M7/M7L/M7LT Modular Satellite Modem
Operation
M7/M7L/M7LT - Rev. 0.05
1-25
The IESS 308 mode automatically adjusts the n and k factors dependent on the data rate. The
“Overhead” ratio is the ratio of the data rate at the RS encoder output to the data rate at the input. It is
defined as n/k. The modem automatically adjusts to accommodate the new rate.
The Reed-Solomon Codec function can be turned on and off under software control, and is
independent of the IBS ESC Data Channel enabling.
1.6.4.
Turbo Product Codes FEC
The addition of the Turbo Product Codes (TPC) option card (Figure 1-20) allows replacement of the
standard Viterbi FEC independently for transmit and receive paths. The performance improvement
achieved by the TPC is significant. For example, the BER vs. Eb/No performance of TPC Rate 3/4 is
approximately equal to Rate 1/2 Viterbi and uses over 40% less bandwidth. TPC also provides better
bandwidth/power utilization than either Reed-Solomon concatenated on Viterbi or 8PSK/TCM with
Reed-Solomon.
Figure 1-20 - TCP Option Card
The modem offers extensive TPC capabilities including first generation 4k block TPC, with both
legacy Datum modem compatibility (PSM500) and Competitive Technology (CT) operating modes,
plus a newer second generation 16k block TPC. This second generation TPC offers superior
performance at the expense of more delay due to larger processing blocks.
The Datum Systems’ proprietary TPC “Advanced” mode has been optimized to provide the highest
performance available in any TPC on the market. These modes not only outperform other
manufacturer’s TPC, but also LDPC in many cases.
1.6.5.
Special Codec CT Modes
The wide range of FECs available today and the possibility of many different operating modes, and
parameters for each, can make compatibility with other brands of modems extremely difficult. To aid
in FEC compatibility with other brands of modems, the modem
offers special “CT” modes, standing
for “Competing Technology”. These modes use the same parameter settings as popular modems by
other manufacturers.
Содержание M7 Series
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