Quality Thresholds
1.1. SigQ Parameter Color Mapping
Direction | Modulation | min. SNR / dB |
|---|---|---|
Downstream | 64QAM | < 24 |
24 - 27 | ||
> 27 | ||
256QAM | < 30 | |
30-33 | ||
>33 | ||
Upstream | QPSK | < 12 |
12 - 15 | ||
> 15 | ||
16QAM | < 18 | |
18 - 21 | ||
> 21 | ||
64QAM | < 24 | |
24 - 27 | ||
> 27 |
max. Upstream Power / dBmV | ||||
|---|---|---|---|---|
N CHs | 1 CH | 2 CHs | 4 CHs | 8 CHs |
< P_rec | < 53 | < 51 | < 48 | < 45 |
P_rec - P_max | 53 - 56 | 51 - 54 | 48 - 51 | 45 - 48 |
> P_max | > 56 | > 54 | > 51 | > 48 |
P_rec = 57 - ceil(3.6*log2(1+N))
P_max = 60 - ceil(3.6*log2(1+N))
1.2. Overview DOCSIS Datarates
1.2.1. Table
Datarates in MBit/s:
Bandwith/Modulation | QPSK | 16 QAM | 32 QAM | 64 QAM | 256 QAM | 1024 QAM |
|---|---|---|---|---|---|---|
1,6 MHz (US) 1,28 MBaud | 2,5 | 5 | 6,25 | 7,6 | 10 | 12,5 |
3,2 MHz (US) 2,56 MBaud | 5,1 (minSNR 15 dB) | 10,1 (minSNR 21 dB) | 12,75 (minSNR 24 dB) | 15,3 (minSNR 27 dB) | 20,4 (minSNR 33 dB) | 25,5 |
6,4 MHz (US) 5,12 MBaud | 10,2 | 20,4 | 25,5 | 30,7 | 41 | 55 |
8 MHz (DS) | 13,9 (minSNR 10 dB) | 27,8 (minSNR 16 dB) | 34,8 (minSNR 19 dB) | 41,7 (minSNR 22 dB) | 55,6 (minSNR 28 dB) | 69,5 |
1.2.2. Theory
DSRate = Bandwidth/1,15 * lb(Symbole)
USRate = Bandwidth/1,25 * lb(Symbole)
1,15 and 1,25 are roll off factors resulting of the slope of the channel (in spectrum)
SNR = 10 x lg ( 2^(Datarate/Bandwidth) - 1)
Sources:
https://volpefirm.com/docsis-3-0-cable-modems/
http://www.scte.org/TechnicalColumns/08-11-01%20total%20power%202.pdf