3
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Generation Rack-
Mount RDMS™
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Quasonix, Inc.
4.5.3.2.2 Derandomizer Settings
The Derandomizer defaults to Off. Click on the drop down arrow to display the menu, then select the desired option
(Figure 219). The standard running mode for non-LDPC, non-Reed-Solomon operation is IRIG. The CCSDS option
is only available when an LDPC Mode is enabled (SOQPSKLDPC or STCLDPC) or when Reed-Solomon decoding
is enabled.
•
IRIG
–
Derandomizes data randomized using the IRIG 15-stage randomizer
•
CCSDS
–
Derandomizes data randomized using the CCSDS 8-stage block synchronous randomizer
Figure 219: Settings Window, Derandomizer Drop Down Menu
4.5.3.2.3 Differential Decoding Settings
The Differential Decoding option is set to On or Off by clicking on the check box (Figure 220) to enable or disable
the differential decoding. Differential Decoding defaults to enabled.
Differential decoding is available in all PSK modes (SOQPSK and legacy BPSK, QPSK, OQPSK, AQPSK,
AUQPSK, and UQPSK). Legacy modes often use differential forms of PCM encoding (e.g., NRZ-M) instead, and
only one or the other form of differential encoding should be used at a time.
Differential encoding and decoding eliminates the phase ambiguity inherent with the received data. The differential
decoder can be enabled or disabled through the Main Menu by pressing Enter when the parameter is selected. The
Enter key acts as a toggle switch. Normal SOQPSK operation requires the differential decoder to be On. The default
value is On.
Differential encoding results in two differentially-decoded bit errors for each received bit error. This doubling
negatively impacts subsequent error-correction capability for block forward error correction. Since the Attached
Sync Marker used to identify block boundaries can also be used to resolve the phase ambiguity inherent in PSK
modulation, differential encoding is unnecessary for block forward error correction. Therefore, differential decoding
is automatically disabled when Reed-Solomon encoding is enabled.
