Prerequisites & Notation

Before You Begin

LEO satellites orbit at ∼7.5\sim 7.5 km/s — an order of magnitude faster than any terrestrial vehicle. At this velocity, Doppler at sub-6 GHz reaches ∼50\sim 50 kHz; at mmWave, ∼500\sim 500 kHz. OFDM simply cannot cope: the subcarrier spacing of 5G NR is 15-120 kHz, so the Doppler is a substantial fraction of a subcarrier. The CommIT contribution of Buzzi-Caire-Colavolpe extends OTFS to this regime, with multi-satellite macro-diversity providing robustness to blockage and beam handover. This chapter develops the LEO-OTFS framework end-to-end.

  • OTFS modulation and detection(Review OTFS Ch. 6, 8)

    Self-check: Can you state the DD input-output relation and basic MP detection?

  • OTFS performance analysis(Review OTFS Ch. 9)

    Self-check: Do you recall full DD diversity order PP and BER scaling?

  • MIMO-OTFS channel tensor(Review OTFS Ch. 16)

    Self-check: Can you write the tensor model with angle?

  • Cell-free massive MIMO with OTFS(Review OTFS Ch. 17)

    Self-check: Do you understand macro-diversity and conjugate BF?

  • Satellite communications basics(Review Telecom Ch. 26)

    Self-check: Are you familiar with satellite orbit types, link budget, and TT&C?

Notation for This Chapter

Symbols introduced for LEO satellite OTFS.

SymbolMeaningIntroduced
vorbitv_{\text{orbit}}Satellite orbital velocity (LEO: ∼7.5\sim 7.5 km/s)s01
horbith_{\text{orbit}}Orbital altitude (LEO: 400-2000 km)s01
θelev\theta_{\text{elev}}Elevation angle from ground station to satellites01
νLEO\nu_{\text{LEO}}LEO Doppler spread: ∼(vorbit/c)⋅f0\sim (v_{\text{orbit}}/c) \cdot f_0s02
SSNumber of visible satellites at time tts03
TvisibilityT_{\text{visibility}}Satellite pass duration (LEO: 5-15 minutes)s01
← Ch 17The LEO Satellite Channel