SDMA Basics and Types: Space Division Multiple Access

SDMA stands for Space Division Multiple Access. It’s a technique used to enhance access to satellite resources, particularly scarce resources like satellite bandwidth and antenna capacity. Satellite bandwidth depends on the number and distribution of transponders. The efficient use of antennas is also critical.

Let’s explore how antennas can be utilized effectively through polarization and spot beams with narrower beamwidths.

Frequency Reuse Through Polarization

If a satellite possesses two antennas – one vertically polarized and the other horizontally polarized – two electromagnetic signals with the same RF carrier frequency can be transmitted to the same satellite. This frequency re-use concept helps use satellite bandwidth effectively.

Spot Beams

Smaller antennas mounted on the satellite can individually capture EM waves from earth stations/VSATs within their line of sight.

Multiple Satellites

If more than one satellite is in the line of sight of an earth station/VSAT, the VSAT station can access each individual satellite by changing the beam direction or the RF carrier frequency.

All these techniques provide spatial separation, often coupled with frequency, time, or code division.

Types of SDMA

Here are the different types of SDMA combinations:

• SDMA with FDMA
• SDMA with TDMA
• SDMA with SS and FDMA
• SDMA with SS and TDMA/FDMA
• SDMA with BH or TH with TDMA
• SDMA with SS or FH with CDMA