Announced Retransmission Random Access Protocols

A new contention-based broadcast multiaccess protocol called announced retransmission random access (ARRA) is introduced and analyzed in this paper. The proposed class of protocols increases the capacity of a slotted random access channel by adding a small amount of potentially useful control information to every message transmission. In particular, the ARRA technique requires users to announce the intended location of their potential retransmission slot (to be used in the event of a collision) over a low-rate announcement subchannel, so that conflicts between new and retransmitted messages can be prevented. The proposed protocols provide significant capacity improvements over conventional contention protocols, without sacrificing the simplicity and operational convenience associated with random access. It is shown that with a modest amount of processing and storage at the terminals, capacities in the range of 0.5-0.6 can be achieved, as compared with 0.37 for slotted ALOHA and 0.4-0.5 for the more efficient tree algorithm-based collision resolution algorithms (CRA´s). Specifically, the basic ARRA protocol, in which announced retransmissions take place unconditionally, has a capacity of about 0.53. An improved algorithm (called extended ARRA), which involves aborting predictably unsuccessful retransmissions, has a capacity of 0.6. In addition, because of delay considerations, the proposed ARRA protocols are well suited for operation on satellite channels.