Fairness-Aware ODDM Design for Secrecy Rate Maximization Among Untrusted Users

This letter presents an analysis of secure transmissions in orthogonal delay-Doppler division multiplexing (ODDM) systems with untrusted users. We uncover a nontrivial trade-off between inter-user interference and the minimum secrecy rate, and formulate a novel fairness-aware max-min optimization problem over power allocation and user count under practical constraints. Simulations reveal an optimal number of users that balances secrecy and throughput, and demonstrate the critical impact of delay bins and user configuration on secrecy performance. Overall, our solution enhances fairness and security, offering valuable design insights for untrusted ODDM systems.