User's Manual

5.6.2 Upstream

The wireless cable modem (WCM) transmits an upstream signal (to the Hub Transceiver) under

timing, power and frequency control of the W-CMTS. The W-CMTS can command the WCM to

transmit its IF signal at an output level between 8 dBmV and 58 dBmV (inclusive), based on the

signal the W-CMTS considers optimum for accurate demodulation. These parameters are

established at the time a WCM is powered up, locates a valid downstream signal, and seeks to

be recognized by the W-CMTS. This process is called ranging. It has been designed to be

non-disruptive to subscribers already operating on the particular upstream channel (sector).

The upstream power level is the most important of these for the tuning of the system. The

timing and frequency agility of the WCM are under the command of the W-CMTS. If a WCM is

reporting frequent timing changes, multipath interference to the particular subscriber upstream

transmission is probable. If the WCM is reporting frequent changes in transmit frequency, a

service issue with the WCM or outdoor subscriber transceiver should be considered. If frequent

frequency changes are reported by several WCMs in the same sector, a service issue with the

receiver module within the Hub Transceiver should be considered.

5.6.2.1 Upstream Power Level

Each subscriber installation configured to transmit to this particular upstream channel (sector) is

likely to have a different amount of signal loss between the WCM and the W-CMTS

. The W-

CMTS uses its ability to command the WCM power at each subscriber individually to ensure

that the signals received from each subscriber arrive at nearly the same signal level. For

example, a nearby subscriber installation may need only a tenth of its possible power output to

provide the W-CMTS with the signal it requires, while a subscriber at the outer range of the

system may be commanded to nearly all of it possible power output to provide the same

received level signal at the W-CMTS.

The UpstreamRxGain parameter in the W-CMTS configuration file provides a set point for the

upstream gain loop. This parameter establishes the nominal upstream signal level at the W-

CMTS input. Each WCM will be commanded (separately) to adjust its signal output such that its

signal arrives at the W-CMTS input at this nominal level. Recall that each WCM is transmitting

its upstream data in turn, under commands of the W-CMTS.

Arcwave recommends that the system installer set the UpstreamRxGain parameter such that

the subscriber WCM with the most path loss (typically the most distant) operates at or just below

55 dBmV WCM output

. This will cause all of the other WCMs in the sector to operate at some

lesser output level

, which the W-CMTS will automatically assign. The optimum value of this

parameter may vary from sector to sector (upstream channel) in a given system due to factors

such as different subscriber path lengths to the base station.

This is due primarily to the different physical distances between the various subscriber installations

and the base station. Other factors are any obstructions in the path, location of the subscriber in the Hub

Transceiver antenna pattern geometry, any misalignment of the subscriber transceiver antenna, different

cable lengths between each WCM and its outdoor transceiver, etc.

This level setting will provide a nominal margin for signal fading of about 3 dB. The W-CMTS will

operate at perhaps 5 dB of additional fading (lower signal) under exceptional conditions but this should

happen rarely in the delivery of high quality performance to the subscriber.

As all remaining subscriber installations have less path loss than the “furthest” subscriber.

June 2003 Page 5-19