（2，1，2）卷积码译码器的JAVA实现

本人编写。

package Veteribi;
import java.util.ArrayList;
public class Veterbi {
	public static void decoder(StringBuffer received) {
		 //  记录四种状态的路径
		StringBuffer route1 = new StringBuffer("0000");  // x00
		StringBuffer route2 = new StringBuffer("0011");  // x10
		StringBuffer route3 = new StringBuffer("1110");  // x01
		StringBuffer route4 = new StringBuffer("1101");  // x11
		
		StringBuffer realway1 = new StringBuffer("00");
		StringBuffer realway2 = new StringBuffer("01");
		StringBuffer realway3 = new StringBuffer("10");
		StringBuffer realway4 = new StringBuffer("11");
		
		

			System.out.println("接收到的数据长度为： " + received.length());
			System.out.println("接收到的数据为 ： " + received);
		
		int [] distance = {0,0,0,0,0};;  //记录4种状态的最小码距

		int length = received.length();

		distance[0] = 0;
		distance[1] +=  (route1.charAt(0)^received.charAt(0) ) + (route1.charAt(1)^received.charAt(1))
					        + (route1.charAt(2)^received.charAt(2)) +(route1.charAt(3)^received.charAt(3)) ;
		distance[2] +=  (route2.charAt(0)^received.charAt(0) ) + (route2.charAt(1)^received.charAt(1))
		        + (route2.charAt(2)^received.charAt(2)) +(route2.charAt(3)^received.charAt(3)) ;
		distance[3] +=  (route3.charAt(0)^received.charAt(0) ) + (route3.charAt(1)^received.charAt(1))
		        + (route3.charAt(2)^received.charAt(2)) +(route3.charAt(3)^received.charAt(3)) ;
		distance[4] +=  (route4.charAt(0)^received.charAt(0) ) + (route4.charAt(1)^received.charAt(1))
		        + (route4.charAt(2)^received.charAt(2)) +(route4.charAt(3)^received.charAt(3)) ;
		

		int i;
		System.out.println();
		for(i=4 ; i< length ; i++) 
		{ 
			int temp1=distance[1];
			int temp2=distance[2];
			int temp3=distance[3];
			int temp4=distance[4];
			System.out.println("i =" + i + "最短路径分别为：" + temp1 + temp2 + temp3 +temp4);
		    String copy1 = route1.toString();
		    String copy2 = route2.toString();
		    String copy3 = route3.toString();
		    String copy4 = route4.toString();
		    String copyway1 = realway1.toString();
		    String copyway2 = realway2.toString();
		    String copyway3 = realway3.toString();
		    String copyway4 = realway4.toString();

			/*   选择下一跳最短码距的路径   */
			
				// jump to S1
				// 1/000 --> 1/00
				// 3/001 --> 1/11 
				if(   temp1 + ('0' ^ received.charAt(i) )  +  ('0' ^received.charAt(i+1))  >
					  temp3 + ('1' ^ received.charAt(i) )  +  ( '1'^received.charAt(i+1))  )
				{
					  route1.replace(0, i, copy3);
					  route1.append("11");
					  realway1.replace(0, i/2, copyway3);
					  realway1.append("0");
					  distance[1] = temp3 + ('1' ^ received.charAt(i) )  +  ( '1'^received.charAt(i+1)) ;
				}
				else
				{ 
					 route1.replace(0, i, copy1);
					 route1.append("00");
					 realway1.replace(0, i/2,copyway1);
					 realway1.append("0");
					 distance[1] =temp1 + ('0' ^ received.charAt(i) )  +  ('0' ^received.charAt(i+1)) ;
				}
				System.out.println("此时i = " + i + " ，路径1的原码：" + route1 + " ，路径1的译码结果：" + realway1);	



				// jump to S2
				// 1/100 --> 2/10
				// 3/101 --> 2/00
				if(  temp1 + ( '1' ^ received.charAt(i) ) + ( '1' ^ received.charAt(i+1))   >
					 temp3 + ( '0' ^ received.charAt(i) ) + ( '0' ^ received.charAt(i+1))    )
				{
					  route2.replace(0, i , copy3);
					  route2.append("00");
					  realway2.replace(0, i/2, copyway3);
					  realway2.append("1");
					  distance[2] = temp3 + ( '0' ^ received.charAt(i) ) + ( '0' ^ received.charAt(i+1)) ;
				}
				else
				{ 
					 route2.replace(0, i , copy1);
					 route2.append("11");
					 realway2.replace(0, i/2, copyway1);
					 realway2.append("1");
					 distance[2] =  temp1 + ( '1' ^ received.charAt(i) ) + ( '1' ^ received.charAt(i+1));
				}
				System.out.println("此时i = " + i + " ，路径2的原码：" + route2 + " ，路径2的译码结果：" + realway2);	

				//jump to S3
				// 2/010 --> 3/10
				// 4/011 --> 3/01
				if(  temp2 + ('1' ^ received.charAt(i)) + ('0' ^ received.charAt(i+1))  >
					 temp4 + ('0' ^ received.charAt(i)) + ('1' ^ received.charAt(i+1))  )
				{
					  route3.replace(0, i, copy4);
					  route3.append("01");
					  realway3.replace(0, i/2, copyway4);
					  realway3.append("0");
					  distance[3] =temp4 + ('0' ^ received.charAt(i)) + ('1' ^ received.charAt(i+1)) ;
				}
				else
				{ 
					 route3.replace(0, i, copy2);
					 route3.append("10");
					 realway3.replace(0, i/2, copyway2);
					 realway3.append("0");
					 distance[3] =temp2 + ('1' ^ received.charAt(i)) + ('0' ^ received.charAt(i+1)) ;
				}
				System.out.println("此时i = " + i + " ，路径3的原码：" + route3 + " ，路径3的译码结果：" + realway3);	

				//jump to S4
			    // 2/101 --> 4/01
			    // 4/111 --> 4/10
				if(  temp2 + ('0' ^ received.charAt(i)) + ('1' ^ received.charAt(i+1))  >
					 temp4 + ('1' ^ received.charAt(i)) + ('0' ^ received.charAt(i+1))   )
				{
					  route4.replace(0, i, copy4);
					  route4.append("10");
					  realway4.replace(0, i/2, copyway4);
					  realway4.append("1");
					  distance[4] =  temp4 + ('1' ^ received.charAt(i)) + ('0' ^ received.charAt(i+1))  ;
				}
				else
				{ 
					 route4.replace(0, i, copy2);
					 route4.append("01");
					 realway4.replace(0, i/2, copyway2);
					 realway4.append("1");
					 distance[4] = temp2 + ('0' ^ received.charAt(i)) + ('1' ^ received.charAt(i+1)) ;
				}
				System.out.println("此时i = " + i + " ，路径4的原码：" + route4 + " ，路径4的译码结果：" + realway4);			
				
				++i;
		
		}
		
		System.out.println(received.length() + "bit的最短距离分别是" + distance[1] + "  " +  distance[2] + "  " + distance[3] + "  " + distance[4]);		
		
		}		
}