On spectrum occupancy measurements at 2.4 GHz ISM band for cognitive radio applications

The 2.4 GHz industrial, scientific and medical (ISM) band is a shared electromagnetic resource where many wireless communications technologies such as wireless local area networks, Bluetooth, ZigBee, cordless phones, amongst others, coexist. Due to the large amount of users of different technologies that might utilize the band at the same time and geographical region, it is reasonable to assume that the band is very busy all the time. In this paper, however, a spectrum measurement campaign is carried out to determine the actual spectrum occupancy of the ISM band in an environment with high density of users. Although many wireless technologies share this frequency band, results show its low spectrum utilization. Indeed, it is shown that the spectral occupation of the band ranges between 7% and 34% of a normal working day, and it is moderate even during busy hours. Therefore, the use of a more sophisticated approach is essential to exploit the unlicensed access to this band, for which cognitive radio is well suited. This is valid despite the fact that, formally speaking, there are no licensed (or primary) users in the ISM band. Nevertheless, ISM users could be treated as pseudo-primary. Thus, cognitive radio techniques can be implemented to improve the spectrum utilization.