Secrecy Outage and Diversity Analysis of Spectrum-Sharing Heterogeneous Wireless Systems
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We study the physical-layer security of a spectrum-sharing heterogeneous wireless network in the face of an eavesdropper, which is composed of multiple source-destination (SD) pairs, where an eavesdropper intends to wiretap the signal transmitted by the SD pairs. In order to protect the wireless transmission against eavesdropping, we propose a heterogeneous cooperation framework relying on two stages. Specifically, an SD pair is selected to access the shared spectrum using an appropriately designed scheme at the beginning of the first stage. The other source nodes (SNs) transmit their data to the SN of the above-mentioned SD pair through a reliable short-range wireless interface during the first stage. Then, the SN of the chosen SD pair transmits the data packets containing its own messages and the other SNs' messages to its dedicated destination node (DN) in the second stage, which in turn will forward all the other DNs' data to the corresponding DNs via the backhaul. We conceive two specific SD pair selection schemes, termed as space-time coding aided source-destination pair selection (STC-SDPS), and the transmit antenna selection aided source-destination pair selection (TAS-SDPS), respectively. We derive the secrecy outage probability (SOP) expressions for both the STC-SDPS and for the TAS-SDPS schemes. Furthermore, we carry out the secrecy diversity gain analysis in the high main-to-eavesdropper ratio (MER) region, showing that both the STC-SDPS and TAS-SDPS schemes are capable of achieving the maximum attainable secrecy diversity order. Additionally, increasing the number of the heterogeneous transmission pairs will reduce the SOP, whilst increasing the secrecy diversity order of the STC-SDPS and TAS-SDPS schemes.
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