Carrier frequency for QPSK Modulator?

[zeshan102]

In order to implement a QPSK modulator what can be the minimum local Oscillator frequency for 400 Mbit/sec data rate.

 

[activewei]

It is hard to tell what is the min LO power. This will depend on the modulator. But it can be predicted if you know the output power. It is normally +/- 5dBm of the output power.

 

[nandopg]

QPSK modulation scheme breaks the data stream in two parallel data streams with a 1/2 data rate. If you are regarding 400MB as the main data stream, you will have applied to the modulator I and Q 200MB, what means a maximum modulating frequency equal to 100MHz. Therefore, theoretically, you would be able to use a 100MHz carrier.
However by using this minimum frequency you will have the following problems:
1- The amplifier chain in the transmission end would have to be very linear over several octaves, what is a hard to achieve;
2- To demodulate such signal you would have to have an ultralinear demodulator from DC to 100MHz what again is very hard, if not impossible, to get.

I think if you use OSQPSK, you would be better off to work with this low carrier frequency, once that is a modulation scheme with constant envelop.

NandoPG

 

[springf2000]

th LO power depend your choise of the MODULATOR,or the mixer