# A Multichannel MAC Protocol without Coordination or Prior Information for Directional Flying Ad hoc Networks

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## Abstract

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## 1. Introduction

- We present a system model for multichannel FANETs with double-directional antennas. One directional antenna is used for neighbor discovery in the control channel, and the other is exploited to transmit data in data channels.
- We establish the theoretical supremum for neighbor discovery during initial access [30] without coordination or prior information and propose a blind rendezvous algorithm to achieve the theoretical supremum. We extend the blind rendezvous algorithm to neighbor the discovery protocols BR-DA and BR-DA-FANET to achieve neighbor discovery for a pair of nodes and the entire network, respectively, in scenarios without prior information or coordination.
- In order to further decrease delay, we propose the neighbor discovery with location prediction (ND-LP) protocol after initial access neighbor discovery and the avoiding communication interruption with location prediction (ACI-LP) protocol during the data transmission process. The predicted location is utilized for quick main lobe rendezvous and channel rendezvous in the ND-LP protocol and beam tracking together with channel rendezvous in the ACI-LP protocol.

## 2. System Model and Problem Definition

#### 2.1. Network Model and Antenna Model

#### 2.2. Multichannel Directional FANET Model

#### 2.3. Problem Definition

- i.
- Guaranteed rendezvous: any two UAVs can achieve main lobe rendezvous in a certain period of time.
- ii.
- Full rendezvous diversity: UAVs can rendezvous on any combination of $({P}_{a},{P}_{b})\in [1,N]\times [1,N]$ and $({I}_{a},{I}_{b})\in $ $[1,N]\times [1,N]$.
- iii.
- Asynchronous environment: in FANETs, it is difficult to employ highly tight time synchronization among users, and each user may start their scan sequence at a different time during initial access.
- iv.
- Without extra expenditure: no additional expenditures, such as a coordination channel and prior information, should be required.

## 3. Multichannel MAC Protocol with Directional Antenna for FANET

#### 3.1. Blind Rendezvous Algorithm with Directional Antenna

**Theorem 1.**

**Proof of Theorem 1.**

**Theorem 2.**

**Proof of Theorem 2.**

**Theorem 3.**

**Proof of Theorem 3.**

#### 3.2. Main Lobe Rendezvous Scheme-Based Blind Rendezvous Algorithm with Directional Antenna for FANET

**Theorem 4.**

**Proof of Theorem 4.**

#### 3.3. Neighbor Discovery with Location Prediction for FANET

#### 3.4. Protocol for Avoiding Communication Interruption with Location Prediction

## 4. Simulation and Analysis

#### 4.1. Simulation on Pair-Wise Neighbor Discovery

#### 4.2. Simulation on Network-Wide Neighbor Discovery

#### 4.3. Simulation on Main Lobe Rendezvous Scheme Based on Location Prediction

#### 4.4. Simulation for Method for Avoiding Communication Interruption Based on Location Prediction

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 7.**The rendezvous period of the system composed of two UAVs. (

**a**) The initial state; (

**b**) the main lobe rendezvous state; (

**c**) the last state; and (

**d**) the initial state of the next period.

**Figure 10.**Antenna scan sequences for clock synchronization discovery of UAV a and b according to Theorem 2.

**Figure 11.**Antenna scan sequences for clock asynchronization discovery of UAV a and b according to Theorem 2.

**Figure 12.**Antenna scan sequences for clock asynchronization discovery of UAV a and b according to Theorem 3.

**Figure 13.**The picture for drift which ranges from 0 to $0{.5\mathrm{T}}_{\mathrm{rs}}$. (

**a**) The rendezvous-slots of the two UAVs are aligned for clock synchronization discovery of a FANET; (

**b**)drift ranges from 0 to 0.5 rendezvous-slot for clock asynchronization discovery of a FANET.

**Figure 14.**The picture for drift which ranges from 0.5 rendezvous-slot to 1 rendezvous-slot. (

**a**) Drift ranges from 0.5 rendezvous-slot to 1 rendezvous-slot for clock asynchronization discovery of a FANET. (

**b**) The process to add a drift which ranges from 0.5 rendezvous-slot to 1 rendezvous-slot.

**Figure 17.**Main lobe rendezvous and channel rendezvous are achieved in one-hop distance of UAV a TS1 as well as UAV b TS1 according to ND-LP.

**Figure 19.**Main lobe rendezvous and channel rendezvous are achieved in a multihops distance of UAV a TS1 as well as UAV b TS1 according to ND-LP.

