Variable Length Ldpc Codes for 45GHz Date: 2015-05-19 Authors: Name Affiliations Address Phone Email Yan Li Gigaray Communication Wuxi China yan_li@gigaray.cn Feng Huang feng_huang@gigaray.cn Slide 1

Quasi-cyclic low density parity check codes A QC-LDPC is defined by a J-by-L base matrix and the size of sub-matrices, p. A J-by-L base matrix has the following representation. (0<=i<J, 0<=i<L) represents a p-by-p sub-matrix: 0 represents an identity matrix; -1 represents a zero matrix; other non-zero less-than-p values represent circulant permutation matrices.

Considerations LDPC codes designed by ZTE has been adopted. Compared to other semi-static wireless channels, indoor mmw communication channel has more variations because of rich reflections/scattering and moving objects. It is desirable for receiver to have more adaptation to channel variation. Besides code rate, code length provides another dimension of coding gain change, thus improves the receiver’s adaptation capability to channel variations It is desirable to be compatible to existing coding scheme and minimize the added complexity.

LDPC Base matrices (1) Same base matrices designed by ZTE Four code rates are 1/2, 5/8, 3/4 and 13/16. Rate 1/2： Rate 5/8： -1  0 34 12 36 18  8 13 16 40 32 22 19 20  2 28 21 30 14 37 31 38  6 26 24 10  5 -1  0 32 22 18 19  8 16 40 34 12 36 21 30 20 38  6 13 31 24  2 28 37 10 14  5

LDPC Base Matrices (2) Rate 3/4： Rate 13/16： 0 -1 8 16 40 34 32 12 22  0 -1  8 16 40 34 32 12 22 36 18 13 19 30 20 38  2  6 28 37 26 21 31 24 10 14 5  0 -1 30 20 18 22 38  2  6 28 32 37 26 21 34 40 24 12 10 14 16 19  8 13  5

Variable LDPC code length Based on the sets of base matrices by ZTE, code length change is achieved by changing p , the sub-matrix size. p=42 maintains the same set of 672 long LDPC codes proposed by ZTE. (672 , 366), (672 , 420), (672 , 504) and (672, 546) codes p=126 introduces a set of LDPC codes with code length of 2016. (2016, 1008), (2016, 1260), (2016, 1512) and (2016, 1638) codes 1-bit signaling field to indicate the code length

Performance of rate ½ codes (1) QPSK modulation and AWGN

Performance of rate ½ codes (2) 16QAM modulation and AWGN

Performance of rate ½ codes (3) 64QAM modulation and AWGN

Performance of rate 5/8 codes(1) QPSK modulation and AWGN

Performance of rate 5/8 codes(2) 16QAM modulation and AWGN

Performance of rate 5/8 codes(3) 64QAM modulation and AWGN

Performance of rate 3/4 codes(1) QPSK modulation and AWGN

Performance of rate 3/4 codes(2) 16QAM modulation and AWGN

Performance of rate 3/4 codes(3) 64QAM modulation and AWGN

Performance of rate 13/16 codes(1) QPSK modulation and AWGN

Performance of rate 13/16 codes(2) 16QAM modulation and AWGN

Performance of rate 13/16 codes(3) 64QAM modulation and AWGN

Benefits of proposed scheme All benefits from ZTE base matrices are maintained. Improved performance of 0.1dB ~ 0.8dB achieved by longer codes compared to short codes. This also means finer coding gain grids for finer ACM adaptation. The short codes and long codes can share the same encoder and decoder. For decoder, larger value of p implies possible higher parallel processing, thus higher throughput, although at the expense of more logic and memory in ASIC implementation.

Complexity Encoding Decoding For long codes, buffer size needs to be tripled. Because the base matrices are the same, logic resources won't be increased if tripling of latency is tolerable, or logic resouces need to be tripled to maintain the same latency. Decoding For layered decoding, logic resources for variable and check node processing won't be increased if throughput keeps the same. However, the shifting network complexity will increase. For full parallel implementation, the logic resources will be tripled.

Conclusion Variable LDPC code length is proposed to improved performance and channel adaptation capability. Compatible to existing LDPC codes adopted by standard. No need to add new encoder and decoder