Study on feasibility of SATCOM for railway communication

Final Report
C.1.1
C.1.1.1
Additional information useful for the assessment
Delay study
Due to Iridium NEXT architecture where user information can travel by different satellites by means of Inter Satellite Links (ISL), delay experienced by a
user will depend on each specific case. Considering a generic situation in which three satellites are needed to travel from the satellite user to the
Gateway (for example), next approximation is done:
Where,
T tx is the transmission time for a given packet
T up is the propagation delay from ground to the overhead satellite
T cross is the propagation time between satellite cross links
T sat is the processing delay per satellite
This parameter is considered negligible
T down is the propagation time from the satellite to the ground
N is the number of satellite in the node
In order to provide an example, following data is assumed:
Data packet: 120 bytes
Transmission in return link: 512 kbps
Transmission in forward link: 1.5 Mbps
Average number of ISL (Inter-Satellite Links) used: 2 (i.e. 3 satellites)
Satellite processing delay can be considered negligible
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Doc.Nº: SRAIL-FNR-010-IND
Edit./Rev.: 1/1
Date: 16/02/2017
Page 223 of 285