Judicious use of redundant transmissions in multi-channel ALOHA networks with deadlines

This paper shows how to improve the classic multi-channel slotted ALOHA protocols by judiciously using redundant transmissions. The focus is on user-oriented requirements: deadlines and a permissible probability of failing to meet them. Subject to those, maximization of throughput is the optimization goal. When there is with no success/failure feedback prior to the deadline, the use of information dispersal with some redundancy provided by error-correcting codes for the data in conjunction with a replicated, separately-transmitted synchronization preamble sharply reduces the overhead resulting from the use of shorter packets and significantly increases the capacity. When the permissible delay is several times greater than the round-trip propagation delay, we propose a novel retransmission policy: all attempts except the final one entail the transmission of a single or very few copies, and the remaining copies are transmitted in the final attempt. This sharply increases channel capacity.