Performance Analysis Of FD-NOMA And IRS-NOMA Short Packet Communication Systems

At present,ultra-reliable and low-latency communications(URLLC)is still the re-search hotspot and difficulty of the 5th-generation(5G)mobile communication and even6th-generation(6G)mobile communication.Non-orthogonal multiple access(NOMA),full-duplex(FD)relaying and intelligent reflecting surface(IRS)assisted communica-tion are considered as potential key technologies to realize URLLC in the future wire-less communication systems.Compared with orthogonal multiple access,NOMA can achieve higher system capacity for wireless communication systems by using superpo-sition modulation.Compared with half duplex relaying,FD relaying enable commu-nication systems to achieve higher spectral efficiency by simultaneously sending and receiving signals.With the rapid development of metasurfaces and the corresponding fabrication technologies,metamaterial-based IRS has become a new research hotspot in the field of communication,which is composed of massive low-cost and programmable elements,and thus,can reconfigure the propagation of incident wireless signals by in-dependently adjusting the amplitudes and phase shifts of each element,which collabo-rates to achieve reflection beamforming and coherent superposition with signals from other paths at the receiver to enhance the received power at the receiver.Also,IRS is less costly than traditional relay and large-scale antenna arrays.Based on the above reasons,the performance of full-duplex relaying and IRS-assisted NOMA short-packet communication system is analyzed,which provides theoretical support for the imple-mentation of URLLC in next-generation wireless communication systems.The main research contents of this thesis are as follows:1.Performance analysis of full-duplex cooperative NOMA short-packet commu-nication system.The performance analysis for the two-user downlink cooperative non-orthogonal multiple access short-packet communication over Rayleigh channels is presented.The near user acts as a relay,which operates in full-duplex(FD)mode and employs decode-and-forward protocol,to forward the information to the far user.Two kinds of resid-ual self-interference models,which are modeled as being free of fading and following Rayleigh fading,are considered.We first derive the approximate closed-form expres-sions of average block error rate(BLER)at both users under these two residual self-interference models.Then,simulations are provided to verify the validity of our theo-retical analysis.Finally,we evaluate the BLER performance difference between long-packet and short-packet transmissions for FD cooperative NOMA and that between FD relaying and half-duplex relaying.The analysis and simulation results show that,for ultra-reliable and low-latency communication,we can use residual self-interference link modeled as being free of fading to simplify the system analysis.Furthermore,com-pared to long-packet communication,for FD cooperative NOMA short-packet commu-nication have a narrow range of power allocation to achieve high-reliable transmission,and because BLER outperformance of FD relaying over half-duplex relaying degrades when the residual self-interference signal becomes strong,the optimal duplex mode for FD cooperative NOMA short-packet communication is determined by the residual self-interference signal and the target BLERs at both users.2.Performance analysis and optimization of IRS-assisted downlink two-user NOMA short-packet communication systemThe performance analysis of an IRS-aided NOMA short-packet communication system over Nakagami-m fading channels is presented.The base station uses NOMA technology to send superposition signals to the near and far users,and the base sta-tion uses IRS to assist communication to improve the reception quality of the far users.The IRS phase adjustment strategy considers a variety of cases with and without phase adjustment errors.Based on the assumption that the instantaneous channel state infor-mation is known,by using order statistic and moment matching,we approximate the end-to-end channel gain to follow the Gamma distribution and then derive the approxi-mate closed-form expressions for the average block error rate(BLER)in the high signal-to-noise ratio(SNR)regime and then conduct a refined analysis of the interplay among the minimum common blocklength,optimal power allocation,and the related parame-ters of IRS(e.g.,the number of elements of the IRS)for achieving target BLERs at two users.Finally,numerical and simulation results demonstrate the accuracy of theoretical analysis.They also show that the IRS-aided short-packet NOMA system outperforms the system without IRS.Compared with the continuous phase adjustment strategy with high implementation complexity,discrete phase shifts with 3-bit quantization achieve a similar performance as the optimal continuous phase shifts.