Satellite TDMA Simulation Laboratory Session

For ECE 514E - Radar & Satellite Engineering

Laboratory Objectives

This laboratory session introduces Time Division Multiple Access (TDMA) as used in satellite communication systems. By the end of this session, students will be able to:

  1. Explain the fundamental principles of TDMA in satellite communications
  2. Understand the frame structure and timing considerations in satellite TDMA
  3. Analyze the trade-offs between number of stations, slot duration, and guard time
  4. Calculate system capacity and efficiency for different TDMA configurations
  5. Identify practical challenges in implementing satellite TDMA systems

Background Theory

Time Division Multiple Access (TDMA) is a channel access method that allows multiple ground stations to share the same satellite transponder by dividing access into different time slots. Each station transmits in rapid succession, one after the other, each using its own time slot.

Key Concept: In satellite TDMA, multiple earth stations share the same satellite transponder by transmitting bursts of data in assigned time slots within a repeating TDMA frame.

TDMA Frame Structure

A TDMA frame consists of:

Satellite-Specific Considerations

Satellite TDMA must account for:

Pre-Laboratory Questions

Question 1: Calculate the round-trip propagation delay for a signal traveling to a geostationary satellite at 36,000 km altitude and back to Earth. (Speed of light = 3×10⁸ m/s)

Question 2: Explain why guard time is necessary in TDMA systems and how it relates to satellite propagation delay.

Question 3: If a TDMA frame is 2 ms long and contains 10 equal time slots, what is the maximum data rate per station if each slot can carry 1000 bits?

TDMA Simulation Experiment

Use the interactive simulation below to explore how different parameters affect a satellite TDMA system. Adjust the settings and observe the changes in the visualization.

Simulation Controls

System Statistics

Frame Efficiency: 85.0%

Effective Data Rate: 425.0 kbps

Total Delay (Tx + Propagation): 245.0 ms

Slot Duration: 19.0 ms

Satellite TDMA Visualization

SAT

TDMA Frame Timeline

Transmission Log

> System initialized with 5 ground stations

> Frame duration: 100 ms, Guard time: 5 ms

> Ready to start simulation...

Note: In actual satellite TDMA systems, precise synchronization is critical. The satellite provides a reference burst that all ground stations use to synchronize their transmissions to account for varying propagation delays.

Laboratory Procedures

Part 1: Understanding Frame Structure

  1. Set the number of ground stations to 4 and frame duration to 200 ms.
  2. Start the simulation and observe how each station transmits in its assigned time slot.
  3. Calculate the slot duration for each station (accounting for guard time).
  4. Record the system efficiency displayed in the statistics panel.

Part 2: Effect of Guard Time

  1. Keep the frame duration at 200 ms and stations at 4.
  2. Vary the guard time from 2 ms to 15 ms in increments of 3 ms.
  3. Record the system efficiency for each guard time value.
  4. Explain the trade-off between guard time and system efficiency.

Part 3: Propagation Delay Analysis

  1. Set propagation delay to 240 ms (typical for GEO satellites).
  2. Observe the total delay (transmission + propagation) in the statistics.
  3. Reduce propagation delay to 10 ms (simulating a LEO satellite).
  4. Compare the impact on total system delay and discuss implications for real-time applications.

Part 4: System Capacity

  1. With a fixed frame duration of 100 ms and guard time of 5 ms, increase the number of stations from 2 to 10.
  2. Record the effective data rate per station as the number of stations increases.
  3. Determine the maximum number of stations that can be supported while maintaining at least 10 ms slot duration.

Post-Laboratory Questions

Question 1: Based on your simulation results, what is the relationship between guard time and system efficiency? Why is guard time necessary despite its negative impact on efficiency?

Question 2: How does propagation delay affect TDMA synchronization? What techniques can be used to compensate for varying propagation delays to different ground stations?

Question 3: Compare TDMA with FDMA (Frequency Division Multiple Access) for satellite communications. What are the advantages and disadvantages of each?

Question 4: Design a TDMA frame structure for a satellite system that needs to support 8 ground stations with varying traffic requirements. Two stations need twice the capacity of the others. The total frame duration should be 125 ms with a guard time of 2 ms between bursts.

References & Further Reading