Capacity Improvement and Power Allocation Algorithm in Multiuser Cluster based Downlink Hybrid CDMA-NOMA Systems

Abstract

Non Orthogonal Multiple Access (NOMA) a prominent fifth generation (5G) wireless communication technique which ensures spectral efficiency, low latency, high data rates with throughput and massive connectivity. NOMA outperforms other OMA techniques like OFDMA etc. NOMA is further divided as power domain NOMA and code domain NOMA. This research thesis consists of two phases SISO downlink power domain NOMA and SISO downlink hybrid CDMA-NOMA. In the first phase we proposed downlink power domain NOMA for multiuser environment. Capacity and performance of multiuser NOMA systems are analyzed in AWGN and NYUSIM channel model. Accurate power allocation in multiuser case is crucial to deal with. We proposed power allocation strategy in multiuser NOMA system on the basis of distances with different UE’s around base station (BS). We also proposed phase shift phenomena to further enhance the system performance with capacity. Interference between users signals are reduced by assigning with different phase shifts at the time of modulation. In the second phase we proposed hybrid CDMA-NOMA approach to ensure serving of simultaneous users having same distances with respect to the base station (BS). User clustering technique is proposed to group UE’s on the basis of distances or channel conditions. Grouping of two, three and four UE’s per cluster are made. Simulations are done with single base station antenna to serve one, two and four clusters around base station. We can add up to an n number of clusters also. Each cluster of hybrid CDMA-NOMA system are assigned with unique spreading codes, PN codes (nonorthogonal) and Walsh codes (orthogonal) to ensure the rejection of inter-cluster interference. While intra-cluster interference is controlled through Successive Interference Cancellation (SIC) technique of NOMA scheme. We further proposed joint systems which accurately serve users with CDMA, NOMA and hybrid CDMA-NOMA simultaneously. BER performance of four, six, eight and sixteen users are observed with different SNR values. This research work provides a foundation of achieving capacity with performance in 5G NOMA systems in the coming future.