Principle : The narrow beam of radio waves is aimed at particular part of space. The same channel is reused over the another narrow beam aimed at another part of the space. This division of space in different directions of base station through highly directional beams is called Space Division Multiple Access (SDMA).

As shown above the space is divided and three channels are transmitted on same frequency.

Advantages

1. It saves the channel bandwidth.
2. Improves the utility of bandwidth.

Role of SDMA in wire and Wireless Communications

• SDMA can be used for mobile communication and satelite communication. The satelite dish antennas transmit signals to various zones on earth’s surface. These antennas are highly directional. Hence same frequency can be used for multiple surface zones, as shown in Fig.
• As shown in Fig, area A₁ and area A₃ are physically apart. Hence same channel-1 is used to send signals to A₁ and A₃ with the help of highly directional atennas. There will be no signal interface between the signals of areas A₁ and A₃.

• Satellite based SDMA required careful selection of zones (area) for each transmitter and precise antenna alignment to avoid co-channel and Fig. Frequency reuse by SDMA interchannel interference.
• In cellular (mobile) communiation, the power of the transmitting antennas is to be controlled to avoid the co-channel and interchannel interference.
• In cellular communication Space Division Multiple Access (SDMA), there are multidirectional horn antennas at the base station (BS). The base station identifies mobile users by means of their spatial signatures.
• The base station has complete control over the power of all the transmitted signals on the forward link. The transmitted power from each mobile user is dynamically controlled to avoid inter channel interference.
• The base station detects the power level from each mobile user and connects it. Adaptive antennas are also used.