3D cognitive radio: A way to improve spectrum utilization by exploiting the height dimension

In this paper, the height dimension is exploited to improve the spectrum utilization and capacity of cognitive radio networks. As we notice that the majority of primary users are distributed in the low-height places, such as the street, shopping mall, subway, etc. Even in the metropolis full of skyscrapers, the users of primary networks at the top of skyscrapers are still the minorities. Thus the spectrum opportunities in the height dimension exist. Using directional antenna, the interference to primary users can be coordinated. This paper explores the possibility of height-dimensional spectrum access and constructs three-dimensional (3D) cognitive radio. Meanwhile, the conditions to exploit height-dimensional spectrum opportunities are provided and the relations are simulated.