  In this paper we propose a new cooperative packet transmission scheme that
allows independent sources to superimpose over-the-air their packet
transmissions. Relay nodes are used and cooperative diversity is combined with
distributed space-time block coding (STBC). With the proposed scheme the
participating relays create a ST code for the over-the-air superimposed symbols
that are received locally and without proceeding to any decoding step
beforehand. The advantage of the proposed scheme is that communication is
completed in fewer transmission slots because of the concurrent packet
transmissions, while the diversity benefit from the use of the STBC results in
higher decoding performance. The proposed scheme does not depend on the STBC
that is applied at the relays. Simulation results reveal significant throughput
benefits even in the low SNR regime.
