Very-high-bit-rate digital subscriber line 2#Vectoring

VDSL2 Vectoring is an extension of VDSL2, designed to reduce the unwanted crosstalk between adjacent subscriber lines. Thus, the transmission rate, especially in unshielded cable bundles conventional telephone networks and with many VDSL subscribers, increased in part apparent. The method is standardized by the ITU- T G.993.5, under the name.

General

For data transfers, the limiting factors for the available transmission rate are mainly the line attenuation and crosstalk. While the attenuation is given mainly by the cable length, the cross-talk depends on the influence which signals of adjacent lines to each other. In main cables are spatially close together up to several thousand subscriber lines, these have by the construction of the cable due to mutual crosstalk. The individual subscriber lines in a main cables are usually used independently for different purposes by different access providers. Examples are data access via ADSL, VDSL or voice services like ISDN or POTS.

With VDSL2 Vectoring in the DSLAM and VDSL2 vectoring modem to reduce the mutual interference of adjacent transmission lines of the customer through a specific channel coding. For this purpose, it is inherently technically necessary that the DSLAM has complete control over all individual lines in a main harness, so that a mutual compensation can take place. The DSLAM is therefore known at any time, which signal is present on said line. So it can reduce an echo compensation mutual interference by methods similar.

Since use of VDSL2 Vectoring the DSLAM complete control must have all participant lines of a cable bundle, it can through the so-called unbundling lead to problems: When unbundling local loops will be provided different access providers, each with its own and independent devices available, so a mutual Störsignalreduktion with VDSL2 vectoring is not possible.

The vectoring process plays a fundamental role in the successor standard G.fast.

Method

With VDSL2 Vectoring mutual crosstalk in the uplink and in the downlink is compensated. The method is designed to compensate for the crosstalk at the line end, this is English far- end crosstalk by the technical term, FEXT refers. In this case, the DSLAM to be modified in the transmission signal in the downlink channel coding such that the data stream at the customer end of the cable having the lowest possible noise components of the other signal lines. In the process, by analogy, the compensation is performed in the uplink from the VDSL2 modem to the DSLAM.

Since the cross-talk is dependent on the physical effects of the line, such as capacitive coupling and operating principle can not be avoided, the expected disturbance is estimated on the transmitter and moved in the constellation diagram of the transmit symbols in the complex plane in quadrature amplitude modulation used in the opposite direction to the expected disturbance.

To estimate the variable and mutually different degrees of disturbance of a specific line information of the adjacent channel cables to the DSLAM is required. In addition, individual transmission channels as part of the Discrete Multitone modulation are used for current noise measurement with known pilot data sequences. Also available as part of the process of back-channel information about faults from the remote available when the remote peer supports vectoring.

It is in the standard, differed depending on the available information on the level of interference variables, between the following characteristics, and the quality of the noise suppression decreases from top to bottom:

Country-specific requirements

In Germany, according to a draft decision of the Federal Network Agency, the German Telekom future in principle to grant its competitors access to the local loop continues. Under certain conditions, but they may deny it, so that it can use vectoring itself or a competitor there. The condition is that there is already a second, from a competitor -driven, fixed in the field. The German Telekom announced in 2012 on the future on the basis of vectoring and FTTC bandwidth of up to 100 Mbit / s downstream and up to 40 Mbit / s to want to offer in the upstream in Germany (previously VDSL2 without vectoring: up to 50 Mbit / s downstream and up to 10 Mbit / s upstream ). In August 2013, the final approval for vectoring use in Germany took place. Previously, the EU Commission approved a second draft decision of the Federal Network Agency from July 2013.