  In this paper, a simple variation of classical Slotted Aloha is introduced
and analyzed. The enhancement relies on adding multiple receivers that gather
different observations of the packets transmitted by a user population in one
slot. For each observation, the packets transmitted in one slot are assumed to
be subject to independent on-off fading, so that each of them is either
completely faded, and then does not bring any power or interference at the
receiver, or it arrives unfaded, and then may or may not, collide with other
unfaded transmissions. With this model, a novel type of diversity is introduced
to the conventional SA scheme, leading to relevant throughput gains already for
moderate number of receivers. The analytical framework that we introduce allows
to derive closed-form expression of both throughput and packet loss rate an
arbitrary number of receivers, providing interesting hints on the key
trade-offs that characterize the system. We then focus on the problem of having
receivers forward the full set of collected packets to a final gateway using
the minimum possible amount of resources, i.e., avoiding delivery of duplicate
packets, without allowing any exchange of information among them. We derive
what is the minimum amount of resources needed and propose a scheme based on
random linear network coding that achieves asymptotically this bound without
the need for the receivers to coordinate among them.
