Low Density Code Design For Downlink Noma System

A Low-Density Code Structure (LDC) spread transmission for Non-Orthogonal Multiple Access (NOMA) system based on modified combinatorial design is studied in this letter. To mitigate the multiuser access interference, the NOMA frequently needs complicated signal processing, which is difficult to be applied in practical scenarios. One potential solution is to design sparse multiple access structure for leveraging detection complexity. The sparse pattern of Balanced Incomplete Block Designs (BIBDs) provide an inherent sparse mapping for this system allowing simultaneous and more efficient usage of given. It is also able to form a bijection mapping with lower complexity and be reconstrued to achieve further sparsity. This new scheme allows a larger number of users transmitting in the downlink.