I would like to implement a DSSS signaling soulution using USRP n200 devices. I start from using PSK Rx and Tx solutions, already available in LabView examples. When I start transmission of a bit pattern everything is working fine, BER is 0. When I add a spread symbols function it spoils the work. What is wrong with my VI, what aspects I don't take into account? I considered synhronisation, time stamps e.g., but I still cannot understand the source of the problem.
Without taking a detailed look at your VI.
Can you try offsetting your carrier away from the LO frequency.You can do this by using the LO frequency niusrp property.
Say you want your carrier to be at 2.02 GHz set the LO to 2 GHz and then pass in 2.02GHz as carrier frequency to the configure signal VI. Do this for both Rx and Tx.
This will help performance if the reason for your VI not working properly is indeed LO leakage or if the internal DC offset correction mechanism on the N200's FPGA is modifying your signal in some way which is not desired.