关于poly2trellis命令的问题

help 里面说是可以支持带反馈的卷积编码，
不过稍微复杂点的我思考了半天也不知道命令的参数该怎么写，
比如《数字通信》p534下面的 Figure8.3-12 中的b和c两个卷积码，怎么使用这个命令啊？
谢谢啦！

今天装了R2007b，communication blocksets的demo里有这样一段：
This demo illustrates how to define and use a trellis that describes a convolutional code.  The particular code in this demo cannot be described by a set of generator and feedback connection polynomials. As a result, the code's trellis cannot be created by the poly2trellis function, which expects generator and feedback connection polynomials as input arguments.
给的例子就是TCM编码器。