Research On The Key Technologies Of Uplink Non-orthogonal Multiple Access In Mobile Communication

The development of mobile communication services has greatly improved people's quality of life.People's demand for traffic flow has increased dramatically.The rapid development of emerging services and the growing number of users and mobile devices require more spectrum resources and higher spectrum utilization.Therefore,how to efficiently use limited spectrum resources has become a research hotspot.Non-orthogonal multiple access(NOMA)has emerged as the times require.NOMA allows multiple users to share the same spectrum resource at the same time and has become a promising multiple access technologies in future mobile communication for its high spectrum utilization,high flexibility and high system capacity.The research in this area is mostly on downlink NOMA at present,while research on uplink NOMA is relatively little.In the downlink,each user receives an overlapped signal(which is sent by BS)from one link.Therefore,the synchronization problem is easier to be solved and the SIC technology is easier to be implemented in downlink NOMA.In the uplink,each user separately sends its own signal to BS.BS receives signals from different links.So uplink NOMA has a synchronization problem.It's necessary for each user to coordinate and control the power in uplink NOMA,which is more difficult than that in downlink NOMA.On the other hand,SIC works on users side in the downlink while on BS side in the uplink.The processing capability of BS is much stronger than users.The synchronization problem in the uplink can also be solved by using the buffer method on BS side.There are still some deficiencies in the research on uplink NOMA.In view of the corresponding deficiencies,the innovations of this thesis are summarized as follows:(1)When transmitting power in uplink NOMA depends on distance between a user and a BS,BS needs to feed back variable distances to users in real time.There is no research on the system performance when the statistical characteristic of the distance replace the specific variable distance in existing literatures.This thesis uses the statistical characteristic of the distance to determine the transmitting power.BS only feeds back the statistical characteristic to the corresponding user.The expressions of two users' outage probability are derived and verified by Monte Carlo simulation.Simulations show that utilizing statistical characteristic to determine the transmitting power can obtain almost the same outage performance if the boundary values of a user's area are not much different.Therefore,in small-scale real scenes such as office,classroom and house,when the distribution of the distance does not change greatly,BS can only feed back the statistical characteristic rather than variable distances and user doesn't need to change the transmitting power in real time,which can reduce the system complexity and ensure the performance of the user.(2)Users are usually assumed evenly distributed in multi-user uplink NOMA system in existing literatures.If many users lie near to BS and few remote users have large traffic volume,the classical pairing method doesn't work because little difference of signal power between two near users is more likely to happen.The above situation is not conducive to the realization of the power domain NOMA.To solve this problem,this thesis proposes a module-based multi-user pairing method(referred to as " module 'pairing' ").In this method,multiple near users as a whole module are grouped with a remote user.The users in such a so-called "pair" use the same spectrum resources.Different near users transmit on different time slots,while the far user transmits on entire time slots.A community usually has many residents which have less traffic,some scattered monitoring devices that need to upload real-time video resources.The residents are usually located in the center of the community and the monitoring devices are usually located at the edge of the community.In this scenario,module "pairing" can be used.Simulations show that the proposed method can achieve higher system capacity than OMA and two-user pairing method.(3)The combination of NOMA with cognitive radio(CR)which improves spectrum utilization is also a current research hotspot in wireless communications.There are very few primary-secondary user pairing methods for uplink underlay CR-NOMA system in the existing literatures.NOMA and CR-NOMA systems have certain differences,for example,CR system must consider the interference control of the primary users.Therefore,pairing methods in NOMA cannot be directly applied to the CR-NOMA.There are two researches about user pairing in uplink underlay CR-NOMA in this thesis:1.The pairing methods in NOMA are applied to underlay uplink CR-NOMA system.The specific designs of secondary user high-high pairing and primary-secondary user random pairing are given.2.The above two methods need to form pairs of secondary users first,and then determine whether a secondary user can be successfully paired with the corresponding primary user.They are not flexible.Therefore,a direct primary-secondary pairing method based on the quality of the primary user is proposed.Simulations show that it can add more secondary users than the other two methods and primary-secondary user random pairing is the worst.