Satellite-enabled LTE systems in LEO constellations

Abstract

LTE-based satellite systems in LEO constellations are a promising solution for extending broadband coverage to areas not connected to a terrestrial infrastructure. However, the large delays and Doppler shifts over the satellite channel pose severe technical challenges to a traditional LTE system. In this paper, two architectures are proposed for a LEO megaconstellation realizing a satellite-enabled LTE system, in which the on-ground LTE entity is either an eNB (Sat-eNB) or a Relay Node (Sat-RN). Focusing on the latter, the impact of large delays and Doppler shifts on LTE PHY/MAC procedures is discussed and assessed. It will be shown that, while carrier spacings, Random Access, and RN attach procedures do not pose specific issues, HARQ requires substantial modifications. Moreover, advanced handover procedures will be also required due to the satellites' movement.

LTE‐based satellite communications in LEO mega‐constellations

“…This work is an extension of the study presented by the Authors in “Satellite‐enabled LTE systems in LEO Constellations,” ICC 2017 …”

Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites

“…This could deeply impact the frequency synchronisation of the resources used to transmit through the NR air interface, as discussed in the following sections. In order to assess the impact of Doppler shifts on the NR specifications, we refer to [13], where the authors provided a closed-form expression for the Doppler shift as a function of the satellite orbital velocity (relative to the user terminal) and the elevation angle:…”

“…As expected, the higher the orbit the lower the differential Doppler. The common Doppler can be compensated by means of a GNSS receiver, according to [13]. On the other hand, it is worth recalling that the maximum differential Doppler, according to LTE Doppler constraint, should be below 950 Hz.…”

“…However, to avoid the above issues, significant attention is being gained by Low Earth Orbit (LEO) megaconstellations, i.e., systems in which hundreds of satellites are deployed to provide global coverage, as also demonstrated by recent commercial endeavours. In [13], [14], a mega-constellation of LEO satellites deployed in Ku-band to provide LTE broadband services was proposed and the impact of typical satellite channel impairments as large Doppler shifts and delays was assessed with respect to the PHY and MAC layer procedures. The introduction of SatCom in 5G systems has been preliminarily addressed by the authors in [15], [16], in which the focus was on the PHY and MAC layer techniques that shall cope with satellite channel impairments.…”

“…In this context, it is of outmost importance to assess the impact that these new requirements will have on future 5G Satellite Communications (SatCom). To this aim, in this paper, we move from the analysis performed in [13]- [16] and assess the impact of large delays and Doppler shifts in two scenarios of interest for future 5G systems, one for enhanced Mobile BroadBand (eMBB) services and one for NarrowBand-IoT (NB-IoT), for which significantly different system architectures are considered.…”