Relay Selection to Improve Secrecy in Cooperative Threshold Decode-and-Forward Relaying

Abstract

In this paper, relay selection is considered to enhance security of a\ncooperative system with multiple threshold-selection decode-and-forward (DF)\nrelays. Threshold-selection DF relays are the relays in which a predefined\nsignal-to-noise ratio is set for the condition of successful decoding of the\nsource message. We focus on the practical and general scenario where the\nchannels suffer from independent non-identical Rayleigh fading and where the\ndirect links between the source and destination and source and eavesdropper are\navailable. Based on channel state information knowledge, three relay selection\nstrategies, namely traditional, improved traditional, and optimal, are studied.\nIn particular, the secrecy outage probability of all three strategies are\nobtained in closed-form. It is found that the diversity of secrecy outage\nprobability of all strategies can improve with increasing the number of relays.\nIt is also observed that the secrecy outage probability is limited by either\nthe source to relay or relay to destination channel quality.\n