oa Analysis of mobility impact on interference for short-range cognitive radio networks

Background & Objectives: Cognitive radios (CRs) strive to utilize the white holes in the radio frequency (RF) spectrum in an opportunistic manner. Because interference is an inherent and a very critical design parameter for all sorts of wireless communication systems, many of the recently emerging wireless technologies prefer smaller size coverage with reduced transmit power in order to decrease interference. Prominent examples of short-range communication systems trying to achieve low interference power levels are CR relays in CR networks and femtocells in next generation wireless networks (NGWNs). It is clear that a comprehensive interference model including mobility is essential especially in elaborating the performance of such short-range communication scenarios. This work focuses on analyzing how interference evolves in time under long and short term fading. Such an analysis is essential, because once the interference behavior is understood, it can be managed in a better way. Also, NGWNs and CRs can be designed in such a way that arduous and expensive planning stage is omitted. This way, deployment costs can be reduced drastically. Methods: It is known that received signal in a general wireless propagation environment includes the effects of both long- and short-term fading. Therefore, a logarithmic transformation reveals the individual impact of each fading phenomenon. The two-dimensional (2D) random walk model is incorporated into the physical layer signal model. Results: The results show that relatively larger displacements in short primary-user-receiver (PU-Rx) and secondary-user-transmitter (SU-Tx) separations lead to drastic power level fluctuations in the observed interference power levels. The impact of path loss is one of the major factors changing the future interference conditions for low-speed mobility scenarios especially within short communication ranges. Conclusions: It is shown that long-term fading plays a crucial role for the temporal evolution of interference for NGWNs and CRs. By using the interference statistics, the design and deployment of future cellular mobile radio systems in Qatar could be optimized. This is crucial, especially for rapidly changing network topographies as is the case with the city of Doha. Even for well-established network topographies, the proposed method provides an analytical way of examining and managing the interference.