I am simulating an OFDM system and want to employ concatenated codes with
different modulation schemes. I have a few queries about it.
1. RS code works on frame-by-frame basis like for a shortened code
RS(32,24) on byte boundary. In this case, I need a minimum of 24*8 uncoded
data bits. If i work on this boundary, the resulting symbols dont map
completely to the OFDM symbol. How can i make it satisfy both the
requirements i.e. RS frame boundary as well as no. of OFDM data carriers.
(It maps directly for some modulation schemes and not the all)
2. Whenever I simulate the system using Matlab rayleighchan command,
either i get .5 ber or 0. I want to evaluate the performance of the
concatenated codes but cannot see it working.
3. What is the design criteria for interleaver depth design for
concatenated codes. All i know is the criteria for individual RS or CC
codes but not for the concatenated ones. My guess in this case is since
data is convolutinoaly coded after RS encoder, the interleaver should be
designed w.r.t. the traceback length of the viterbi decoder.
Best Regards,
Ubaid
