Energy Allocation for Short-Packet Massive Multiple Access with Two-Iteration Successive Decoding

An optimum energy allocation for massive user networks operating under iterative successive interference cancellation (I-SIC) is derived in this work. We analyze an uplink setting where a large network of cost-effective low-power users employ a practical transmission scheme consisting of the same channel encoder followed by spread spectrum modulation. Variational calculus (VC) is utilized to derive the asymptotic large-user energy distribution that favors I-SIC's performance, in terms of spectral efficiency (SE), when at most two decoding attempts per user are performed. The capacity region under random spreading and SIC operating in the infinite blocklength regime is evaluated and contrasted with the maximized SE using short packets.