ITR: Differential Modulation in Space and Time

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One of the goals of third and fourth generation cellular systems is to provide broadband data access to highly mobile users. Space-time transmission strategies, which exploit the presence of multiple antennas at the transmitter or receiver, have been cited recently as one of the key technologies needed to achieve this goal. While there has been great progress on space-time coding and modulation in recent years, most of this work has assumed that perfect channel estimates are available at the receiver. In certain situations, however, it may be difficult or costly to obtain accurate channel estimates. The goal of this project is to design new space-time modulation strategies that do not require channel estimates at the transmitter or receiver. The core idea is a new and general architecture for differential modulation using multiple antennas, which can be applied to any number of antennas and any signal constellation. Modulation techniques adhering to this architecture can be demodulated coherently or noncoherently. These techniques permit the receiver to exploit accurate channel estimates when they are available, but performance degrades only slightly when estimates are not available. The tools developed here also over a fresh perspective on pilot-assisted space-time modulation and provide a systematic way to jointly design the training symbols, receivers, and modulation schemes. This project addresses a broad spectrum of issues, including fundamental performance limits, new modulation and coding techniques, and low-complexity receivers. The ultimate goal of this work is to more fully exploit the potential of multi-antenna radio channels, and in the process reduce the power and bandwidth requirements of wireless communication.