Using OFDM to transmit bit level data

Hi all,
I’m using a grc flow chart (attached) to transmit data. My purpose is to
transmit a sequence of known data bits specified by myself. (These data
bits are actually from Matlab.) So which file format should I use to
feed into the File Source and how to set File Source output data type?
Or do you suggest any other way?
Any suggestion is highly appreciated! Thank you very much in advance.