Relay-Selection Improves the Security-Reliability Trade-off in Cognitive Radio Systems (1411.0228v2)

Abstract: We consider a cognitive radio (CR) network consisting of a secondary transmitter (ST), a secondary destination (SD) and multiple secondary relays (SRs) in the presence of an eavesdropper. We rely on careful relay selection for protecting the ST-SD transmission against the eavesdropper with the aid of both single-relay and multi-relay selection. To be specific, only the "best" SR is chosen in the single-relay selection for assisting the secondary transmission, whereas the multi-relay selection invokes multiple SRs for simultaneously forwarding the ST's transmission to the SD. We analyze both the intercept probability and outage probability of the proposed single-relay and multi-relay selection schemes for the secondary transmission relying on realistic spectrum sensing. We also evaluate the performance of classic direct transmission and artificial noise based methods for the purpose of comparison with the proposed relay selection schemes. It is shown that as the intercept probability requirement is relaxed, the outage performance of the direct transmission, the artificial noise based and the relay selection schemes improves, and vice versa. This implies a trade-off between the security and reliability of the secondary transmission in the presence of eavesdropping attacks, which is referred to as the security-reliability trade-off (SRT). Furthermore, we demonstrate that the SRTs of the single-relay and multi-relay selection schemes are generally better than that of classic direct transmission. Moreover, as the number of SRs increases, the SRTs of the proposed single-relay and multi-relay selection approaches significantly improve. Finally, our numerical results show that as expected, the multi-relay selection scheme achieves a better SRT performance than the single-relay selection.

• The paper finds that relay selection significantly improves the security-reliability trade-off by reducing intercept probability while managing outage probability.
• The authors compare single-relay and multi-relay selection schemes, revealing that multi-relay selection offers superior performance despite increased complexity.
• Increasing the number of secondary relays enhances overall network performance, providing actionable insights for designing robust cognitive radio systems.

Relay Selection and the Security-Reliability Trade-off in Cognitive Radio Systems

In the documented paper, the authors investigate the effects of relay selection on the security-reliability trade-off (SRT) in cognitive radio (CR) networks. The paper addresses the dilemma of maintaining both secure and reliable transmissions in the presence of eavesdroppers, a critical issue for cognitive radio systems where secondary users (SUs) opportunistically utilize the spectrum bands primarily assigned to primary users (PUs). The paper explores the interplay between the security and reliability metrics, defined by intercept probability (IP) and outage probability (OP), respectively.

Methodology and Analysis

The authors analyze a CR network configuration that includes multiple secondary relays (SRs) assisting in the transmission from a secondary transmitter (ST) to a secondary destination (SD), with an eavesdropper attempting to intercept the transmission. Two distinct relay selection schemes are proposed:

1. Single-Relay Selection (SRS): This method selects one optimal relay, which maximizes the legitimate transmission capacity to the SD.
2. Multi-Relay Selection (MRS): This approach utilizes multiple relays to simultaneously forward the transmission, aiming to enhance the transmission's security and reliability further.

Both schemes are evaluated against direct transmission and artificial noise-based approaches, considering realistic scenarios involving spectrum sensing and Rayleigh fading channels.

The SRT is assessed by analytical derivations and simulations focusing on the IP and OP metrics. The paper examines the impact of varying factors such as the number of SRs, the probability of the spectrum being unoccupied (denoted as $P_0$), and the reliability of spectrum sensing, characterized by the detection probability ($P_d$) and false alarm probability ($P_f$).

Key Findings

• Trade-off between Security and Reliability: The analysis unequivocally demonstrates a trade-off between security and reliability. As the intercept probability decreases (enhanced security), the outage probability tends to increase (reduced reliability) and vice versa.
• Performance of Relay Selection Schemes: Both SRS and MRS schemes outperform the conventional direct transmission and artificial noise-based strategies in terms of the SRT.
• Effect of Relay Count: Increasing the number of SRs significantly improves the security-reliability performance, highlighting the benefit of exploiting multiple relays within the cognitive radio framework.
• Advantage of Multi-Relay Selection: MRS consistently achieves superior SRT over SRS, though at the cost of increased complexity due to the need for symbol-level synchronization among the relays.

Implications and Future Work

The results underline the advantage of employing relay selection strategies to enhance the security and reliability of cognitive radio systems under eavesdropping threats. Practically, these findings can guide the design and deployment decisions in CR networks, balancing the trade-off between the system's security and reliability according to specific application requirements.

The paper opens avenues for future exploration, particularly focusing on more sophisticated relay selection techniques that might further refine the SRT. Extensions could examine the use of machine learning for relay selection decision-making, adaptive relay selection in dynamically changing environments, and the impact of imperfect channel state information (CSI) on relay selection.

Conclusion

This investigation into relay selection in CR systems provides robust insights into managing the inherent trade-offs between security and reliability. It sets a foundation for ongoing enhancement of CR network capabilities, seeking optimal balance points that address eavesdropping threats while maintaining high-quality service delivery. This balance is crucial as cognitive radio technologies continue to evolve in complexity and application scope.