Coded modulation with Low Density Parity Check codes

Abstract

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references (leaves 78-80).Issued also on microfiche from Lange Micrographics.This thesis proposes the design of Low Density Parity Check (LDPC) codes for cases where coded modulation is used. We design these codes by extending the idea of Density Evolution (DE) that has been introduced as a powerful tool to analyze LDPC codes. We first discuss methods by which we can design these codes for higher order constellations like 8 Phase Shift Keying (PSK) and 16 Quadrature Amplitude Modulation (QAM). We present simulation results that are within 0.22 dB and 0.4 dB within the constrained capacity of 8 PSK and 16 QAM constellations respectively in an Additive White Gaussian Noise (AWGN) channel. In the second part, we investigate serial concatenation of LDPC codes and minimum shift keying (MSK) with iterative decoding. We show that the design of LDPC codes is crucially dependent on the realization of the MSK modulator. For MSK modulators with non-recursive continuous phase encoders (CPEs), optimal codes for BPSK are optimal whereas for MSK modulators with recursive CPEs the BPSK codes are not optimal. We show that for non-recursive CPEs, iterative demodulation and decoding is not required even though the CPE has memory. However, iterative demodulation is essential for recursive CPEs. For recursive CPEs, we design LDPC codes using density evolution and differential evolution by looking at the graph structure of the CPE and considering message passing between both these codes. The resulting codes provide significantly improved performance over the existing codes