OFDMA-Based DF Secure Cooperative Communication With Untrusted Users

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.