Transmit diversity and transmit adaptive arrays for broadband mobile OFDM systems

This paper explores the performance of several frequency-domain transmit array processing strategies for broadband mobile turbo-coded OFDM systems. We consider transmit adaptive array (TXAA) techniques (also known as maximal ratio transmission) with various assumptions on mobile- to-base channel response feedback in a two-transmit antenna OFDM system. We compare the performance of such techniques with the well-known Alamouti diversity scheme, which requires no channel response knowledge at the transmitter. The various techniques are compared with both simulated channels and with channel responses measured with an experimental broadband mobile MIMO-OFDM system. With perfect instantaneous feed- back of the matrix frequency response, the TXAA schemes have the expected 3 dB gain over the Alamouti scheme. However, if the transmit array cannot track the time and frequency selectiv- ity of the channel, the Alamouti method can in some cases out- perform the transmit adaptive array techniques.