A cooperative relay network in the presence of eavesdroppers, whose locations are distributed according to a homogeneous Poisson point process, is considered. The relay is equipped with a very large antenna array and can exploit maximal ratio combing (MRC) in the uplink and maximal ratio transmission (MRT) in the downlink. We consider a realistic model that the channel state information of every eavesdropper is not know as eavesdroppers tend to hide themselves in practice. The destination is

more »

... s in a much weaker position than all the eavesdroppers because it only receives the retransmitted signal from the relay. Under such setting, we investigate the security performance in two schemes for relaying operation: amplify-andforward (AF) and decode-and-forward (DF). The secrecy outage probability, the connection outage probability, and the trade-off problem which is controlled by the source power allocation are examined. Finally, suitable solutions for the source power (such that once the transmission occurs with high reliability, the secure risk is below a given threshold) are proposed for a trade-off between security and reliability issue.