Study On Rateless Coded Continuous Phase Modulation Over Burst-Error Channels

In modern wireless communications,especially tactical data link,magnetic recording channel,satellite communications,deep-space communications,GSM-R and ao on,burst errors frequently occur because of deep fading,strong interference and high mobility,damaging the reliability seriously.Thus it is necessary to design a reliable and efficient encoding and modulation scheme in burst-error channels to deal with burst errors.Rateless codes are desiged based on digital fountain which is applied over erasure channel,AWGN channel and fading channel.In the case that the transmitter has no channel state information(CSI),Rateless codes can adaptively adjust the real code rates to realize reliable data transmission.Considering the time-varying character of burst-error channel,the paper adopts Rateless codes as channel code technology,which both reduce feedback delay and improve transmission efficiency.With a view of the requirement of high energy efficiency and spectrum efficiency,the paper combines continuous phase modulation(CPM)scheme with constant envelope and continuous phase.Moreover,it introduces the nonrecursive form of CPM modulator to eliminate the error propagation caused by burst errors.When the CSI is unknown at the receiver,a simplified noncoherent soft in soft out demodulation algorithms is presented to achieve the trade-off between the demodulation performance and the complexity.In the paper,a class of Rateless coded CPM system is designed over burst-error channel.It first researches the character of burst error channel,introducing several familiar models such as burst noise channel,burst-fading channel and burst erasure channel.In the same time,an algorithm of burst error detection is proposed.Then the paper presents a new method to construct nonbinary Rateless codes.Combining algebraic-based and graph-based construction methods,rate-compatible LDPC codes of code rates 3/4,3/5 and 1/2 are constructed based on the steps of superposition,extension and protograph Extrinsic information transfer(EXIT)chart optimization.By optimizing p sequence with greedy algorithm,Kite codes of code rates from 0.3 to 0.9 are constructed.All these constructed Rateless codes encode easily and perform well,then the encoding and decoding principles and algorithms are described in the paper.The burst-correcting capality of binary and nonbinary LDPC codes is studied over different burst-error channels and under different modulation scheme.The results show that nonbinary LDPC codes with the same parameters to binary LDPC are better in correcting burst error and are more suitable for burst-error channels.Finally,combined frequency hopping technology and special frame structure,Rateless coded CPM system over Gilbert channel and AWGN erasure channel is focused,and the performances between binary and nonbinary Rateless codes in the concatenated system are contrasted.For binary LDPC codes whose check matrices are of diagonal structure,it is necessary to introduce channel interleaver for correcting burst error,while nonbinary LDPC codes need not.For Kite coded CPM system,the simulation results reflect that when the code rate is between 0.8 to 0.5,nonbinary Kite owns strong burst-correcting capality.Moreover,when the code rate is 0.4 and 0.3,the conclusion is opposite,thus in the poor channel environment,binary Kite codes of low code rate can be also considered.