Space-time codes in wireless communications

The need to provide reliable high data rate communication over the wireless channel has led to the development of efficient modulation and coding schemes. Diversity (time, frequency, space, polarization, angle) is an effective method to combat fading and improve the link reliability of the wireless channel. Time and frequency diversity lead to loss in bandwidth efficiency. However, by employing multiple antennas at the transmitter and/or at the receiver, spatial diversity mitigates fading without sacrificing the precious bandwidth resource. It is difficult to implement receive diversity in the downlink because of size and power limitations on the portable/mobile terminal. This has motivated the use of transmit diversity schemes wherein multiple antennas are used at the transmitter for the downlink transmission from the base station to the portable terminal. In space-time coding, intelligent coding of symbols across space and time can be done to reap the advantages due to coding and diversity. The coding in space is obtained by using multiple antennas at the transmitter. The article discusses aspects of space-time coding. This is an important research topic in the design of emerging wireless systems. Deployment of wireless systems using space-time codes is expected in the near future.