Colluding Eavesdroppers in Large Cooperative Wireless Networks

Securing communication against non-colluding passive eavesdroppers has been extensively studied. Colluding eavesdroppers were considered for interference-limited large networks. However, collusion was not investigated for large cooperative networks. This paper closes this gap: we study the improvement the eavesdroppers achieve due to collusion in terms of the information leakage rate in a large cooperative network. We consider a dense network with n(l) legitimate nodes, n(e) eavesdroppers, and path loss exponent alpha >= 2. We show that if n(e)((2+2/alpha)) (log n(e))(gamma) = o (n(l)) holds, for some positive gamma, then zero-cost secure communication is possible; i. e., n(e) colluding eavesdroppers can be tolerated. This means that our scheme achieves unbounded secure aggregate rate, given a fixed total power constraint for the entire network.