Overview

decode butterfly for one bit in polar decoder graph.

Dispatcher Prototype

volk_32f_8u_polarbutterfly_32f(float* llrs, unsigned char* u,
   const int frame_size, const int frame_exp,
   const int stage, const int u_num, const int row)

Inputs

• llrs: buffer with LLRs. contains received LLRs and already decoded LLRs.
• u: previously decoded bits
• frame_size: = 2 ^ frame_exp.
• frame_exp: power of 2 value for frame size.
• stage: value in range [0, frame_exp). start stage algorithm goes deeper.
• u_num: bit number currently to be decoded
• row: row in graph to start decoding.

Outputs

• frame: necessary LLRs for bit [u_num] to be decoded

Example

int frame_exp = 10;
int frame_size = 0x01 << frame_exp;
 
float* llrs = (float*) volk_malloc(sizeof(float) * frame_size * (frame_exp + 1),
volk_get_alignment()); unsigned char* u = (unsigned char) volk_malloc(sizeof(unsigned
char) * frame_size * (frame_exp + 1), volk_get_alignment());
 
 {some_function_to_write_encoded_bits_to_float_llrs(llrs + frame_size * frame_exp,
data)};
 
unsigned int u_num;
for(u_num = 0; u_num < frame_size; u_num++){
    volk_32f_8u_polarbutterfly_32f_u_avx(llrs, u, frame_size, frame_exp, 0, u_num,
u_num);
    // next line could first search for frozen bit value and then do bit decision.
    u[u_num] = llrs[u_num] > 0 ? 0 : 1;
}
 
volk_free(llrs);
volk_free(u);