Medium Access Control for 60 GHz Outdoor Mesh Networks with Highly Directional Links

We investigate an architecture for multi-Gigabit outdoor mesh networks operating in the unlicensed 60 GHz "millimeter (mm) wave" band. In this band, the use of narrow beams is essential for attaining the required link ranges in order to overcome the higher path loss at mm wave carrier frequencies. However, highly directional links make standard MAC methods for interference management, such as carrier sense multiple access, which rely on neighboring nodes hearing each other, become inapplicable. In this paper, we study the extent to which we can reduce, or even dispense with, interference management, by exploiting the reduction in interference due to the narrow beamwidths and the oxygen absorption characteristic of the 60 GHz band. We provide a probabilistic analysis of the interference incurred due to uncoordinated transmissions, and show that, for the parameters considered, the links in the network can be thought of as pseudo-wired. That is, interference can essentially be ignored in MAC design, and the challenge is to schedule half-duplex transmissions in the face of the "deafness" resulting from highly directional links. We provide preliminary simulation results to validate our approach.