MT312 Forward Error Correction
M SNR[14:0]: These two registers provide a indication of the signal to noise ratio of the channel being received
by the MT312. It should not be taken as the absolute value of the SNR.
13312 - M SNR[14:0]
Eb/N0 = ~ ------------------------------------------------------- dB.
683
The equation given only holds for Es/No values in the range 3 to 15 dB, i.e. Eb/No values in the range 0 to 12
dB.
7.2.4 Viterbi Error Count at Viterbi Input. Registers 11 - 13 (R)
Def
hex
NAME
ADR
B7
B6
B5
B4
B3
B2
B1
B0
VIT ERRCNT H
VIT ERRCNT M
VIT ERRCNT L
11
12
13
VIT ERRCNT[23:16] - Viterbi error count (high byte)
VIT ERRCNT[15:8] - Viterbi error count (middle byte)
VIT ERRCNT[7:0] - Viterbi error count (low byte)
R
R
R
00
00
00
This is effectively the QPSK Bit Error Rate.
VIT ERRCNT[23:0]: This is the count of bits corrected by the Viterbi decoder. This value is updated when the
Viterbi error timer (VIT_ERRPER) expires (indicated by B2 in register FEC_INT) and is NOT reset by reading.
VIT_ERRCNT[23:0]
QPSK BER = -------------------------------------------------------------
VIT_ERRPER[23:0] * 4
7.2.5 Reed Solomon Bit Errors Corrected. Registers 14 - 16 (R)
Def
hex
NAME
ADR
B7
B6
B5
B4
B3
B2
B1
B0
RS BERCNT H
14
RS BERCNT[23:16] - Reed Solomon bit errors corrected
(high byte)
R
R
R
00
RS BERCNT M
RS BERCNT L
15
16
RS BERCNT[15:8] - Reed Solomon bit errors corrected
(middle byte)
00
00
RS BERCNT[7:0] - Reed Solomon bit errors corrected (low byte)
This is effectively the Viterbi Bit Error Rate.
RS BERCNT[23:0]: These three registers provide a measurement of the number of bit errors corrected by the
Reed Solomon decoder. Reading the high byte stops the count incrementing. Reading the low byte resets all
three bytes and restarts the count incrementing again.
RS_BERCNT[23:0]
Viterbi BER = --------------------------------------------------
dt * Rs * 2 * CR
Where: dt = delta time between two readings in sec (recommend 20s for 20 - 30 MBaud signals)
Rs = Symbol rate in Baud
CR = Viterbi code rate
In denominator: the factor 2 is for QPSK, change it to 1 for BPSK
e.g.
for Rs = 27.5Mbaud, CR = 3/4 and dt = 20 sec
RS_BERCNT[23:0] * 4
Viterbi BER = -----------------------------------------------------------
20 * 27.5E6 * 2 * 3
50
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