Robust multiple-input multiple-output communications

"Multiple antennas at both the transmitter and receiver is known as multiple-input multiple-output (MIMO) system. This has emerged as the most promising technique for improving the performance of wireless digital transmission systems as well as allowing higher data rates to be obtained for a given bandwidth. A consequence of the MIMO wireless communications revolution is that multipath scattering of the transmitted signal has moved from being a problem to being a valuable resource. This has happened to such extent that MIMO systems have come to rely on this resource. However, away from dense urban and indoor environments such as Australian rural and remote areas with wide open spaces and flat or smooth undulating terrain such rich scattering can be hard to find. This research seeks to develop MIMO schemes which will give robust and reliable perfor?mance in environments that can change rapidly from rich scattering environment to clear line of sight between transmitter and receiver. Wireless communications system which are robust to changing environment conditions are a particular important factor in military communication systems as well as for civilian emergency services. In this work, polarization is proposed as a source of diversity in wireless communications. Polarization diversity is particularly suited to the Australian rural and remote environment where wide open spaces and flat or smooth undulating terrain give rise to line of sight conditions between the transmitter and the receiver. The polarization diversity of transmitted signals is mostly preserved by the line-of-sight environment, presenting an opportunity for transmitter and receiver diversity techniques. Another aspect of the research presented here is the development of fast, fixed complexity, decoding algorithms for space-time codes that are robust to the changing transmission conditions. Reliable high rate transmission over the MIMO system can only be achieved through "space-time coding". The major drawback of a number of potentially useful space-time codes is the high computational complexity of the known decoding algorithms. This is particular true for a number of codes which are best suited to the exploitation of polarization diversity. The existing "fast" decoding algorithm for this decoding problem, the so-called sphere decoder, has performance which depends crucially on the channel conditions. When the channel is close to singular, that is, when the channel between the base station and terminal is close to pure line-of-sight, the sphere decoder defaults to an exhaustive search. If such conditions persist the communication system could be in outage purely due to computational overload. In this project we develop fast decoding algorithms which have fixed complexity across all channel conditions. In particular, we present the fastest known fixed complexity decoding algorithm for the Golden code, an important code used in the WiMax standard for fully mobile internet access"--P. iii.