The mobile communications group (MCG) at the LKN deals with a large variety of topics, alltogether aiming at future wireless and mobile systems, which provide high data rates, rich services, multihop and self-organizing capabilities, location- and context-awareness, as well as reliable security and trustability.

Multihop Communication: Traditionally, mobile and wireless communication is based on a direct wirelless link between a mobile terminal and a base station or an access point. In contrast to this, multihop concepts are receiving a lot of attention in the research community recently. In multihop communication, information is transmitted between a source and a destination with the help of wireless relays, which are forwarding the data in a hop-by-hop fashion. Multihop communication can be applied in a variety of different scenarios. For instance, the coverage area of cellular base stations can be extended if multihop relays are introduced, which is specifically important for future cellular systems which will be using much higher frequencies than todays cellular networks and thus require a direct line of sight between a sender and a receiver. Another important application scenario for multihop communication is in infrastructure-less self-organizing networks. Such so called ad hoc networks can be established on the fly in a fast and flexible manner. Ad hoc networks can also be applied to provide indirect, i.e. multihop Internet access. Other examples applying the multihop concept are sensor networks (e.g. used for environmental monitoring or data collection) and wirless mesh networks. The latter are based on a wireless interconncetion between WiFi access points in a self-configering fasion. A variety of research projects within the MCG is dealing with open research issues concerning wireless multihop communication, like: connectivity, routing, mobility management, resource management, media access, Quality of Service, planning aspects, adaptivity, self-organization, self-configuration, and security.

Heterogeneous Networks:

With the continuous development of novel mobile cellular network generations and the parallel establishment of technologies like WiFi and WiMax as well as broadcast and satellite services, the world of wireless and mobile networks will become increasingly heterogeneous in the future. One of the challenges arising from this heterogeneity lies in providing users with functionalities, which adaptively choose the most appropriate network in an automated way, in order to provide the user with services and applications of his/her choice, depending on available networks, device capability, location and context. One of the research activities within the MCG with respect to heterogeneous networks is concerned with location- and context-aware services, utilizing location information from the heterogeneous network environment.

MIMO and Cross-Layer: In order to provide various flovors of voice-, data-, and multimedia-services in future packet based cellular communication systems, the spectrum must be utilized in a much more efficient way than in current systems. For this purpose, MIMO (Multiple Input Multiple Output) systems are well suited since they potentially provide very high data rates. In order to utilize the potential MIMO data rates and provide user individual Quality of Service (QoS), novel approaches are required for packet scheduling and call admission control. Within a project supported by the DFG, we develop novel scheduling and admission control algorithms for packet based wireless systems. Our approaches are aiming at enabling user-individual QoS management, while exploiting channel fluctuations. To achieve this goal, we use a cross layer approach, incorporating information from both the physical layer and from the application (QoS) to perform optimal scheduling decisions. With our novel schedulers more traffic can be carried with better QoS support as compared to classical approaches found in the literature.

Adaptive Antennas in Ad Hoc Networks: Ad hoc networks are considered to be a key technology for future wireless communication systems. In such self-organizing networks, mobile stations communicate with each other without network infrastructure. Researches are still challenged when trying to facilitate the use of adaptive antennas in self-organized ad hoc networks. Problems arise throughout the protocol stack, and strong interdependencies between functional layers exist. It is thus an objective of an ongoing research project to develop novel algorithms, protocols and a system architecture for ad hoc networks using adaptive antennas. The benefit of such novel approaches is the exploitation of adaptive antennas in order to provide better connectivity, higher capacity, better quality, as well as improved energy efficiency as compared to networks with conventional omnidirectional antennas.