Physical Layer Security in Wireless Sensor Networks Using Distributed Co-Phasing

In this paper, we consider physical layer security in wireless sensor networks (WSNs) using distributed co-phasing (DCP) based transmissions. For this protocol, we first analyze the achievable ergodic secrecy rate of a single stream DCP system in the presence of one or more eavesdroppers. We show that the coherent combining gain offered by DCP leads to the signal to interference plus noise ratio (SINR) over the main channel increasing as the square of the number of SNs N, and that over the eavesdropper channel increasing linearly with N. This results in a strictly positive ergodic secrecy rate that increases as logN. We then analyze the performance of multi-stream DCP and show that using K data streams in DCP leads to a K fold increase in the achievable secrecy rate at high SNRs. We also discuss an alternative power allocation scheme for multi-stream DCP, viz. distributed maximal ratio transmission with a per user power constraint, and show that this improves the achievable secrecy rates as compared to standard multi-stream DCP. Finally, we analyze the role of artificial noise in improving the achievable secrecy rates. We validate the accuracy of these derived results and illustrate the efficacy of DCP in ensuring secure data fusion in WSNs using Monte Carlo simulations.