P300H
P300 Series Modem Installation and Operating Handbook
Page 70
For
Ì«®¾±
FEC the FEC rate selection screen is as follows:
Select Turbo Mode/Code rate, then (YES)
[0.750 Industry de-facto 3/4 rate]
Change, Tx/Rx, Mod/Demod, FEC Rate Menu (Turbo)
The Turbo FEC code rate may be selected from the scroll list of preset rates displayed on the screen.
pressing
YES
will accept the current FEC rate and return to the Change, Tx, Modulator menu. This list
can contain up to 31 different rates, but currently only the following are defined:
Screen Description
Exact
code rate
Delay
(bits) *
Modulation Schemes from
BPSK
QPSK
OQPSK
8PSK
"0.3125 Industry de-facto 5/16 rate"
0.3125
2662
V3.57
n/a
"0.477 Industry de-facto 21/44 rate"
21/44
4056
V3.57
n/a
"0.493 Paradise 1/2 rate"
2028/4116
4056
V3.40
n/a
"0.666 Paradise 2/3 rate"
2499/3748
4998
V3.57 V3.57 V3.57
n/a
"0.750 Industry de-facto 3/4 rate"
0.750
4446
V3.40
n/a
"0.789 Paradise 3/4 rate"
3249/4116
6498
V3.40
n/a
"0.875 Paradise 7/8 rate" **
(Low Latency)
0.875
450
(yes 450)
V3.40
n/a
* Note on processing delay. Use the data rate
before
the FEC to determine the delay in milliseconds from
the delay in bits. For example at 1Mbps using Rate 0.789 Turbo FEC, the FEC delay is (6498/1000000)
seconds, which is 6.5ms.
** Note on Low Latency 7/8 Rate Turbo: As Turbo FEC schemes go this is a relatively poor performer.
BUT it does provide about a 1dB performance improvement over 7/8 rate Viterbi, and for links where the
transponder space is fixed to accommodate a 7/8 Viterbi coded link, switching from Viterbi to Turbo will
give a useable 1dB improvement. It also provides significantly lower latency than subsequent Turbo
schemes (which offer a better 7/8 rate performance at the cost of significant latency). If you`re stuck with a
channel that can only accommodate 7/8 Rate FEC, then this will give you an extra dB over using Viterbi.
