On The Rate-Distance Adaptability of Slotted Aloha

In wireless communication systems, the signal strength/quality generally varies with the distances between transmitters and receivers. As a consequence, the throughput in the MAC layer (or the transmission data rate in the PHY layer) also varies accordingly. In this paper, we call this phenomenon as the rate-distance nature of the wireless communications. Inspired by our success in the study of the random distances between nodes in the wireless ad hoc networks, we pioneer employing the distance-related concept to study the rate-distance nature of the multiple access protocols. By selecting slotted Aloha as a pilot multiple access protocol, we successfully analyze and demonstrate the rate-distance adaptability of slotted Aloha with finite and infinite populations. We also demonstrate how the rate- distance concept can be applied to the rate adaptation of the MAC protocol in the cognitive radio.