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Asynchronous two-way relay networks

This thesis summarises the work during the four year Ph.D. study at the University of Reading. It focused on the design for emerging two-way relay network (TWRN) strategies respecting various practical and theoretical conditions. Our work concerns four main topics. The first topic is the synchronisation for time-domain (TD) based physical-layer network coding (PLNC) with timing asynchrony under Rayleigh block-flat-fading channels. In such a system, it is essential to estimate the channel coefficients at the relay to perform PLNC mapping and detection. We have proposed a training-sequence-based delay and channel estimation algorithm and presented a low-complexity estimation design based on Alamouticode structure. Among our findings, we revealed that as long as the signals arrives at the relay with symbol alignment and the relative delay information is sent to the destination nodes, timing asynchrony does not affect the system performance. The second topic targets the interference mitigation schemes in practical PLNC systems. In TD-based PLNC systems, signals may arrive at the relay with fractional symbol delay which introduces inter-symbol interference (ISI) Orthogonal frequency-division multiplexing (OFDM) can be combined with PLNC to combat the timing mismatch, however on the other hand it is sensitive to carrier frequency offset which introduces inter-carrier interference (ICI). In these systems, ISI and ICI need to be carefully handled, otherwise it will cause serious performance degradation. The thesis has looked into both cancellation and mitigation in PLNC systems and novel schemes were proposed accordingly. For TD-PLNC systems, the first scheme is a multi-dimensional transmission scheme through pre-coding. lSI can be fully avoided through separate decoding. The second scheme is an iterationbased algorithm, which enables the relay to reconstruct and eliminate the interference to achieve better performance with reduced complexity compared to other existing schemes. The second method is also extended to OFDM-based PLNC systems to mitigate the ICI. The third topic is concentrated on limited feedback (LFB) power control in PLNC, which has been rarely mentioned in the literature. We have proposed a feedback ratio design based on the characteristics of the channels, where each feedback ratio covers a ratio range of equal probability in cumulative distribution function of the ratio between two channels' power gains. The effectiveness of the proposed scheme shows that the proposed LFB power control scheme with 3 bits can approach optimal power control scheme. The last topic examines the relay selection and dynamic power allocation in analogue network coding CANe) system. Three novel power allocation schemes are proposed, which show significantly performance improvement and provide a tradeoff between computational complexity and performance.
Date January 2014
CreatorsLi, Yixin
PublisherUniversity of Reading
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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