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Description
Mode
Compatibility
Disabled
N/A
IESS-308
IESS-308
IESS-308
IESS-308
IESS-309
IESS-309
CT220,200
Comtech
Custom
Modified
IESS-309
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 R-S 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.
1.2.8.3 Turbo Product Codes FEC Capability
The addition of the Turbo Product Codes (TPC) option allows replacement of the standard Viterbi
FEC selectively for the transmit and receive paths independently. The performance improvement
achieved by the TPC is significant. For example, the BER vs. Eb/No performance of TPC Rate ¾ is
approximately equal to Rate ½ 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.
The PSM-500 series offers extensive TPC capabilities including both first generation 4k block TPC
with both PSM-4900 compatibility (M5) and Competitive Technology (CT) operating modes plus a
newer second generation 16k block TPC. This second 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.
The Turbo Product Codes FEC is more fully explained in Appendix TPC.
1.2.8.4 FlexLDPC FEC Capability
The addition of the FlexLDPC FEC option allows replacement of the standard Viterbi FEC selectively
for the transmit and receive paths. The performance improvement achieved by FlexLDPC is the
highest and most flexible of any specialized FEC technology to date, outperforming TPC in across
all modes. FlexLDPC at rate ½ are capable of operating at a sustained Eb/No of only 1.5 dB with an
-9
error rate less than 10
.
Page 1-20
Terrestrial
Overhead
Data Rate
Ratio
1/1
1.2 kbps to
9/8
<1.544 Mbps
1.544 Mbps to
45/41
<2.048 Mbps
>2.048 Mbps
73/67
All
73/67
All
11/10
All
Variable
PSM-500/500L/500LT SCPC Satellite Modem
n, k and depth Values
126, 112, 4 (M4 modem compatible)
225, 205, 4
219, 201, 4
219, 201, 4
220, 200, 4
Allows setting the "n", "k" and "depth"
values for special requirements. Can
also be set for M4 compatibility to
max M4 data rate.
PSM-500/500L/500LT - Rev. 0.91
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