difference between msk and oqpsk
Halfsine pulse shaped OQPSK is one of the method to generate MSK signal.
So Halfsine pulse shaped OQPSK is same as MSK.
My quesion is difference of results of the following three EVMs:
(1) EVM measured as MSK with Tsymb=Tbit, reference_filter=none
and measurement_filter=none.
(2) EVM measured as QPSK with Tsymb=Tbit, reference_filter=none
and measurement_filter=none.
(3) EVM measured as OQPSK with Tsymb=2*Tbit, reference_filter=halfsine
and measurement_filter=none.
Here Tbit mean bit period and Tsymb mean symbol period.
As far as my understanding, the constellations of MSK and QPSK are identical although their trajectories are different.
So ideally EVM of (1) and (2) have to be same.
Anyone please teach me.
The nice thing about MSK is that is only changes phase. It stays on a circle in the constellation plane. This makes that the output waveform will only change frequency while moving from one constellation point to another. This ensures that the magnitude of the output waveform is constant, and there are less issues with the PA: It can be pushed into saturation without big problems.
The waveform of QPSK doesn't look as nice: The peak value is larger than the magnitude of the carrier. So PA non-linearities and EVM are more significant.
Thanks for response.
But my question is not difference between QPSK and MSK.
Their trajectories are different. And MSK have constant envelope.
My question is EVM's difference of MSK signal when I use three different measurement setups.
As far as my understanding, (1) and (2) has to be identical.
On the other hand, I'm not sure about (3).
See the following where I discuss this topics in more detail.
http://www.designers-guide.org/Forum...num=1195226387