The throughput of some wireless multiaccess systems

The throughput performance of some multiaccess wireless systems is compared on the basis of the average energy per successfully received information bit Eb =N0 . We assume that an infinite uncoordinated population of users access at random a block fading channel and that channel state information is available at the decoder only. To cope with multiaccess interference and fading, the users retransmit erroneously received packets that are then combined at the receiver to improve decoding. We prove that, for an optimal choice of the system parameters, some systems are not interference limited and have a similar behavior: at high Eb =N0 they "self-orthogonalize", i.e., on the average only one user per degree of freedom is active, while at low Eb =N0 they have the same throughput of conventional CDMA, achieved by infinite users per degree of freedom transmitting with vanishing rate.