Abstract
In OFDM based two-way relay channels, carrier frequency offsets (CFOs) between relay and terminal nodes introduce severe inter-carrier interference which degrades the performance of traditional physical-layer network coding. In this paper, we present a two-step asynchronous physical-layer network coding scheme, which consists of an interference cancelation step and a network coding mapping step, to deal with the frequency asynchrony in two-way OFDM relay system. We show through the average signal-to-interference-plus-noise ratio (SINR) and bit error rate (BER) that the proposed scheme can efficiently map the received superimposed signal, which is corrupted by the CFOs, into the exclusive OR of two terminals’ transmitted symbols. Moreover, a simple upper bound of the average SINR for the proposed scheme is derived. Through the simulation results, it is shown that the exact average SINR curve of the proposed scheme is very close to the upper bound even when the normalized CFO is as large as 0.15. Finally, we show that the average SINR and BER performances of the proposed scheme outperform the reference schemes considerably.
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Notes
Herein, perfect timing-synchronization is assumed.
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Acknowledgments
This work is supported by Major Research Plan of National Natural Science Foundation of China (No. 91438115), Special Financial Grant of the China Postdoctoral Science Foundation (2015T81079), National Natural Science Foundation of China (Nos. 61371123, 61301165), Jiangsu Province Natural Science Foundation (BK2011002, BK2012055), China Postdoctoral Science Foundation (2014M552612) and Jiangsu Postdoctoral Science Foundation (No. 1401178C).
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Appendix
Appendix
After combing the received samples \(\varvec{Y}_R(k)\) and \(\varvec{Y}_R^*(N-1-k)\), the decision variable of SDC based scheme can be written as [13]
The reason of the \(1 / {\sqrt{2}}\) is that the scheme takes two subcarriers to transmit one symbol at terminals. The average SINR on the kth subcarrier can be expressed approximately as
Using the condition \(\varvec{X}_i(k,k) = \varvec{X}_i^*(k,k)\), \({\beta _i}\left( {k,l} \right)\) can be written as
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Xia, X., Xu, K. & Xu, Y. Asynchronous Physical-layer Network Coding Scheme for Broadband Two-Way Relay Channels. Wireless Pers Commun 89, 149–163 (2016). https://doi.org/10.1007/s11277-016-3257-1
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DOI: https://doi.org/10.1007/s11277-016-3257-1