Joint LDPC And PNC For Two-way Relay Channels With Different Frequency Offsets

Network Coding is one of important fields of Network Information Theory and Physical-layer Network Coding is the natural extension of Network Coding in the wireless channels, which fully takes advantage of electromagnetic broadcast and superposition characteristics to improve the communication system throughput. This paper presents some basic concepts of Network Coding and its some advantage and disadvantage. And then describe the process of information exchange with traditional way, direct Network Coding and Physical-layer Network Coding in wireless Two-way Relay Channels. We demonstrate the superiority of Physical-layer Network Coding in terms of improving system throughput. This paper mainly focuses on joint LDPC and PNC for Two-way Relay Channels with different frequency offsets in Multiple Access phase. Besides, taking information transmission delay brought by LDPC decode in relay into account, we improve the LLR BP algorithm for LDPC decoding in order to reduce information transmission delay.In LDPC decoding, this paper proposes a new modified LLR BP algorithm to solve unnecessary repeated decoding operation in a low signal noise rate and reduce calculation complex of belief propagation in horizontal direction. On the one hand, we introduce test factor to monitor whether decoding output is stable or not to decrease iteration times. On the other hand, using rational function or modified rational function to replace the belief propagation equation reduces the amount of calculation. Simulation results reveal that this modified LLR BP algorithm can reduce iteration times widely for LDPC decoding in condition of little decoding performance loss. Also we analyze the amount of computation in horizontal direction for decoding.In the joint design of PNC and LDPC, we mainly consider the joint design of PNC and LDPC with carrier frequency offsets in Multiple Access and propose two kinds of corresponding scheme, namely complete frequency offset of single-node and average frequency offset of two-node. In response to above two schemes, designing corresponding frequency offset filters and reanalyzing useful signal part and noise distribution. Simulation results indicate that two proposed joint PNC and LDPC with carrier frequency offsets have a great performance compared to traditional Physical-layer Network Coding with no Channel Coding. Also the joint design scheme of average frequency offsets of two-node is slightly worse than the joint design scheme of complete frequency offsets of single-node. However, both of above joint design schemes with carrier frequency offsets have widely application value.