Non-orthogonal multiple access with two sets of orthogonal signal waveforms

Abstract

The rapid development of the mobile systems causes dramatic increase on data traffic. Due to the bandwidth scarcity, existing multiple access systems may not over come this problem [1]. These multiple access techniques are called as orthogonal mul tiple access (OMA) in which different users utilize orthogonal resource blocks such as frequency, time or code domain. Therefore the number of the users which can be sup ported by a wireless system is strictly restricted by the number of the resource blocks. However in non-orthogonal multiple access (NOMA), orthogonal resource blocks are shared by different users. Interference cancellation method is used by receiver at the cost of complexity. Thanks to NOMA, users more than orthogonal resource block size, can communicate. In addition to that, NOMA is more spectral efficient multiple access technique than OMA. For instance even if a user has poor channel condition, she/he occupies at least one resource block in OMA. This situation reduces total throughput of the overall system. However in NOMA, since all resource blocks are shared by more than one user, weak users do not occupy any resource block on his own. Existing NOMA techniques can be divided into two main categories as code domain and power domain NOMA [2]. Power differences between non-orthogonal users are very important for power domain NOMA. Weakness of the code domain is that even if the number of the users do not exceed the number of the orthogonal blocks, non-orthogonality still occurs. These problems can be overcome by using two sets orthogonal signal waveforms which are non-orthogonal to each others [3]. In addition to that, its error performance on different channel conditions is encouraging.