AboutMark C J Posen Expertise I am happy to answer questions of a technical and regulatory nature in the area of satellite and radio communications. I am best able to answer questions about systems and technology and less able to respond to questions about specific hardware and equipment setup and installation, but I'm happy to try and address any question put my way.
My main areas of expertise are link analysis (link budgets, performance, Eb/No, capacity), interference analysis (C/I, protection ratios, interference avoidance), spectrum management (frequency coordination, inter-system sharing), Radio Regulation (ITU, ITU-R) and satellite technologies and trends.
Experience I have worked as a satellite communications engineer at a professional level since 1983. Since 1990, as Managing Director of RPC Telecommunications Limited, I have operated a private satellite communications consultancy and have provided technical support to many satellite operators and national governments.
Organizations IET - Institution of Engineering and Technology, IEEE - Institute of Electrical and Electronic Engineers
Question QUESTION: Please tell me that what would be the symbol rate which i can configure in my modulator for 6Mhz occupied bandwidth when my roll-off factor would be 0.35.The bandwidth is the total bandwidth which is allocated by ISRO to me. So tell me the exact symbol rate which i can configure in my modulator.?
ANSWER: Hi Anurag,
Really the issue depends on what ISRO mean when they allocate you 6 MHz. Do they allow a guard-band between your allocation (in which you can completely fill the 6 MHz with your carrier, or if they require you to leave some guard band at the edge of your allocation to protect the adjacent carrier from interference.
If you can fill the entire 6 MHz then I think that you can use the 0.35 roll-off to define the Symbol Rate, which means that you can fit 4.44 MSym/s (4.44*1.35=6).
However, if you need to allow for a carrier spacing factor, typically 1.4 or 1.45 then you can fit only around 4.14 MSym/s (4.14*1.45=6).
I have made a simple spreadsheet that lets you play around with these numbers to see how they relate to each other and which might help you understand better what is going on, which you can see at:
For you operational system, however, I strongly advice you to consult with ISRO and to agree a link budget and transmission plan with them, to avoid breaking the terms of your lease.
I hope this helps. Please remember to rate this answer.
QUESTION: Thanks allot Mark, you gave me such an important information. Support if i want to calculate symbol rate for 6Mhz bandwidth where i have to consider guard band also, so the SR= 6/1.45 = 4.14 which will occupy 5.59 Mhz bandwidth with 410 khz guard band. just tell me am i right??
Answer Hi Anurag,
Yes, what you have stated is exactly the case. BUT there is an important clarification here. It is true based *only* on the assumption that the roll-off factor is 0.35 and that the "carrier spacing factor" ("allocated" bandwidth on the satellite, i.e. allowing for guard-bands) is 1.45.
Now of course, different values for roll-off and carrier spacing factor will give you a different result. The roll-off is determined principally by your modulation/coding scheme and the receiving system characteristics, but, as I said in an earlier answer, the carrier spacing factor will be determined by the requirements of the satellite operator and the terms of your transponder lease.
So do please check carefully with ISRO in order to be sure of the specific requirements. Don't rely only on this somewhat theoretical discussion that we have been having!
I hope this helps. Please remember to rate this answer.
