  Combined with space-time coding, the orthogonal frequency division
multiplexing (OFDM) system explores space diversity. It is a potential scheme
to offer spectral efficiency and robust high data rate transmissions over
frequency-selective fading channel. However, space-time coding impairs the
system ability to suppress interferences as the signals transmitted from two
transmit antennas are superposed and interfered at the receiver antennas. In
this paper, we developed an adaptive beamforming based on least mean squared
error algorithm and null deepening to combat co-channel interference (CCI) for
the space-time coded OFDM (STC-OFDM) system. To illustrate the performance of
the presented approach, it is compared to the null steering beamformer which
requires a prior knowledge of directions of arrival (DOAs). The structure of
space-time decoders are preserved although there is the use of beamformers
before decoding. By incorporating the proposed beamformer as a CCI canceller in
the STC-OFDM systems, the performance improvement is achieved as shown in the
simulation results.
