The IS-GPS-800D standard defines an irregular Parity Check Matrix (PCM) for 2 subframes (2 and 3) encoded using Low Density Parity Check (LDPC) Forward Error Correction (FEC). Subframe 2 has a total of 600 bits and subframe 3 has a total of 274 bits. Both subframes are separately encoded using rate 12 LDPC codes. In effect, there are 1200 symbols (coded bits) for subframe 2, and 548 symbols (coded bits) for subframe 3.
The VK3061 LDPC IP implements the error correction module in the GPS receiver, as well as the memories. It integrates the de-interleaver, subframe 2 LDPC decoder and subframe 3 LDPC decoder with both the DPRAM and the FIFO.