# Reliable Internet of Things: Challenges and Future Trends
## 1 Introduction  
The Internet of Things (IoT) is one of the important technologies of this era that can add automation and smartness in several sectors such as transportation, health care, industries, agriculture, energy, and infotainment. It works by deploying sensors on different devices used in these sectors, hence allowing the measurement of important real-time data. These data are transmitted to the remote servers where it can be analyzed, and intelligent actions can be taken based on it [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15].  
IoT enables many important applications, including intelligent traffic management, safety-aware autonomous driving, saving electricity usage using smart grids, remote patient monitoring, machine health monitoring, smart industrial automation, and smart home security solutions [4, 5]. In the era of Industry 4.0 and 6G communications, IoT applications will revolutionize how different industries operate.  
There are several use cases of IoT in these industries. It can facilitate smart usage of electricity and communication flow between devices and the grid. Related to smart transportation, IoT can provide safety to drivers and passengers. Similarly, health care has several potential benefits offered by IoT regarding patient health monitoring and early diagnosis. IoT can also ensure health monitoring of machines used in various industries, thus improving the lifetime and working of the equipment.  
The three major components of IoT will be sensing, communications, and data analytics. In the sensing part, various sensors such as temperature, current, humidity, heart rate, etc., will be deployed to get regular data measurements. In the communications part, technologies such as 6G will disseminate data from sensors to the cloud servers. Finally, data analytic algorithms will be extensively used to improve the working of IoT applications.  
The successful working of IoT applications relies on reliable data transmission between sensors and servers. Reliability refers to robust communication with a high packet deliveryratio, low latency, and defense against network attacks. Each IoT application may have different Quality of Service (QoS) requirements. To realize a reliable and robust IoT network, meeting the QoS requirements is needed [16; 17; 18; 19; 20; 21; 22; 23; 24; 25].  
Efficient data transmission is a key challenge to ensure reliable IoT applications. This means that data are transmitted at a high data rate such that latency is within the QoS requirement. This is possible when resources such as spectrum utilization, medium access, transmit power, computation task offloading to fog nodes, etc., is optimized. Moreover, privacy and secrecy of communication, along with maintaining data integrity, are required.  
In this paper, we provide an overview of research related to reliable data transmission in IoT. We first present a discussion on massive IoT and its application requirements. This is followed by four major use cases of the IoT and categorize the reliability related IoT work into four major units, i.e., resource allocation, latency management, security and reliability metrics. We discuss the recent literature review for each category above and highlight the key idea and achieved results. Finally, we present challenges that still need to be addressed to realize a reliable IoT network.