Entwurf und Analyse optimaler Übertragungsverfahren für Mehrnutzer-Kommunikationssysteme mit adaptiven Sende- und Empfangsstrategien sowie Anpassung der Sendeleistungen
Zusammenfassung der Projektergebnisse
Future wireless transmission systems place greater demands on the user's Quality of Service (QoS). However, the crosstalk among users (interference) degrades the system performance. Techniques for avoiding or suppressing interference, and resource allocation (the allocation of transmission powers under consideration of the existing interference) are key technologies for future wireless standards. One major outcome of the project is a theoretical framework for modeling certain interference-induced performance tradeoffs in wireless systems. By defining the interference as a function of transmission powers, it is possible to describe the typical behavior of various types of wireless systems. Such a generic approach has the advantage of being applicable to many different kinds of system layouts. At the same time, the framework is specific enough to allow for the development of iterative algorithms for resource allocation. Another main outcome of the project was the development of new transmit and receive strategies to reduce and manage the interference and different iterative algorithms for transceiver optimization were proposed. Basically, these algorithms were based on an alternating optimization approach, i.e., optimizing one of the variables while fixing the others fixed. During the optimization procedure, the uplink/downlink duality plays an important role, since the duality ensures that the same performance in terms of MSE/SINR can be achieved in both uplink and downlink. The algorithms are able to include multiantenna (MIMO) links, as will be seen in future standards. The results extend the state-of-art research described in the project proposal. The duality-based approach to transmitter optimization was used before in information-theoretic publications on MIMO channels. In this project, we have extend this optimization principle to MMSE-based designs, which leads to new iterative algorithms, which outperform state-of-the art techniques. This is demonstrated by numerical simulations. The development of the interference calculus largely extends the current state-of-the-art in the area of interference functions. The theory provides a theoretical background for various types of multiuser problems, where users are coupled by interference. This framework allows for a deeper understanding of the effects of interference. This new insight and the resulting algorithmic techniques serve as a basis for future research in this area. The theoretical framework shows how the "structure" of the interference coupling can be exploited. Important properties are comprehensiveness (free disposibility of utility) and convexity. In the project we have fully characterized these properties in the context of interference functions and utility sets. This paves the way for the development of new resource allocation techniques exploiting these properties. Convexity is often considered as the dividing line between "easy" and "difficult" optimization problems. Our work shows that certain monotonicity properties referred to as "comprehensiveness" are sufficient for providing a basis for iterative algorithms, jointly optimizing resource allocation and adaptive receive/transmit strategies in multiuser networks. Some cases, like downlink or uplink channels were already investigated in the project. There is much room for further research, extending these principles to more general types of networks. A big challenge lies in the joint optimization of decentralized multicellular networks, where uncoordinated cells cause mutual interference. This is an emerging research focus, especially since the importance of interference coordination was recognized in recent years. As systems tend to accomodate more and more users, and data rate demands go up, system designers are trying to approach the physical limits of such networks. The ultimate limit ofa multibase wireless system is still not known, because of the high degree of complexity. Therefore, a fundamental theoretic understanding is of utmost importance. With the proposed interference calculus, it is possible to handle this complexity in an analytical way. By abstracting away from technical details, we are able to optimize the system as a whole, by focusing on the core properties of interference coupling. The theoretical results from this project can be seen as a theoretical basis for analyzing and optimizing multicellular systems. This approach can be combined with game-theoretical strategies, which are gaining more and more interest from the wireless communication community in recent years. The ultimate goal should be a self-organizing system, where interference is handled in a fully adaptive manner, allowing for interoperability of different user, systems, and standards. This would create the basis for new high-rate wireless services which are currently not feasible because of current performance limits. However, much more research is needed in order to achieve this challenging long-term objective.
Projektbezogene Publikationen (Auswahl)
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"Downlink MMSE transceiver optimization for multi-user MIMO systems: MMSE balancing," IEEE Trans. Signal Processing, vol. 56, no. 8, pp. 3702-3712, Aug. 2008
Shuying Shi, Martin Schubert, and Holger Boche
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"MMSE optimization with per-base-station power constraints for network MIMO systems." in Proc. IEEE Int. Conf. on Comm. (ICC), Beijing, China, June 2008
Shuying Shi, Martin Schubert, and Holger Boche
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"Per-antenna power constrained rate optimization for multiuser MIMO systems," in ITG/IEEE Workshop on Smart Antennas (WSA), Darmstadt, Germany, Feb. 2008
Shuying Shi, Martin Schubert, and Holger Boche
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"Physical layer multicasting with linear MIMO transceivers," in Conf. on Information Sciences and Systems (CISS), Mar. 2008
Shuying Shi, Martin Schubert, and Holger Boche
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"Rate optimization for multiuser MIMO systems with linear equalization," IEEE Trans. Signal Processing, vol. 56, no. 8, pp. 4020-4030, Aug. 2008
Shuying Shi, Martin Schubert, and Holger Boche
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Transceiver Design for Multiuser MIMO Systems, Ph.D. thesis. Technische Universität Berlin, 2009
Shuying Shi
