Search

This letter investigates the utility of a trusted decode-And-forward relay in OFDMA-based secure communication system with untrusted users. For deciding on the use of relay, we first present optimal subcarrier allocation policies for direct communication (DC) and relayed communication (RC). Next, we identify exclusive RC mode, exclusive DC mode, and mixed (RDC) mode subcarriers which can support both the modes. In RDC mode, we present optimal mode selection policy and a suboptimal strategy independent of power allocation which is asymptotically optimal at both low and high SNRs. Via numerical results we present insights on relay utility regions.

In this letter, we consider resource allocation for OFDMA-based secure cooperative communication by employing a trusted decode and forward (DF) relay among the untrusted users. We formulate two optimization problems, namely, 1) sum rate maximization subject to individual power constraints on source and relay, and 2) sum power minimization subject to a fairness constraint in terms of per-user minimum support secure rate requirement. The optimization problems are solved utilizing the optimality of KKT conditions for pseudolinear functions.