# Jammer-Assisted Resource Allocation in Secure OFDMA With Untrusted Users

## TL;DR

This paper investigates how a friendly jammer can enhance secure communication and fairness in OFDMA systems with untrusted users, proposing novel resource allocation schemes and demonstrating their effectiveness through simulations.

## Contribution

It introduces new jammer-assisted resource allocation schemes, including PFA and ODA, for secure OFDMA systems with untrusted users, along with suboptimal solutions and asymptotic benchmarks.

## Key findings

- Jammer improves sum secure rate and fairness.
- Proposed schemes outperform equal power allocation.
- Suboptimal solutions reduce computational complexity.

## Abstract

In this paper, we consider the problem of resource allocation in the orthogonal frequency division multiple access system with single source and M untrusted users in presence of a friendly jammer. The jammer is used to improve either the weighted sum secure rate or the overall system fairness. The formulated optimization problem in both the cases is a mixed integer non-linear programming problem, belonging to the class of NP-hard. In the sum secure rate maximization scenario, we decouple the problem and first obtain the subcarrier allocation at source and the decision for jammer power utilization on a per-subcarrier basis. Then, we do joint source and jammer power allocation using primal decomposition and alternating optimization framework. Next, we consider fair resource allocation by introducing a novel concept of subcarrier snatching with the help of jammer. We propose two schemes for jammer power utilization, called proactively fair allocation (PFA) and on-demand allocation (ODA). PFA considers equitable distribution of jammer power among the subcarriers, while ODA distributes jammer power based on the user demand. In both cases of jammer usage, we also present suboptimal solutions that solve the power allocation at a highly reduced complexity. Asymptotically optimal solutions are derived to benchmark optimality of the proposed schemes. We compare the performance of our proposed schemes with equal power allocation at source and jammer. Our simulation results demonstrate that the jammer can indeed help in improving either the sum secure rate or the overall system fairness.