The Effect of Codebook Design on the Conventional SCMA System Performance

In 4G systems, Orthogonal Frequency-Division Multiple Access (OFDMA) has been used conventionally for multiple access purposes. This technique has low spectral efficiency since it allocates the resources orthogonally to each user. As an alternative to this technique, Non-orthogonal Multiple Access (NOMA) has been proposed for new generation systems as it allows different users to use the same resources and therefore, increases spectral efficiency. Sparse Code Multiple Access (SCMA) is a code-based NOMA technique and its performance depends on codebook design. In this study, a conventionally used codebook design in the literature has been considered and the system performance has been improved by increasing the distance between the signal constellation points. Considering two different design approaches, the conventional codebook has been modified and about 1dB gain has been achieved in the high signal-to-noiseratio (SNR) region.