Spectrum Sharing For M2m Applications Through Whitetime Exploitation In Wifi Networks

The demand placed on wireless networks operating within fixed allocations of licensed or unlicensed spectrum has introduced the development of cognitive radios, capable of intelligently utilising spare resource whenever it is available. Since WiFi is an ubiquitous method for localized high speed mobile internet access it exists in almost all typical radio environments however the spectrum in which it operates is not exploited to its full potential. This paper introduces a concept called Whitetime to describe the free time between frame transmissions on a typical WiFi channel and across all networks. Initial measurements of real environments indicate that more than 85% of time on a channel is unused however this predominantly consists of short interframe spaces. Detailed analysis reveals periods of inactivity greater than 10ms are synchronised with the beacon interval from observable access points on the channel. For applications that require opportunistic network access such as non deterministic machine to machine (M2M) communication, Whitetime presents a reliable opportunity to transmit packets as long as 1500 bytes using standard physical layer techniques.