Ruediger Halfmann

A frequency agile air-interface for inter-vehicle communication

One of the most promising deployment areas of mobile ad hoc networks are inter-vehicle communication and road telematics. The diverse spectrum of applications requires the full range from low to high data rates. To provide broadband services with moderate terminal complexity and explore the available radio spectrum at the same time, frequency division multiple access (FDMA) should be introduced. In the FleetNet project an appropriate air-interface based on UMTS Terrestrial Radio Access Time Division Duplex (UTRA TDD) is under development. One component is the novel FDMA concept, which is introduced in this paper, and which enters an evolutionary path towards higher data rates. The concept takes into account the complexity of the hardware, the distributed character of self-organizing networks, and the efficient exploration of the scarce frequency spectrum. Simulation results for the new decentralized FDMA scheme show high and efficient utilization of available resources.

Dynamic Cell Clustering in Cellular Multi-Hop Networks

This paper proposes, examines and compares different algorithms for dynamic cell clustering in cellular multi-hop networks. The basic idea is to balance load among different cells by creating cell clusters dynamically. For that purpose, it is distinguished between centralized and decentralized heuristics, which both are compared with results of a numerical optimization. At first, the evaluation is performed based upon a graph-theoretical network model. In a second step, an implementation of the decentralized approach in ns-2 is used to analyze and prove the protocols behavior and feasibility in a more realistic environment

Wireless OSPF in Cellular Multi-Hop Networks

Future mobile communication networks will be characterized by three facts: high data rates, guaranteed quality of premium services and multi-hop communication over several wireless devices. In the domain of public access networks, cellular multi-hop architectures are a promising solution to achieve these ambitious goals. This paper illustrates the issue of cellular multi-hop and analyzes the routing problem related to this new type of network. For that purpose, a new approach based on proactive link-state routing is presented. Additionally, a convenient manner to efficiently integrate routing in the medium access control layer is shown. Simulation results illustrate the feasibility, limitations and consequences of the proposed routing approach. The paper ends with a final conclusion, summing up previous results and providing an outline to further research issues

Adaptive Routing in Wireless Multi-Hop Networks

This paper examines the question, whether iterative routing based on Dijkstras algorithm is a suitable routing algorithm for the operation of cellular multi-hop or mesh network scenarios with gateway access to some backbone network. For that purpose, the general performance of different routing metrics is examined. Various load scenarios are generated in order to illustrate load-balancing effects and stability issues, as permanent re-routing may also lead to oscillations, where traffic is shifted back-and-forth between alternative paths. Therefore, different methods to stabilize the network are presented additionally. It turns out that the omission of the impact of a flows own traffic on its routing metrics manages to prevent these oscillations efficiently