OBPSK modulation and demodulation in Simulink

Hello, I've got a task to make an OBPSK modulator and demodulator in Simulink, and to simulate the signal transmittion with such modulation.

However, I could not find any description on OBPSK modulation. There are no build in example or blocks of OBPSK modulation in Simulink R2016b, and, as I'm afraid, in later versions too.

I've tried to do mine Simulink model which would transmit Barker code, based on my understanding of OBPSK.

However, the constellation diagram I see is kidna wrong (?). I suppose it should be like this

Instead, I'm getting this:

The dot's are moving left and right symmetrically.

Please help, what I'm doing wrong? Is there another way to make OBPSK in Simulink.

Thank you for your responces.