feedback connection polynomial convolutional codes

Can anyone give me a good example on how describe CodeGenerator and FeedbackConnection inputs of the poly2trellis function of a systematic convolutional encoder with feedback with more than one bit input, my matlab help gives example of one input with feedback and two input feedforward, and the description of the systematic encoder with feedback is confusing and I can't work it for the 2 or more inputs cases.

Answer 1

[Mohandas]

The help on poly2trellis does not describe how to define the generator matrix for k>1 feedback. I guess, it also does not describe how to define the constriant length for a observer canonical form structure with k>1.

Answer 2

[Imed Amamra]

I can't give you an example at this time, because I am trying to solve the same problem.

I thought that the following code was for a recursive systematic convulutional encoder, but I was wrong, it doesn't give a correct trellis :

H=poly2trellis([m1 m2],[G11 G12 G13;G21 G22 G23],[G11 G21]) for a rate R=2/3.

I am now trying to do a combination of (k) RSCC of one input to design an RSCC with k inputs.

[John Cioffi]

It appears poly2trellis malfunctions when k>1 for encoders with nonzero feedback, including in particular systematic encoders with feedback. A rate 2/n code with 2^nu states will have (2^nu)^2 states in the output, even though it should remain 2^nu because the noncatastrophic realization uses only that minimum number of states. The only fix I know is to transform the encoder to a basic minimal feedback-free encoder of same rate, and then poly2trellis has correct number of states. Decoding programs basked on poly2trellis output object then decode correctly (e.g. vitdec.m) and then the decoded input can be run (in the receiver) through a copy of the basic encoder to produce an output that corresponds to the systematic encoder input in the information bits generated by the reciever's 2nd encoder. The minimal basic encoder requires use of the invariant factors (Smith Normal over binary field, which matlab does not appear to support only complex/real numbers) to generate. I know of no such online program, so one needs to do it by hand.

It would be great if someone knew how to fix matlab's bug on poly2trellis?