QVP-based relay selection to improve secrecy for rateless-codes in delay-constrained systems

Rateless codes (RCs) have the ability of successfully recovering the message from any subset of the fixed number of encoded symbols, making them a good candidate for delay-tolerant systems. However, most of the applications are delayconstrained. In this study, quality of violation probability (QVP) is used as the performance metric which includes reliability, secrecy, considering delay-constraint conditions. The performance of the RC in the presence of an eavesdropper is studied, and a relay selection technique is used to minimise the QVP in a system with regenerative relays. The authors derive an expression for the QVP when adequate mutual information (MI) is obtained at the receiver, and compares it to the energy accumulation (EA) receiver. Further, based on the direct link channel state information available, relay selection scheme is analysed. They observe that MI accumulation reduces QVP significantly in comparison to the EA. It is also observed that initially on increasing the maximum number of allowed channel usages, the QVP gets reduced and later gets saturated. They observe an improvement in outage probability and intercept probability due to diversity gain. A closed-form expression of QVP for relay selection is determined for the EA and the MI accumulation receiver.