# LoRaWAN Communication Protocols: A Comprehensive Survey under an Energy Efficiency Perspective  
[PERSON]  
1 Department of Electrical and Computer Engineering, University of Western Macedonia, Karamalli & Lygeris, 50100 Kozani, Greece; [EMAIL_ADDRESS] (K.B. ); [EMAIL_ADDRESS] (I.K. ); [EMAIL_ADDRESS] (T.D. ); [EMAIL_ADDRESS] (A.-A.B. ); [EMAIL_ADDRESS] (T.K.) LoRaWAN was standardized in 2015 by the LoRa-Alliance group and uses the ISM band [2]. LoRaWAN constitutes one of the leading LPWAN technologies and has received considerable attention in industrial and research communities, because of its inherent connectivity support for a massive amount of IoT end-devices, the broad coverage achieved in non-urban environments, the easy, scalable, and low-cost design and development of the network, its operation in the unlicensed radio frequency bands for ISM purposes and its low energy consumption [5]. Unlike SigFox and NB-IoT, LoRaWAN has the advantage that is an open protocol and it allows the deployment of its own low-cost network without a third-party infrastructure, as well as offering the possibility for private network deployments [6] and, thus, the support of several verticals. Several LoRaWAN-related design challenges and issues have recently received significant attention by the research community, such as network capacity maximization [7, 8], range expansion [9], as well as the minimization of network's delay [10]. Additionally, in LoRaWAN, issues of scalability and robustness [11], abatement of network capacity, and augmentation of collisions [12] arise as the number of devices increases. As collisions increase they lead to a decrease in throughput [13]. Additionally, collisions result in lost and retransmitted data, which, in turn, raises energy consumption [14]. Furthermore, limited energy resources are an inherent constraint of LoRaWAN. As a result effective resource management is one of the principle aspects in LoRaWAN design [15]. End-devices are usually battery-powered and not connected to an electricity network; thus, they have a limited lifetime, since replacing or charging batteries may be impossible in harsh environments. Thus, due to the limited computational, communication, and energy resources imposed on end-devices, energy efficiency should be carefully considered to avoid degradation of network lifetime. Appropriate selection of the communication protocol constitutes a crucial factor concerning the energy consumption and the overall performance of LoRaWANs. There is a rising research and industrial interest in designing energy efficiency communication protocols for LoRaWAN. However, to the best of our knowledge, no detailed survey investigating the effect on energy efficiency of the various categories of communication protocols for LoRaWAN has been so far documented in the research literature. Several state-of-the-art surveys on LoRaWAN [3, 5, 6, 16, 17, 18, 19, 20, 21] have proposed that focus on various aspects. For instance, [3] reviews LoRaWAN scalability issues and the proposed solutions in massive IoT networks. In [5], the authors present a technical overview of LoRaWAN technology and state-of-the-art studies proposed about LoRaWAN. In [6], the authors provide an overview of LPWAN technologies, a discussion about the challenges and critical aspects of LoRaWAN and their recent solutions, as well as a comparison of the most commonly used LoRaWAN simulation tools. The authors of [16] present a general discussion of long-range (LoRa), explore different applications of LoRa, and propose a solution to integrate edge computing in IoT-based applications. In [17], the authors present a brief overview of LoRa, investigate the challenges of LoRa and their recent solutions, and discuss some open issues. Authors in [18] present a review of state-of-the-art works for LoRaWAN focusing on aspects that affect network performance and categorize them.