Capacity estimation and code design principles for continuous phase modulation (CPM)

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Title: Capacity estimation and code design principles for continuous phase modulation (CPM)
Author: Ganesan, Aravind
Abstract: Continuous Phase Modulation is a popular digital modulation scheme for systems which have tight spectral efficiency and Peak -to -Average ratio (PAR ) constraints . In this thesis we propose a method of estimating the capacity for a Continuous Phase Modulation (CPM ) system and also describe techniques for design of codes for this system . We note that the CPM modulator can be decomposed into a trellis code followed by a memoryless modulator . This decomposition enables us to perform iterative demodulation of the signal and improve the performance of the system . Thus we have the option of either performing iterative demodulation , where the channel decoder and the demodulator are invoked in an iterative fashion , or a non -iterative demodulation , where the demodulation is performed only once followed by the decoding of the message . We highlight the recent results in the estimation of capacity for channels with memory and apply it to a CPM system . We estimate two different types of capacity of the CPM system over an Additive White Gaussian Noise (AWGN ) . The first capacity assumes that optimum demodulation and decoding is done , and the second one assumes that the demodulation is done only once . Having obtained the capacity of the system we try to approach this capacity by designing outer codes matched to the CPM system . We utilized LDPC codes , since they can be designed to perform very close to capacity limit of the system . The design complexity for LDPC codes can be reduced by assuming that the input to the decoder is Gaussian distributed . We explore three different ways of approximating the CPM demodulator output to a Gaussian distribution and use it to design LDPC codes for a Bit Interleaved Coded Modulation (BICM ) system . Finally we describe the design of Multi Level Codes (MLC ) for CPM systems using the capacity matching rule .
URI: http : / /hdl .handle .net /1969 .1 /53
Date: 2004-09-30

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Capacity estimation and code design principles for continuous phase modulation (CPM). Available electronically from http : / /hdl .handle .net /1969 .1 /53 .

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