Trellis help please

Hi everyone,
I want to implement convolutional coding using the trellis block. I
don’t
want to use any modulation scheme or anything else after the encoder.
The
flow graph I want is shown below

vector source---->trellis encoder----> viterbi or any
decoder------->sink
Part of the code is shown below

src_d = (1,0,1,0,0,0,1,1,0,0,1)
sorc = gr.vector_source_b (src_d) //source
encoder = trellis.encoder_bs(f,0) //encoder
s2f= gr.short_to_float()
dec=trellis.viterbi_s(f,len(src_d),0,-1) //decoder
dst = gr.vector_sink_s () //sink
tb.connect (sorc,encoder,s2f,dec,dst)
return(dst.data())

When I run the above flow graph I get nothing just empty, ( ), list.

I am using “awgn1o2_4.fsm” file. I got the correct result after encoder.
I
can’t use the trellis.metric or trellis.viterbi_combined_X to implement
decoder as I am not using any modulation :frowning: .
Can anybody please help me in this ??

Regards
Smith