Abstract
In traditional multichannel cognitive radio networks (CRNs), users are split into two different priorities. Because of the low priority of secondary users (SUs), SU packets’ transmissions are easily interrupted by primary users (PUs). In this paper, two control parameters, called preemption threshold H and preemption probability q, are used to regulate the preemption behavior of PU packets to improve the transmission performance of SU packets. When all channels in the system are occupied, the preemption behavior of PU packets will be adjusted according to the amount of SU packets that are transmitting in the system. If the amount is larger than H, the recently arrived PU packet either preempts a channel with probability q or leaves the system with probability 1 − q . The central controller manages the system’s channel usage right and determines a series of access behaviors of user packets. Considering the possible imperfect sensing, a discrete-time queueing model is developed with the proposed preemption control mechanism. Then we obtain some performance index expressions of PU and SU packets founded on the system’s state transition matrix and make the corresponding performance figures through numerical experiment. Finally, we construct a system utility function and determine the optimal preemption threshold and preemption probability through the seagull optimization algorithm (SOA). Experimental data show that the proposed mechanism by setting preemption threshold and preemption probability can significantly reduce SU packets’ outage rate and improve SU packets’ throughput rate.
Highlights
Controlling the preemption behavior is another way to ensure the transmission continuity of secondary users (SUs)
primary users (PUs) Packets’ Performance Analysis. e mechanism with preemption threshold and preemption probability proposed in this paper can regulate the preemption behavior of PU packets, which may have a certain impact on PU packets’ average queue length, blocking rate, and throughput rate
Two new parameters, preemption threshold and preemption probability, were introduced to centralized cognitive radio networks (CRNs) based on overlay sharing mode to control the preemption behavior of PU packets and improve the quality of service (QoS) of SU packets
Summary
At the beginning of each time slot, the central controller will update the database according to the real-time state of the system and allocate idle channels for the packets arriving at the moment. When a recently arrived PU packet needs to enter the system for data transmission, if there is more than one unoccupied channel, it will occupy one randomly for data transmission; if there are no idle channels, the central controller will decide whether to allow this PU packet to preempt a channel according to the amount of SU packets that are transmitting in the system. We use E to represent the system’s one-step transition matrix, use (i, j)(i, j) ∈ T to represent the state before the state transition, and use (k, l){(k, l) ∈ T} to represent the state after the state transition. erefore, the probability of one-step transition from state (i, j) to (k, l) is denoted by E(i,j)⟶(k,l), which is expressed as
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