dynamic spectrum management (DSL) (DSM)
Dynamic Spectrum Management (DSM) are procedures developed in xDSL technologies to increase transmission rates. It should be noted that DSL services are transmitted between the digital subscriber line access multiplexer( DSLAM) in the local exchange and the DSL modem at the subscriber end via local loop lines(ULLs). These may well be old copper double lines with limited transmission characteristics.
To get the most out of these local loop lines, various methods have been developed that are used in Dynamic Spectrum Management (DSM). These are optimization procedures used in DSL services with multiple tone techniques( DMT) that compensate as far as possible for the weak points in the transmission link between the digital subscriber line access multiplexer (DSLAM) and the DSL modem. This primarily involves compensation of crosstalk( XT) between the copper pairs, but also near-end c rosstalk( NEXT) and far-end crosstalk( FEXT) between several copper pairs of the subscriber line.
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Dynamic spectrum management has several DSM levels, which differ in terms of their procedures. At DSM level 1, for example, bit rate adaptation is used to reduce the transmission rate for the DSL service during transmission and to reduce the transmission power in order to keep the interference caused by crosstalk as low as possible. The signal level can be reduced so that it is just above the noise level. With DSM level 1, a separate transmission level is defined for each individual DSL line, based on the number of bit errors.
DSM level2 ensures that the transmission powers and frequencies for each individual DSL line in the local loop line bundle are adjusted so that they interfere with each other as little as possible. And DSM level 3 relies on signal compensation. This technique, known as interference cancellation, suppresses mutual interference, thereby increasing the signal-to-noise ratio. In the technique used in vectoring, a real-time compensation signal is generated that is in phase opposition to the interference signal. This compensation signal is added to the transmitted DSL signal and compensates for the interference signal caused by crosstalk and near-end crosstalk.
Dynamic Spectrum Management is used in ADSL, ADSL2+andADSL2+, as well as in VDSL and VDSL2.