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Datum Systems PSM-500, 500H & 500L VSAT/SCPC Modem Specification

Rev. 0.86

A-9

Bit Error Rate Performance

The following tables and their associated “waterfall” curves show typical Bit Error Rate vs. Eb/No

performance for a modem including the effect of using differential encoding and the appropriate

scrambler.

The values shown are typical, but are extremely repeatable since the entire transmit and receive

processes that affect the performance are digitally produced.

The volume of measurements required plus the significant data that must be collected to

characterize the low error rates achievable by Turbo Product Codes and S-Tec FECs are difficult

and time consuming. Therefore all of these measurements are made by carefully calibrated and

temperature controlled test equipment under computer control. Single measurements of a BER in

the 10

-9

range may require several days.

Although the tables show Eb/No values at fixed logarithmic BER increments for easy reading, the

graphs are created from the actual measurment points. That data and the graph program (GPL

open source) used are available from Datum Systems.

The tabular data contains a 5 digit number above each column of Eb/No data. This number is

called “MTOCR”. It is a short nemonic acronym for M

odulation, FEC Type, Option, Code Rate and

eed-Solomon selection options. To set the modem for any particular combination of MTOCR you

would first select the modulation type (by the number if desired), then the Type, Option and Code

Rate for the FEC and then the Reed-Solomon option. The M, T, O and C values for all currently

available FEC modes are shown in Table 6.

The Eb/No values shown are those referenced to the customer data rate at the decoder output.

Performance would appear improved if measured relative to the decoder input (i.e. at the satellite

data rate).

Note that the performance is subject to change. We periodically have improved the performance of

multiple options via software revisions.

Viterbi FEC and Concatenated Reed-Solomon Performance

The standard Viterbi FEC plus the Viterbi concatenated with Reed-Solomon performance is shown

in the following table and the accompanying graph.

The typical performance with the optional Reed-Solomon codec (concatenated on the Viterbi

codec) is shown in the table below. All values shown are using the standard IESS-308 Reed-

Solomon codec values of n = 126, k=112, depth =4, and the synchronous IESS-308

scrambler/descrambler. Significant changes in performance, positive and negative, are achieved

using different n, k and depth values.

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