Abstract
SummaryFrom a geostationary Earth orbit (GEO) satellite's perspective, a low Earth orbit (LEO) satellite is visible on more than half of its orbit. Albeit the free‐space loss of an inter‐satellite link is much higher than the one of a direct ground link, considerable data rates and download volumes can be achieved. In this paper, we describe the system architecture of an integrated approach for a data relay satellite system and the development of LEO satellite and ground station modems. The approach allows serving several small and inexpensive LEO satellites at the same time both with low rate telemetry/telecommand links and with high rate download of sensor data.
Highlights
There is a plethora of applications for low Earth orbit (LEO) satellites
In order to support parallel communication to several LEO satellites even in one beam, a multi-frequency time division multiple access (MF-time-division multiple access (TDMA)) scheme is used on the high rate links and on the low rate telemetry links, whereas a time-division multiplexing (TDM) scheme is used on the low rate telecommand link
In the modulation/mapping block, the data frames/headers are mapped to binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), or 8-phase-shift keying (8-PSK) modulation schemes and the frame components are combined to physical layer (PL) frames, that are forwarded to the digital signal forming
Summary
There is a plethora of applications for low Earth orbit (LEO) satellites. A non-exhaustive list of examples includes remote sensing with passive and/or active sensor systems, communication payloads for ground-to-ground or air-to-ground data exchange, various scientific missions like space observatories, and academic micro/nano/pico satellite projects for the in-orbit verification of technologies. In comparison to geostationary Earth orbit (GEO) satellites both free-space loss and latency of direct links between a LEO satellite and a ground station are considerably smaller, but a single. A GEO data relay increases the access time to a satellite on a polar orbit by a factor of around 10 to 15 in comparison to a single ground station. TDRSS satellites can receive data by means of electronically steerable antenna beams in the S-band from five senders simultaneously (ground-based beam-forming), while transmitting data to one [6]. An advanced DLL protocol realizes flexible multi-frequency time-division multiple access (TDMA) and multiplexing schemes and supports both simultaneous bidirectional low rate TT&C links and unidirectional high rate download of sensor data with defined quality of service (QoS) levels. We describe the demonstration of the complete transmission chain and in the conclusion we summarize the paper
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