I'm fairly new to GNU Radio and was looking for a way to communicate using OFDM without using packet headers. I am trying to implement a simple version of OFDM with fixed length frames. I have currently implemented a simple loop-back example without timing offset estimation that excludes the cyclic prefix block. I am simply repacking the received signal in to vectors and processing them. I would like to use the "Schmidl & Cox OFDM synch." block which is typically used in conjunction with the "Header/Payload Demux". Problem is, I am not sure if is possible to use the "Header/Payload Demux" effectively without using packet headers. I am still transmitting a repeated preamble sequence followed by a training sequence for channel estimation.
I thought about creating an OOT block that simply takes trigger from the "Schmidl & Cox OFDM synch." block and passes through the required samples at the correct timing, however I've had a number of issues doing so. I am looking for a possible built-in solution that I may use. Any help would be greatly appreciated. Below is an image of the flow-graph I am working with.