2.6. Impairment Modeling
General impairment modeling is treated in great depth in [1]. Chapters 3 and 7 also study some specifics pertinent to ADSL and VDSL respectively.
2.6.1. Background Noise
Background noise in DSL systems today is often presumed to be –140 dBm/Hz. There is no justification for this level other than early DSL designers agreed that this would represent a noise floor caused by a reasonable ADCs quantization level in 1990.[8] The number stuck. Today, noise floors can be considerably lower as conversion technology has advanced. DSL modems with lower quantization noise will often perform better. The actual thermal limit of line noise at room temperature is –173 dBm/Hz. Usually line noise is slightly higher than this limit and ...
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