Hi,
I'm currently developing a testbed for spectrum aggregation and fragmentation using GNURadio and USRPs (B200s and B210s). My approach is to emulate aggregation and fragmentation using Non-Contiguous OFDM: Theoretically, each node should be able to transmit in any subset of the sub-carriers available.
Everything seems to be fine when tested in a loop back(the GRC OFDM Tx example in gr_digital was used). And connected to USRPs, a single pair transmission and reception is fine while transmitting in any subset of subcarriers. The problem arises when I have more than one node transmitting in the same OFDM configuration. No matter how wide the OFDM span is (I began from 64 and increased it to 1024), and no matter how far apart the two transmitting channels are, the cross-interference is enough to corrupt both transmissions. I have played with the transmission power of both transmitters to see if lowering it makes any difference, to no avail.
I have also thought of applying a bandpass filter before feeding OFDM signals to USRPs to limit their out of band emissions, but as the system is supposed to handle fragmentation and requires complete spectrum agility, a single filter would not solve the problem.
I would greatly appreciate any advice on the matter.
Many Thanks,
Vahid