Turbo Product Codec (Hardware Option); Introduction; Tpc Modes Available In The Cdm-570L; Table 14. Available Tpc Modes - Comtech EF Data CDM-570L Installation And Operation Manual

CDM-570L Satellite Modem with IP Module

7.5 Turbo Product Codec (Hardware Option)

7.5.1 Introduction

Turbo coding is an FEC technique developed within the last few years, which delivers
significant performance improvements compared to more traditional techniques. Two
general classes of Turbo Codes have been developed, Turbo Convolutional Codes (TCC),
and Turbo Product Codes (TPC, a block coding technique). Comtech EF Data has chosen
to implement an FEC codec based on TPC. A Turbo Product Code is a 2 or 3 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 output error rate
becomes unusable. This is considered to be an advantageous characteristic in fading
environment. Typically, in QPSK, 8-PSK and 16-QAM TPC modes the demod and
decoder can remain synchronized 2 – 3 dB below the Viterbi/R-S or TCM cases
With this release of the CDM-570L, Comtech EF Data now provides the best Forward
Error Correction technology currently available, offering a very broad range of TPC code
rates, combined with the entire range of modulation types, from BPSK to 16-QAM.

7.5.2 TPC modes available in the CDM-570L

Rate 21/44 BPSK
Rate 5/16 BPSK
Rate 21/44 QPSK, OQPSK
Rate 3/4 QPSK, OQPSK
Rate 3/4 8-PSK
Rate 3/4 16-QAM
Rate 7/8 QPSK, OQPSK
Rate 7/8 8-PSK
Rate 7/8 16-QAM
Rate 0.95 QPSK, OQPSK
Rate 0.95 8-PSK

Table 14. Available TPC Modes

Code Rate/Modulation Data Rate Range
2.4 kbps to 1.19 Mbps
2.4 kbps to 0.78 Mbps
4.8 kbps to 2.38 Mbps
7.2 kbps to 3.75 Mbps
10.8 kbps to 5.0 Mbps
14.4 kbps to 5.0 Mbps
8.4 kbps to 4.37 Mbps
13.6 kbps to 5.0 Mbps
16.8 kbps to 5.0 Mbps
9.1 kbps to 4.72 Mbps
15.3 kbps to 5.0 Mbps
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