Motorola BSR 2000, Configuration And Management Manual

Page: 213 / 650

Release 1.0 Configuring the CMTS
526360-001-00 Rev. B MGBI 6-27
Configuring Spectrum Power Density Maintenance for a
Logical Channel
The Maintain Power Spectral Density feature can be enabled for each logical channel.
If Maintain Power Spectral Density is enabled and the modulation rate is different
from the previous UCD, the cable modem must change its transmit power level to
keep the power spectral density as close as possible to what it was prior to the
modulation rate change. If Maintain Power Spectral Density is disabled, the cable
modem maintains the same power level that it was using prior to the modulation rate
change.
Use the cable upstream maintain-power-density on command, in Cable Interface
Configuration mode, to enable the Maintain Power Spectral Density feature, as shown
below:
MOT(config-if)#
cable upstream <
X
/
Y
> maintain-power-density on
where:
X
/
Y
the upstream port number and logical channel number (0-3).
Additional S-CDMA Logical Channel Configurations
The S-CDMA logical channel type introduces additional complexities in the timing
and synchronization of upstream scheduling. The upstream channel is still scheduled
using intervals described in terms of minislots.
In S-CDMA channel types, determining the minislot size in time ticks is no longer
used. S-CDMA groups data and codes into S-CDMA frames. A minislot in S-CMDA
is defined as an interval of time and a code (or combination of codes). Mini-slots are
mapped to frames. S-CDMA uses the concepts of spreading intervals, the number of
allowed active codes, and the number of active codes per mini-slot to determine
scheduling intervals per S-CDMA frame. A spreading interval is the time it takes to
send one symbol per code across all 128 possible codes in an S-CDMA frame. The
time duration of an S-CDMA frame is determined by a configurable number of
spreading intervals and the signaling rate. The number of codes per mini-slot is also
configurable as is the number of codes used.
The S-CDMA channel type allows multiple modems to transmit on the same
upstream channel at the same time. S-CDMA spreads the signals transmitted based on
the particular code used so that messages will not interfere with each other. The
coding has the effect of creating channels within the same spectrum. With S-CDMA,
more than one mini-slot can occupy the same place in time in the upstream bandwidth
allocation. Mini-slots are separated by the code(s) used.