Design and Investigation Of Channel Assignment Techniques in Cognitive Radio System

Abstract

Cognitive radio systems have two types of calls, namely, primary user (PU) calls and secondary user (SU) calls. PU calls get preference over the SU calls when the resources are to be allocated. The first right to resources lies always with the PU calls. When a call arrives for propagation through a network, the network resources like the path of links and channels are assigned to the call. If it is a cognitive radio system, additionally, the system needs to identify if the call is a PU or SU call. In case, a call is found to be a PU call, a channel and a path is assigned. When a SU call arrives in the next moment, the next available free channel and path are assigned. If this process repeats, equal treatment is given to both PU and SU calls. But, when all the free channels are exhausted and if a PU call arrives, then the call will not have any free channel to be assigned to PU call and hence will result in blockage of the PU call. In order to avoid this situation, SU call is abruptly removed from the service and network so that the channel assigned to SU call can now be assigned to the PU call. If this process continues, the SU call users are affected with the service. To avoid this kind of issues, a novel methodology is proposed in this research work. In this research work, a new algorithm, namely, selective assignment method is proposed to assign channels to both PU and SU calls. The performance of the selective assignment method is compared with the baseline methods, namely, first fit method and random assignment method. The selective assignment method, basically separates the available channels into different zones for PU and SU calls. As soon as free channels are available in PU zone, the PU calls are not blocked. In case, no free channel is available in PU zone, the free channels of SU will be allocated. In case, if SU zone does not have any free channel, the SU call is removed from the SU zone and the channel is assigned to PU call. With this approach, there is lower blocking probabilities for PU calls.