Comtech EF Data CIM-300L - Manual (Page 126)

CiM-300L IP Enabled Satellite Modem Rev. 1
FEC & Turbo CD/CIM300L.IOM
100
6.3 T
URBO
P
RODUCT
C
ODEC
(H
ARDWARE
O
PTION
)
6.3.1 I
NTRODUCTION
Comtech EF Data implements the FEC Codec based on TPC. A Turbo Product Code is a
two dimensional array of block codes. Encoding is relatively straightforward, but
decoding is a very complex process requiring multiple iterations of processing for
maximum performance to be achieved.
Unlike the popular method of concatenating a Reed Solomon Codec with a primary FEC
Codec, Turbo Product Coding is an entirely stand-alone method. It does not require the
complex interleaving/de-interleaving of the RS approach, and consequently, decoding
delays are significantly reduced. Furthermore, the traditional concatenated RS schemes
exhibit a very pronounced threshold effect – a small reduction in Eb/No can result in total
loss of demod and decoder synchronization. TPC does not suffer from this problem – the
demod and decoder remain synchronized down to the point where the output error rate
becomes unusable. This is considered to be a particularly advantageous characteristic in a
fading environment. Typically, in QPSK, or 8PSK TPC modes the demod and decoder
can remain synchronized 2 – 3 dB below the Viterbi/Reed-Solomon or TCM cases.
Table 6-1 is a listing of all the available TPC modes and rates.
Table 6-1. Available TPC Modes
Code Rate/Modulation Data Rate Range
Rate 21/44 BPSK 4.8 kbps to 1193 Mbps
Rate 5/16 BPSK 4.8 kbps to 781.25 kbps
Rate 1/2 QPSK/OQPSK 4.8 kbps to 2386 Mbps
Rate 3/4 QPSK/OQPSK 7.2 kbps to 3750 kbps
Rate 3/4 8PSK 384 kbps to 5.0 Mbps