Physical layer network coding based on compute-and-forward

Abstract

In this thesis, Compute-and-Forward is considered, where the system model consists of multiple users and a single base station. Compute-and-Forward is a type of lattice network coding which is deemed to avoid backhaul load and is therefore an important aspect of modern wireless communications networks. Initially we propose an implementation of construction D into Compute-and-Forward and investigate the implementation of multilayer lattice encoding and decoding strategies. Here we show that adopting a construction D lattice we can implement a practical lattice decoder in Compute-and-Forward. During this investigation and implementation of multilayer lattice encoding and decoding we discover an error floor due to an interaction between code layers in the multilayer decoder. We analyse and describe this interaction with mathematical expressions and give detail using lemmas and proofs. Secondly, we demonstrate the BER performance of the system model for unit valued channels, integer valued channels and complex integer valued channels. We show that using the derived expressions for interaction that the decoders on each code layer are able to indeed decode. The BER results are demonstrated for two scenarios using zero order and second order Reed-Muller codes and first and third order Reed-Muller codes. Finally, we extend our system model using construction D and existing conventional decoders to include coefficient selection algorithms. We employ an exhaustive search algorithm and analyse the throughput performance of the codes. Again, we extend this to both our models. With the throughput of the codes we see that each layer can be successfully decoded considering the interaction expressions. The purpose of the performance results is to show decodability with the extension of using differing codes

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