The idea of using multiple transmit and receive antennas in future wireless communication systems to accommodate high data rate has attracted considerable attentions recently. A challenging problem is to develop new coding and modulation methods to exploit all of the diversities available in space, time and frequency domains. In case of frequency non-selective fading channels for narrowband transmission, diversities are available only in space and time domains. The coding approach that is developed for this scenario is termed as space-time (ST) code. First, we will briefly review some of existing space-time block codes (STBCs) that can guarantee full diversity in space and time domains. Then, we will focus on the STBCs from orthogonal or block-orthogonal designs. These codes not only achieve full diversity, but also have a very simple maximum-likelihood (ML) decoding algorithm. Finally, we will talk how to combine orthogonal or block-orthogonal designs with sphere packing to further increase the coding advantage.

In case of frequency selective fading channels for broadband wireless communications, there is additional frequency diversity due to the multi-path fading. A mature technique to mitigate the frequency selectivity is to use OFDM. We will discuss space-frequency (SF) and space-time-frequency (STF) coding strategies for MIMO-OFDM systems. The basic idea of SF coding is to encode the source data stream over the transmit antennas and the OFDM tones, but restricting the codewords within one OFDM block period. The problem is how to design SF codes to achieve the spatial and frequency diversities available in MIMO frequency selective channels. First, we will briefly review previous works on SF coding. Then, we will introduce a systematic design method to construct full-diversity SF codes by taking advantage of the existing ST codes and discuss an approach to design SF block codes that can guarantee full-rate full-diversity transmission in MIMO-OFDM systems. Finally, if coding delay is allowed, we will discuss how to obtain a STF code that reaches the maximum achievable diversity in space, time, and frequency.

Professor K. J. Ray Liu received the B.S. degree from the National Taiwan University in 1983, and the Ph.D. degree from UCLA in 1990, both in electrical engineering. He is a Professor and Director of Communications and Signal Processing Laboratories of Electrical and Computer Engineering Department and Institute for Systems Research of University of Maryland, College Park. His research contributions encompass broad aspects of wireless communications and networking; information security; multimedia communications and signal processing; signal processing algorithms and architectures; and bioinformatics, in which he has published over 300 refereed papers.

Dr. Liu is the recipient of numerous honors and awards including IEEE Signal Processing Society 2004 Distinguished Lecturer, the 1994 National Science Foundation Young Investigator Award, the IEEE Signal Processing Society's 1993 Senior Award (Best Paper Award), IEEE 50th Vehicular Technology Conference Best Paper Award, Amsterdam, 1999, and EURASIP 2004 Meritorious Service Award. He also received the George Corcoran Award in 1994 for outstanding contributions to electrical engineering education and the Outstanding Systems Engineering Faculty Award in 1996 in recognition of outstanding contributions in interdisciplinary research, both from the University of Maryland. Dr. Liu is a Fellow of IEEE. Dr. Liu is the Editor-in-Chief of IEEE Signal Processing Magazine and was the founding Editor-in-Chief of EURASIP Journal on Applied Signal Processing. Dr. Liu is a menber of the Board of Governors and has served as Chairman of the Multimedia Signal Processing Technical Committee of the IEEE Signal Processing Society.