Research On Coexistence Technologies Between LTE-U And WIFI Based On Spectrum Cognition Mechanism

With the emergence of a large number of intelligent terminals,wireless data traffic keeps growing exponentially.In this context,the 5th-generation mobile communication systems need to evolve towards increasing the system capacity and ameliorating the spectrum efficiency.The advent of LTE systems operating in the unlicensed spectrum(a.k.a.LTE-Unlicensed,LTE-U)provides a promising option for the global operators among various potential spectrum solutions.However,to realize the deployment of LTEU system,it is necessary to solve the spectrum sharing problem between the LTE-U systems and other wireless communication systems,such as WIFI systems,and hence enable them to coexist over the unlicensed spectrum in a reasonable and efficient manner.With this purpose and starting from the perspective of spectrum cognition,a multi-slot structure based spectrum sensing algorithm is proposed for channel state identification,and a coexistence scheme with cognitive multi-channel access and adaptive muting functionality is designed in this thesis as well.The main contents and innovations of this thesis include the following two aspects:The thesis firstly analyzes the listen-before-talk(LBT)mechanism based clear channel access(CCA)strategy for LTE-U systems,which is intrinsically equivalent to a typical process of spectrum cognition,with a special emphasis on the non-full-alignment of the LTE-U receiving window and the WiFi packet window.In order to enhance the capability of channel state identification under the misalignment condition,this thesis proposes to divide the LTE-U receiving window into several time slots.On the basis of the multi-slot structure,hard decision and soft data fusion aided spectrum cognition schemes are presented respectively.Subsequently,the optimal criterion for multi-slot hard decision fusion is analyzed and derived,and a soft data fusion algorithm which combines the multi-slot observations with a weighting eigenvalue matrix is proposed.Compared with the current clear channel assessment scheme in the literature,the proposed hard decision fusion algorithm under the multi-slot structure can not only diminish the amount of data processed but also strengthen the channel state recognition ability under certain scenarios.In addition,the soft data fusion algorithm can reduce the probability of channel state misjudgment and therefore boost the system coexistence performance.Secondly,on the basis of the LBT mechanism formulated by the ETSI and the proposed spectrum recognition algorithms,a multi-channel access scheme with adaptive channel-switching and channel-muting strategy is proposed.This scheme allows LTE-U system to perform multiple channel state cognition in parallel,and if necessary,the LTEU will switch to some other channel in order to avoid interference to the WIFI system which is caused by the occupying the current channel for a long time.In addition,the optimal muting duration of the LTE-U system is analyzed and calculated by using the Markov modeling of the WIFI systems with the binary exponential backoff strategy.Finally,a channel access parameter configuration strategy is proposed to make LTE-U adjust the transmission and muting duration adaptively,which achieves the purpose of harmonious coexistence with WIFI system.