# Low-Complexity Transmit Power Control for Secure Communications in Wireless-Powered Cognitive Radio Networks

## Abstract

**:**

## 1. Introduction

- We present a practical system model for WPCRNs, in which multiple SUs share the same spectrum with PUs and EH nodes are not allowed to interpret information but are licensed to collect energy from the transmitted signals.
- To prevent eavesdropping of untrusted EH nodes and share the spectrum efficiently, an optimization problem is formulated to derive the optimal transmit powers of SU transmitters (Txs) to maximize the average secrecy rate of SUs while ensuring the requirements of allowable interference on PU receiver (Rx) and minimum amount of energy for each EH node. Given that the formulated problem is non-convex, dual decomposition is performed to identify the suboptimal value of the transmit power and develop a low complexity TPC strategy.
- Performance evaluations based on intensive simulations show that the proposed scheme achieves near-optimal performances in terms of the average secrecy rate and outage probability and significantly reduces the computational complexity compared with the optimal scheme.

## 2. System Model and Problem Statement

## 3. Low-Complexity Transmit Power Control Algorithm

Algorithm 1 Low-complexity transmit power control algorithm |

1: Randomly initialize $\overrightarrow{p}$, $\overrightarrow{\lambda}$, $\overrightarrow{\mu}$ and $\overrightarrow{\kappa}$ 2: repeat3: ${\overrightarrow{p}}_{\mathrm{old}}\leftarrow \overrightarrow{p}$ 4: for$i=1$ to N5: Compute ${t}_{i}^{\left[s\right]}$ according to (18) 6: Compute ${p}_{i}$ according to (17) 8: end for9: $\overrightarrow{p}=\{{p}_{1},{p}_{2},\cdots ,{p}_{N}\}$ 10: until$\parallel \overrightarrow{p}-{\overrightarrow{p}}_{\mathrm{old}}\parallel <\u03f5$ |

## 4. Simulation Results and Discussion

- Optimal scheme: With the complete CSI at SU Txs, the ES can attain near-optimal performance with $Q=100$.
- Proposed TPC scheme: The transmit powers of SU Txs are determined using the proposed algorithm described in Algorithm 1.
- Binary TPC scheme: The transmit power of each SU Tx is determined as either ${P}_{\mathrm{max}}$ or zero in the direction of maximizing the average secrecy rate [17].
- Maximum power scheme: The transmit powers of SU Txs are always determined as their maximum transmit powers, ${P}_{\mathrm{max}}$.
- Random power scheme: The transmit powers of SU Txs are randomly determined.

## 5. Conclusions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 2.**Performance comparison against allowable interference level (${I}_{\mathrm{max}}$). (

**a**) Average secrecy rate vs. ${I}_{\mathrm{max}}$. (

**b**) Outage probability vs. ${I}_{\mathrm{max}}$.

**Figure 3.**Performance comparison against required harvested energy (${E}_{\mathrm{min}}$). (

**a**) Average secrecy rate vs. ${E}_{\mathrm{min}}$. (

**b**) Outage probability vs. ${E}_{\mathrm{min}}$.

**Figure 4.**Performance comparison against number of node sets (N). (

**a**) Average secrecy rate vs. N. (

**b**) Outage probability vs. N. (

**c**) Computation time vs. N.

Parameter | Value |
---|---|

Number of node sets | N = 3 |

Maximum transmit power for SU Txs | ${P}_{max}$ = 30 dBm |

Transmit power for PU Tx | ${p}_{0}$ = 30 dBm |

Noise power | ${\sigma}^{2}=-100$ dBm |

Required harvested energy | ${E}_{\mathrm{min}}=-15$ dBm |

Allowable interference level | ${I}_{\mathrm{max}}=-50$ dBm |

Energy conversion efficiency for EH nodes | ${\zeta}_{i}$ = 0.5 for $i\in \mathbb{N}$ |

Size of area for distributing nodes | 50 m × 50 m |

Path loss exponent | 2.7 |

K-factor of Rician fading | 6 |

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Lee, K.
Low-Complexity Transmit Power Control for Secure Communications in Wireless-Powered Cognitive Radio Networks. *Sensors* **2021**, *21*, 7837.
https://doi.org/10.3390/s21237837

**AMA Style**

Lee K.
Low-Complexity Transmit Power Control for Secure Communications in Wireless-Powered Cognitive Radio Networks. *Sensors*. 2021; 21(23):7837.
https://doi.org/10.3390/s21237837

**Chicago/Turabian Style**

Lee, Kisong.
2021. "Low-Complexity Transmit Power Control for Secure Communications in Wireless-Powered Cognitive Radio Networks" *Sensors* 21, no. 23: 7837.
https://doi.org/10.3390/s21237837