Making a DOCSIS 4.0 Upstream Measurement

Overview

This topic describes how to configure the VSA to make a DOCSIS 4.0 Upstream measurement.

Signal Setup

Before selecting DOCSIS 4.0 Upstream demodulation, make sure that the input signal is correctly captured by the analyzer. Specify the VSA basic signal measurement setup parameters so that the input signal is fully captured including the center frequency, span, input range, etc.. You can use the Spectrum and Time traces to verify that the signal of interest is properly captured.

Set the Center frequency to subcarrier (FFT Length / 2) and set the Span wide enough so that all active subcarriers are captured by the Span.

Tutorial Demo Signal

This measurement tutorial uses a demo signal based on a DOCSIS 3.1 Upstream signal, although the configuration is the same for DOCSIS 4.0. The DOCSIS Upstream configuration developed below can be used with the supplied VSA Demo Signal "docsis3.1-us.htm" which uses the "docsis3.1-us.sdf" recorded signal.

To use the demo signal, recall the "docsis3.1-us" Demo Signal, click File > Recall > Recall Demo > docsis3.1-us.htm.

Configuring the Demodulator

Setup for the demodulator can be quite automated such that the user needs only to set the appropriate center frequency, span, amplitude. In addition three DOCSIS US burst parameters will be entered – the pilot pattern index, the bit-loading (modulation format), and the burst size. In this mode, the VSA will attempt to automatically configure the remaining settings such as the FFT size, Cyclic Prefix, Rolloff Period, exclusion and guard bands, and mini-slot allocations.

If necessary, the automatic mode can be disabled, and the user may elect to manually enter the parameters necessary to demodulate the signal.

These parameters are available on the DOCSIS 4.0 Upstream Demod Properties dialog.

Format Tab:

  1. Manual Initial Settings Configuration

    1. Set Initial Settings to Manual mode (uncheck Auto Detect)

    2. Select the desired FFT length (2048 or 4096)

    3. Select the appropriate Cyclic Prefix Length and Rolloff Period

  2. Manual Excluded / Guard Band Configuration

    1. Set Excluded/Unused/Guard Band Config to manual mode (uncheck Auto Detect)

    2. The threshold level for subcarrier detection is not used in manual mode

    3. Use the Edit button to configure all desired excluded/unused/guard bands by entering the starting subcarrier number, and the length in subcarriers for each band. Typically there will be at least two bands – one at the lower edge starting at subcarrier 0, and one at the upper edge of the band extending to either subcarrier 2047 or 4095 depending on the FFT Length.

  3. Burst/Minislot manual configuration

    1. Select manual mode for burst/minislot configuration (uncheck Auto Detect minislot start and length)

    2. Use the edit button to enter the starting minislot and number of minislots in the allocation, then press the Apply button and the Ok button to dismiss the edit dialog.

Advanced Tab:

You may also adjust the system sampling frequency from its default of 102.4 MHz as defined in the specification. This can be useful if a system is running in some bread-board implementation which cannot run at full speed.

See Also

Selecting the DOCSIS 4.0 Upstream Demodulator