Non Orthogonal Multiple Access for Multi-carrier Code Division Multiple Access Systems with Energy Harvesting

In this paper, we propose to increase the throughput of Multi-Carrier Code Division Multiple Access (MC-CDMA) systems using Non Orthogonal Multiple Access (NOMA). During the first slot, the base station harvests energy from Radio Frequency (RF) signals received from node A. The harvested energy is used to transmit data to users. The suggested system model uses K different spreading sequence with low intercorrelation. The base station combines the symbols of L NOMA users and transmit them over the same spreading code. The obtained chip sequence is transmitted over different subcarriers. Each user removes the guard interval then it performs a Discrete Fourier Transformation (DFT) to compute the soft output. The weak user uses the soft output of a given NOMA symbol to detect its own symbol. Strong users uses the soft output to detect the symbol of weak users as it is transmitted with a large power. Then, strong user performs Successive Interference Cancelation (SIC) to remove the signal of weak user and to detect its own symbol. We also optimize the powers dedicated to NOMA users and harvesting duration to maximize the total average throughput. When there are two (respectively three or four) users per spreading code, the total throughput of MC-CDMA using NOMA is twice (three times or four times) the throughput of conventional MC-CDMA systems.