Design Of High Performance Dual-mode Decoder Based On The LDPC And Turbo Codes

LDPC codes and Turbo codes not only used in wireless LAN,optical fiber communications and underwater communications,also used in the video and image encryption,digital watermarking technology,network security and so on.Since these two codes have excellent decoding performance and close to Shannon's theoretical limits,there is a strong resistance to fading and anti-jamming in the communication process.At present,different codes are used by communication companies of different regions in the global mobile communication equipments,and most of the produced baseband communication chips are support only one code,which will cause some troubles.So how to implement a dual-mode decoder that support LDPC codes and turbo codes decoding has become the subject of this paper.In the current research results,LDPC/Turbo dual-mode decoder has a certain prototype,but there are still much space to improve.This paper studies the basic framework of LDPC/Turbo dual-mode decoder which has been developed from the following aspects.（1）Algorithm improvement of LDPC/Turbo code dual-mode decoder.Dual-mode decoder requires two kinds of algorithms for differnet codes with the same decoding process,so that can share more resources in the hardware design.In this paper,based on the existing LDPC/Turbo double-mode algorithm,the nonlinear operation in the state transition function is approximated by the look-up-table approximating and the normalized approximation.The TDMP algorithm of LDPC codes is improved to LUT-Nor-TDMP algorithm,and the LUT-LogMAP algorithm of Turbo code is improved to the LUT-Nor-LogMAP algorithm.Both improved algorithms reduce nearly 33%and 47%of the look-up-tables,respectively,and replace them with shift addition,this will not only speed up the decoding rate,but also improve the decoding performance.In this paper,compared with the LUT-TDMP algorithm,the proposed LUT-Nor-TDMP algorithm has the performance improvement of 0.15dB when BER reaches 10^-4,at the same time,the decoding performance of the LUT-Nor-LogMAP algorithm and the LUT-LogMAP algorithm is basically the same.（2）Improvement of LDPC/Turbo dual-mode decoder calculation unit.The core of the dual-mode decoder computing unit is the state metric calculation unit.Combining these two proposed algorithms,we design a function unit NFU which supports the look-up-tables and the normalized approximation can be switched in different decoding modes.Based on the NFU unit,the design of SISO calculation unit compared to the previous SISO unit have a decrease of 6.6%and 6.7%of the logical resources consumption in the mode of LDPC and Turbo,respectively.The proposed LDPC/Turbo dual-mode decoder supports all the LDPC codes under the WiMAX standard and all the Turbo codes under the 3GPP TD-LTE standard.On the Cyclone IV platform EP4CE115F29C7 chip,for the maximum code length of 2304 LDPC code,it can achieve the maximum throughput of63.4Mbit/s with 55.8MHz operating frequency and 10 iterations,and for the maximum code length of 6144 Turbo code,with the operating frequency of55.8MHz and 5 iterations,it can achieve the maximum throughput of 22.8Mbit/s.Compared to the previous design,the dual-mode decoder of our design not only enhance decoding performance also reduces the logical resources consumption,and it has reached a good throughput in the same design condition,therefore,the decoder has realized high performance.