Abstract
Sparse code multiple access (SCMA) is one of the most intensively investigated non-orthogonal multiple access (NOMA) techniques for the fifth generation communication (5G) system. In this paper, a new multi-stage optimization approach for codebook design is proposed for the uplink SCMA system. The proposed schemes includes two parts: i) multi-dimensional mother constellation design ii) mapping matrix design. Firstly, the multi-dimensional complex mother constellation design is implemented by a series of two-dimensional real constellations which can be obtained by the lattice theory and the symbol switch algorithm (SSA). The Secondly, we construct user-specific mapping matrix by optimizing the phase rotation of the user constellation to effectively reduce the interference between the multi-user codewords superimposed on every single time-domain resource elements (REs). Finally, the multi-user codebooks are generated by combining the multi-dimensional mother constellation and the user-specific mapping matrix. The simulation results demonstrate that the proposed codebooks can greatly decrease bit error rate (BER) value compared to the existing codebooks under different channels, different codebook sizes and different overloading ratios, and the performance is also improved for the large-scale SCMA codebook. More importantly, in order to verify the proposed codebook applicability, two different message passing algorithm (MPA) are used to simulate the SCMA system with different codebook sizes, both of which obtain faster convergence speed and better BER performance than other existing codebooks.
Highlights
With the rapid development of wireless communication, there are tighter requirements such as throughput, spectrum utilization, very low latency, and massive device connectivity for the Network throughput analysis (5G) system [1]–[3]
Different from conversional OMA technologies, non-orthogonal multiple access (NOMA) can accommodate much more users via resource allocation, so as to achieve massive connectivity, low latency and high spectral efficiency, but its system performance still be affected by interference and receiver complexity [4], [5]
The low-density signature (LDS) [8] technique is a special approach of CD-NOMA spreading sequence with a few nonzero elements within a large signature length
Summary
With the rapid development of wireless communication, there are tighter requirements such as throughput, spectrum utilization, very low latency, and massive device connectivity for the 5G system [1]–[3]. In order to reduce the interference between the codewords and achieve good system performance, SCMA codebook need to be designed delicately by increasing power diversity and Euclidean distance between interfering codewords Both designing high efficient multi-user codebooks and a low complexity detection algorithm are critical to SCMA system. Cai et al showed a multi-dimensional SCMA codebook design method based on constellation rotation and interleaving under downlink Rayleigh fading channel [20] This method can be used to design different codebooks for the aim of spectral efficiency or power efficiency, but the minimum Euclidean distance (MED) between mother codebook did not reach its expectation under the large codebook size.
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