We analyze the performance of enhanced spread spectrum Aloha (E-SSA) in the framework of unsourced multiple access (UMAC). The asynchronous, unframed transmission of E-SSA is modified to enable a direct comparison with framed UMAC schemes, as well as with the Polyanskiy's achievability bound. The design of E-SSA is tailored to the peculiarities of the UMAC setting, resorting to short polar codes and the use of a timing channel to improve the energy efficiency of the protocol. We assess the impact of the preamble length and of the spreading factor on the system efficiency. The resulting scheme exhibits simplicity at the transmitter and linear complexity with respect to the number of active users at the receiver, approaching the UMAC achievability bound in close competition with the best known UMAC schemes.

翻译：我们在无源多址接入（UMAC）框架下分析了增强型扩频ALOHA（E-SSA）的性能。为与成帧UMAC方案及Polyanskiy可达界进行直接比较，对E-SSA的异步非成帧传输方式进行了改进。通过引入短极化码并利用定时信道提升协议能效，使E-SSA设计适配UMAC场景的特殊性。我们评估了前导码长度和扩频因子对系统效率的影响。所提方案在发射端保持简洁性，且接收端计算复杂度与活跃用户数呈线性关系，在与最先进UMAC方案的激烈竞争中逼近UMAC可达界。