Each symbol represents several
transmitted bits depending on
the modulation:
Et
Signal / noise expressed
No at transmitted bit rate
Es
Signal / noise expressed
No
at the symbol rate
BPSK = 1 Transmitted bit / symbol
QPSK / OQPSK = 2 Transmitted bit / symbol
8PSK = 3 Transmitted bit / symbol
BPSK
- 0 dB
QPSK / OQPSK
- 3 dB
8PSK
- 4.77 dB
i
i
i
Es
No
Et
No
C Es
N No
No
Et
Measure:
Noise
C Noise
(C+N)/N
FEC decoder reduces data rate
& corrects errors. Data rate reduced
by FEC code rate:
E DE
Signal / noise expressed at
No
FEC decoder output rate
1 / 2 Rate = 1 Decoded bit / 2 transmitted bits
3 / 4 Rate = 3 Decoded bits/ 4 transmitted bits
7 / 8 Rate = 7 Decoded bits / 8 transmitted bits
2 / 3 Rate = 2 Decoded bits / 3 transmitted bits
1 / 2 Rate
+3 dB
3 / 4 Rate
+1.25 dB
7 / 8 Rate
+0.58 dB
2 / 3 Rate
+1.76 dB
i
i
i
i
Et
No
No
E DE
No
Et
E DE
No
Eb
No
EDE
No
EDE
No
Eb
No
RS decoder reduces data
rate & corrects errors. Data
rate reduced by RS code rate:
Eb Signal noise expressed at
No composite information rate
Code rate
expressed as (n,k,t)
(126,112,7) = 112 Information bits / 126 Decoded
(219,201,9) = 201 Information bits / 219 Decoded
(225,205,10) = 205 Information bits / 225 Decoded
(126,112,7)
+0.51 dB
(219,201,9)
+0.37 dB
(225,205,10)
+0.40 dB
i
i
i
Bandwidth change due to
framing is ignored in
INTELSAT definition of
Eb/No as Eb refers to the
composite data rate.
o
p
o
p
N
C
o
p
C+N / N
o p
dB = 10 Log
o
p
10
-1
10
10
i
i
i
- 10 Log (#Bits / Symbol)
- 10 Log (FEC Code Rate)
- 10 Log (FEC Code Rate)
- 10 Log (RS Code Rate)
- 10 Log (
)
- 10 Log (#Bits / Symbol)
=
=
=
=
k
k
DEMOD
FEC
DECODER
RS
DECODER
DEFRAMING
From Satellite
Rx Data
(C+N) / N dB
Spectrum Analyser
Noise
Noise
Symbol
Rate
Transmitted
Bit Rate
FEC Decoded
Data Rate
Composite
Information Rate
Summary
=
Measure
Vit / Seq /
TCM / Turbo
DEC
DEC
DEC
DEC
n
n
DEC
to
6.5dB
5.40dB - 3dB
(QPSK)
2.40dB + 1.25dB
(3 / 4 Rate)
2.40dB
3.65dB + 0.51dB
(126,112,7)
3.65dB
4.16dB
i
i
i
i
i
i
i
i
i
Example
1
1
Calculate ratio of
Noise power
Carrier power
2
Es
Energy per symbol
C
No
Noise power density
N
=
=
Determine Es
No
3
4
5
6
3
4
5
6
o
p
C+N / N
o
p
10
-1
10
10 Log
10
2
Carrier power
Noise power
P300H
P300 Modem Installation and Operating Handbook
Page 150
8.12.4
Eb/No Explanatory Diagram