Analysis And Research On The Full-Duplex Relay Systems

With the development of the wireless communication systems,the traditional half-duplex mode has been challenged by the exponential increasing data traffic demand due to the deficiency of the spectrum utilization.The full-duplex mode has been one of the most important breakthroughs to improve the network performance.By transmitting and receiving simultaneously on the same resource block,the full-duplex mode has the potential to double the spectrum efficiency.However,the inherent self-interference leakage from the transmitting antenna to the local receiving antenna could overwhelm the desired signals and erode the performance gain of the full-duplex mode.The practical experiment results have shown that the self-interference cannot be perfectly canceled due to the hardware nonlinearity,limited dynamic,phase noise,channel estimation errors and so on.Studying the impacts of the residual self-interference on the system performance is significant prior to the practical implementation of the full-duplex systems.Based on the experimental statistical modeling of the residual self-interference signals,this thesis investigates the full-duplex two-way relay system under the single user pair or multiple user pairs scenario,adopting amplify-and-forward or decode-and-forward protocols,with or without buffer at the relay node,in terms of the outage probability and achievable rate,respectively.In addition,based on the theoretical results,the power allocation schemes,relay placement schemes,and multi-user scheduling schemes are proposed.The main contributions of this thesis are summarized in the following.1.Considering the effects of the residual self-interference,the full-duplex two-way decode-and-forward relay system under single user pair scenario is investigated.The exact outage probability and asymptotic behavior have been analyzed with the relay power allocation and relay node placement schemes being proposed.Based on the experimental statistical model of the residual self-interference,we model the residual self-interference as circular symmetrical complex Gaussian distributed random variables.The full-duplex two-way decode-and-forward relay system where both the user and relay nodes work in the full duplex is studied.We first derive the system exact outage probabilities,based on which the asymptotic behavior is analyzed.To improve the system performance,the relay power allocation and relay node placement schemes are proposed.The results show the power sensitive characteristics of full-duplex mode under asymptotic case.2.Extending to the multi-user scenario,the relationship between the residual selfinterference and the system outage probability have been analyzed.In addition,the optimal scheduling scheme within high SINR regime is further proposed.The multi-user two-way relay system,where multiple user pairs exchange pair-wise information via the relay node,is investigated.Considering the residual self-interference and assuming the relay node can obtain the global CSI,the optimal multi-user scheduling scheme within high SINR regime is theoretical obtained.As the performance benchmark,the Round-Robin and outage-aware scheduling schemes are considered.Comparing the full-duplex and half-duplex modes,the results show that the full-duplex mode could improve the outage performance over an order of magnitude.3.Based on the amplify-and-forward protocol,the system performance in terms of the achievable rate and the outage probability of the multi-user scheduling system under independent and non-identically distributed channel environment is investigated.The amplify-and-forward two-way multi-user full-duplex relay system is studied.To model the user location differences,the independent and non-identically distributed channel environment is considered.By deriving the selection probability density functions,the weighted outage probability and weighted achievable rate of different user pairs are obtained.Then based on the total probability theorem,the system performance can be evaluated.The results show that within low transmission power regime,the full-duplex mode achieves better performance over the half-duplex mode.4.Utilizing the buffer at the relay node,two multi-user scheduling schemes under fixed power transmission and adaptive power transmission are proposed to solve the performance degradation problems caused by the weak links.With the data storage capability,the relay node can first store the data and then forward to the destination until the channel becomes moderate.Due to the relay channel involve at least two links,the end-to-end throughput is always restricted by the worse link.To solve this problem,two multi-user scheduling schemes are proposed under the fixed and adaptive power transmission scenarios,respectively.By designing the optimal weighted factors of different user pairs,the utility ratio of different links can be adjusted.For the adaptive power transmission,the closed-form power allocation scheme is proposed based on the statistical channel state information.The results show that the scheduled user still needs to keep silent when the channel gain is below a certain value.The comparison of the proposed scheme with the existing schemes indicates the effectiveness of proposed schemes.