Inter-Sensing Time Optimization in Cognitive Radio Networks

We consider a set of primary channels that operate in an unslotted fashion, switching activity at random times. A secondary user senses the primary channels searching for transmission opportunities. If a channel is sensed to be free, the secondary terminal transmits, and if sensed to be busy, the secondary transmitter remains silent.We solve the problem of determining the optimal time after which a primary channel needs to be sensed again depending on the sensing outcome. The objective is to find the inter-sensing times such that the mean secondary throughput is maximized while imposing a constraint over the maximum tolerable interference inflicted on the primary network. Our numerical results show that by optimizing the sensing-dependent inter-sensing times, our proposed scheme reduces the impact of sensing errors caused by false alarm and misdetection and outperforms the case of a single sensing period.

💡 Research Summary

The paper addresses the problem of determining optimal re‑sensing intervals for a secondary user (SU) operating in a cognitive radio network where primary channels follow an unslotted, random activity pattern. Traditional approaches assume a single, fixed sensing period for all channels, which is suboptimal when the primary traffic is asynchronous and when sensing errors (false alarms and missed detections) are present. The authors propose a sensing‑dependent inter‑sensing time policy: after each sensing event the SU selects one of two waiting times, (T_{\text{free}}) if the channel is sensed idle and (T_{\text{busy}}) if it is sensed busy.

The system model treats each primary channel as a two‑state (busy/idle) process with exponentially distributed sojourn times. The SU’s sensing outcome is characterized by probabilities of false alarm ((P_{FA})) and missed detection ((P_{MD})). Using a Markov chain representation, the authors derive the posterior probabilities (\pi_{\text{free}}) and (\pi_{\text{busy}}) that a channel is actually idle or busy given the sensing result. The average SU throughput is expressed as

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