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Title: Physical layer network coding using lattice codes
Author: Liu, William
ISNI:       0000 0004 6421 143X
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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In this thesis, using lattice codes and channel codes, we propose several solutions to improve the performance of physical-layer network coding (PNC) schemes over the two-way relay network as well as the multi-way relay network. In the first part of our work, we propose an efficient equation-coefficient search algorithm for compute-and-forward over complex-valued channels, which guarantees to find the optimal coefficients over the ring of Gaussian integers as well as the ring of Eisenstein integers. We also propose an optimal coefficient search algorithm for the Integer-Forcing compute-and-forward receiver, when multiple receive antennas are available at the relay. The proposed algorithms are shown to have low polynomial complexity in transmitting user number and we use numerical results to verify the performance of our algorithms against other competitive search algorithms in literature. In the second part of our work we investigate the performance of popular PNC schemes for the two-way relay network and derive their end-to-end achievable rates with channel inversion precoding over the Rayleigh fading channel. We also propose a power efficient precoding scheme based on compute-and forward-to improve the network throughput. In the third part of our work, after introducing the novel concept of compatibility between channel code and lattice code, we propose several low complexity joint channel coded network coding (JCCNC) schemes for PAM and QAM two-way relay networks. Firstly, using LDPC codes, we propose the lattice-decoded JCCNC (LD-JCCNC) scheme. Secondly, we propose two JCCNC schemes using low density construction A (LDA) lattices and polar lattices, which we call LDA-JCCNC and PLA-JCCNC respectively. In both JCCNC schemes, channel coding and network coding operations are integrated through the use of lattice decoding at the relay, where the arithmetic addition of lattice codewords is directly decoded using their corresponding lattice decoding algorithm. In contrast with most existing JCCNC schemes which are restricted to set types of modulation schemes, we also give clear methodology on how our JCCNC schemes can be applied to general types of higher order PAM and QAM modulation schemes. In the final part of our work, we extend our novel JCCNC schemes to the general multi-way relay network for the compute-and-forward scheme, and show how they can be used with general types of PAM and QAM modulation systems. Detailed simulation analysis are carried out to evaluate and compare the performance of all proposed JCCNC schemes in relation to existing schemes in literature.
Supervisor: Ling, Cong Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral