Hi there,
I am working on a project to implement the physical layer of the standard WCDMA by using the PXI unit (modules PXI-5421, PXI-5610, PXI-5600 & PXI-5620) and the modulation toolkit. The kind of modulation used in this standard is mainly QPSK, so I am using as a template the examples of PSK modulation and demodulation. To generate the signal of each user I generate a PN sequence (random data), then this data is QPSK modulated and finally all symbol sequences of all users are added. After this, the obtained sequence is scrambled (the scrambling sequence is the same for all users and it just rotates the constellation 45 degrees). With this, I get different constellation patterns (depending on the number of users and the relative power between them), as it can be seen in the attached file.
The problem I am having is on the demodulation side. How can I do this with the PSK demodulation block?. I get good results when there is only one user (all I do is to change the symbol map to 1+0i,0+1i,-1+0i and 0-1i for the PSK demodulation block), but what do I have to do when there are more users?. In this case the PSK demodulation doesn't work given that not all the groups of points are located the same distance from the center. Any suggestions?
Best regards,
Wilbert
