Downstream Data; Interpreting Qam Constellation Data By Visual Inspection - Cisco GS7000 Installation And Operation Manual

Chapter 5 Using the Web Interface

Downstream Data

Frequency — is the downstream frequency given in Hz.

Power — is the downstream power given in dBmV.

SNR / (RxMER) — this is the downstream signal quality. Modulation Error

Ratio (SNR).
EVM —Error Vector Magnitude calculated from MER.

CER Interval — Codeword Error Rate (CER) refresh rate.

Pre FEC CER — Codeword error rate (CER) BEFORE forward error correction is

applied.
Post FEC CER — Codeword error rate (CER) AFTER forward error correction is

applied.
Updates Remaining — this is the number of sample updates remaining for this

session.

Interpreting QAM Constellation Data by Visual Inspection

The usefulness of the QAM constellation comes in the ability to recognize common
shapes and configurations within the map. The following table summarizes the
shapes commonly visible in the RF Constellation page. Examples of these shapes are
illustrated in the figures that follow.
Shape
64
Focus Impairment
Individual cells Normal
and entire QAM
constellation
Individual cells Low CNR and/or
Low MER
Description
Dots are centered in the
individual QAM quadrants.
The QAM constellation has a
uniform square shape.
Individual cells of QAM
constellation contain a fuzzy
and diffused pattern.
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