As DOCSIS 3.0 evolved and most ISPs/MSOs replaced their DOCSIS 2.0 Modems with DOCSIS 3.0 Modems, there was a challenge with “DOCSIS 3.0 Upstream Power Levels” in the field. What is the Challenge? Do we really need our DOCSIS 3.0 Modems to support “Extended Upstream Transmit Power”? How do I find if my Modem supports this feature? This article tries to answer these questions.
Maximum power allowed in DOCSIS 2.0 Modems
As defined in DOCSIS 2.0 RFI specifications in section 6.2.18, maximum transmit power of a 64-QAM Upstream TDMA channel (Pmax) is 54 dBmV. Most of the DOCSIS networks were designed around this and there would be end-points (customer houses) in the nodes which would be at max power level of 54 dBmV. (At 16-QAM, the Pmax level is 55 dBmV).
Maximum power allowed in DOCSIS 3.0 Channel Bonded Modems
Early DOCSIS 3.0 modems came with 4 upstream channel bonding. 8 Upstream bonded channel modems came much later. As per DOCSIS 3.0 PHY specifications, maximum transmit power allowed for single 64-QAM Upstream TDMA channel (Pmax) is 57 dBmV. So DOCSIS 3.0 increased overall power levels by 3dB. However, this power is for single channel only. When the Cable modem bond multiple channels, power levels will reduce by 3dB (for 2 channel bonding) and 6dB (for 4 channel bonding). Now if MSO deploys 4 bonded US channels, transmit power per channels was only 51 dBmV. This accounts to overall 3dB loss from DOCSIS 2.0 where each channel used to transmit 54 dB (64-QAM).
Extended Upstream Power in DOCSIS 3.0
An ECN (Engineering Change Notification) ECN MULPIv3.0-N-10.0943-5 Extended Upstream Power was done in 2010 in CableLabs MULPI and PHY specifications to allow Cable modems to transmit beyond 51 dBmV. This allows Cable Modems to transmit more power when they are bonded 2,3, 4 or more channels in upstream.
Now a days in most Cable modems you would see Cable Modems transmitting > 51 dBmV when bonded with 4 channels in Upstream.
What Modems are recommended for best Signal levels?
It is always advisable to choose a modem with extended upstream power capability. Some of the modems in the market which have this capability are: Arris SB6183, NETGEAR CM500, Motorola SB8200, NETGEAR CM1000, etc
Extended Upstream Power Configuration
Extended Upstream power is configured using DOCSIS Config files on the modem by the operator. In US, Comcast typically configures most of their leased and most retail modems with extended Upstream power. Most of the new DOCSIS 3.0 and all DOCSIS 3.1 devices are capable of Extended Upstream power. If your home is at edge of the node, you would need this capability in the modem as otherwise, you would land up in the partial service mode with few bonded upstreams.
This diagram from Excentis explains power levels across DOCSIS specifications.
Also read, post from Excentis here