OFDM Synchronisation Example Not Working

I have been trying to create my own OFDM synchronisation model in Simulink and I have based my design off of the Matlab example. I noticed that for the standard message being sent the example works perfectly but if I change the message to simply be a binary sequence of all 1's or all 0's then the synchronisation no longer works. When i try sending these bits, the Preamble Start Location is rarely found and results in almost no frames being detected. Could someone please explain to me why this is happening and how I can stop it from doing so?

Thanks, Callum

Answer 1

[Siriniharika Katukam]

Hi

There might be few reasons in this case of wrong synchronization like

1. Preamble might not be present in the frame that you defined.
2. There might be another part of the frame resembling the preamble which makes the preamble detection wrong.

Further, try adding few ramp up bits at the start of the frame which improves the probability of preamble detection.

[Callum Hodgkinson]

Hi Siriniharika, thank you for your answer to my question but I'm not sure these are the issues cause the frame detection errror.

1. I have included a loop that will move the index of the frame bits (that I cross correlate against the preamble) in the case that the frame is not found. So it should loop until the preamble is within the frame and then consistently find the preamble start location.
2. There could be another part of the frame resembling the preamble and that might give the wrong strat location but the problem isn't that the model finds the wrong location, it is that it often finds no start location at all.

As I am bit of a novice when it comes to signal processing I am not sure what ramp up bits are exactly so I was wondering if you could please provide so more information on these so that I could try your recommendation and imporve my frame detection reliability.