Implementation of a high throughput LDPC codec in FPGA for QKD system

The contribution of this paper is implementing a high throughput LDPC codec in FPGA for quantum key distribution (QKD) system. By software, the throughput of error correction in QKD system via LDPC codec could only reach 1.8Mbps, which is not satisfactory for high speed QKD systems. Thus, it is desirable that LDPC error correction is realized in FPGA to increase the throughput. LDPC codec is implemented according to IEEE802.16e standard. The encoder directly uses a parity-check matrix of lower triangular structure without the construction of generator matrix, so that it effectively reduce the encoding complexity of Richardson encoding algorithm. The decoder uses the BP Min-Sum algorithm to balance performance and complexity. The codec is implemented in an Altera Arria II EP2AGX260 FPGA with a 2304-bit code length and 2/3 code rate. The partly parallel decoding structure achieves a 99.95 Mbps processing throughput on the condition that the maximum number of iterations for each code block is 20. The achievable throughput is much higher than the requirements of current QKD systems.