Information-theoretic aspects of spread ALOHA

Slotted ALOHA is often analysed in terms of throughput and delay. These quantities do not take into account the restrictions on information transmission imposed by noise. The (potential) information per symbol interval of slotted ALOHA is calculated for an AWGN channel. It is further shown that the use of orthogonal spreading sequences does not affect system performance if bandwidth is kept constant. Finally, an example demonstrates that the use of non-orthogonal spreading sequences, which enables a certain capture effect, actually decreases the information per symbol interval.