# Spatial division multiple access  If you have n transmit antennas and n receive antennas, you can in theory separate into n spatial streams. n parallel channels - one per user. More antennas = more users! ## What does it do Control the radiated energy for each user in space Imagine a laser beam - transmit the energy in a focused beam and separate in a spatial domain. The [base station](Base%20station.md) uses same/different frequencies to serve multiple users simultaneously. ## Static Approach [Sectoring](Sectoring.md) ## Dynamic [Beamforming](Beamforming.md) ## Ultimate goal Create parallel spatial data pipes (no multiuser interference) Might need [interference cancellation](interference%20cancellation.md) ## Advantages Many advantages (I-phone has 2 transmit antenna and 2 receive antennas) - Users can be served concurrently by the same frequency or different frequencies  - Spatial degrees of freedom can be exploited for resource allocation ([multiplexing](multiplexing.md) and [diversity scheme](diversity%20scheme.md) gains) ## Disadvantages - More antennas needed - More power consumption - Need to keep tracking the channel - High signalling overhead (not related to the communication, just as assistance)  - Not suitable for small devices (yet) - Energy consumption for non-radiating components (transmit filter, mixer, frequency synthesizer, [DAC](DAC.md)) [^1] # References [^1]: