What is the best way to send PDUs over the air on Gnuradio without any delay?

Hi Everyone,

I tried to send burst packets over the air with limesdr usb but there is huge amount of delay on the tx side related to the timestamping issue. I know that ettus devices support stream tags so instead of sending with burst, I decided to send PDUs like this way.

ZMQ SUB —>PDU control to PDU vector—> pdu to tagged stream—>Constellation modulation block(QPSK mod)—>Osmocom sink

Has anyone tried to send pmt messages like this way with low latency? Or Is there a better way to send pmt/pdu messages with limesdr?