[Discuss-gnuradio] how does OFDM receiver distinguish the wanted signal

[Shi Yang]

Dear list,

I am implementing a full duplex DOCSIS 3.1 using GNU Radio. I use two 
usrp, one as CMTS and another as cable modem. The CM acts as the 
receiver, receiving both the signal from CMTS and from itself. What I 
am trying to do is subtract the self interference from the CM. My 
question is, when there are two signals mixed on the receiver side, 
how does the OFDM receiver distinguish the wanted signal?

I know the transmitter and receiver have to have the same FFT_length, 
so when using 2 FFT_length for each transmitter, the receiver picks up 
the transmitter with the matching FFT_length. But I am using the same 
FFT_length for two senders (because I want to use the default sync 
words from the rx_ofdm examples, so I kind of am stuck with the 
FFT_len 64), then the receiver regards the weaker signal as noise and 
recovers the stronger signal, which is not so ideal, since 
theoretically the self interference should be several tens decibels 
stronger, based on the so much shorter transmission path in a real 
scenario. So can anyone please tell me, how can the receiver recognize 
the wanted signal, or what else should I do (like write my own channel 
estimation block) to subtract the self interference?

Thanks in advance and best regards,
Yang