Backward compatible transmit diversity by antenna selection for IEEE 802.11a devices

802.11n MIMO system should be built upon 802.11a SISO system. This paper suggests simple way to implement 802.11a backward compatible transmitter diversity using multiple antennas in an 802.11a/802.11n device. This paper also presents the method of antennas selection and shows the improved results of simulation. In transmitter, the channel state information (CSI) can be measured by using preamble of ACK response or of pre-received packet at each antenna. With this CSI, selecting an antenna which has the largest channel gain for every subcarrier enables transmitter diversity implementation.