Systemkonzepte für ein künftiges OFDM basiertes zellulares Datenfunknetz. JointTransmission & Joint Detection in OFDM-Mobilfunksystemen
Zusammenfassung der Projektergebnisse
Although 3G mobile radio systems are not widely used today, a lot of research activities on beyond 3G (B3G) mobile radio systems have been undertaken. As a novel B3G system proposal, the joint transmission and detection integrated network (JOINT) aims at increasing the capacity as compared to 3G cellular systems and WLAN systems while keeping the complexity of the mobile stations (MSs) low. In contrast to conventional mobile radio systems where each channel is exclusively occupied by one MS, the introduction of the service area (SA) concept and the application of joint signal processing in JOINT allow multiple MSs to be simultaneously active on the same subcarrier without causing interference to each other. Because of the reduced interference the SA based JOINT systems outperform conventional cellular systems at a cost of complexity. Besides interference cancellation as applied in JOINT, dynamic resource allocation which can further improve system performance is attracting more and more interest in recent years. In the context of this report resources refer to OFDM subcarriers and transmit powers. Unfortunately, jointly optimizing power and subcarrier allocation in SA based networks is too complicated. To reduce the complexity the joint optimization problem is separated into two sub-problems, i.e., dynamic subcarrier allocation and adaptive power allocation. Theoretically, any system exhibiting interference can be modeled as interference channels. Motivated by the prohibitively high complexity of the optimum power allocation in interference channels, several suboptimum schemes including greedy power allocation, waterfilling power allocation and iterative waterfilling power allocation are investigated. In strong interference scenarios the greedy scheme which simply allocates all transmit power to the best user is shown to be near-optimum. Waterfilling power allocation which is known as the optimum scheme in parallel channels is near-optimum in weak interference scenarios. The iterative waterfilling scheme which updates power allocation iteratively in the presence of interference may outperform other suboptimum schemes in moderate interference scenarios. Dynamic channel (subcarrier} allocation (DCA) has been drawing considerable attentions with the increasing demand on spectrum efficiency. In SA based networks, the frequency selective nature of wireless channels, the correlation among the users' spatial signatures and the presence of interference provide great potentials which can be exploited by DCA to enhance the performance. In order to avoid an exhaustive search required for the optimum DGA in SA based networks, several practical DCA algorithms such as binary integer programming based DCA, 3-D channel gain matrix based DCA and sequential DCA are discussed. The significance of the potential benefits to various DCA algorithms is demonstrated through simulations. It is revealed that exploiting frequency selectivity is very beneficial, especially to interference-unaware DCA techniques. Properly considering the correlation of users' spatial signatures can significantly improve the performance. Furthermore, the benefit from adapting inter-SA interference depends on the interferer diversity. Essentially, in scenarios with small interferer diversity such as the case of universal frequency reuse to adapt to interference is necessary.
Projektbezogene Publikationen (Auswahl)
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"Dynamic resource allocation in JOINT". Proc. 10-th International OFDM-Workshop (InOWo'05), Hamburg, Sept. 2005, S. 270-274
T. Weber, S. Deng and M. Meurer
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"Interference statistics in the downlink of service area based mobile radio networks". Proc. 11-th International OFDM-Workshop (InOWo'06), Hamburg, Aug. 2006, S. 31-35
S. Deng, T. Weber and A. Ahrens
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"A novel decentralized MIMO-OFDM uplink detection scheme". Proc. International ITG/IEEE Workshop on Smart Antennas (WSA), Feb. 2007, Vienna
A. Ahrens, X. Wei, T. Weber and S. Deng
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"Decentralized interference cancellation in mobile radio networks". Proc. IEEE Wireless Communications and Networking Conference (WCNC), Mar. 2007, Hong Kong
T. Weber, A. Ahrens and S. Deng
