  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 and with Polyanskiy's achievability bound. The design of E-SSA is
tailored to 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.
