#### Panoramix

##### Newbie level 3

**16 qam**

I am having a problem in how to send my data through a flat-fading Rayleigh channel using 16-QAM modulation. I am using the MATLAB built-in function to create the channel and am using FEC techniques for channel coding. The FEC techniques applied are divided into outer coding (Reed Solomon) and inner coding (convolutional) combined with interleavers. The RS code I use is RS(252, 168) and ½ rate convolutional coding with 10 constraint length. The coding does work for an AWGN channel so it proves that is done correctly. But is does not work for a Rayleigh channel. In my simulations the bit error probability has values nearly equal to 0.5.

The fading model appears to work correctly in differential PSK (D-BPSK – D-QPSK D-8ASK) but when I use no-differential (coherent) modulation I get error rate of 0.5. I have the same results for all values of SNR (small or large). I think that I lose symchronisation between receiver and transmitter so the decoder decides randomly, that is why I think I have the 0.5 response. What do you think I may be doing wrong? Is there something i should add to my system?

I don't know what am I doing wrong and I would really appreciate it if you could give some suggestions on how to overcome this problem.