# A Survey on LoRaWAN Architecture, Protocol and Technologies
## 2 LoRa & LoRaWAN Technologies
### Related Work  
In this section, we will discuss the state of art MAC layer researches. [PERSON] et al. [56] summarize LoRa, LoRaWAN application scenarios with open search areas. Similar studies exist to overview the technology [57] and to highlight the bottlenecks [58]. LoRa channels are orthogonal and provide interference-free communication using the same channel with different SF values. [PERSON] and [PERSON] [59] focuses on interference which is unique to LoRa networks which they call co-spreading factor interference. In the study, using single GW a mathematical tool is presented the evaluate UL and coverage of the network. Authors use Stochastic Geometry to model uplink coverage with a spatial distribution of the end-nodes. It is shown that LoRa networks are resistance to cumulative interferences. And, [PERSON] et al. [60] analyze interframe spacing and interference with co-channel in LoRa. Using the same SF with min overlapping and PER is evaluated up-to 100%. Figure 21: Coverage area illustrated. Figure 22: LoRaWAN simulation: Packet success ratio vs. number of nodes. LoRaWAN link capacity is studied with a single node by [PERSON] et al. [61] and in detail, results are shared. The study shows that UL capacity is limited to 2 kbit/s and highly related to the distance between node and GW. An interference modeling using frequency and time domain is presented by [PERSON] et al. [62] to compare LWPANs. Model is based on card toasting and in the study, Sigofx and LoRaWAN are selected and analyzed. Given the model in the study, it can be used to solve LPWAN deployments and MAC layer problems. The MAC layer of the protocol has been investigated by researchers to model channel access strategies for different LoRaWAN Classes. Since Class A is mandatory for all LoRaWAN devices, performance evaluation of the channel is highly investigated. By [PERSON] et al. [63], Class A, uplink message performance is analyzed and the presented model is compared with ALOHA for model validation. [PERSON] et al. [64] analyze the LoRaWAN Class A, UL performance in-terms of collision latency in a regulated duty cycling. A realistic Class A, MAC layer bounds analysis is performed by the authors [65] to model the channel. Also, [PERSON] et al. [66] developed an ALOHA based channel access model and tested with Python based simulation(LoRaWAN-sim) for model validation with realistic duty-cycle restrictions. ALOHA based mathematical models help to estimate error rates for LoRaWAN including Acknowledgment mechanisms [67]. [PERSON] et al. [68] analyze and outline the limitations of the Class B devices. The communication delay is evaluated with different parameters and a Markov Chains DL model is presented. A realistic traffic generation is studied by [PERSON] et al. [69] for LoRaWAN networks. Using generated traffic, interference in node-to-GW radio communication is evaluated. According to the study, sudden data burst affects the GW. LoRaWAN's built-in ADR (Section 2.4.8) is extended with SNR margin estimation algorithms. The presented model evaluated with The Things Network (Open Source LoRaWAN infrastructure provider) coexisting algorithms. LoRaWAN is considered as star-of-stars network topology and only a single relay (which is GW) is used to access nodes. Alternative approaches are still under consideration to extend this behavior. [PERSON] et al. [58] aim to bring multi-hop networking LoRa for better performance indoor uses cases for CT (concurrent transmissions) flooding mechanism. In the study, the authors analyze the physical layer effects of CT scenarios. Cross technology integration is an alternative approach to provide new MAC functionalities. A LoRa - WiFi bridge for flexible use cases are presented by [PERSON] et al. [70]. Multi hope mesh network design has been studied [71; 72; 73] by many researchers and alternative methods presented for content forwarding [74] and distributed channel access [75]. Beside multi-hop MAC layer studies, more interoperability work efforts exit to integrate 6 LowPAN and IPv6 [76; 74].