###### Abstract  
The new generation of capsules that circulate through vacuum tubes at speeds up to 1200 km/h, which is being developed, demands communication systems that can operate at these speeds with high capacity and quality of service. Currently, the two technologies available are the new generation of 802.11 ax networks and 5G NR. Using these technologies at such high speeds in a confined environment requires a careful study and design of the configuration of the network and optimization of the physical interface. This paper describes the requirements for critical and business communications, proposing a WLAN and 5G network design based on the analysis of the propagation characteristics and constraints of vacuum tubes and using propagation measurements and simulations made in similar environments at frequencies of 2.5/5.7/24 GHz. These measurements and simulations show that propagation losses in this environment are low (4-5 dB/100 m), as a consequence of the guided propagation, so that the use of bands is preferred. Finally, considering the propagation constraints and requirements of a Hyperloop system, a complete wireless communication system is proposed using two networks with 802.11 and 5G technology.  
Hyperloop; railway; high speed; HSR; propagation; vacuum train; wireless channel; WiFi; GSM-R; LTE-R; 5G; 5G NR; network architecture; vacuum tube high-speed train; critical communication; Doppler shift; delay spread; MIMO +
Footnote †: journal: Accepted: 8 February 2021  
Concerning wireless communications, HST has to use a cellular network parallel to the line, working with propagation in free space. This network is highly influenced by multipath, interference and other factors [4; 5], which makes it considerably difficult to achieve a high quality of service for broadband communications at speeds of 350 km/h.  
About wireless communications, the confined environment of the steel tube used in Hyperloop allows high-frequency signals to be propagated over very long distances, with losses lower than those of free space thanks to guided propagation [6] and minimizing interferences and multipath. This makes it possible to have high-capacity and high-performance communications with a very low network deployment cost [7], although there is an important challenge that is the speed of the capsule. In summary, the Hyperloop system was designed to overcome the physical limitations present in high-speed rail at speeds higher than 600 km/h [8].  
In this paper, first, we analyze all the aspects of communications for Hyperloop capsules, describing the communications services and applications needed for critical, performance, and business applications. Then, the different wireless communications systems available for the applications and requirements are carefully reviewed considering the influence of the speed and the performance required. Next, the characteristics of the propagation channel are analyzed, considering the environment of the vacuum tubes and the extremely high speed of the capsules. This propagation study is based on measurements made at different frequencies in tunnel environments and simulations carried out with a ray-tracing simulator that allows for modeling these environments. Based on these results, a design of the two communication networks necessary for critical and passenger communications is proposed. Then, propagation models and tools are described, such as simulators, showing some examples of simulations applied to this case, taking into account the problematic characteristics of Hyperloop propagation such as path loss, Doppler, multipath, and MIMO.  
Finally, the conclusions are presented, highlighting the challenges that the development of a communications system for this environment must face.