A dual-hop cognitive (secondary) relaying systemincorporating collaborative spectrum sensing to opportunisticallyswitch between data transmission and energy harvesting isintroduced. The secondary relays, first scan the wireless channelfor a primary network activity, and then convey their reportsto a secondary base station (SBS). Afterwards, the SBS, basedon these reports and its own estimation, decides cooperativelythe presence of primary transmission or not. In the formerscenario, all secondary relays start to harvest energy from thetransmission of one or more primary nodes. In the latter scenario,the system initiates secondary communication via a best relayselection policy. The performance of the proposed scheme isthoroughly investigated by assuming realistic channel conditions,i.e., non-identical link-distances and outdated channel estimation,while its overall energy consumption is evaluated, indicating theefficiency of the switching approach.
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