New CDM-type diversity scheme for broadband MIMO-OFDM system

The paper proposes a new code division multiplexing (CDM)-type diversity scheme for broadband multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. The scheme performs spectrum spreading and despreading using orthogonal spreading codes for multiple transmitting and receiving antennas, and achieves frequency diversity gain by combining despread data. When changing a transmission bit rate by changing the baseband bit rate, or the number of antennas, without changing air interface parameters, such as the OFDM parameters, the proposed scheme just needs to change the spreading factor. In that respect, the proposed scheme has the advantage over the space-time coding (STC)-type diversity scheme which needs to change the STC encoder and decoder in the same case. We evaluated the performance of the proposed diversity scheme in frequency selective fading environments by computer simulation. The 2×1 proposed diversity scheme had a diversity gain of 1.6-3.2 dB, which is comparable gain to the 2×1 STC-type transmission diversity scheme in wireless LAN environments.