An Efficient Spectrum Handoff Method to Improve the QOS of Secondary Users in Cognitive Radio Networks

In Cognitive radio Networks unlicensed users are temporary visitors to the licensed spectrum, they may be required to vacate the spectrum when a licensed user reclaims it. This process is called spectrum handoff. Spectrum Handoff has a large overhead for secondary users. This overhead includes the time required for sensing the spectrum and finding new channels, communication delay between secondary transmitter/receiver as well as packet loss. To decrease this overhead it is necessary to reduce the number of handoff as much as possible. To this end secondary users should have a proper decision about going to a new channel or to stay on the current channel, during the handoff procedure. Also they have to select target channel so that the channel be available with a high probability and long idle period to avoid unnecessary handoff. In this paper a proactive approach is proposed for spectrum handoff reduction in cognitive radio networks. The preemptive resume priority (PRP) M/G/1 queuing network model is used to characterize the spectrum usage behaviors in secondary and primary users. Then, based on this model, a value is calculated for each channel to demonstrate how much a channel is suitable for handoff, when interrupt occurs. In this scheme the value assigned to each channel is depends on channel idle probability and average waiting time in the channel queue. Moreover a dynamic threshold which is known as hysteresis value is used to reduce redundant handoff. The proposed method is compared to other proactive handoff scheme based on preemptive resume priority (PRP) M/G/1 queuing network model. Simulation results show that proposed spectrum handoff scheme reduces the handoff rate of secondary users significantly with the same data delivery rate and a slight increase in service time at the light traffics.

Keywords:

cognitive radio , cognitive radio networks , primary user , secondary user , spectrum handoff , preemptive resume priority (PRP) M/G/1 queuing network model , hysteresis