# Enhanced Beacons Dynamic Transmission over TSCH
## 1 Introduction  
The Internet of things (IoT) paradigm has been experiencing rapid development in recent years. Nowadays, all kinds of objects are connected to the Internet and can communicate without human intervention. The autonomy and performance of these devices depend on the technologies present in each functional block of IoT systems [1; 2; 3]. Wireless sensor networks (WSNs) and low-power and lossy networks (LLNs) are the building blocks of the IoT. They provide scalability and support for diverse applications, such as environmental monitoring and remote sensing, patient monitoring and telemedicine, logistics and transportation industries, asset tracking, and other smart city applications [4]. Maintaining good performance to face this type of adverse scenario despite the limitations of the devices imposes challenges in terms of hardware design, protocols, and applications.  
Communication in LLNs is unreliable due to the error-prone wireless media, with high bit error rates and variable link capacity. To work properly, an LLN network must implement protocols that, depending on the application, allow it to deliver information reliably. To facilitate the efficient deployment of LLNs in the context of IoT and address their resource constraints, the IEEE 802.15.4 standard was proposed [5]. IEEE 802.15.4 defines the medium access control (MAC) and physical (PHY) layers for low-rate wireless local area networks (WLANs) as part of the IEEE standardization effort for LLN networks. Ease of installation, data transfer reliability, and reasonable battery life are some benefits of the IEEE 802.15.4 standard. On the other hand, ref. [6] discusses some limitations suchas poor communication reliability, no recovery from external interference and multipath fading, and large data delay.  
To improve the performance of the standard in applications that demand strict requirements in terms of latency and reliability, the IEEE 802.15.4e task group was created to define a MAC amendment to the existing standard. This amendment offers functional improvements like radio duty cycling, multichannel operation, node synchronization through enhanced beacons, flexible frame format, and a mechanism for feedback on channel quality [6]. Time slotted channel hopping (TSCH) stands out against other access mechanisms defined in the IEEE 802.15.4 standard, meeting strict requirements in terms of power consumption with a good balance for overall performance [7]. Additionally, the scheduling of communications in the time slots tries to avoid internal interference (collisions), whereas the channel hopping tries to mitigate external interference [8]. To participate in a TSCH network, a node needs to synchronize with the network. This synchronization is handled through the reception of enhanced beacons. The absence of a standard scheduling mechanism to disseminate enhanced beacons has motivated several researchers to find an optimized algorithm for network formation and synchronization.  
In the present paper, a dynamic association mechanism is proposed to enhance the formation process of TSCH-based networks. The rest of the paper is organized as follows. Section 2 describes the TSCH mode and related work. Section 3 presents TSCH implementation in Contiki-NG. In Section 4, a dynamic association method is presented. Section 5 illustrates the experimental results obtained from the multi-scenario performance comparison between the proposed mechanism and the TSCH default association algorithm. Finally, conclusions are presented in Section 6.