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Question
If my signal is QPSK modulated having data rate 100 Mbps, FEC-1/2 rate and without any pulse shaping filter, then how much bandwidth is required for distortion-less transmission?

Can post modulation filtering be done to save the bandwidth and what is minimum bandwidth required?

Answer
Rajesh:
First question:
Please refer to https://jaunty-electronics.com/blog/2012/05/bpsk-qpsk-8psk-and-qam-calculator/.
Assuming that 100 Mbps is the information rate, the values that you provided result in following:
Data rate (Mbps) = 200
Symbol Rate = 100 Msym/s
3-dB BW = 100 MHz
Occupied BW = 119 MHz
Allocated BW = 135 MHz
Second question:
It is good practice to place a low-pass filter between modulator and HPA to reduce the level of higher-frequency harmonics. If you tried to reduced occupied bandwidth with a combination of low- and high-pass filters, I believe that you would distort the signal.
I hope that this was helpful.
Thomas E. Burke

Satellite Communications

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Thomas E. Burke

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Experience

Forty years of experience with satellite communications. Have held roles as system engineer on JPL Mariner 9 program and a program manager for a number of classified communication satellite programs. Served as head of TRW / Defense Communications Division / Engineering Development Operation, a 1,400-person organization responsible for all aspects of classified communication satellite design and development.

Education/Credentials
Ph.D. Chemistry, California Institute of Technology (1969) B.A. magna cum laude Chemistry, University of Minnesota (1962)

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