Research On LDPC Code Of Satellite Navigation System

Satellite navigation system can provide the services of navigation, fixingposition, accurate time and so on, it plays an important part in our modern life. Thechannel coding of the satellite navigation system directly affects the quality ofservice, so the choice of channel coding is an important part of the design of thenavigation system. As a type of advanced channel codes approaching Shannon limit,LDPC codes are being accepted in many applications. The LDPC codes will be firstused in GPS navigation message in2013, which can promote the modernization ofsatellite navigation system. Methods for constructing LDPC code and the applicationof LDPC in satellite navigation system will be discussed in the paper.Firstly, satellite navigation theory is introduced, including the structure ofnavigation message and the channel coding methods. Then we studied the theory ofLDPC code, as well as the encoding and decoding methods, finding the fast encodingalgorithm and the excellent decoding algorithm which can be using in software andhardware. We also introduce two categories methods to construct LDPC code, thefirst one is based on finite geometries, the second one is based on circulantpermutation matrices. On this basis we introduce some helper method to make itpossible to use finite geometries method construct an LDPC code with arbitrary codelength and code rate. Using hill-climbing algorithm and hierarchical algorithmconstruct circulant permutation matrices. Proposed the fast hill-climbing to make iteasier to find the circulant permutation matrices, finding a structure which can makethe LDPC code searched by the hill-climbing and hierarchical algorithm easily to beencode. Emulating the designed LDPC codes to confirm the methods’ performanceand feasibility.First, we emulate three convolution coded navigation messages in whiteGaussian noise channel. Secondly, we use the methods based on finite geometries andcirculant permutation to produce multiple LDPC codes which correspond to theparameter given in GPS CNAV-2navigation message, then emulate these LDPCcodes. We compare the performance of the two categories navigation messages whichuse diffident channel code. Finally, we calculate the complexity of encoding anddecoding LDPC codes, analyze the impact of coding delay on the application of theLDPC codes in the navigation systems, listing the notice of selecting the LDPC codes.Analyze the LDPC codes’ application prospects in satellite navigation system.