SNR
Tab: Displays the SNR per tone (available on certain BX100 models only). The results can be displayed in graphical format
or tabular formats.
As with all transmission lines, signal quality depends primarily on the attenuation and signal to noise ratio. The frequency of the bin
can therefore determine how many bits can be encoded i.e. SNR can differ from bin to bin. Generally speaking, 1 bit can be
encoded reliably for each 3 dB of available dynamic range above the noise floor e.g. a bin with a SNR of 21 dB would be able to
carry 7 bits. However due to the fact that a
minimum of 2 bits
(QAM-4) are encoded per bin, the SNR of any single bin
cannot
drop below 6dB
.
BX100V SNR/Tone Graph
BX100V SNR/Tone Table
Note:
Bit Swapping:
During initial modem link up, a signal to noise measurement is made for each tone and the
bit distribution is optimized to deliver the desired bit rate. During showtime, modems constantly monitor the
SNR/tone and the bit distribution is adjusted to optimize bandwidth based on noise, interference and cross
talk. If a tone degrades in quality, a bit swap command adjusts the bit allocation for that particular tone and
BX100A/V e-Manual D07-00-001 Rev E01
Page 25 of 52
