Satellite Communications/Satellite communication

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Question
HI Mr.Rao,
Hope u doing well.
I would like to know about following situations:

Suppose during uplink, situation is
1.DVB-S , FEC-3/4 , QPSK. Forward PWR HPA-200 Watts.
2.DVB-S2, FEC-3/4 , QPSK.
3.DVB-S , FEC-5/6 , QPSK.
4.DVB-S , FEC-3/4 , 8PSK.

My question is what are the requirements of FORWARD PWR (Increase/Decrease) for situations 2,3 and 4. WHY ?

Thanks in advance.

Answer
Hi Mr Sumit,
I am fine and thanks for the enquiry.
In satellite communications situations the most important first step is to design Link Budget: both Uplink and Down Link calculations based on the Satellite parameters. The Uplink EIRP, Downlink C/N are all linked solutions. FEC is also a parameter to be considered for evaluation of Baseband performance in terms of BER and link margins. However the actual parameters are decided on the baseband requirements. And EIRP decides the capability of the total link for achieving the required C/N and S/N along with BER specifications.
In your query the effect of Uplink Power is mostly decided on the Total link specifically the receiver characteristics. Correspondingly the uplink power can be changing.
I am giving you below a typical performance specification scenario for DVB S and DVB as receive C/No specs. You can see the effect of Margin in each of the cases for DVB and DVB S that need to be maintained for each of the types of Modulations.

Multi-Standard Demodulation
QPSK: 1.5 to 45 Msps (DVB-S)
QPSK: 1.5 to 45 Msps (DVB-S2)
8PSK: 1.5 to 30 Msps (DVB-S2)

Data Throughput   80 Mbps

Multi-Standard Decoding FEC   
DVB-S   Viterbi 1/2, 2/3, 3/4, 5/6, 6/7, 7/8 rates Reed Solomon
DVB-S2    LDPC 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10 BCH decoder

Typical DVB-S Performance @ 30 Msps   C/N
QPSK FEC 1/2          3.5 dB

QPSK FEC 3/4          5.2 dB
8PSK FEC 3/4          9.2 dB

QPSK FEC 5/6          6.3 dB
QPSK FEC 7/8          7.4 dB
QPSK FEC 2/3          8.1 dB

Typical DVB-S2 Performance @ 30 Msps   C/N

QPSK FEC 1/2          1.2 dB

QPSK FEC 2/3          3.3 dB
8PSK FEC 2/3          6.9 dB

QPSK FEC 3/4          4.2 dB
8PSK FEC 3/4          8.2 dB

QPSK FEC 5/6          5.4 dB
8PSK FEC 5/6          9.7 dB

QPSK FEC 8/9          6.4 dB
8PSK FEC 8/9          11.1 dB

QPSK FEC 9/10          6.7 dB

You may please analyse from the Table above all the info required and transpose them back to the Uplink power requirements and/ or the effect on the Output Power from your reference 400W. May be a bit of Link Calculations need to be undergone for actual values.
You may contact me further for any clarifications and comment on how useful this information has been.
Cheers/GTRao  

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TIRUMALA RAO G

Expertise

Satellite Communications Applications, Link Calculations, Teleports, Earth Stations,VSAT, Tracking, Mobile Communications, Next Generation Networks.

Experience

40 Years. Indian Space Research Organisation, PANAMSAT, Satellite Based VSAT Networks, IP Networks.

Organizations
ISRO, PANAMSAT, Engineering Institution for Higher Education (GVP College of Engineering), Consultancy.

Education/Credentials
Graduate in Electronics and Communication Engineering with Distinction. Guiding scholars for their Doctoral thesis in related areas in Academics.

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