Non-orthogonal multiple access in downlink coordinated multipoint transmissions

Abstract

In this paper, a joint transmission coordinated multi-point based non-orthogonal multiple access (JT-CoMP NOMA) combined with spatial modulation (SM), termed as JT-CoMP NOMA-SM, is proposed to enhance capacity. User capacity and ergodic sum capacity (ESC) of K coordinated multi-point base stations (CoMP BSs) within N number of cells are analyzed by considering imperfect successive interference cancellation (SIC) and imperfect channel state information (CSI). The performances of the proposed system are compared with orthogonal multiple access (OMA), non-orthogonal multiple access (NOMA), and joint transmission coordinated multi-point combined with virtual user pairing based non-orthogonal multiple access (JT-CoMP VP-NOMA) through both simulation and analysis. The results show that the proposed system has the same cell center user (CCU) capacity compared to JT-CoMP VP-NOMA and a higher cell edge user (CEU) capacity than the other schemes. ESC of the proposed system outperforms the other schemes due to enhancing CEU capacity. Imperfect SIC and imperfect CSI may degrade capacity. To achieve an optimal capacity, the power allocated for CCU should be increased if the transmit signal-to-noise ratio (SNR) is reduced. The proposed system can maintain CEU capacity better than the other schemes if the number of cells is increased. It happens because SM works beyond Shannon upper bounds, which can mitigate inter-cell interference (ICI).