I have two SDRs and I want to do a simple test: I want to send data values using QPSK modulation with coordinates: (1,1), (-1, 1), (1, -1), (-1, -1), but on Rx site I got all possible values on the circle created by rotation of the square. Why phases of received signal are changed?
Your receiver has to track the reference phase of the transmitter. It can extract this from the data, or it can use embedded reference sequences. Somewhere in the Rx QPSK setup, there are some parameters that choose what method it uses. It sounds like these are set by default to something incompatible with the present transmission format.