# A Semi-Random Elliptical Movement Model for Relay Nodes in Flying Ad Hoc Networks
## 1 Introduction  
While reliance on pre-established networks may be effective in many situations, in practice, it often encounters challenges related to deployment complexity, cost, and time consumption [1]. Particularly in unforeseen scenarios such as natural disasters, accidents, or intentional interference, existing network infrastructures are highly vulnerable and may collapse entirely. For instance, in disaster zones where communication infrastructure has been destroyed, or in combat zones where rapid network deployment is infeasible, traditional static infrastructure-based networks are rendered unusable. In this context, there is a growing demand for network solutions that require no prior installation, leading to the emergence of the Mobile Ad hoc Network (MANET) concept [2]. MANETs are a type of wireless network that are spontaneously formed, wherein mobile nodes autonomously establish and maintain communication without relying on fixed infrastructure. MANETs possess self-healing capabilities, allowing the network to recover dynamically from node or link failures [3]. These networks operate without centralized control, and each node functions simultaneously as a transmitter, receiver, and router. The defining characteristic of a MANET lies not in the type of nodes it employs, but in their ability to perform essential networking functions. Research on MANETs predates the widespread adoption of wireless LAN technologies such as IEEE 802.11 (Wi-Fi), and numerous implementations based on the IEEE 802.11 standard have since been proposed. Notable examples include power-efficient communication control mechanisms [4], media access schemes supporting multicast functionality [5], protocol enhancements for performance optimization [6], and adaptive algorithms designed to respond flexibly to environmental changes [7]. FANET is an extension of MANET that is distinguished by its use of autonomously flying UAVs (Unmanned Aerial Vehicles) to form networks in real-time within dynamic three-dimensional space, where altitude, speed, and position constantly change [8]. These characteristics make FANETs highly promising for time-sensitive and flexible applications such as military operations [9], disaster response, surveillance [10], and reconnaissance. However, due to the high mobility of UAVs--typically flying at speeds between 30 and 460 km/h [11]--FANETs experience rapidly changing network topologies and frequent link disconnections, presenting major challenges in maintaining consistent connectivity in latency-sensitive and reliability-critical environments. Various FANET-specific routing protocols have been proposed, but most focus on theoretical performance and lack sufficient validation in real-world conditions [12]. Given FANETs' high-speed mobility and dynamic environments, effective communication requires not only robust routing design but also mobility models that accurately reflect UAV behavior and adapt to changing conditions [13]. As FANET applications expand, selecting appropriate mobility models for specific experimental goals is becoming increasingly important [14]. Mobility models used in FANET simulations are generally classified into four types: group-based, path-planned, time-dependent, and random-based, each designed for various application purposes [15]. Existing research has primarily focused on improving energy efficiency or supporting UAV-based search operations [16]. In contrast, research on mobility models tailored for relay-based communication--one of the core applications of FANETs--remains relatively limited. In relay network scenarios, it is crucial for nodes to remain stably distributed along communication paths; however, existing models often fail to adequately reflect such requirements in terms of spatial structure and path alignment, resulting in limitations in the accuracy of network performance evaluation. This study proposes SREM, a mobility model suitable for FANET experiments applicable to relay networks.