Performance Analysis And Optimization Of Degree Distribution Of LDPC Codes For Turbo Equalization

Multipath propagation of wireless channel leads to ISI(Intersymbol Interference), and normally equalization is used to reduce this influence in communication system. Applying turbo principle to equalization is called ‘turbo equalization’, and its main idea is to make full use of the output soft information of equalizer and decoder by using iterative decoding principle to increase the BER performance of the whole communication system. LDPC code is a kind of block code and its performance can approach Shannon limit. LDPC code has been the hot spot in coding area for decades. In this paper, we mainly study the performance of LDPC code using turbo equalization transmitted over ISI channel. The main contents of this paper includes(1) Graph structure, encode algorithm and decode algorithm of LDPC code.(2) A model of ISI channel, principle of turbo equalization and several common equalization algorithms. This paper analyses the performance of LDPC code, through simulations of turbo equalization system.(3) This paper gave the EXIT charts of three different equalization algorithms and introduced the EXIT chart of LDPC code. Based on EXIT analyze of MAP equalization algorithm, this paper proposed a method of getting the EXIT chart of LDPC code transmitted over ISI channel. Then this paper proposed methods to calculate the threshold of LDPC code and to optimize the degree distribution of LDPC code. Using this method, degree distribution of LDPC code were optimized.