Signal power variation with applications to cognitive radio

The performance of cognitive radio systems will depend critically on the ability of the secondary user to relinquish borrowed spectrum when it´s interference level at the primary user exceeds a certain threshold. Hence, in this paper we investigate the temporal behaviour of this interference power. In particular, we derive the level crossing rate (LCR) of the power. This gives the rate at which a cognitive radio´s interference level increases above the acceptable threshold. The LCR is derived for the case of lognormal shadow fading and two different mobility models. The results cater for temporal variations in both shadowing and distance. The basic nature of the LCR appears to be insensitive to the mobility model and suggests that a simple Gaussian LCR can be used as a good approximation in a broad range of cases.