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| Directional distributed coordination function (D-DCF), a modified medium access control protocol of IEEE 802.11, is proposed in this paper to support smart adaptive array antennas over WLAN. D-DCF based on hybrid virtual carrier sense (HVCS) mechanism can coexist with DCF. A smart antenna has omni-directional and directional mode in operation. In D-DCF, before sending any data-frames, the sender and receiver node transmit a pilot sequence by means of omni-directional request-to-send/clear-to-send (ORTS/OCTS) handshake mechanism. Based on the pilot, the directional beam can be formed by the smart antenna. Then the node can transmit its data-frame in directional mode. The other nodes save the transmission time between the sender and receiver in omni-directional mode in their network allocation vectors. When the sender and receiver communicate in directional mode, the other nodes can contend channel to send their data-frames. Hence, D-DCF supports space division multiple access (SDMA). Moreover, D-DCF supports both forward and backward transmission in one access period. Simulation results show that D-DCF can support smart antennas effectively and provide much higher network throughput, lower delay, jitter and packet-loss-rate than DCF does. |
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| Keywords:WLAN, Smart Adaptive Array Antennas, MAC, SDMA, TDD |
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