The seventh International Symposium on Wireless Communication Systems (ISWCS 2010) was held just a few days ago in York, UK. Many of the technical contributions and two out of the six tutorials focused on sensor networks and cognitive radio.
Among the presentations I’ve attended, I found most interesting a talk discussing a set of measurements of spectrum occupancy over the 2.4 GHz ISM band. Many other published papers have investigated how spectrum utilization varies over this region of the spectrum; however, almost all the works I’m aware of have quantified the amount of available white spaces using omnidirectional antennas. This paper instead envisaged a new approach that makes use of two directional devices. By rotating these antennas authors found that the channel occupancy perceived at a given location might vary significantly depending on the considered direction: this is especially true in indoor environments when the spectrum is used for short range communications such as for instance the ones of WLAN devices or wireless sensor nodes. Directional white spaces might further enhance spectrum reuse opportunities and could be exploited by devices with directional antennas to communicate over the increasingly overcrowded unlicensed bands.
The paper, M. Matinmikko et al. “Distributed and Directional Spectrum Occupancy Measurements in the 2.4 GHz ISM Band”, will soon be available on IEEE Xplore. Check it out!
Absolutely correct. Finally people start to realize that “white space” is not only a frequency domain issue but definitely a spatial issue. It is really a “no-brainer” that it is the path loss between secondary transmitters and primary receivers what it is all about – the relative location, propagation conditions and, for sure, the antenna radiation patterns for both secondary transmitter as well as primary receiver play critical parts in this equation.