# What is the minimum sampling rate for QPSK or what is the bandwidth of QPSK signal?

Consider we have created a QPSK signal with a carrier frequency 100kHz. Before applying matched filter or demodulation we need to take sampls from the received signal. So what is the minimum sampling rate we must have? Cosider that somehow we have perfect synchronization and there is no drift of the carrier.

Any help would be apreciated.

I have asked this question (for more attention) in

https://dsp.stackexchange.com/questions/59003/what-is-the-minimum-sampling-rate-for-qpsk-or-what-is-the-bandwidth-of-qpsk-sign

• this depends on the bit rate. and if the S/N ratio is so high that no error correction is needed, then QPSK should have twice the total bit rate for a given bandwidth than simple binary ASK. – robert bristow-johnson Jun 20 '19 at 4:56

What is the SNR Signal Noise Ratio?

For perfect synchronization, with I and Q mixers, filtered with "boxcar" sin(x)/x filters that match to NRZ (on, off) data, then only ONE sample per symbol will suffice; you must simultaneously sample both the I and the Q mixer outputs.

And the SNR will not matter, because for certain assumptions about the noise statistics, the matched-filter is optimal.

• @analogsystemrf did mention one sample per symbol, i. e., sampling frequency equals symbol rate – joribama Jun 20 '19 at 4:53
• @joribama lol yes, i missed it. – Creator Jun 20 '19 at 5:02