Coexistence Among Wireless Networks Operating at Different Power Levels

Unlicensed wireless access is becoming increasingly popular because of its low cost. However, different wireless applications have different requirements in terms of range and power, which makes them difficult to coexist in the same unlicensed spectrum. One such example is Zigbee and WiFi coexistence where low-power Zigbee nodes are frequently starved by WiFi nodes. Recent standardization of several power levels for unlicensed White Space medium access will make this problem even more prevalent and pronounced in future. We propose a novel PHY and MAC protocol for coexistence. Our protocol is decentralized and simple. The key building block is an adaptive preamble support at PHY layer that allows high-power nodes to detect an on-going low-power transmission at SNR levels as low as -10dB. We show that this technique can prevent starvation of low-power nodes in almost all existing scenarios. We further propose a MAC protocol that builds on CSMA MAC and exploits the adaptive preambles functionality. We extensively evaluate our system in a testbed and in simulations. We show that we can improve the data rates of low-power links by as much as 10x over existing MACs, without sacrificing more than 20%-40% of throughput of the rest of the system.