# Architecture of Emergency Communication Systems in Disasters through UAVs in 5G and Beyond

## Abstract

**:**

## 1. Introduction

_{B}) among the CMs, such that if the CH disappears, the CH

_{B}will become the new CH. The election processes for CH and CH

_{B}are presented. The traditional IEEE 802.11 backoff method is specifically intended for direct communication which is not appropriate for communication in cluster-based systems. Thus, a new backoff mechanism is proposed based on cluster size to optimize performance. The effectiveness of the suggested mechanism is investigated analytically using the Markov chain model. The analysis takes into consideration Nakagami-m fading channels. Throughput, packet dropping rate (PDR), outage probability, and delay expressions are obtained by taking into account the performance-influencing variables and establishing the relationships between them. Furthermore, simulation results are provided which verify the analytical studies. The simulation results indicate that the suggested technique enhances system performance and complies with the safety message delay constraint of 100 ms. A quantitative comparison with current cluster-based methods is also presented. In comparison to current cluster-based systems, the proposed approach achieves significant achievements with higher throughput and lower delay.

## 2. Proposed Architecture

#### 2.1. Cluster Formation

_{min}) between CM and CH, and FCS. RTM packet consists of frame control, duration, CID, HA, the number of CMs (NM), and FCS. The details of the mechanism will be provided in this section.

#### 2.1.1. Cluster Membership

#### 2.1.2. Selection of the CH and CH_{B}

_{B}in each cluster with enough CMs. If the CH disappears for any reason, the CH

_{B}will become the CH and a new CH

_{B}will be defined. To elect a CH

_{B}in the cluster, each CM will send RTBCH where the minimum distance (d

_{min}) between that CM and CH will be added. The d

_{min}can be obtained using Equation (3), where the starting point is the location of the CM, and the destination point is the location of the CH. The CM that has the minimum distance will become the CH

_{B}.

#### 2.1.3. Leaving Process

#### 2.1.4. Merging Process

_{B}with the highest NM during cluster merging will continue to be the CH and CH

_{B}. The cluster will welcome more CHs and CMs as CMs. The CH of the combined clusters then broadcasts an update to the list of CMs to all CMs.

#### 2.2. Safety Messages Transmission

_{ACK}be the set of acknowledgment N

_{ACK}where ACK is sent by the N

^{th}CM after successful transmission. The number of elements in U

_{ACK}is equal to the number of CMs. The symbol ϯ

_{re}denotes retransmission and ϯ

_{max}is the maximum retransmission limit. The most important messages in FANETs, which must have rigorous delay requirements, are the SMs. The CH sends out an SM and waits for all CMs to respond with an ACK. The transmission is deemed successful if an ACK is obtained from each and every CM. However, if an ACK has not been received from a CM or waiting time (T

_{wait}) is equal to the SIFS duration (T

_{SIFS}), then the transmission to that CM has failed. When the number of retransmissions (ϯ

_{re}) is lower than or equal to the maximum retransmission limit (ϯ

_{max}), the SM will be resent to the CMs whose ACKs have not been received. Otherwise, the SM transmission to the CM will be abandoned, and that CM will cease to be a member of the relevant cluster.

Algorithm 1. Algorithm of SM Broadcast |

1. SM is broadcast by CH 2. Wait for ACK, or, T _{wait} = T_{SIFS}3. IF N_{ACK} ∈ U_{ACK} for all CMs4. Then the transmission is successful 5. End6. ELSE IF N_{ACK} ∉ U_{ACK} and ϯ_{re} ≤ ϯ_{max}7. Then CH retransmits to the CM 8. ELSE Discard9. End |

#### 2.3. Backoff Mechanism

_{C}) in response to changes in the network load. Fixed Ҩ

_{C}backoff techniques estimate the Ҩ

_{C}without considering the state of the network. As a result, the Ҩ

_{C}must increase for each collision to achieve successful broadcasts. However, when the network load changes to heavy/light, success/collision is not guaranteed, and this dramatic volatility in the Ҩ

_{C}influences how well the backoff algorithms operate [32]. The Ҩ

_{C}is proposed in accordance with the number of CMs in the cluster to solve this issue.

_{UAV}be the number of UAVs in the FANET. If N

_{CL}clusters are formed in the network, the mean number of UAVs in a cluster may be calculated as:

_{C}for a cluster size X can be given as [25]:

_{C}depends on the mean number of UAVs in a cluster, as per given in Equation (2). The proposed backoff mechanism is presented in Algorithm 2. Let $\mathscr{H}$ denote a channel and $\mathscr{H}$

_{i}denote an idle channel. T

_{DIFS}is the duration of the DCF inter-frame space (DIFS). When a UAV has an SM to transmit, it first senses $\mathscr{H}$. If $\mathscr{H}$ is idle and continues to be idle for a T

_{DIFS}duration, then the UAV transmits the SM. Otherwise, backoff is initiated randomly with a value from 0 to (Ҩ

_{C-opt}–1). Backoff is reduced by 1 when the channel is idle in a slot time, and the existing backoff value remains when the channel becomes busy and decremented when the channel is idle once more for a higher duration than T

_{DIFS}. The packet will be sent when backoff is 0.

