A Study on Non-Orthogonal Multiple Access with Stored Device-to-Device Communication in Cellular Systems

In recent years, wireless communication traffic has exploded. Therefore, non-orthogonal multiple access (NOMA), which expands communication capacity to accommodate the growing wireless communication traffic, is attracting attention. In addition, relay transmission by the cell-center user communication is a promising solution to solve the inequality of communication capacity among terminals (users) in cellular systems. However, there is a problem in that throughput per unit time decreases due to the expansion of communication time required for relaying. In this study, we investigated a method of combining NOMA and Device-to-Device communication (D2D) in the downlink of a cellular system, where D2D uses transmission in the millimeter wave band to reduce the transmission time required for relaying by increasing the capacity. On the other hand, to overcome the large difference in throughput between D2D and D2D communication from a base station to user, the transmission bandwidth of the millimeter wave band used for transmission is maximized by storing data at the users as a relay station. This is called store-and-forward relaying. Computer simulations have confirmed that the proposed system achieves higher throughput when compared to the case where stored relaying is not used. It was also found that there is an appropriate number of information storage at cell-edge users to achieve high throughput.