User's Manual Part 2

Tech-X Flex User Guide - Firmware v06.50 Tech-X Flex

(NG2)

8-20

Intro

Overview

Wi-Fi

Ethernet

System

IP/Video

MoCA

Specs

Figure 8-13 16-QAM constellation diagram

Aside from a basic chart of binary numbers supported by a QAM scheme, a constellation graph is also a

useful means of visually presenting the quality of an actual QAM signal, especially with respect to the

consistency of amplitude measurements and their intended binary representations. Using a graph in this

manner, the exact center of each “square” is designated as the point where the I and Q signals fall

exactly upon a prescribed data point (that is, an expected amplitude), when the symbol is sampled and

demodulated. For example, the following figure shows a “perfect” symbol that would be plotted as follows

in the “1011” square:

Figure 8-14 The plot of a “perfectly” modulated symbol

Consider, however, a symbol that appears as follows at the point of demodulation:

Figure 8-15 Imperfect amplitude levels

0000 0100 1100 1000

0001 0101 1101 1001

0011 0111 1111 1011

0010 0110 1110 1010

I-signal

(10)

Q-signal

(11)

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