Research On NOMA Technology In Full-Duplex Cooperative Communications

Supported by advanced 5G wireless communication technologies,a series of newly emerging businesses are springing up on the 2019 World 5G Convention.More impressively,the crucial communication scenes create a brand-new future city,including digital city,unmanned aerial vehicle emergency,5G-based self-driving technology and telemedicine.The scenarios covered in 5G network should meet such four basic requirements as seamless wide-area coverage,high-speed and high-capacity,low-power and massive connectivity,low latency and high reliability.With the explosive growth of data requirements in future wireless network,one of the most important goal for 5G deployment is to fully improve spectral efficiency and energy efficiency.Consequently,both the existing wireless transmission mode and networking technology require further reforms.To solve the confliction between massive connectivity and limited spectrum resources,on the one hand,we can introduce non-orthogonal multiple access(NOMA)to enhance user access ability;on the other hand,double spectrum efficiency for a full-duplex(FD)relaying could be achieved in theory,since FD mode involves transmission and reception simultaneously and it only requires one time slot.As a result,the application of NOMA to a FD cooperation scheme could fit some key communication needs in future mobile communication,such as low latency and massive connectivity.Moreover,since perfect instantaneous channel state information(CSI)comes at the price of complex signal overhead and heavy feedback,the performance analysis based on partial channel state information is worthy to be further studied.Lastly,the influence of some non-ideal factors in two pivotal techniques like self-interference,channel estimation error and inter-user interference should not be overlooked,then summarizes up the bias between theoretic analysis and real application effect.Above all,considering a multiple users scenario,this thesis provides a systematic research on NOMA technology in full-duplex cooperative communication.More specifically,the key contributions of our work are summarized as follows:Firstly,considering a multi-user full duplex relaying network,we exploit NOMA technology to achieve the efficient resource sharing between multiple users.Further,to alleviate design challenges in successive interference cancellation(SIC)process,we design a user pairing algorithm based on partial instantaneous channel conditions.Assuming a more generalized Nakagami-m fading and using mathematical tools like numerical integration and order statistics theory,outage probability and ergodic capacity of each user in fixed power allocation scheme are derived respectively in closed form.As closed form expressions get more complicated,the asymptotic expression of outage performance under high signalto-noise radio region is also attained.Numerical and simulation results show that:(1)the users with the highest and second highest channel conditions,when paired together,could have the maximum ergodic capacity,meanwhile,the user pairing with the largest difference over channel conditions achieves near maximum ergodic capacity;(2)the residual selfinterference in full-duplex node is the main performance-limiting factor.After undergoing effective self-interference cancellation mechanisms,the outage performance and capacity of NOMA-based FD relaying scheme outperform NOMA-based half-duplex(HD)relaying network;(3)compared to orthogonal multiple access scheme,NOMA-based cooperative scheme ensures user fairness,thus significantly improving ergodic capacity.Secondly,due to the broadcast nature of wireless channels,idle nodes or users with better channel conditions are mobilized as relays for enhancing transmission reliability of celledge user.Therefore,the application of NOMA in user-assisted cooperative network is proposed,where a source simultaneously serves a cell-center user and multiple cell-edge users by NOMA principle.There are two types of users for researching,one is single-hop users that can directly communicate with source and can be viewed as relays for assisting multiple cell-edge users.The other one is two-hop users and its communication mode consists of direct transmission and cooperative transmission.Furthermore,only partial statistical properties of CSI is obtained at base station,when users are scattered at random and its location can be modeled based on stochastic geometry.Utilizing Gaussian-Chebyshev quadrature formula,analytical expressions for FD-NOMA and HD-NOMA networks in terms of outage probability and ergodic capacity are respectively derived.After that,since both NOMA transmission and FD cooperative scheme are more vulnerable to interference,we attempt to develop a hybrid FD/HD mode by dynamically selecting appropriate modes.The analytical results reveal that:(1)the performance of NOMA-based cooperative scheme under partial statistical CSI approximates to that of the network with full instantaneous CSI;(2)zero diversity order for cell-edge user inherent to FD-NOMA system is overcame by using direct transmission.Finally,the effect of non-ideal factors including channel estimation error and inter-user interference on system performance is analyzed.First,the channel estimation error always exists in communication scenarios with limited feedback.With the imperfect CSI,exact expressions of outage performance and approximate results for ergodic capacity are provided.The theoretical analysis and numerical simulation show that,compared with NOMA-based relaying network under perfect CSI,there obviously exists error floor brought by channel estimation error,while the ergodic capacity in high signal-to-noise ratio region will converge to a constant.Next,when multiple users in NOMA protocol are being supported by a single spectrum resource,the assumption of ideal SIC at considered network seems unreasonable.By using the Monte Carlo method,we analysis the impact of error propagation in imperfect SIC process on the outage probability and ergodic capacity.The numerical results demonstrate that the subsequent signal detection suffers from the residual interference signals.As a result,the error floor appears in NOMA-based cooperative scheme with non-ideal SIC receiver,while the ergodic capacity tends to definite value in high signal-to-noise ratio condition.