# IoT: A Long-Reach Fully Passive Low-Rate Upstream PHY for IoT over Fiber
## 4 Conclusions  
This work made a case for IoToF focusing on niche applications which require low data rates along extended reach links. It presented an innovative low-cost FBG based acousto-optic modulation scheme suitable for IoT demands. A simple implementation with off-the-shelf components was able to upstream 300 bps with 8-FSK over links exceeded \(\sim\)30 km, which can unleash IoT applications beyond the limits of LoRa and Sigfox. The proposed scheme can be extended to multiple devices due to the multiplexing flexibility offered by the FBG technology. A proper short framing link layer solution over IoToF PHY should also be developed as future work. Another important parameter is the AOM's power consumption, and IoToF device autonomy as a result. We envisage that distributed Raman amplification can be used to extend reach while its pump power recycling is used for power transmission over optical fiber as an ingenious solution that could be applicable for feeding IoToF devices [40]. In addition, an important challenge related with the receiver stage of the IoToF needs to be addressed. Despite the edge-filtering technique allows to interrogate FBGs with high frequency and low-cost, the channel multiplexing is a common issue among the proposed techniques in the state-of-the-art. Commercial devices such coarse or dense WDMs can be used as multichannel edge-filters, increasing the interrogation cost when compared with techniques proposed in the state of the art. Therefore, it is necessary to develop novel strategies or devices to perform the edge-filtering process keeping in mind the low-cost approach. In AOMs fabrication terms, it is necessary to propose more compact and sensitivity devices. In addition, to increase the bit rate is the main aim. Finally, a more realistic scenario with several AOMs and IoT devices need to be implemented to validate the overall performance of the IoToF approach. All underlying data used in this publication can be found [[[https://doi.org/10.5281/zenodo.2602184](https://doi.org/10.5281/zenodo.2602184)]([https://doi.org/10.5281/zenodo.2602184](https://doi.org/10.5281/zenodo.2602184))]. **Author Contributions:** [PERSON], [PERSON] and [PERSON] conceived and designed the experiments; [PERSON], [PERSON] and [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] and [PERSON] contributed materials/analysis tools/revised the paper; [PERSON] and [PERSON] wrote the paper. **Funding:** This research received no external funding. **Acknowledgments:** This work was partially supported by Petrobras S.A. 2017-00702/6, CAPES-financing code 001, CNPq-408480/2018-1, FAPES, in the scope of PVE/CNPq407093/2013-3, Instituto de Telecomunicacoes, Aveiro, and Institute of Nanostructures, Nanomodelling and Nanofabrication. This work was financed in the scope of programs UID/EEA/50008/2013, UID/ CTM/50025/2013 and UID/EEA/50008/2019, by the National Funds through the Fundacao para a Ciencia e a Tecnologia (ICT)/ Ministerio da Educacao e Ciencia, and by the European Regional Development Fund under the PI2020 Partnership Agreement. This work is also funded by national funds (OE), through FCT, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. [PERSON] and [PERSON] thank the support received from the PREDICT (FCT-IT-LA) and REAct (FCT-IL-LA) scientific actions, respectively. FUTBOL has received funding from the European Union's Horizon 2020 for research, technological development, and demonstration under grant agreement No. 68984 (FUTEBOL), as well from the Brazilian Ministry of Science, Technology and Innovation (MCTI) through RNP and CTIC. Figure 9: Bit error rate (BER) as a function of the transmission distance. **Conflicts of Interest:** The authors declare no conflict of interest.