LTE-based Satellite Communications in LEO Mega-Constellations

TL;DR

This paper explores LTE-based satellite communication architectures in LEO mega-constellations, analyzing the impact of satellite channel impairments and proposing modifications to LTE procedures for effective integration.

Contribution

It introduces two satellite-enabled LTE architectures and assesses the effects of delays and Doppler shifts, highlighting necessary protocol modifications.

Findings

HARQ requires significant modifications

Carrier spacing and attach procedures are unaffected

Advanced handover procedures are necessary due to satellite movement

Abstract

The integration of satellite and terrestrial networks is a promising solution for extending broadband coverage to areas not connected to a terrestrial infrastructure, as also demonstrated by recent commercial and standardisation endeavours. However, the large delays and Doppler shifts over the satellite channel pose severe technical challenges to traditional terrestrial systems, as LTE or 5G. In this paper, two architectures are proposed for a LEO mega-constellation realising a satellite-enabled LTE system, in which the on- ground LTE entity is either an eNB (Sat-eNB) or a Relay Node (Sat-RN). The impact of satellite channel impairments as large delays and Doppler shifts on LTE PHY/MAC procedures is discussed and assessed. The proposed analysis shows 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.