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2.1.6
Downstream and Upstream Transmissions
The terms "downstream" and "upstream" refer to data traffic flows, and indicate the
direction in which the traffic is traveling. "Downstream" refers to traffic from the
service provider to the CODA-57/57-EU, and "upstream" refers to traffic from the
CODA-57/57-EU to the service provider.
2.1.7
Cable Frequencies
Just like radio transmissions, data transmissions over the cable network must exist
on different frequencies in order to avoid interference between signals.
The data traffic band is separate from the TV band, and each data channel is
separate from other data channels.
2.1.8
Modulation
Transmissions over the cable network are based on a strong, high frequency periodic
waveform known as the "carrier wave." This carrier wave is so called because it
"carries" the data signal. The data signal itself is defined by variations in the carrier
wave. The process of varying the carrier wave (in order to carry data signal
information) is known as "modulation." The data signal is thus known as the
"modulating signal."
Cable transmissions use a variety of methods to perform modulation (and the
"decoding" of the received signal, or "demodulation"). The modulation methods
defined in DOCSIS 3 are as follows:
QPSK: Quadrature Phase-Shift Keying
QAM: Quadrature Amplitude Modulation
QAM TCM: Trellis modulated Quadrature Amplitude Modulation
In many cases, a number precedes the modulation type (for example 16 QAM). This
number refers to the complexity of modulation. The higher the number, the more data
can be encoded in each symbol.
NOTE:
In modulated signals, each distinct modulated character (for example, each
audible tone produced by a modem for transmission over telephone lines) is
known as a symbol.
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Version 1.0, 12/2022. Copyright
Version 1.0, 12/2022. Copyright
Hitron CODA-57/57-EU User's Guide
2022 Hitron Technologies
2012 Hitron Technologies
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