Robust Secure Transmission in MISO Channels Based on Worst-Case Optimization (1104.3161v1)

Abstract: This paper studies robust transmission schemes for multiple-input single-output (MISO) wiretap channels. Both the cases of direct transmission and cooperative jamming with a helper are investigated with imperfect channel state information (CSI) for the eavesdropper links. Robust transmit covariance matrices are obtained based on worst-case secrecy rate maximization, under both individual and global power constraints. For the case of an individual power constraint, we show that the non-convex maximin optimization problem can be transformed into a quasiconvex problem that can be efficiently solved with existing methods. For a global power constraint, the joint optimization of the transmit covariance matrices and power allocation between the source and the helper is studied via geometric programming. We also study the robust wiretap transmission problem for the case with a quality-of-service constraint at the legitimate receiver. Numerical results show the advantage of the proposed robust design. In particular, for the global power constraint scenario, although cooperative jamming is not necessary for optimal transmission with perfect eavesdropper's CSI, we show that robust jamming support can increase the worst-case secrecy rate and lower the signal to interference-plus-noise ratio at Eve in the presence of channel mismatches between the transmitters and the eavesdropper.

• The paper introduces worst-case secrecy rate maximization to secure MISO wiretap channels despite imperfect eavesdropper CSI.
• It transforms a challenging non-convex problem into a quasi-convex optimization using geometric programming for efficient power allocation.
• Extensive simulations validate the approach and confirm its practical benefits under QoS and global power constraints.

Robust Secure Transmission in MISO Channels: A Study on Worst-Case Optimization

The paper investigates robust transmission strategies for multiple-input single-output (MISO) wiretap channels where there is imperfect channel state information (CSI) on the eavesdropper link. It considers both direct transmission and cooperative jamming schemes, aiming to enhance secrecy rate performance even under unfavorable channel conditions. This research is significant in the field of physical layer security, where the objective is to ensure secure communication in the presence of potential eavesdropping.

Key Contributions

1. Worst-Case Secrecy Rate Optimization: The paper focuses on maximizing the worst-case secrecy rate under both individual and global power constraints. This approach is particularly useful when there is uncertainty in the eavesdropper's CSI.
2. Transformation to Quasi-Convex Problems: One significant contribution is the transformation of the non-convex maximin optimization problem into a quasi-convex optimization problem. This transformation makes the problem computationally tractable using existing optimization techniques.
3. Geometric Programming for Global Power Constraints: For scenarios involving global power constraints, the paper employs geometric programming to jointly optimize power allocation and transmit covariance matrices between the source and the helper. This method streamlines the optimization process, allowing for efficient calculation of optimal transmission schemes.
4. Quality-of-Service Constraints: The paper extends the robust wiretap transmission problem to cases where a quality-of-service (QoS) constraint at the legitimate receiver must be met. This inclusion makes the research applicable to practical systems that require a certain level of service reliability.
5. Numerical Validation: Extensive numerical simulations are provided to validate the theoretical claims and demonstrate the substantial performance improvements offered by the robust designs over non-robust counterparts.

Implications and Future Directions

The research presented in the paper has several practical and theoretical implications:

• Enhanced Security in Wireless Networks: By focusing on worst-case scenarios, the proposed robust designs offer enhanced security guarantees, making them attractive for real-world applications where CSI imperfections are inevitable.
• Applications in Cooperative Communication Systems: The cooperative jamming scheme, especially under global power constraints, provides insights into how helpers (or friendly jammers) can be used effectively to confuse eavesdroppers and improve security.
• Potential for Broader Applications: The principles outlined could be extended beyond eavesdropper scenarios to other contexts where signal interference needs to be minimized while meeting specific performance metrics.
• Theoretical Insights into Non-Convex Optimization: The transformation techniques applied in the problem could pave the way for tackling other complex non-convex optimization problems prevalent in wireless communications and security domains.

Looking forward, future research may focus on expanding these robust optimization approaches to more complex scenarios, such as multi-eavesdropper environments or channels with more severe CSI uncertainties. Moreover, integrating these robust designs with adaptive systems that can learn and dynamically adjust to changing environments could further enhance their effectiveness and applicability.