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 α ≥ 2. We show that if n_e^(2+2/α) (log n_e)^γ = o(n_l) holds, for some positive γ, 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.