Unlicensed transmissions in TV white spaces and its impacts on the incumbent services

Unutilized TV spectrum is soon opened up for use by unlicensed devices (UDs). The main concern is whether the unlicensed operations could cause harmful interference to the licensees. In this paper we present an evaluation framework that allows us to assess the quality of licensed service in the presence of unlicensed transmissions. In our model, the UDs can spatially reuse a channel and hence, two closest UDs are separated by the cochannel reuse distance. The licensed service quality is measured in terms of outage probability, which is also susceptible to channel fading and shadowing. We then derive the exact expressions for the outage probability under the following channel conditions: (i) Rayleigh fading, (ii) lognormal shadowing, and (iii) the two being superimposed. This is followed by numerical examples that demonstrate the possibility of restricting the interference caused by UDs by increasing the cochannel reuse distance¹.