Dynamic spectrum access: secondary user coexistence in the FM band

The explosion of wireless everything in recent years has placed a strain on the radio spectrum, and has led to the so-called ‘spectrum crunch’, where the spectrum is described as being nearly at capacity [1]. It is widely accepted that in reality this is not the case, as great numbers of ‘allocated’ bands are underutilized or not in use at all. In other words, the radio spectrum is not used as efficiently as it could be.

Commonly, bands (containing many channels) are classified by spectrum regulators for a particular type of use, such as those for FM Radio, Digital TV and cellular services. If there are not enough Primary Users (PUs) to use all of the channels in these bands, they lie empty. Using new spectrum access techniques, these channels can be targeted for 5G and IoT applications.

This work focuses on targeting the FM Radio band (88-108 MHz). Signals broadcast at these frequencies have excellent propagation characteristics, and are able to diffract around objects such as hills and human-made structures, and penetrate through buildings well. Recent studies [2] have shown that a significant portion of the 100 individual 200 kHz-wide FM Radio channels are unused at any given location.