Christian Schindelhauer

Randomized rumor spreading

Investigates the class of epidemic algorithms that are commonly used for the lazy transmission of updates to distributed copies of a database. These algorithms use a simple randomized communication mechanism to ensure robustness. Suppose n players communicate in parallel rounds in each of which every player calls a randomly selected communication partner. In every round, players can generate rumors (updates) that are to be distributed among all players. Whenever communication is established between two players, each one must decide which of the rumors to transmit. The major problem is that players might not know which rumors their partners have already received. For example, a standard algorithm forwarding each rumor form the calling to the called players for /spl Theta/(ln n) rounds needs to transmit the rumor /spl Theta/(n ln n) times in order to ensure that every player finally receives the rumor with high probability. We investigate whether such a large communication overhead is inherent to epidemic algorithms. On the positive side, we show that the communication overhead can be reduced significantly. We give an algorithm using only O(n ln ln n) transmissions and O(ln n) rounds. In addition, we prove the robustness of this algorithm. On the negative side, we show that any address-oblivious algorithm needs to send /spl Omega/(n ln ln n) messages for each rumor, regardless of the number of rounds. Furthermore, we give a general lower bound showing that time and communication optimality cannot be achieved simultaneously using random phone calls, i.e. every algorithm that distributes a rumor in O(ln n) rounds needs /spl omega/(n) transmissions.

Energy, congestion and dilation in radio networks

We investigate the problem of path selection in radio networks for a given set of sites in two-dimensional space. For some given static point-to-point communication demand we define measures for congestion, energy consumption and dilation that take interferences between communication links into account.We show that energy optimal path selection for radio networks can be computed in polynomial time. Then, we introduce the diversity

Mobility in wireless networks

g(V)

Minimal energy path planning for wireless robots

of a set

Distributed Maintenance of Resource Efficient Wireless Network Topologies

V\subseteq \REAL^2

Weighted distributed hash tables

. It can be used to upperbound the number of interfering edges. For real-world applications it can be regarded as

Acoustic Self-calibrating System for Indoor Smartphone Tracking (ASSIST)

\Theta(\log n)

Why robots need maps

. A main result of the paper is that a weak

Indoor localization using a smart phone

c

Self-localization application for iPhone using only ambient sound signals

-spanner construction as a communication network allows to approximate the congestion-optimal communication network by a factor of