This paper explores the co-existence of a macro cell and a small cell forheterogeneous cellular networks, where a macro-cell base station (MBS) andsmall-cell base station (SBS) transmit to respective macro-cell user (MU) andsmall-cell user (SU) through their shared spectrum in the face of a commoneavesdropper. We consider two spectrum sharing mechanisms, namely the overlayspectrum sharing (OSS) and underlay spectrum sharing (USS). In the OSS, MBS andSBS take turns to access their shared spectrum. By contrast, the USS allows MBSand SBS to simultaneously transmit over the shared spectrum with the aid ofpower control for limiting their mutual interference, thus calledinterference-limited USS (IL-USS). We propose an interference-canceled USS(IC-USS) scheme, where a sophisticatedly-designed signal is emitted at MBS tocancel out the interference received at MU, which is also beneficial in termsof defending the common eavesdropper. Closed-form expressions of overall outageprobability and intercept probability are derived for OSS, IL-USS and IC-USSschemes by taking into account both MBS-MU and SBS-SU transmissions. We provethat the proposed IC-USS can achieve an absolute security with zero interceptprobability for the MBS-MU transmission. The secrecy diversity analysis is alsocarried out by characterizing an asymptotic behavior of the overall outageprobability with a given intercept probability in high signal-to-noise ratioregion. It is shown that the secrecy diversity gains of conventional OSS andIL-USS are zero, whereas the proposed IC-USS achieves a higher secrecydiversity gain of one. Additionally, numerical results demonstrate an obviousadvantage of the proposed IC-USS over OSS and IL-USS against eavesdropping.
展开▼
