Performance Analysis of Physical Layer Security: From Far-Field to Near-Field
<|reference_start|>Performance Analysis of Physical Layer Security: From Far-Field to Near-Field: The secrecy performance in both near-field and far-field communications is analyzed using two fundamental metrics: the secrecy capacity under a power constraint and the minimum power requirement to achieve a specified secrecy rate target. 1) For the secrecy capacity, a closed-form expression is derived under a discrete-time memoryless setup. This expression is further analyzed under several far-field and near-field channel models, and the capacity scaling law is revealed by assuming an infinitely large transmit array and an infinitely high power. A novel concept of "depth of insecurity" is proposed to evaluate the secrecy performance achieved by near-field beamfocusing. It is demonstrated that increasing the number of transmit antennas reduces this depth and thus improves the secrecy performance. 2) Regarding the minimum required power, a closed-form expression is derived and analyzed within far-field and near-field scenarios. Asymptotic analyses are performed by setting the number of transmit antennas to infinity to unveil the power scaling law. Numerical results are provided to demonstrate that: i) compared to far-field communications, near-field communications expand the areas where secure transmission is feasible, specifically when the eavesdropper is located in the same direction as the intended receiver; ii) as the number of transmit antennas increases, neither the secrecy capacity nor the minimum required power scales or vanishes unboundedly, adhering to the principle of energy conservation.<|reference_end|>
@article{zhao2024performance,
    title={Performance Analysis of Physical Layer Security: From Far-Field to
  Near-Field},
    author={Boqun Zhao, Chongjun Ouyang, Xingqi Zhang and Yuanwei Liu},
    journal={arXiv preprint arXiv:2408.10706},
    year={2024},
    archivePrefix={arXiv},
    eprint={2408.10706},
    primaryClass={cs.IT eess.SP math.IT}
}