Opportunistic relay selection for cooperative networks with secrecy constraints

Abstract

Abstract-In this paper, a relay selection policy is proposed that fully exploits the flexibility offered by the buffering ability of the relay nodes in order to maximize the achieved diversity gain. The suggested scheme incorporates the instantaneous strength of the wireless links as well as the status of the finite relay buffers and adapts the relay selection decision on the strongest available link by dynamically switching between relay reception and transmission. We show that the proposed relay selection scheme significantly outperforms conventional relay selection policies for all cases and ensures a diversity gain equal to two times the number of relays for large buffer sizes. I. INTRODUCTIONWe focus on a simple decode-and-forward (DF) cooperative network where a source communicates with a destination through a set of half-duplex relay nodes with the objective of performance optimisation. For this fundamental problem, the max − min relay selection scheme [1], [2], where the selected relay holds the strongest end-to-end relaying path, achieves the optimal performance and ensures a full diversity equal to the number of the relays. However, this relay selection policy refers to a two-slot cooperative transmission where the selected relay receives the source's data during the first time slot and immediately in the next time slot forwards the data towards the destination. In order to overcome this limitation imposed by the max − min selection scheme, recently in [3] the authors introduced data buffers at the relay nodes that allow the selection of a different relay for reception and transmission in order to extract further diversity gains. In that work, the max − max relay selection scheme that selects the relay with the strongest source-relay channel and the strongest relaydestination channel for reception and transmission, respectively, has been investigated. The max − max scheme refers to applications without critical delay constraints and provides a significant coding gain in comparison to the conventional max − min selection scheme. However, despite the efficient use of the channel fading and the related performance benefits, the max − max relay selection policy requires a predefined schedule for the relaying transmission (e.g., the second slot is always allocated for relaying) and therefore the available diversity degrees are not fully exploited. It is worth noting that the use of buffers in order to boost the achieved performance (in terms of throughput) has been reported in the literature in different contexts ( [4]-[7] and references therein).

Secure Multiple Amplify-and-Forward Relaying With Cochannel Interference

“…There are two fundamental relaying protocols: amplify-and-forward (AF) and decode-and-forward (DF). For DF-aided relay networks, the system secure communication has been extensively studied, by deriving analytical expressions for the SOP in [16]- [18]. In order to enhance the security for multi-DF relay networks, these works [16]- [18] used relay selection techniques to exploit the dynamic nature among multi-relay fading channels.…”

“…For DF-aided relay networks, the system secure communication has been extensively studied, by deriving analytical expressions for the SOP in [16]- [18]. In order to enhance the security for multi-DF relay networks, these works [16]- [18] used relay selection techniques to exploit the dynamic nature among multi-relay fading channels. Compared with DF relaying, it is, however, much more complicated to obtain analytical SOP expressions for AF relay networks, since the received signal-to-noise ratios (SNRs) at the destination and eavesdroppers are represented in complex forms.…”

Survey on Relay Selection Techniques in Cognitive Networks

“…In these systems a relay node located closer to the main destination delivers a higher capacity to the main link than the eavesdropper link [45]. This been said, relay selection for cooperative networks with secrecy constraints has arisen as an interesting research topic Alternatively, jamming techniques which produce an artificial interference at the eavesdropper node to reduce the capacity of the associated link seem to be an attractive approach for practical applications [48][49][50][51]. In [52] the interaction between relay and jammer is presented as a non-cooperative game where both nodes have conflicting objectives and the Nash equilibrium (NE) of the system is derived.…”

Secrecy Performance of Wirelessly Powered Wiretap Channels

“…The exact secrecy outage probability is difficult to characterize, instead, we apply the following approximation as in [39] …”