A Multi-Overloading-Factor Sparse Code Multiple Access Decoder for 5G Communications

This paper presents a multi-overloading-factor sparse code multiple access (SCMA) decoder IC for 5G massive machine-type communications. This design supports three different overloading factors. We applied the delayed update technique and an early-stop method to the message-passing algorithm (MPA) for better pipeline and decoding efficiency. Moreover, novel techniques, such as common term reuse, approximate distance, and sum/max circuit sharing, significantly reduce the circuit complexity and critical path delays. At 560MHz, the $40 \mathrm{~nm}$ decoder IC achieves $2.777 \mathrm{Gbps} / \mathrm{mm}^{2}$ area efficiency and $46.8 \mathrm{pJ} / \mathrm{b}$ energy with 152.7Mbps throughput. The decoder can achieve maximum energy efficiency of $28 \mathrm{pJ} / \mathrm{b}$ when working at $0.66 \mathrm{~V}$ Vdd and 360MHz clock rate.