Subcarrier Pairing as Channel Gain Tailoring: Joint Resource Allocation for Relay-Assisted Secure OFDMA with Untrusted Users

TL;DR

This paper introduces a novel joint resource allocation framework for secure OFDMA systems with untrusted users, emphasizing the innovative concept of channel gain tailoring through optimal subcarrier pairing to enhance spectral and energy efficiency.

Contribution

It proposes a new approach to subcarrier pairing as channel gain tailoring, providing optimal solutions for joint resource allocation in relay-assisted secure OFDMA systems with untrusted users.

Findings

Optimal subcarrier pairing minimizes variance among effective channel gains.

SCP improves spectral efficiency significantly in AF relayed systems.

SCP enhances energy efficiency depending on power budgets in DF systems.

Abstract

Joint resource allocation involving optimization of subcarrier allocation, subcarrier pairing (SCP), and power allocation in a cooperative secure orthogonal frequency division multiple access (OFDMA) communication system with untrusted users is considered. Both amplify and forward (AF), and decode and forward (DF) modes of operations are considered with individual power budget constraints for source and relay. After finding optimal subcarrier allocation for an AF relayed system, we prove the joint power allocation as a generalized convex problem, and solve it optimally. Compared to the conventional channel gain matching view, the optimal SCP is emphasized as a novel concept of channel gain tailoring. We prove that the optimal SCP pairs subcarriers such that the variance among the effective channel gains is minimized. For a DF relayed system, we show that depending on the power budgets of source and relay, SCP can either be in a subordinate role where it improves the energy efficiency, or in a main role where it improves the spectral efficiency of the system. In an AF relayed system we confirm that SCP plays a crucial role, and improves the spectral efficiency of the system. The channel gain tailoring property of SCP, various roles of SCP in improving the spectral and the energy efficiency of a cooperative communication system are validated with the help of simulation results.