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Dynamic Directional RTS/CTS

The Dynamic Directional RTS/CTS (Request To Send/Clear To Send) protocol in Wireless Local Area Networks (WLANs) is designed to prevent data collisions in the wireless medium. First the transmitting station will send a RTS packet that includes an ID of the intended receiving station and a notification of how long the transmission will take. The receiving station will then respond with a CTS packet acknowledging that it is ready to receive the data. This packet also contains the information about how long the transmission will take. At this point any other station that has received either of these packets knows not to transmit any information for the specified amount of time.

The RTS/CTS protocol was originally designed with the assumptions that all of the stations have omni-directional antennas with the same power. At the time this was a reasonable assumption. Now, with the use of multi-antenna stations and adaptive beamforming, this can be improved upon. The transmitting station can reduce its effect on the medium by transmitting the RTS packet with a dynamically chosen directional beam pattern that targets the intended recipient. The receiving station can then transmit its CTS in a omni-directional pattern. This will inform other stations to not transmit anything in that direction. But, this allows other stations to select radiation patterns that attenuate the signal in the direction that the CTS frame arrived from, and transmitting in another direction.

By dynamically choosing radiation patterns for transmission of RTS and data packets, it is possible to reduce interference between stations in a WLAN. This increases how much data can be transferred on the network by allowing stations that are not involved in one data exchange to initiate their own data exchange without interfering. This benefit comes at a cost: added complexity. Each station must choose the optimal antenna configuration to transmit to a given receiver. Additionally, they must be able to choose a beam pattern that not only directs the signal towards one receiver, but at the same time keeps the signal from being transmitted in another direction.

VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713