Gen2-UHF-RFID-Reader Trouble

[hiblackgirl]

Now I want to use USRP to implement Gen2 UHF RFID reader. I would like to ask you some questions and look forward to your reply.
We are currently using N210 and SBX child board, environment is Ubuntu 16.04, UHD3.14.0, GnuRadio3.7, protocol package Gen2-UHF-RFID-Reader.
The sending query was set to '1000', but in most cases, you could not send so much data. Is it because of the buffer size? Is there any way to solve it?
The second problem is that when multiple tags are read at the same time, the number of EPCs decoded correctly decreases significantly.We guess that this problem is due to the influence of label coupling. We tried to put the label farther away, but it could not be detected after the distance of the label reached 5cm.So, I also want to ask you, is it because the front-end gain size is not set properly? How to determine the gain of N210 in general?
Moreover, when reading multiple tags, the number of times each tag is read varies greatly.Is it also due to the gain.
Look forward to your reply!