# SCHC over LoRaWAN Efficiency: Evaluation and Experimental Performance of Packet Fragmentation
## 2 Related Works  
In this section, we describe the works related to the modeling of the performance of the SCHC standard. Since the standard was finalized recently--SCHC in 2020 and SCHC over LoRaWAN in 2021--there is still uncertainty regarding its efficiency and performance under different LPWAN conditions. We surveyed previous works that propose models evaluating different aspects of the performance of SCHC when used over Sigfox and LoRaWAN technologies. In [3], the author chose several performance metrics for an experimental evaluation of SCHC over Sigfox. The analysis focuses on metrics such as the transmission duration of a packet (which is evaluated both theoretically and experimentally), the amount of uplink and downlink messages exchanged to transmit a SCHC Packet, and the energy performance. In [4], [PERSON] et al. propose the modeling and evaluation of packet transfer times, and the required number of uplink and downlink messages in a Sigfox network, considering the conditions when the end device is deployed in different radio zones, i.e., with different physical transmission rates and duty cycles. [PERSON] et al. [5], provide an experimental evaluation of SCHC over LoRaWAN to determine the latency and delivery ratio improvements as a consequence of different compression and fragmentation levels. In addition, the authors also examine the relationship between the overhead and useful payload sent per fragment. [PERSON] et al. [6] present a model to evaluate the performance of the SCHC ACK-on-Error mode, applicable to the generic standard; hence,it may be considered for both Sigfox and LoRaWAN technologies. The model considers the number of SCHC ACK messages on the downlink to evaluate four metrics, namely the ACK message overhead, ACK bit overhead, ACK bit overhead with L2 headers, and the percentage of used bits per fragment. The theoretical results show that the channel occupancy has a direct relationship with the parameters of the SCHC specification: the tile and window sizes. In [7], the authors perform an analysis of the fragmentation modes of the SCHC specification [1]. The work introduces three performance metrics: channel occupancy (CO), goodput, and the total delay. Regarding the CO metric, the authors do not describe how CO is calculated. They also indicate that the channel occupancy was calculated without considering errors in the message reception. Our model does consider these errors. The authors simulated an error-free scenario using the OpenSCHC [8] simulation tool. In the no-ACK mode, the results were shown to have the lowest total delay and the highest goodput. In addition, the results showed that the total delay and channel occupancy, in both ACK-always and ACK-on-Error modes, are directly proportional to the number of windows required to transmit a SCHC Packet.  
Table 1 is a list summarizing the related works. The table shows a reference to the publications and the technology used in the model (LoRaWAN or Sigfox), in addition to the metrics used. The works presented in this section contribute to determining the performance of SCHC. Nevertheless, previous works did not address the channel efficiency analysis in the presence of errors, which is critical in constrained networks and devices such as the ones employed with LoRaWAN. Therefore, in this work, we design a new model to determine the channel efficiency that is evaluated both theoretically and experimentally using a real LoRaWAN implementation.