Wireless communications for frequency-selective
fading channels is realized by employing a
system including
orthogonal frequency division multiplexing (OFDM) in combination with an at least two antenna
transmit diversity arrangement. Specifically, OFDM converts a multipath channel into a plurality of
narrowband subchannels each having flat
fading. Then, the signals on the same frequency subchannels of the at least two antennas are grouped together. Considering a first frequency subchannel, during a first OFDM time interval, a first
signal and a second
signal are transmitted on the first frequency subchannel from a first antenna (0) and from a second antenna (1), respectively. During a second OFDM time interval, a reverse sign (−) complex conjugate of the second
signal and a complex conjugate of the first signal are transmitted from the first antenna and the second antenna, respectively. In a specific embodiment of the invention, reduced complexity in the implementation is realized by a
reverse order complex conjugate and a
reverse order, reverse sign (−) complex conjugate and judicious selection of the processed data signals in order to transmit the appropriate ones of the signals during the first and second OFDM intervals. Again, if the channel remains constant over the two OFDM intervals, diversity combination is realized for each frequency subchannel. In another embodiment of the invention, antenna-group hopping is employed in conjunction with
pairing in time of the OFDM frequency subchannel signals to realize increased
transmit diversity without rate loss.