trellis.m
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上传日期:2013-06-30
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- function [next_out, next_state, last_out, last_state] = trellis(g)
- % copyright Nov. 1998 Yufei Wu
- % MPRG lab, Virginia Tech
- % for academic use only
- % set up the trellis given code generator g
- % g given in binary matrix form. e.g. g = [ 1 1 1; 1 0 1 ];
- % next_out(i,1:2): trellis next_out (systematic bit; parity bit) when input = 0, state = i; next_out(i,j) = -1 or 1
- % next_out(i,3:4): trellis next_out (systematic bit; parity bit) when input = 1, state = i;
- % next_state(i,1): next state when input = 0, state = i; next_state(i,i) = 1,...2^m
- % next_state(i,2): next state when input = 1, state = i;
- % last_out(i,1:2): trellis last_out (systematic bit; parity bit) when input = 0, state = i; last_out(i,j) = -1 or 1
- % last_out(i,3:4): trellis last_out (systematic bit; parity bit) when input = 1, state = i;
- % last_state(i,1): previous state that comes to state i when info. bit = 0;
- % last_state(i,2): previous state that comes to state i when info. bit = 1;
- [n,K] = size(g);
- m = K - 1;
- max_state = 2^m;
- % set up next_out and next_state matrices for systematic code
- for state=1:max_state
- state_vector = bin_state( state-1, m );
-
- % when receive a 0
- d_k = 0;
- a_k = rem( g(1,:)*[0 state_vector]', 2 );
- [out_0, state_0] = encode_bit(g, a_k, state_vector);
- out_0(1) = 0;
-
- % when receive a 1
- d_k = 1;
- a_k = rem( g(1,:)*[1 state_vector]', 2 );
- [out_1, state_1] = encode_bit(g, a_k, state_vector);
- out_1(1) = 1;
- next_out(state,:) = 2*[out_0 out_1]-1;
- next_state(state,:) = [(int_state(state_0)+1) (int_state(state_1)+1)];
- end
- % find out which two previous states can come to present state
- last_state = zeros(max_state,2);
- for bit=0:1
- for state=1:max_state
- last_state(next_state(state,bit+1), bit+1)=state;
- last_out(next_state(state, bit+1), bit*2+1:bit*2+2) ...
- = next_out(state, bit*2+1:bit*2+2);
- end
- end