Study on feasibility of SATCOM for railway communication

Final Report
T down is the propagation time from the satellite to the ground
In order to provide an example, following data is assumed:
Data packet: 120 bytes
Transmission in return link: 500 kbps
Transmission in forward link: 2 Mbps
Then, the end-to-end transmission packet delay in return link is:
T tx = packet_size / throughput = 120 bytes / 500000 bps = 1.92 ms
T up = T down = sat_distance / speed = 36000 km / 300000 km/sec = 120 ms
This result shows that the very big part of transmission delay in a GEO / Ku-band (and also Ka-band) system is due to the GEO satellite. The data rate
could be even greater than the considered one, but transmission delay will not be smaller than the ~240 ms, i.e. the time due to the GEO satellite.
Doc.Nº: SRAIL-FNR-010-IND
Edit./Rev.: 1/1
Date: 16/02/2017
Page 276 of 285