Integrated satellite unmanned aerial vehicle relay networks (ISUAVRNs) have become a prominent topic in recent years. This paper investigates the average secrecy capacity (ASC) for reconfigurable intelligent surface (RIS)-enabled ISUAVRNs. Especially, an eve is considered to intercept the legitimate information from the considered secrecy system. Besides, we get detailed expressions for the ASC of the regarded secrecy system with the aid of the reconfigurable intelligent. Furthermore, to gain insightful results of the major parameters on the ASC in high signal-to-noise ratio regime, the approximate investigations are further gotten, which give an efficient method to value the secrecy analysis. At last, some representative computer results are obtained to prove the theoretical findings.

The future requirements of wireless communication networks have so many characters, such as wider coverage, higher energy utilization, et al. Wider coverage has become an important requirement for the wireless networks [

As mentioned previously, the ISTN has been regarded as a hot research topic these years. In [

Another important demand for the 6G network and next wireless communication network is higher energy efficiency, which has been an important factor for the urban networks [

By summarizing all and trying the authors’ best efforts, the study for the effect of RIS-based ISTN with a UAV on the ASC remains unreported, which motivates our work.

Accordingly, this paper first considers the UAV relay and an eavesdropper. Specifically, the RIS is mounted on a tall building to augment the transmission. Then, we research the ASC for the considered network. The detailed works of this paper are given in what follows as

By taking the satellite, the UAV, the legitimate user and an eavesdropper into consideration, the considered secrecy network appears. Furthermore, in order to enhance the secrecy transmission and improve the energy utilization, the RIS is stalled in the high building to help the UAV. In addition, the decode-and-forward (DF) forwarding method is used at the UAV to assist the satellite’ transmission. For some practical reasons, the direct transmission link does not exist in the considered network, namely, the satellite can not communicate with the legitimate user directly.

Relied on the considered networks, detailed investigations for the ASC are obtained. The detailed investigations provide efficient methods to evaluate the effects of key parameters, i.e., the channel and system parameters on the ASC. Especially, these derivations can derive the impacts of RIS’ parameters.

To gain further investigations of the ASC on the considered networks, the asymptotic investigations for the ASC are gotten, which give deep insights on the considered secrecy networks.

The structure of this paper is as follows. Through

SatCom | Satellite communication |
---|---|

TCNs | Terrestrial communication networks |

UAV | Unmanned-aerial-vehicle |

OP | Outage probability |

PLS | Physical layer security |

ISTNs | Integrated satellite terrestrial networks |

AWGN | Additive white Gaussian noise |

BF | Beamforming |

SOP | Secrecy outage probability |

NOMA | Non-orthogonal multiple access |

ASC | Average secrecy capacity |

RIS | Reconfigurable intelligent surface |

DF | Decode-and-froward |

SR | Shadowed-Rician |

Probability density function | |

LoS | Line of sight |

SNR | Signal-to-noise ratio |

FSL | Free space loss |

LMS | Land mobile satellite |

CDF | Cumulative distribution function |

MC | Monte Carlo |

FHS | Frequency heavy shadowing |

AS | Average shadowing |

TDMA | Time division multiple access |

GEO | Geosynchronous earth orbit |

ILS | Infrequent light shadowing |

i.i.d | Independent and identically distribution |

LMS | Land mobile satellite |

As shown in ^{1}

Although in this paper, we just use only one UAV, the obtained results can also suit for the case with multiple UAVs.

relay^{2}

It is mentioned that, in this paper, each node owns only one antenna, while the remaining results are also suitable to the case that transmission nodes having multiple antennas when beamforming (BF) is utilized at the multiple antenna node.

^{3}

Owing to obstacles, fogs, rain attenuation, in this paper direct transmission link between the source and destination is not available, which will be considered in our future works.

Two time slots will last for the whole link. In the first one,

where

For the second one,

where

By utilizing [

As mentioned before, a secrecy problem exists in the considered networks. Thus, the information overheard by the Eve is shown as

where

From

For the reason that DF protocol is applied for the UAV, then the legitimate SNR of the secrecy system is obtained as

Relied on [

where

From [

Before getting the final derivations of ASC, the first important one is to gain the CDF and PDF for

Through this paper, the geosynchronous earth orbit (GEO)^{4}

Although in this paper, we take the GEO satellite for an example, the obtained investigations can be also used to the scenario with medium Earth orbit (MEO) and low Earth orbit (LEO) satellites.

satellite is assumed. In addition, the satellite is considered to own many transmission beams. Moreover, time division multiple access (TDMA)^{5}

TDMA scheme is used in the satellite to keep only one satellite beam and one UAV is used in each data transmission time slot. TDMA scheme is both adopted for the satellite downlink and uplink data transmission.

Then,

where

where

From [

where

where

For

By utilizing [

where

Then, by utilizing [

where

and

From [

By utilizing the similar method, from [

Recalling

with

and

By submitting

where

where

Then, the detailed expression for the ASC of the regarded secrecy system is given by

In the following, the asymptotic analysis for the ASC will be given. When SNR becomes lager enough, namely,

where

Thus, by utilizing

By replacing

Then, by utilizing

In this section, some typical Monte Carlo (MC) simulations are presented to prove the efficiency of the investigation results. The effects of the key parameters are evaluated. With loss of no generality, in

Shadowing | |||
---|---|---|---|

Average shadowing (AS) | 5 | 0.251 | 0.279 |

Infrequent light shadowing (ILS) | 10 | 0.158 | 1.29 |

Frequent heavy shadowing (FHS) | 1 | 0.063 | 0.0007 |

Parameters | Value |
---|---|

Satellite orbit | GEO |

Frequency band | |

3 dB angle | |

Maximal beam gain | |

The antenna gain |

As proved in [

In the section, the summary of this work was given. In this work, we researched the ASC for the RIS-based integrated satellite UAV relay networks. To enlarge the coverage area, the satellite was utilized. In order to enhance the transmission, the UAV was utilized to help the satellite’s transmission. Moreover, to save the energy, the RIS was utilized in a high building to enhance the transmission. Thus, the considered secrecy model was proper and acceptable. In particular, the final expressions were obtained for the ASC, and from the derived results, we could get the impacts of key parameters on the ASC. Especially for the asymptotic results, we could observe the following effects: the light channel fading, a lower

The authors wish to express their appreciation to the reviewers for their helpful suggestions which greatly improved the presentation of this paper. The authors are grateful for the support by National Natural Science Foundation of China.

This work was supported by the National Natural Science Foundation of China under Grants 62001517 and 61971474, in part supported by the Beijing Nova Program under Grant Z201100006820121.

The authors confirm contribution to the paper as follows: study conception and design: Ping Li, Kefeng Guo and Feng Zhou; date collection: Ping Li, Kefeng Guo, and Xueling Wang; analysis and interpretation of results: Ping Li, Kefeng Guo, Feng Zhou, Xueling Wang and Yuzhen Huang; draft manuscript preparation: Ping Li, Kefeng Guo, and Feng Zhou. All authors reviewed the results and approved the final version of the manuscript.

The raw/processed data required to reproduce the above findings cannot be shared at this time as the data also forms part of an ongoing study.

The authors declare that they have no conflicts of interest to report regarding the present study.