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W. Konrad:
"Design of an Adaptive Antenna Demonstrator for Digital Beamforming";
Supervisor, Reviewer: E. Bonek, A.L. Scholtz; Institut für Nachrichtentechnik und Hochfrequenztechnik, 2003.

The application of adaptive antennas to mobile communications has attracted considerable interest in the last decade. Adaptive antennas, in a broad sense, implement spatial filtering by means of beamforming, using an antenna array with a small number of antenna elements at the base station. In uplink, the received signals of all antenna elements are complexly, and adaptively weighted according to some prescribed performance criterion, to either enhance the carrier-to-interference-ratio for the reception of a single mobile´s signal, or, ultimately, serve many mobiles, transmitting at the same time, and at the same frequency, but spatially separated, by utilizing the spatial filter to separate the mobile´s signals, thus implementing spatial-domain-multiple-access, SDMA. To establish the performance criterion, adaption algorithms need a known reference for operation, either a training sequence embedded in the received signals (temporal reference), or the direction-of-arrival of the impinging signals (spatial reference), no explicit reference, except some knowledge of the impinging signal´s properties (blind algorithms), or combinations thereof.
Algorithm research for adaptive antennas is a vivid and ongoing discipline, as new mobile communication applications, and requirements emerge. While performance evaluation of these algorithms is possible by computer simulation to a certain extent, an experimental assessment by means of a dedicated adaptive antenna testbed, or demonstrator, reveals the real-world performance, and allows the examination and the demonstration of new ideas.
In this thesis, I present the design of an adaptive antenna demonstrator for digital beamforming, that is especially targeted at algorithm evaluation and demonstration. The system works in the 2.45 GHz ISM - band according to a modified DECT- air interface. A nine- channel transceiver unit allows the real-time reception of the signals of several mobiles via a 9 - element antenna array, and is interfaced to an embedded personal computer, where off-line digital beamforming or direction-of-arrival estimation is performed. The demonstrator system implements a digital quadrature demodulation / modulation concept, i.e. passband sampling of the received signals at the second intermediate frequency of the double heterodyne receivers allows further signal processing in the digital domain. For transmitting downlink information to the mobiles, necessary for synchronization to the demonstrator, the system is capable of cyclic transmission of data packets, with fixed, non-adaptive beamforming.
I explain adaptive antennas in general, their application to mobile communications, recent examples, and the benefits that are gained for cellular systems. Then, I discuss adaptive digital beamforming, and explain some important concepts and algorithms that are representative to set the scene for the design of the demonstrator system. I give a detailed reasoning and the design procedure that I used. Based on the requirements due to the algorithms under consideration, and the needs of the algorithm research team of the mobile communications group at the department of communications and RF technoloy at the Technical University of Vienna that I had the privilege to join for some time, I derive firstly a system concept, and basic design parameters. Because digital quadrature conversion is required for this system, I explain the solution I have chosen. Secondly, with respect to these parameters, I perform the system design of the digital transceivers. The results are figures of merit to be implemented for the analog, and the digital part of the system. This finally leads to the detailed presentation of the resulting demonstrator structure, and the circuit designs that have been designed according to the requirements and the figures of merit derived previously. This includes the whole transceiver chain from antenna ports, to the embedded personal computers, the required synthesized signal sources, and interfacing and control units. Additionally, I briefly describe the mobiles that accompany the core demonstrator, and a simplified demonstrator that was derived from the designs described previously.