Product specifications

CDD-562L/564 Demodulator with IP Module Revision 1
Forward Error Correction MN/CDD564L.IOM
5–2
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, 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 demodulator, Comtech EF Data now provides the best Forward Error
Correction technology currently available.
5.2.2 End-to-End Processing Delay
In many cases, FEC methods that provide increased coding gain do so at the expense of increased
processing delay. However, with TPC, this increase in delay is very modest. Table 5-1 shows the
processing delays for the three TPCs at 64 kbps based on the latency through a CDM-570/570L
with IP Module and either a CDD-564/564L or CDD-562L.
Table 5-1. Turbo Product Coding Processing Delay Comparison
FEC Mode (64 kbps data rate) End-to-end delay, ms
Turbo Product Coding, Rate 3/4
47
Turbo Product Coding, Rate 7/8
249
Turbo Product Coding, Rate 0.95
69
Note that, in all cases, the delay is inversely proportional to data rate, so for 128 kbps, the delay
values would be half of those shown above.
5.2.3 Comparison of All TPC Modes (Contains Additional Information)
Mode
Eb/No at
BER = 10
-6
Guaranteed
(Typical in
parentheses)
Eb/No at
BER = 10
-8
Guaranteed
(Typical in
parentheses)
Spectral
Efficiency
Symbol Rate
Occupied
Bandwidth
for 1 Mbps
Carrier
QPSK
Rate 3/4 Turbo
3.8 dB
(3.4 dB)
4.4 dB
(4.0 dB)
1.50 bits/Hz 0.67 x bit rate 793 kHz
QPSK
Rate 0.95 Turbo
6.4 dB
(6.0 dB)
6.9 dB
(6.5 dB)
1.90 bits/Hz 0.53 x bit rate 626 kHz
*8-PSK Rate 3/4 Turbo
6.2 dB
(5.8 dB)
6.8 dB
(6.3 dB)
2.25 bits/Hz 0.44 x bit rate 529 kHz
*8-PSK Rate 0.95 Turbo
9.3 dB
(8.9 dB)
10.3dB
(9.9 dB)
2.85 bits/Hz 0.35 x bit rate 377 kHz
*16-QAM Rate 3/4 Turbo
7.4 dB
(7.0 dB)
8.2 dB
(7.7 dB)
3.00 bits/Hz 0.33 x bit rate 396 kHz
*Future offering, firmware upgrade and FAST option.
The additional advantages of Turbo – lower delay, performance during fades, etc. – should also
be considered.