Eachsymbol represents several
transmittedbits depending on
themodulation:
Et Signal / noise expressed
No attransmitted bit rate
Es Signal / noise expressed
No at the symbol rate
BPSK=1Transmittedbit / symbol
QPSK/ OQPSK=2Transmittedbit / symbol
8PSK=3Transmittedbit / 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
FECdecoder reduces data rate
&corrects errors. Data rate reduced
byFEC code rate:
EDE 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 +3dB
3/ 4 Rate +1.25dB
7/ 8 Rate +0.58dB
2/ 3 Rate +1.76dB
i
i
i
i
Et
No No
EDE
No
Et
EDE
No
Eb
No
EDE
No
EDE
No
Eb
No
RSdecoder reduces data
rate& corrects errors. Data
ratereduced by RS code rate:
Eb Signalnoise expressed at
No compositeinformation rate
Coderate expressedas (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) +0.40dB
i
i
i
Bandwidthchange due to
framingis ignored in
INTELSATdefinition of
Eb/Noas Eb refers to the
compositedata rate.
op
op
N
C
opC+N/N
op
dB=10Log op10 -1
10
10
iii
-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
FromSatellite RxData
(C+N)/NdB
SpectrumAnalyser
Carrier+Noise
Noise
Symbol
Rate
Transmitted
BitRate
FECDecoded
DataRate
Composite
InformationRate
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
iii
i
iii
Example
1
1
Calculateratio of
Noisepower
Carrierpower
2
Es Energy per symbol C
No Noise power density N
==
DetermineEs
No
3
4 5 6
3 4 5 6
opC+N/N
op10 -1
10
10Log 10
2
Carrierpower Noise power
P300H P300 Series Modem Installation and Operating Handbook Page 161