CAREER: Cooperative Communication Systems: Resource Allocation, Self-Organization, and Synchronization

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The key to reliable communications over wireless channels is diversity. Of the various methods used to achieve diversity, spatial diversity through the use of multiple transmit and/or receive antennas is particularly attractive in that it does not require additional bandwidth or loss of transmission rate. Spatial diversity does, however, require the use of multiple antennas which must be separated by at least a few wavelengths in order to be effective. This physical constraint precludes the use of spatial diversity in many scenarios, but recently, researchers considered this problem in the context of multiuser communication systems in which there may be multiple sources and/or destinations each with only a single antenna. In these types of systems, communicating nodes can form "partnerships" to achieve a new kind of spatial diversity: "user cooperation diversity". Nodes in a partnership pool their antenna resources to form a virtual antenna array and many of the benefits of spatial diversity are achieved without the need for a "real" antenna array.While user cooperation diversity can provide many of the advantages of antenna arrays to devices that would otherwise only have access to a single antenna, the implementation issues are significantly different than those of antenna arrays. Unlike a traditional antenna array, the nodes in a cooperative partnership are at least semi-autonomous in the sense that they each typically have their own local resources, quality-of-service requirements, and timing references. This project is centered around the questions created by the inherent autonomy of nodes in cooperative multiuser communication systems: how to initiate and maintain cooperative partnerships, how to optimally allocate resources in cooperative partnerships, and how to synchronize cooperating nodes.