因为在快变信道下,矩阵H进行带状处理后,状态数可以减少。所以可以用减少状态数的MAP算法来实现均衡器的软输出。而MAP算法可以根据BCJR算法来实现。
BCJR算法最初是应用于卷积码的译码软输出,因此先学习在卷积码的情况下BCJR算法的实现。
void CViterbi::Malloc()
{
int t,s,i,j,edge_cnt;
int temp,temp_out;
int state_temp,sub_state;
m_num_trellis=5;
m_num_input_bits=1; //输入比特数 1
m_num_output_bits=2; //输出比特数 2
m_num_reg=2; //寄存器数 2
m_num_input=1<<m_num_input_bits; //输入比特状态0,1
m_num_output=1<<m_num_output_bits;
m_num_state=1<<m_num_reg; //trellis图状态数
m_edge_no=m_num_input*m_num_state; //边标号
m_in_lable=new int [m_edge_no]; //输入标签{0 ,1, 0 ,1, 0,1,0,1}
m_left_vertex=new int [m_edge_no]; //左边状态 {00,00,01,01,10,10,11,11}
m_right_vertex=new int [m_edge_no]; //右边状态 {00,10,00,10,01,11,01,11}
m_out_lable=new int [m_edge_no]; //输出标签{00,11,11,00,10,01,01,10}
m_G=new int [m_num_output_bits]; //生成多项式
m_G[0]=7; //g0=1 1 1
m_G[1]=5; //g1=1 0 1
m_input_bit=new int [m_num_input]; //输入比特[0,1]
m_input_bit[0]=0;
m_input_bit[1]=1;
m_output_bit=new int *[m_num_output];
for(i=0;i<m_num_output;i++)
m_output_bit[i]=new int [m_num_output_bits];
m_output_bit[0][0]=0; m_output_bit[0][1]=0;
m_output_bit[1][0]=0; m_output_bit[1][1]=1;
m_output_bit[2][0]=1; m_output_bit[2][1]=0;
m_output_bit[3][0]=1; m_output_bit[3][1]=1;
m_delta=new double *[m_num_output];
m_gama=new double *[m_edge_no];
for(i=0;i<m_num_output;i++)
m_delta[i]=new double[m_num_trellis];
for(i=0;i<m_edge_no;i++)
m_gama[i]=new double [m_num_trellis];
m_difference=new double**[m_num_state];
for(s=0;s<m_num_state;s++){
m_difference[s]=new double *[m_num_trellis+1];
for(t=0;t<=m_num_trellis;t++)
m_difference[s][t]=new double[m_num_input];
}
m_edge_to_state=new int*[m_num_state];
for(s=0;s<m_num_state;s++)
m_edge_to_state[s]=new int [m_num_input];
//trellis的构建
state_temp=0; //临时状态
sub_state=0;
temp=0;
edge_cnt=0;
for(s=0;s<m_num_state;s++)
{
sub_state=s;
for(i=0;i<m_num_input;i++){
m_left_vertex[edge_cnt]=sub_state; //当前状态
m_in_lable[edge_cnt]=i; //当前输入
m_out_lable[edge_cnt] = 0;
m_right_vertex[edge_cnt] = 0; //初始化都是0
state_temp=(m_input_bit[i]<<m_num_reg)+sub_state;
temp_out=0;
for(j=0;j<m_num_output_bits;j++){ //第1,2个输出
temp=BitDotProd(state_temp,m_G[j],m_num_reg+1);
temp_out=( temp_out<<1)+temp; //输出码字比特
}
m_out_lable[edge_cnt]=(m_out_lable[edge_cnt])^temp_out; //输出码字
m_right_vertex[edge_cnt]=(m_right_vertex[edge_cnt]<<m_num_reg)+ state_temp>>1; //新状态 m_right_vertex[edge_cnt]初始时都是零
edge_cnt++;
}
}
for(s=0;s<m_num_state;s++){
edge_cnt=0;
for(i=0;i<m_edge_no;i++){
if(m_right_vertex[i]==s){
m_edge_to_state[s][edge_cnt]=i; //到达s状态存储的边号
edge_cnt++;
}
}
}
m_backtrace=new int **[m_num_state];
for(s=0;s<m_num_state;s++){
m_backtrace[s]=new int *[m_num_trellis];
for(t=0;t<m_num_trellis;t++){
m_backtrace[s][t]=new int [m_num_input];
}
}
}
//编码
void CViterbi::Encode(int *uu,int *cc)
{
int i,t,input,output,state;
state=0;
for(t=0;t<m_num_trellis;t++){
input=uu[t]; //输入
for(i=0;i<m_edge_no;i++){
if(m_left_vertex[i]==state&& m_in_lable[i]==input)
output= m_out_lable[i];
state=m_right_vertex[i];
break;
}
for(i=0;i<m_num_output_bits;i++)
uu[t*m_num_output_bits+i]=m_output_bit[output][i];
}
m_end_s = state; //把最后的状态当做已知的结束状态
}
“`