Abstract:
The wireless communication channel suffers from many impairments such as the
thermal noise often modeled as Additive White Gaussian Noise (AWGN), the path
loss in power as the radio signal propagates, the shadowing due to the presence of
fixed obstacles in the radio path, and the fading which combines the effects of
multiple propagation paths and the rapid movement of mobile units reflectors.
Deploying multiple antennas at the transmitter has been shown to increase
diversity and therefore improve signal quality with increased throughput. This
paper proposes a transmit diversity scheme, where multiple transmit antennas are
used at the transmitter. A feedback path is provided from the receiver to
communicate the channel seen by the receiver to the transmitter (closed-loop).
When closed-loop transmit diversity is applied, the symbol from each transmit
antenna is multiplied with a complex number corresponding to the inverse of the
phase of the channel so as to ensure that the signals add constructively at the
receiver. From this research it was found that sending the same information on
multiple transmit antenna does not always provide diversity gain. However if the
transmitted symbols are multiplied by a complex phase to ensure that the phases
align at the receiver, there is diversity gain though the bit error rate performance
seems to be slightly poorer than the maximal ratio combining case.
