Transmit Diversity at the Cell Border Using Smart Base Stations
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Research Article Transmit Diversity at the Cell Border Using Smart Base Stations Simon Plass, Ronald Raulefs, and Armin Dammann German Aerospace Center (DLR), Institute of Communications and Navigation, Oberpfaffenhofen, 82234 Wessling, Germany Received 27 October 2006; Revised 1 June 2007; Accepted 22 October 2007 Recommended by A. Alexiou We address the problems at the most critical area in a cellular multicarrier code division multiple access (MC-CDMA) network, namely, the cell border. At a mobile terminal the diversity can be increased by using transmit diversity techniques such as cyclic delay diversity (CDD) and space-time coding like Alamouti. We transfer these transmit diversity techniques to a cellular environment. Therefore, the performance is enhanced at the cell border, intercellular interference is avoided, and soft handover procedures are simplified all together. By this, macrodiversity concepts are exchanged by transmit diversity concepts. These concepts also shift parts of the complexity from the mobile terminal to smart base stations. Copyright © 2007 Simon Plass et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
The development of future mobile communications systems follows the strategies to support a single ubiquitous radio access system adaptable to a comprehensive range of mobile communication scenarios. Within the framework of a global research effort on the design of a next generation mobile system, the European IST project WINNER—Wireless World Initiative New Radio—[1] is also focusing on the identification, assessment, and comparison of strategies for reducing and handling intercellular interference at the cell border. For achieving high spectral efficiency the goal of future wireless communications systems is a total frequency reuse in each cell. This leads to a very critical area around the cell borders. Since the cell border area is influenced by at least two neighboring base stations (BSs), the desired mobile terminal (MT) in this area has to scope with several signals in parallel. On the one hand, the MT can cancel the interfering signals with a high signal processing effort to recover the desired signal [2]. On the other hand, the network can manage the neighboring BSs to avoid or reduce the negative influence of the transmitted signals at the cell border. Due to the restricted power and processing conditions at the MT, a network-based strategy is preferred. In the region of overlapping cells, handover procedures exist. Soft handover concepts [3] have shown that the usage of two base stations at the same time increases the robustness of the received data and avoids interruption and calling
resources for reinitiating a call. With additional information about the rough position of the MT, the network can avoid fast consecutive handovers that consume many resources, for example, the MT moves in a zigzag
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