Algorithm 2. Algorithm of the Proposed Backoff Mechanism |

1. IF $\mathscr{H}$ = $\mathscr{H}$_{i}2. T _{wait} = T_{DIFS} and still $\mathscr{H}$= $\mathscr{H}$_{i}3. Broadcast 4. END5. IF T_{wait} > T_{DIFS}6. backoff _{i} = [0, Ҩ_{C-opt} − 1]7. While backoff_{i} > 0, continue to sense the channel, do8. IF $\mathscr{H}$ = $\mathscr{H}$_{i} in a slot9. backoff _{i} = backoff_{i} − 1,10. ELSE backoff_{i} = backoffi11. END12. END13. While backoff_{i} = 0 do14. Broadcast 15. END |

## 3. Performance Analysis

#### 3.1. Network Model

_{s}, y

_{s}, h) denote the starting point and (x

_{d}, y

_{d}, h) the destination. The distance from the starting point to the destination will be denoted by d. The minimum d between the starting point and the destination point can be given as:

_{CL}number of CHs. The expression for the average number of CMs in a cluster is:

_{a}, we can calculate the probability of a packet’s arrival σ as:

_{ɛ}. T

_{ɛ}can be given as:

_{slot}is the period of a slot, T

_{S}is the interval of a successful packet transmission, and T

_{C}is the duration of a packet transmission with a collision. T

_{S}and T

_{C}can be given as:

_{h}is the MAC and PHY headers’ length, and R

_{d}is the data transmission rate. T

_{ACK}and T

_{delay}are the duration of the ACK and propagation delay, respectively.

#### 3.2. Outage Analysis

_{t}and G

_{r}denote the antenna gain for the transmitter and the receiver, respectively. λ is the wavelength of the signal (c = 3 $\times $ 10

^{8}m/s, is the light speed, and f = 5 GHz, is the carrier frequency). σ

_{R}and d represent the transmission power at the receiver and the distance between transmitter and receiver, respectively. The transmitted power of all UAVs is the same. The parameter α expresses the exponent of path loss. ${\sigma}_{N}$ indicates the additive white Gaussian noise (AWGN). Block fading patterns, in which a packet to be delivered is divided into B blocks, are taken into account in order to account for effect of fading. $\delta $ is the probability of an error frame, and the relationship between $\delta $ and $\Upsilon $ is the following [34],

#### 3.3. Throughput Analysis

^{th}cluster, the μ can be calculated as:

#### 3.4. PDR Analysis

#### 3.5. Delay Analysis

_{int}] is the average time of the mean packet interval between two successfully received packets at a single receiver, and E[T

_{dr}] is the average time of a dropped packet. E[T

_{int}] can be obtained by using Equation (11) as:

_{dr}] can also be given using Equation (11) as:

_{dr}] is the average slot time for the dropped packet and can be expressed as:

## 4. Simulation Results

_{UAV}) in Figure 5 where the cluster size is 10. It is clear that the proposed system’s throughput has significantly improved, as compared to the traditional system. The throughput increases as N

_{UAV}increases within a specific range, since fewer collisions would occur. However, as N

_{UAV}increases, more packets will compete for transmission, increasing the collision probability and reducing throughput.

_{UAV}for various channel types. The Nakagami fading-m channel (m = 2) system has a higher throughput than the Rayleigh fading channel system. As m increases, the bit error rate (BER) decreases. A decrease in BER reduces the error frame transmission, thus increasing throughput and decreasing the outage probability.

## 5. Conclusions

## Funding

## Data Availability Statement

## Conflicts of Interest

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Abbreviation | Meaning | Abbreviation | Meaning |
---|---|---|---|

ATJC | Acceptance To Join in the Cluster | NM | number of CMs |

AWGN | additive white Gaussian noise | NSM | non-safety messages |

CH | cluster head | probability density function | |

CH_{B} | backup cluster head | PDR | packet dropping rate |

CI | cluster information | PHY | physical |

CID | cluster ID | RTBCH | Request To a Backup Cluster Head |

CM | cluster member | RTJC | Request To Join in the Cluster |

ECV | emergency communication vehicle | RTM | Request To Merge |

FANET | flying ad hoc network | SIFS | short inter-frame space |

GPS | global positioning system | SM | safety message |

HA | cluster head address | SNR | signal-to-noise ratio |

MAC | medium access control | UAV | unmanned aerial vehicle |

MID | cluster member ID | WLAN | wireless local area network |

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

Transmission range | 300 m |

${T}_{SIFS}$, ${T}_{slot}$, ${T}_{DIFS}$, ${T}_{delay}$ ($\mathsf{\mu}\mathrm{s}$) | 10, 20, 50, 1 |

L_{h}, L, ACK (bytes) | 50, 300, 14 |

R_{d} (Mbps) | 11 |

ϯ_{max}, Ҩ_{C-min}, ${G}_{r},{G}_{t}$ | 7, 64, 1, 1 |

N_{UAV} | 2–50 |

UAV speed | 10–30 m/s |

h | 50 m |

${\sigma}_{R},\text{\hspace{0.33em}}{\sigma}_{N},\text{\hspace{0.33em}}{\gamma}_{th}$ (dB) | 10, −50, 5 |

f (GHz), $\alpha $ | 5, 3 |

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**MDPI and ACS Style**

Shah, A.F.M.S.
Architecture of Emergency Communication Systems in Disasters through UAVs in 5G and Beyond. *Drones* **2023**, *7*, 25.
https://doi.org/10.3390/drones7010025

**AMA Style**

Shah AFMS.
Architecture of Emergency Communication Systems in Disasters through UAVs in 5G and Beyond. *Drones*. 2023; 7(1):25.
https://doi.org/10.3390/drones7010025

**Chicago/Turabian Style**

Shah, A. F. M. Shahen.
2023. "Architecture of Emergency Communication Systems in Disasters through UAVs in 5G and Beyond" *Drones* 7, no. 1: 25.
https://doi.org/10.3390/drones7010025