Secrecy capacity in large cooperative networks in presence of eavesdroppers with unknown locations

In this paper, an extended large wireless network, with a single transmitter-receiver pair, under the secrecy constraint is considered. In contrast to works which use idealized assumptions, a more realistic network situation with unknown eavesdroppers locations is investigated: the legitimate users only know their own Channel State Information (CSI), not the eavesdroppers CSI. Also, the network is analyzed by taking in to account the effects of both fading and path loss. Under these assumptions, a power efficient cooperative scheme, named stochastic virtual beamforming, is proposed. Applying this scheme, any desired pair of secure rate and outage level denoted by (Rs, ε) will be achievable given that the density of the legitimate users tends to infinity. Although, the derived constraints limit the density of eavesdroppers for any fixed density of legitimate users, but by tending the legitimate users density to the infinity, the tolerable density of eavesdroppers will become unbounded too.