Abstract: Allocated Spectrum band has always been a limited resource; being later a more challenging issue due to the growth of user demands. The past decade is marked by important changes in spectrum access through especially cognitive radio technology. Here, spectrum access issue can be studied in all the different aspects of cognitive capabilities. This paper focuses on spectrum handoff in spectrum mobility. We will then study secondary connections behaviours after multiple interruptions providing from multiple secondary connections. In the IEEE 802.22 standards , two Spectrum Handoff Sequences have been defined to characterize Secondary Connections behaviours after each Primary Connections interruption. These sequences are known as always-leaving and always-staying sequences. A recent analysis uses the extended data delivery time metric to analyse these Spectrum Handoff Sequences. It shows the exponential value of connections service time in the first sequence (always-leaving sequence) and in the other (always-staying sequence), the lack of fairness due to the acquisition of channelís low-priority queue by the ongoing secondary connection (i.e. the secondary connection actually being served in the low-priority queue. We propose the pre-emptive resume priority (PRP) M/G/1 queuing network model to characterize the spectrum usage behaviours with all the three design features. This model aims to analyse the extended data delivery time of the secondary connections with proactively designed target channel sequences under various traffic arrival rates and service time distributions. These analytical results are applied to evaluate the latency performance of the connection-based spectrum handoff based on the target channel sequences mentioned in the IEEE 802.22 wireless regional area networks standard. Then, to reduce the extended data delivery time, a traffic-adaptive spectrum handoff is proposed, which changes the target channel sequence of spectrum handoffs based on traffic conditions. Compared to the existing target channel selection methods, this traffic-adaptive target channel selection approach can reduce the extended data transmission time by 35 percent, especially for the heavy traffic loads of the primary users.
Keywords: Cognitive Radio; Spectrum Handoff; Lifetime of Secondary Connection; PRP M/G/1 Queuing Theory.