Secure Transmission in Linear Multihop Relaying Networks

Abstract

This paper studies the design and secrecy performance \nof linear multihop networks, in the presence of randomly \ndistributed eavesdroppers in a large-scale two-dimensional space. \nDepending on whether there is feedback from the receiver \nto the transmitter, we study two transmission schemes: on-off \ntransmission (OFT) and non-on-off transmission (NOFT). In \nthe OFT scheme, transmission is suspended if the instantaneous \nreceived signal-to-noise ratio (SNR) falls below a given threshold, \nwhereas there is no suspension of transmission in the NOFT \nscheme. We investigate the optimal design of the linear multiple \nnetwork in terms of the optimal rate parameters of the wiretap \ncode as well as the optimal number of hops. These design \nparameters are highly interrelated since more hops reduces the \ndistance of per-hop communication which completely changes the \noptimal design of the wiretap coding rates. Despite the analytical \ndifficulty, we are able to characterize the optimal designs and \nthe resulting secure transmission throughput in mathematically \ntractable forms in the high SNR regime. Our numerical results \ndemonstrate that our analytical results obtained in the high SNR \nregime are accurate at practical SNR values. Hence, these results \nprovide useful guidelines for designing linear multihop networks \nwith targeted physical layer security performance.