Abstract
In the last decade, multi-hop cooperation has evolved bringing several
advantages including coverage improvement, more reliability of wireless
links, and power consumption reduction. Still, its application has
raised several challenges, such as the need for secure transmission at
each hop, algorithms to perform relay selection and the accurate models
to facilitate performance analysis. This paper addresses the problem of
physical layer (PHY) security in a multi-hop wireless cooperative
network, where communication at each hop is assisted by multiple relays
forming a cluster, each cluster being surrounded by multiple
eavesdroppers which together may tap transmissions from both the source
and the relays. The main focus of the study is on analyzing the benefits
of various relay selection schemes for protecting the source-destination
transmission against the eavesdroppers, which can collude and combine
information via diversity combining techniques. To be specific, four
relay selection schemes, which differ in the way they employ available
measures link quality, are considered to deliver the source information
to the destination via a decode-and-forward (DF) strategy. To evaluate
the security performance of the multi-hop cooperative link in the
presence of colluding eavesdroppers, we derive novel closed-form
analytical expressions for the secrecy outage probability (SOP) with
consideration of special cases of practical interest.