Problem in Reded solomon decoding using QPSK modulation in Engg. project , help plz

Problem in Convolutional decoding using QPSK modulation in Engg. project , help plz

hello everyone,

I have used convolutional encoding with qpsk modulation using AWGN channel. During decoding if the signal to noise ratio is less than 5 like 1, 2 etc. It shows error i.e.

??? Error using ==> vit
Invalid input for chosen decision-type. Allowed input values for hard-decision decoding are 0 and 1.

But if keep SNR higher it shows no error and output data matches with input.



Kindly tell me why is this happening and how to solve this problem without increasing much SNR....????

(note:- in red is SNR about what i have mentioned above.)

Code :-

clc

clear all

data=[1 0 1 1 1 1 1 1 ] % data generate.

trellis = poly2trellis(7,[133 171],[133]) ; % polynomial to trellis conversion.

Final_code = convenc(data,trellis) ; % RSC encoder.

Modulated_data = pskmod(Final_code,4) % Bpsk modulation.

y=awgn(Modulated_data,1,'measured') % AWGN channel.

demodulated_data= pskdemod(y,4) % Bpsk de-modulation

Final_data=vitdec(demodulated_data ,trellis,8,'trunc','hard') % viterbi decoder