Deaf cooperation for secrecy in multiple-relay networks

In this paper, we investigate the roles of cooperative jamming (CJ) and noise forwarding (NF) in improving the achievable secrecy rates of a Gaussian wiretap channel (GWT). In particular, we study the role of a deaf helper in confusing the eavesdropper in a GWT channel by either transmitting white Gaussian noise (cooperative jamming) or by transmitting a dummy codeword of no context yet drawn from a codebook known to both the destination and the eavesdropper (noise forwarding). We first study the conditions in which each mode of deaf cooperation improves over the secrecy capacity of the original wiretap channel. Secondly, we derive the optimal power allocation for both the source and the helping node to be used in each of the two modes of deaf helping. Thirdly, we consider the deaf helper selection problem where there are N relays present in the system and it is required to select the best K deaf helpers, K ≥ 1, that yield the maximum possible achievable secrecy rate with deaf cooperation using K relays. First, we give an optimal strategy for the case of K = 1, i.e., for the selection of a single deaf helper. We propose a suboptimal strategy for selection in the general case where K >; 1. We discuss the complexity of each of the two strategies. Finally, we verify the performance of the proposed strategies through numerical examples.