Space Time Trellis Code (STTC) BER increasing with increase in trellis states.

I am writing a matlab code about convolutional encoder. I have created trellis for 4,8,16 and 32 states and their corresponding viterbi decoder(using vitdec matlab function). My system goes like this: Trellis Encoder-->DPSK Modulator-->Rayleigh fading Channel + awgn Noise-->DPSK Demodulator-->Viterbi Decoder

For the 4 state trellis it is fine,but as I go on increasing the states of trellis encoder, the BER increases.But actually by theory it should decrease. I think I have problem with passing arguments in the vitdec function (may be problem with track back length). I have presented my matlab code here. Please suggest,why the error is increasing with the increasing of states.

Matlab Code: http://pastebin.com/JXJ9P02f