# Review and Evaluation of MAC Protocols for Satellite IoT Systems Using Nanoatellites
## 7 Conclusions  
The evolution of satellite systems and the introduction of CubeSats as low-cost satellite technology has made it possible to provide massive communications services for IoT applications, opening the opportunity for countries with no experience in space science and small corporations to participate competitively in the growing satellite communications market. However, the existent protocols in satellite technology, in particular for medium access control, were not designed with the IoT scenario, nor the low-cost technology constraints in mind.  
This paper has presented a thorough review of MAC protocols designed for satellite environments, considering the specific characteristics of the IoT networks and applications together with the conditions of a wireless network served by CubeSats deployed in a low earth orbit. The study has shown that many of the reviewed protocols are not suitable for deployment in the scenario of interest, although they have been successfully implemented and deployed in other satellite systems. From the comparative evaluation, the protocols employing interference cancellation techniques are shown to have the best communications performance, but they behave poorly with regards to the demands of processing/channel resources and energy consumption. Furthermore, the Aloha-based protocols are good candidates for the MAC layer in nanosatellites devoted to IoT connectivity due to their simplicity of implementation and their minimum hardware requirements. However, these protocols report having poor communications performance when the traffic load--related to the growing number of expected nodes in the IoT--increases, and also when the delays vary greatly due to variable link lengths.  
From our analysis, a better balance among performance, complexity, energy consumption, and sensitivity to topology should drive the design of future MAC protocols for nanosatellite IoT solutions. Aspects related to the network protocol design, the integration capabilities of CubeSat connectivity with other wireless technologies, and the evolution of the nanosatellites industry are some of the open challenges identified and discussed in this review.  
Conceptualization, T.F., S.C., and A.B.; Methodology, S.C. and A.B.; Investigation, T.F. and A.B.; Data curation, T.F. and A.B.; Formal analysis, T.F.; Visualization, T.F., S.C., and A.B.; Supervision, S.C. and A.B.; Funding acquisition, S.C. and A.B.; Writing--original draft, T.F. and A.B.; Writing--review & editing, S.C. and A.B.  
This work has been funded in part by the Complex Engineering Systems Institute, ISCI (CONICYT: FB0816) and in part by the NIC Labs Chile.  
The authors would like to thank the technical support from the Space and Planetary Exploration Laboratory (SPEL) at Universidad de Chile.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} ACK & Acknowledgement \\ ADCS & Attitude determination and control system \\ ADS-B & Automatic dependent surveillance broadcast \\ AIS & Automatic identification system \\ CDMA & Code division multiple access \\ CRDSA & Contention resolution diversity slotted Aloha \\ CSA & Coded slotted Aloha \\ CSMA & Carrier sense multiple access \\ CSMA/CA & CSMA with collision avoidance \\ CSS & Chirp spread spectrum \\ CTS & Clear-to-send \\ DA & Diversity Aloha \\ DSA & Diversity slotted Aloha \\ E-SSA & Enhanced spread spectrum Aloha \\ ESA & European Space Agency \\ FCC & Federal communications commission \\ FC-TDMA & Fixed competitive TDMA \\ FDMA & Frequency division multiple access \\ GEO & Geosynchronous equatorial orbit \\ GLONASS & Global orbiting navigation satellite system \\ GNSS & Global navigation satellite system \\ GPS & Global positioning system \\ HEO & Highly elliptical orbit \\ ISIC & Iterative soft interference cancellation \\ IRSA & Irregular repetition slotted Aloha \\ IoT & Internet of things \\ ISM & Industrial, scientific and medical \\ \end{tabular}