Inter-Carrier Interference Cancellation For Cooperative Communication

High-data-rate,spectrally efficient and reliable cooperative communication tech-nique significantly enhances the performance of wireless communication systems in terms of throughput,coverage and quality of experience.Existing frequency offset in the cooperative communication system gives rise to inter-carrier interference.It de-stroys the code structure of the received signals at the destination node,and greatly reduces the performance of the system.This thesis is dedicated to eliminating the inter-carrier interference in cooperative communications.This thesis first studies the basic techniques of synchronous cooperative commu-nications,including distributed space-time block codes and their decoding algorithms.From this we conclude and prove a theorem,the "Equivalent Maximum Likelihood Decoding Theorem".The theorem states that if the equivalent channel matrix of the co-operative communication system is a complex orthogonal matrix,then the zero-forcing decoding algorithm is equivalent to the maximum likelihood decoding algorithm.The proof of "Equivalent Maximum Likelihood Decoding Theorem" presents the concept of" simplified zero-forcing decoding algorithm".Under the guidance of "Equivalent Maximum Likelihood Decoding Theorem",this thesis designs a cooperative communication scheme which can completely elim-inate the inter-carrier interference and applies to any-relay scenarios.In this pro-cess,two cooperative communication schemes with good performance are studied first,namely frequency-reversal space-frequency codes and frequency-asynchronous distributed alamouti-coded system.However,these two schemes can not completely e-liminate the inter-carrier interference.Thus this thesis proposes and designs frequency-reversal orthogonal space-frequency codes(OSFCs),including two-relay's frequency reversal Alamouti code(FRAC)and three-relay's OSFC,and gives the design rules of OSFCs for any-relay scenarios.According to "Equivalent Maximum Likelihood De-coding Theorem",this thesis designs a simplified zero-forcing decoding algorithm for OSFCs.The reversal operations of these codes make the equivalent channel matrix complex orthogonalized.Thus when these OSFCs are employed in the cooperative communication system with frequency offset,the destination node achieves the ad-vantages of maximum likelihood decoding by using only the simplified zero-forcing decoding algorithm.The theoretical deduction points out that the reliability of this transmission scheme is exactly the same as that of the synchronous cooperative com-munication scheme.Finally,this thesis evaluates the performance of the simplified zero-forcing de-coding algorithm for OSFCs,including the bit error rate performance and the com-putational complexity.The evaluation results show that the simplified zero-forcing decoding algorithm for OSFCs can completely eliminate the inter-carrier interference,so that the reliability of the system is not affected by frequency offset.This conclusion is true even if the decoding errors in the first phase of cooperative communications are taken into account.In the evaluation of computational complexity,the simplified zero-forcing decoding algorithm has a lower complexity than existing methods.