**Figure 26.**The average delay of the BR-DA and ODND protocols when ranging the number of sectors from 8 to 32.

**Figure 27.**The worst-case discovery delay under different transmission ranges and different numbers of sectors.

**Figure 28.**The average discovery delay under different transmission ranges and different numbers of sectors.

**Figure 29.**Discovery delay of continuous 100 times neighbor discovery under different numbers of sectors.

Abbreviation | Definition | Abbreviation | Definition |
---|---|---|---|

MAC | Media Access Control | BER | Bit Error Rate |

ND-LP | Neighbor discovery with location prediction | ACI-LP | Avoiding communication interruption with location prediction |

GPS | Global positioning system | SDR | Software-defined radio |

FA-MMAC-DA | Multichannel MAC protocol with directional antennas for a FANET | WCDMR | Worst-case-delay-to-main-lobe-rendezvous |

Symbol | Definition | Symbol | Definition |
---|---|---|---|

$\mathsf{\theta}$ | The main lobe angle of the directional antenna | ${l}_{1}$ | The length of the segment of 1′s in a specific control sequence |

N | The number of sectors | ${l}_{2}$ | The length of the UAV’s unique ID |

${\mathsf{\theta}}_{S}$ | The width of the main lobe for the switched beam antenna | U | The maximum number of UAVs in a FANET |

${\mathsf{\theta}}_{P}$ | The main lobe angle of the phased array antenna | $({x}_{i},{y}_{i})$ | The location of the i-th UAV |

$\mathsf{\phi}$ | The direction of communication | ${v}_{i}$ | The speed of the i-th UAV |

$\psi $ | The direction of the main lobe boresight | ${\mathsf{\zeta}}_{i}$ | The angle between the movement direction of the i-th UAV and the positive direction of the X axis |

$u$ | The indexes of sectors | ${t}_{i}$ | The time that information is transmitted in by the i-th UAV |

${P}_{b}$ | The UAV b’ sector that UAV a is located in | $({x}_{\mathrm{T}},{y}_{\mathrm{T}})$ | The transmitter location |

${P}_{a}$ | The UAV a’ sector that UAV b is located in | $({x}_{\mathrm{R}},{y}_{\mathrm{R}})$ | The receiver location |

${I}_{a}$ | The sector that UAV a points towards in the initial state | ${\mathrm{D}}_{\mathrm{T},\mathrm{R}}$ | The distance between the transmitter and receiver |

$S$ | The antenna scan sequence | ${\mathrm{D}}_{\mathrm{max}}$ | The maximum communication distance |

${S}_{a}$ | The antenna scan sequence for UAV a | ${T}_{CS}$ | The delay for sensing and judging channels’ availability |

${\mathrm{T}}_{\mathrm{rs}}$ | The worst-case discovery delay for a pair of UAVs | ${T}_{TS2-RTS}$ | The delay of TS2-RTS |

${M}_{T}\mathrm{T}$ | The time duration for the transmitter UAV | ${T}_{TS2-CTS}$ | The delay of TS2-CTS |

${M}_{R}\mathrm{T}$ | The minimal slot duration to exchange discovery beacons between the pair of UAVs | ${T}_{\mathrm{Inf}}$ | The duration of the preparation-to-transmit information |

${l}_{0}$ | The length of the segment of 0′s in a specific control sequence | $\Delta \mathrm{t}$ | The sum of the duration of the data packet and ${T}_{\mathrm{Inf}}$ |

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

${T}_{CS}$ | 1 ms |

${T}_{TS2-RTS}$ | 1 ms |

${T}_{TS2-CTS}$ | 1 ms |

${T}_{\mathrm{Inf}}$ | 5 ms |

${T}_{\mathrm{ACK}}$ | 1 ms |

${T}_{TS1-RTS}$ | 1 ms |

${T}_{TS1-CTS}$ | 1 ms |

The number of sectors | 30 |

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## Share and Cite

**MDPI and ACS Style**

Liang, S.; Zhao, H.; Zhang, J.; Wang, H.; Wei, J.; Wang, J.
A Multichannel MAC Protocol without Coordination or Prior Information for Directional Flying Ad hoc Networks. *Drones* **2023**, *7*, 691.
https://doi.org/10.3390/drones7120691

**AMA Style**

Liang S, Zhao H, Zhang J, Wang H, Wei J, Wang J.
A Multichannel MAC Protocol without Coordination or Prior Information for Directional Flying Ad hoc Networks. *Drones*. 2023; 7(12):691.
https://doi.org/10.3390/drones7120691

**Chicago/Turabian Style**

Liang, Shijie, Haitao Zhao, Jiao Zhang, Haijun Wang, Jibo Wei, and Junfang Wang.
2023. "A Multichannel MAC Protocol without Coordination or Prior Information for Directional Flying Ad hoc Networks" *Drones* 7, no. 12: 691.
https://doi.org/10.3390/drones7120691