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Chapter 9: Upstream Cable Access Modules (UCAMs)

STANDARD Revision 1.0 C4® CMTS Release 8.3 User Guide

SCDMA Spreader Enable

According to the DOCSIS RFI specification, if SCDMA is enabled, IUC 3 must have the spreader off and the IUCs 1, 9, 10 and

11 must have the spreader on. This only leaves IUC 4. The specification states that it can have the spreader on or off.

However, the current version of the software only supports spreader off for IUC 4. Therefore, all of the values for the

spreader must remain the same as what is currently in the default modulation profiles. This is shown in the show cable

modulation-profile command in the Scdma Sp En column.

SCDMA Codes Per Subframe

This parameter is used in with the SCDMA interleaver step size to determine how data is interleaved with SCDMA. This

parameter is shown in the show cable modulation-profile command in the Scdma Sub Code column.

When interleaving with SCDMA, preamble and TCM-encoded symbols are interleaved in one way and non-TCM-encoded

symbols are interleaved in another. This parameter has the greatest effect on the preamble and TCM-encoded symbols.

Since in general TCM is not recommended, this simply leaves the preamble symbols. As such this parameter does not tend

to have much effect on the overall performance of the system.

Arris C4C User Manual

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