Bandwidth-effecient cooperative diversity techniques for wireless systems

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The wireless radio channel poses a severe challenge as a transmission medium for reliable high-speed communications. As a signal propagates through a wireless channel, it experiences random fluctuations in time due to changing reflections and attenuation. This random variation of the channel quality is generally referred to as fading and it is the main reason for poor performance of wireless transmission. Diversity offers an effective solution to combat fading by providing the receiver with multiple copies of the same information that are effectively transmitted with independent channel gains. Spatial diversity with the use of multiple transmit and/or receive antennas is the most effective and attractive diversity method. Achieving the full diversity gain, however, requires multiple antennas be placed sufficiently far apart, which is problematic for size-limited terminals. An alternative approach to provide spatial diversity without using multiple antennas is cooperative communications. This approach is motivated by the fact that the wireless channels from different users to the destination are likely to fade independently and users can assist each other with the transmission of their messages. Because information is transmitted multiple times, once from the user itself and then from the partnering users (or relays), spatial diversity can be achieved. Cooperative diversity has been recognized as a very promising solution for future wireless ad-hoc and wireless sensor networks. Developing practical transmission schemes to realize cooperative diversity is the main subject of this proposed research, which includes both user-cooperation diversity and cooperative diversity with the help of relays and network coding. Different from the previous works, our emphasis is placed on the high bandwidth efficiency of the cooperative schemes in order to support high data-rate transmission. The research work includes both analysis and computer simulation to develop and evaluate the performance of the new techniques. The success of the proposed research program should enhance Canada's competitive position in providing advanced broadband wireless communications systems.