VLSI Implementation of LDPC Codes

Abstract

Coded modulation is a bandwidth-efficient scheme that integrates channel coding and modulation into one single entity to improve performance with the same spectral efficiency compared to uncoded modulation. Low-density parity-check (LDPC) codes are the most powerful error correction codes (ECCs) and approach the Shannon limit, while having a relatively low decoding complexity. Therefore, the idea of combining LDPC codes and bandwidth-efficient modulation has been widely considered. In this thesis we will consider LDPC codes as an Error Correcting Code and study it’s performance with BPSK system in AWGN environment and study different kind of characteristics of the system. LDPC system consists of two parts Encoder and Decoder. LDPC encoder encodes the data and sends it to the channel. The LDPC encoding performance depends on Parity matrix behavior which has characteristics like Rate, Girth, Size and Regularity. We will study the performance characteristics according to these characteristics and find performance variation in term of SNR performance. The decoder receives the data from the channel and decodes it. LDPC decoder has characteristics like time of iteration in addition all parity check matrix characteristics. We will also study the performance according to these characteristics. The main objective of this thesis is to implement LDPC system in FPGA. LDPC Encoder is implementation is done using Shift-Register based design to reduce complexity. LDPC decoder is used to decode the information received from the channel and decode the message to find the information. In the decoder we have used Modified Sum Product (MSP) Algorithm to decode, In the MSP we have used some quantized values to decode the data using Look Up Table (LUT) approximation. Finally we compare the SNR performance of theoretical LDPC system’s with FPGA implemented LDPC system’s performance.