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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=1Transmitted bit / symbol
QPSK / OQPSK=2Transmitted bit / symbol
8PSK=3Transmitted bit / symbol
BPSK - 0 dB
QPSK / OQPSK - 3 dB
8PSK - 4.77 dB
i
i
i
Es
No
Et
No
CEs
NNo
No
Et
Measure:
Noise
Carrier + 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
EDE
No
Et
EDE
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.
op
op
N
C
opC+N/N
op
dB=10Log
op10 -1
10
10
ii i
- 10 Log (#Bits / Symbol) - 10 Log (FEC Code Rate)
- 10 Log (FEC Code Rate)
- 10 Log (RS Code Rate)
-10Log( )- 10 Log (#Bits / Symbol)
=
=
==
k
k
DEMOD
FEC
DECODER
RS
DECODER
DEFRAMING
From Satellite Rx Data
(C+N)/NdB
Spectrum Analyser
Carrier+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
ii
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
opC+N/N
op10 -1
10
10 Log
10
2
Carrier power Noise power
P300H P300 Series Modem Installation and Operating Handbook Page 161
8.12.4 Eb/No Explanatory Diagram