Module 07: Starlink Direct to Cell, LTE Roaming, and Mobile Backhaul

Phase: 2 - Acceleration Builds on: Modules 04, 05, and 06

Math You’ll Learn

Calculus I Completion + Calculus II Introduction

You will finish single-variable calculus and start the math needed for accumulated capacity and signal analysis.

• Integrals and the Fundamental Theorem of Calculus - accumulated quantities over time.
  • Starlink application: total data transferred during a satellite visibility window equals the integral of rate over time.
• Average value of a function - average cell capacity during a pass.
• Integration techniques - approximate area under variable-rate curves.
• Sequences and series intro - coding and signal-analysis preparation.
• Doppler/timing budget analysis - rate and accumulated error over time.

After this: You can estimate Direct to Cell contact windows, total data delivered, timing constraints, and backhaul requirements.

Resources:

• Stewart, Calculus: Early Transcendentals, Chapters 5-7
• Starlink Direct to Cell - https://www.starlink.com/business/direct-to-cell
• LTE/EPC architecture references

What You’ll Learn

This module narrows broad 5G NTN study into Starlink Direct to Cell as publicly described: standard LTE phones, onboard satellite eNodeB, roaming-style integration with mobile operators, and laser backhaul.

Direct to Cell Public Architecture

• Existing LTE phones with no special hardware.
• Satellite payload functioning as an eNodeB from the phone’s perspective.
• Roaming-like integration with partner mobile operators.
• Laser backhaul from satellite to the Starlink network.
• Service evolution: text, IoT, voice, data as public roadmap categories.

LTE/EPC Concepts

• UE, eNodeB, EPC, MME, SGW, PGW, HSS, PCRF.
• Attach, authentication, bearer setup, paging, and data transfer.
• S1AP concepts, GTP-U tunneling, Diameter/S6a, DNS, and IPsec tunnels.
• Roaming interfaces and trust boundaries.
• IoT device classes and low-data-rate service design.

Satellite Constraints

• Doppler and timing advance for cellular bands.
• Link budget and antenna constraints for phones.
• Beam footprint, paging area, and mobility/handover.
• Backhaul path from phone to satellite to laser mesh/gateway to partner mobile core.
• Security and lawful-intercept awareness as operational constraints.

C++ and Python Skills

C++ focus: std::thread, std::mutex, condition variables, concurrent state machines.

Python focus: Skyfield, NumPy, timing/capacity analysis, tabular output.

Projects

Project 1: Satellite eNodeB Roaming State Simulator (C++)

Build a simplified Direct to Cell control-flow simulator.

What you’ll build:

• Model UE, satellite eNodeB, backhaul link, and partner core as interacting components.
• Simulate attach, authentication, bearer setup, data transfer, and detach.
• Add variable satellite backhaul latency and short degraded periods.
• Log control-plane events, bearer state, and data-plane availability.
• Use threads or an event-loop style to model concurrent actors.

C++ skills used: threads, mutexes, condition variables, state machines, structured logs.

Toolkit: Add DirectToCellModel.

Project 2: Direct-to-Cell Doppler and Capacity Analyzer (Python)

Analyze feasibility constraints.

What you’ll build:

• Compute visibility windows for a satellite over a user location.
• Estimate Doppler and timing-advance ranges for LTE-band service.
• Integrate rate over a pass to estimate total bytes transferred.
• Compare IoT, text, voice, and low-rate data demand profiles.
• Plot contact duration, Doppler, rate, and accumulated data.

Python skills used: Skyfield, NumPy, matplotlib, numerical integration.

Technology Reference

Where This Tech Is Used

Books and Resources