Satellite Space Division Multiple Access (SDMA) Laboratory Session

A hands-on exploration of SDMA techniques in satellite communication systems for undergraduate electrical engineering students

Laboratory Details

  • Subject: Satellite Communications
  • Duration: 3 hours
  • Level: Undergraduate (Year 4-5)
  • Prerequisites: Basic understanding of satellite communication and multiple access techniques

Equipment Required

  • Computer with MATLAB/Python
  • SDMA simulation software
  • Satellite communication kit (optional)
  • Spectrum analyzer (software-based)
  • Documentation materials

Learning Objectives

  • Understand SDMA principles in satellite context
  • Simulate beamforming and spatial separation
  • Analyze interference patterns in SDMA
  • Compare SDMA with other multiple access techniques

Introduction to SDMA

Space Division Multiple Access (SDMA) is a channel access method used in satellite communications where the satellite's antenna beam is spatially directed to create separate channels. This technique allows multiple users to access the satellite simultaneously by separating them in space using directional antennas or beamforming.

SDMA Concept in Satellite Communications

Interactive visualization of SDMA beamforming. Adjust the controls below to change beam characteristics.

SDMA Beamforming Simulation

Observation: Notice how each beam covers a specific geographical area, allowing multiple users in different locations to communicate simultaneously with the satellite without interfering with each other.

Laboratory Procedure

1

SDMA System Configuration

Configure the simulation parameters for a geostationary satellite serving four different geographical regions. Set the following parameters:

  • Satellite altitude: 35,786 km (GEO)
  • Number of spot beams: 4
  • Beam width: Adjustable (30° default)
  • Frequency band: Ku-band (12-18 GHz)

Safety Note: This is a simulation lab. If using physical equipment, ensure proper handling of RF components and follow laboratory safety protocols.

2

Beam Pattern Analysis

Generate and analyze beam patterns for different antenna configurations. Record the beam characteristics in the table below:

Beam # Beamwidth (°) Gain (dBi) Sidelobe Level (dB) Coverage Area
1 30 42.5 -18 Region A
2 28 43.2 -20 Region B
3 32 41.8 -16 Region C
4 29 42.8 -19 Region D
3

Interference Measurement

Measure co-channel interference between adjacent beams. Adjust beam overlap and observe the effect on signal-to-interference ratio (SIR).

  • Position user terminals at beam edges
  • Measure received signal strength from intended and adjacent beams
  • Calculate SIR for different beam separations
4

Capacity Comparison

Compare the capacity of SDMA with other multiple access techniques (FDMA, TDMA) under the same bandwidth and power constraints.

Calculate spectral efficiency (bps/Hz) for each technique and document your findings.

5

Adaptive Beamforming

Implement an adaptive beamforming algorithm to track moving user terminals. Observe how the beam adjusts to maintain communication link quality.

Advanced Task: For advanced students, implement a Least Mean Squares (LMS) algorithm for adaptive beamforming and compare its performance with fixed beamforming.

Expected Outcomes & Analysis

After completing this laboratory session, students should be able to:

Data Analysis Task: Plot beam patterns for different antenna configurations and calculate the -3dB beamwidth and sidelobe levels. Determine the optimal beam spacing to minimize interference while maximizing coverage.

Discussion Questions

  1. How does SDMA improve spectrum utilization compared to FDMA and TDMA in satellite communications?
  2. What are the main factors that limit the number of beams a satellite can generate simultaneously?
  3. How does beamforming technology enable SDMA in modern satellite systems?
  4. What is the relationship between beamwidth and antenna gain in SDMA systems?
  5. How does rain fade affect SDMA performance differently than other multiple access techniques?
  6. What are the challenges in implementing SDMA for non-geostationary satellite constellations?
  7. How can adaptive beamforming improve SDMA system performance in mobile satellite communications?

Conclusion

This laboratory session has provided hands-on experience with Space Division Multiple Access (SDMA) techniques in satellite communications. Through simulation and analysis, you have explored how spatial separation enables multiple users to access satellite resources simultaneously, significantly improving system capacity compared to conventional multiple access techniques.

SDMA, combined with adaptive beamforming, is a key technology for modern high-throughput satellites (HTS) and next-generation satellite constellations. Understanding these principles is essential for electrical engineers working in satellite communications and wireless systems.