Joint Codebook Design for Multi-cell Noma

Abstract

For spreading-based multiple access, whether orthogonal (OMA) or non-orthogonal (NOMA), the spreading sequences (signatures) are selected from a predefined codebook. When operating in a cellular system, intercell interference will be inherently present between close base stations that share the same resources. If the codebook is reused across the different cells, then intercell interference can cause a full collision of the interfering users in the code-domain, thus deteriorating their performance, especially those at the cell-edge. In this paper, we propose a method for reducing intercell interference by means of jointly designed codebooks. The criterion for the code-book design is to minimize the maximum cross-correlation between the signatures of the interfering cells. In order to obtain such code-books, we employ the algorithm of alternating projection. We finally apply the method to two interfering cells for both NOMA and OMA systems, with the users being uniformly distributed in the cells, and show that it can provide a considerable gain to the cell-edge users.