  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.
