Space Division Multiple Access (SDMA)
Space division multiple access (SDMA) controls the radiated energy for each user in space.SDMA serves different users by using spot beam antennas. These different areas covered by the antenna beam may be served by the same frequency or different frequencies
- SDMA utilizes the spatial separation of the users in order to optimize the use of the frequency spectrum
- With SDMA all users within the system would be able to communicate at the same time using the same channel.
- It uses a Smart Antenna technique that employs antenna arrays backed by some intelligent signal processing to steer the antenna pattern in the direction of the desired user and places nulls in the direction of the interfering signals.
- Since these arrays can produce narrow spot beams, the frequency can be re-used within the cell as long as the spatial separation between the users is sufficient.
- Figure shows three users served by SDMA using the same channel within the cell
Figure 7.9 SDMA
- SDMA utilizes the spatial separation of the users in order to optimize the use of the frequency spectrum.
- When different areas are covered by the antenna beam, frequency can be re-used, in which case TDMA or CDMA is employed, for different frequencies FDMA can be used.
- Sectorized antennas may be thought of as a primitive application of SDMA.
- The limiting case of infinitesimal beam width and infinitely fast tracking ability, adaptive antennas implement optimal SDMA, thereby providing a unique channel that is free from the interference of all other users in the cell.