I would consider neither hard. Thanks to Almighty, I have decent Matlab skills and also comm. algo skills to attempt any of these.
I suggest that, if you have about 4 months, then choose any topic, take 2 weeks to learn how to create a simple modem in Matlab.
After that, learn the theory of your Error Correcting Code and once you are aware of theory, you would naturally know how to write a Matlab code for it (Matlab has a built in function for LDPC)
Use the function in your modem code to get the output.
So if you have good skills in logic, no topic is difficult
If you need some help, you can send an email to yahoo group "telecom_research" and if you are interested in ofdm you can send an email to yahoo group "ofdmandmatlab". Some one might help you there too