Research On Key Techniques Of Fountain Codes And Polar Codes

With the advancement of the fifth generation of mobile communication system, thereis higher requirement for the reliability of channel coding, as a part of the wholecommunication system. Therefore, much more research work is done in the area of modernchannel coding technique. Different from conventional channel coding techniques likeTurbo codes or LDPC codes, fountain codes can generate infinite number of encoded bits,and the transmitter side does not need to know the channel state information. Thus theadvantage of fountain codes is that they are able to adapt to various channel conditions.Polar codes are the first class of codes that are proved to achieve the channel capacity andthey have great potential in many practical applications. In this work, the performance offountain codes and polar codes are studied, and then five improved algorithms are proposedin the aspect of encoding, decoding and practical applications.First, we propose an extended packetization aware mapping algorithm for wirelesspacket switching channels. The proposed algorithm is able to scatter the edges amonginformation bits and encoded packets in the tanner graph. Therefore, even if one or some ofthe encoded packets are lost, the corresponding information bits still can be recovered. Theeffectiveness of the proposed algorithm is verified by simulation results.Second, we study fountain codes in low overhead regions. By designing via And-Ortree, we propose degree distributions that can outperform conventional fountain codes inlow overhead regions. Furthermore, we apply the proposed degree distribution in apoint-to-point transmission scenario and a distributed multi-source relay scenario. We couldachieve unequal error protection, apart from performance gain.Third, we propose an encoding algorithm based on short cycle elimination for shortlength fountain codes. Through a two-phase encoding process, the short cycles in the tannergraph can be eliminated. Simulation results show the performance improvement comparedwith conventional fountain codes, in both hard-decision decoding and soft-decisiondecoding methods.Fourth, we propose low complexity list successive cancellation decoding method ofpolar codes. Through observing the state-of-art decoding algorithms, we design twothresholds, namely the likelihood ratio threshold and the Bhattacharyya parameter threshold.A low complexity decoding algorithm is proposed that can achieve high performance based on the two thresholds. We compare the peroformance and complexity of the proposeddecoding algorithm with other decoding algorithms.Finally, we study high performance bandwidth efficient coded modulation schemes,and propose interleaver division multiple access schemes based on polar codes. By jointlydesign encoding and modulation, and performing iterative detection and decoding at thereceiver side, we aim to cancel the interference among multiple users and improve thesystem performance. Simulation results show that the proposed multi-user scheme canachieve the performance that is quite close to a single-user scheme.