Research On User Pairing Scheme For Uplink Non-orthogonal Multiple Access

Non orthogonal multiple access(NOMA)technology allows multiple users to share a spectrum resource at the same time,significantly improves the spectrum efficiency,provides technical support for the next generation mobile communication technology,and has become a research hotspot in the current communication field.By employing NOMA,multiple users can be multiplexed in the same frequency band.However,due to the limited decoding ability of the receiver,it is impossible to multiplex all users at the same time.The multiplexing mode of grouping and orthogonal multiple access between groups is often adopted to reduce the complexity of the system.Therefore,for NOMA how to pair users has become a research hotspot.In many current research results,user pairing in uplink NOMA system has become a research hotspot,but there are still many deficiencies.First,there are still the following deficiencies in the research of two user pairing: users always want to pair with their own channel gain difference in the process of pairing,so as to improve the overall performance.However,after pairing users with large channel gain(users near the base station)and users with small channel gain(generally cell edge users),because the channel gain of small users is too small,it may be unable to decode and communicate,so that the paired large users cannot communicate with NOMA,and instead use OMA for communication,which affects the improvement of system and rate and loses a certain communication rate.Secondly,mobile communication system users are dynamic.When there are new users in the cell,the existing algorithm generally re-executes the algorithm for all the original users and new users in the cell to complete the new pairing.In this way,there are the following shortcomings:(1)When the original users in the cell are much larger than the new users,all users will be separated and re paired,and the workload of the pairing process will be greatly increased;(2)The pairing of original users is based on security and other factors and needs to be stable.All re pairing has adverse factors on the security of the overall system.The author makes an in-depth study on the above shortcomings and puts forward a new solution.The main work and innovations of this thesis are summarised follows:(1)Aiming at the situation that the small user channel gain is too small to adopt NOMA communication after the users with large channel gain and small channel gain are paired in the actual communication process,an uplink NOMA user pairing scheme based on bilateral matching model and user preference is proposed.In this thesis,pre grouping is adopted according to the user channel gain to avoid user pairing with large channel gain gap and user pairing with small channel gain gap,so as to improve the overall performance of the system;Considering that users with too small channel gain cannot carry out NOMA communication in the real scenario,a channel gain threshold is set as the judgment condition of whether they can communicate.After pre grouping,the channel gain difference and whether they meet the minimum threshold of channel gain are used as the criteria for preference calculation.Finally,the pairing is completed by using the bilateral matching model.The simulation results show that compared with the existing traditional noma pairing scheme and orthogonal multiple access network,the scheme proposed in this thesis effectively improves the traversal and speed of the system.In particular,when the channel gain threshold changes,the proposed scheme is still better than other schemes.(2)In order to effectively solve the problem of user pairing in the scenario of new users in the cell,a new user pairing scheme for uplink NOMA using three user pairing is proposed without interrupting the communication of old users and ensuring their quality of service.In the uplink cell,if the original users have completed pairing and a certain number of users are added,first,for the new users,calculate the sum of the absolute value of the channel gain and the difference between the channel gain of the two users in the cell.Setting a minimum threshold of channel gain difference as the constraint condition,and each difference is required to be greater than the minimum threshold of channel gain,so as to avoid the difficulty of three user pairing decoding caused by the proximity of channel gain.The maximum value of the summation of the channel gain of the new user and the absolute value of the difference between the channel gain of the two users in the original user pair of the cell is solved,and the user pair corresponding to the maximum value is the target user pair of the new user.For each new user in the cell,it will be combined with the target user pair in the original user pair to form three user pairs.The remaining user pairs in the original user pair remain unchanged.The simulation results show that the system and speed of this scheme are significantly improved compared with the traditional scheme.