstream transmission signal) and on an adaptive filter Given FKN1, the adaptive filter FKN1 the relative (Equal-Level) remote crosstalk, so that the most The resulting FEXT disturbance is greatly reduced is.

To adjust the compensators FKN1 must be done in the context of a Training modes Information about a residual error e from the part receiver-side transmitter / receiver (transceiver) for cable connection two KVZ-side transmitter / receiver are transmitted.

The advantage of this method is that it is independent on the topology of the transmitter / receiver on the participant side Tn is and if necessary use under different downstream transmission powers allowed what z. B. also to reduce the maximum spectral power density in the amateur radio RFI frequency bands at short Cables can lead between the KVz and subscriber terminal.

When transmitting signals from the switching node to the subscriber mer can adjust the sensitivity of bandwidth efficient Modulation method (16-QAM, 64-QAM) against changes of the FEXT interference level by means of FEXT compensation on the transmission side be reduced.

Different line lengths from the subscriber Tn to the cable branching KVz can with appropriate coefficients filter units FKN1 are taken into account.

Claims (4)

1. A method for compensating for long-distance crosstalk on data lines, characterized in that
that a signal transmission directed to a subscriber on the transmitter side is predistorted by at least one correction signal,
that a subscriber-specific correction signal is generated by an adaptive filter (FK (N1)) to which a data stream of an adjacent data line is applied. 2. The method according to claim 1, characterized, that the adaptive filter (FK (N1)) by one, at the respective Participant minimized residual errors can be optimized. 3. The method according to claim 1, characterized, that through a training mode information about the rest of the mistake ler (s) from the participant's transmitter / receiver to the distributor transmitters / receivers. 4. The method according to claim 1 characterized, that the adaptive filter is a finite impulse response filter.