Sparse code multiple access (SCMA) is a promising 1 uplink multiple access technique that can achieve superior 2 spectral efficiency, provided that multidimensional codebooks are 3 carefully designed. In this letter, we investigate the multiuser 4 codebook design for SCMA systems over Rayleigh fading chan-5 nels. The criterion of the proposed design is derived from the 6 cutoff rate analysis of the equivalent multiple-input multiple-7 output system. Furthermore, new codebooks with signal-space 8 diversity are suggested, while simulations show that this criterion 9 is efficient in developing codebooks with substantial performance 10 improvement, compared with the existing ones.
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