3
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Generation Rack-
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Quasonix, Inc.
Figure 106: Advanced Menu, PCM Encoding
Figure 107: PCM Encoding Selections
4.4.2.22 FEC Menu
Forward Error Correction (FEC) may be accomplished by using Low-Density Parity Check (LDPC) encoding, in
SOQPSK or STC modes, or by using convolutional encoding/Viterbi decoding, and/or ReedSolomon encoding in
legacy PSK modes (BPSK, QPSK, OQPSK, AQPSK, AUQPSK, or UQPSK). All of these forms of FEC are
discussed in the following sections.
Figure 108: Advanced Menu, FEC
Figure 109: FEC Menu (LDPC Version)
4.4.2.22.1 LDPC Code (SOQPSKLDPC or STCLDPC Modes Only)
Low-Density Parity Check (LDPC) encoding is a form of forward error correction. It works by adding redundant
information at the transmitting end of a telemetry link and then using that redundancy to detect and correct errors at
the receiving end of the link. Details of LDPC coding are presented in IRIG 106-17 Appendix 2-D.
LDPC encoding can have many benefits. Its most common use is in range extension, where bit errors occur due to a
weak received signal. LDPC can improve the point at which errors start to occur by over 9 dB. This increase in link
margin is equivalent to almost tripling the operating distance of the telemetry link. Another application is error
suppression
—
for links like compressed video that suffer major degradation due to small numbers of errored bits.
LDPC has such a steep bit error rate curve that it converts the channel into essentially binary performance
—
perfection or highly errored. Since perfection is achieved deep into the area where occasional bit errors would
normally occur, compressed video performance is greatly enhanced. Ultimately, any channel that can benefit from
error reduction and has bandwidth available will likely benefit from LDPC encoding.
