Simple asynchronous multiple access (SAMA) for ad hoc wireless networks in unlicensed bands

Effective spectrum sharing between non-interoperable radio devices as well as collocated but non-communicating radio networks is an important goal for the designers of RF spectrum. Apart from the traditional approach of selecting separate channels for distinct systems, there are methods such as spread spectrum, scheduling of transmissions in non-overlapping intervals to reduce collisions and also spatial diversity to reduce the effects of interference. The last two are the most promising methods to use to achieve multi-megabit data rates and high traffic densities. The listen-before-transmit (LBT) etiquette has been used with limited success in the past in decentralized RF environments to enable non-interoperable systems to share spectrum. We introduce the simple asynchronous multiple access (SAMA) scheme that combines some of the known channel access techniques in a novel way to achieve an implicit reservation effect that allows high throughput with modest overhead and low complexity without demanding interoperability or even explicit communications between the collocated systems. We analyze the throughput and spatial performance of SAMA. The analysis is based on the radio propagation law and the geometry of the users and antennas in the plane. It is aimed at establishing the fundamental performance bounds dictated by our basic assumptions. We cover the omni-directional antenna case and give preliminary results for the directional antenna