Since cognitive radios use the licensed spectrum opportunistically, they always suffer from primary user activities. Assume CR nodes are communicating in WLAN network. Meanwhile, a PU appeared on the CCC of some CR users. When the assigned CCCs are affected by PU activity, CR users must vacate the channel and negotiate for new CCC. Because data communication is suspended until they setup a new CCC, the reestablishment should be fast and reliable. Now consider the following cases, what if most of the spectrum is occupied and competition is high for the few spectrum holes? - Searching for new CCC becomes very difficult and it takes long time. And what if there are no spectrum holes or fails in the competition and could not find a new CCC? - Communication stops. Therefore, we must device a mechanism which allows the communication until new CCC is set up.
In this thesis we propose UWB network for temporal communication until new CCC is reestablished on the WLAN.
The main contribution of this thesis is two-fold:
First, when a PU is detected on the CCC of a CR, the CR vacates the channel and searches for new spectrum hole. While doing so it needs to interrupt the communication, sense the whole spectrum to find unused spectrum hole, listen for beacons from other CR nodes in the network, exchange control message and share the spectrum. This process takes a longer time. But in our proposed idea, the CR does not need to repeat all steps. It simply changes its network from WLAN to UWB and continues the control message exchange. Therefore, there will not be communication interruption.
Second, the continuous control message exchange enables the CR to find a new CCC faster because both transceivers are active in searching spectrum hole without any discontinuity.