Research On Non-orthogonal Multiple Access Technology In Cloud Radio Access Networks

Nowadays,the 4th Generation(4G)mobile networks have been achieved large-scale deployments on a global scale.Although 4G supports very high user rates,to meet the higher reliability,higher energy efficiency,lower latency and higer quality of mobile Internet and Internet of things(IoT)for 2020 and beyond,research on the 5th Generation mobile communication technology(5G)has been in full swing.The cloud radio access network(C-RAN)is a novel and green wireless network architecture which combines the information technology with the wireless network.The non-orthogonal multiple access(NOMA)allows multiple users to share time and frequency resources in the same spatial layer via power domain multiplexing.Both of them are key techniques with great potential in 5G.Extensive research has been done to show the superior spectral efficiency of NOMA in various wireless networks,however,there is few literature to propose a transmission model of downlink C-RAN which employs NOMA between remote radio heads(RRHs)and users.In order to improve spectral efficiency,support more connections and reduce transmission delay of C-RAN,this paper considers the application of NOMA into C-RAN and researches on theoretical performance analysis and resource allocation in NOMA-based C-RAN,and the research contents and main contributions are as follows:In the first aspect,this paper completes the outage probability analysis of non-orthogonal multiple access in cloud radio access networks.Firstly,stochastic geometry is used to capture the randomness of RRH locations and signal transmission model is obtained.In this paper,we use the Gauss-Chebyshev integration to approximate the probability density function(pdf)of the channel gain and use Laplace transform and inverse Laplace transform to obtain the closed form approximation for the outage probabilities of two users.Finally,Monte Carlo simulations are provided to validate the accuracy of the theoretical analysis and the superiority of the proposed NOMA.In the second aspect,this paper proposes a power allocation strategy of multi-user NOMA based on system throughput maximization.Because the traditional power allocation scheme of NOMA can not be extended to the C-RAN scenario,this paper proposes a new sum rate maximization problem under limited fronthaul capacity and each user's quality of service(QoS)requirements.To solve this problem,we convert it into a linear fractional programming problems and then use linear programming method to obtain the optimal value and corresponding power factor vector.Finally,the simulation results show that the NOMA achieves a higher sum rate compared to orthogonal multiple access(OMA)scheme.In order to meet high spectral efficiency and large connectivity requirements in continuous wide area coverage scenarios and hot spot large connectivity scenarios in 5G,this paper considers the application of NOMA into C-RAN and utilize the advantages of NOMA to further improve the system performance of C-RAN.