Mathias Bohge

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Recent results indicate scalability problems for flat ad hoc networks. To address the issue of scalability, self-organizing hierarchical ad hoc architectures are being investigated. In this paper, we explore the task of providing data and entity authentication for hierarchical ad hoc sensor networks. Our sensor network consists of three tiers of devices(More)
In this paper we review contributions regarding dynamic, i.e., channel-state adaptive schemes for OFDM systems. As the wireless broadband channel is frequency-selective, the OFDM transmission scheme provides an efficient technique to overcome this impairment. However, the OFDM transmission scheme provides further advantages. Various system metrics can be(More)
In the near future wireless networks will consist of low-powered, compute-constrained devices. These devices will have limited ability to perform the expensive computational operations associated with public key cryptography. This will limit the usefulness of conventional authentication mechanisms based on public key certificates in these domains. In this(More)
— OFDM systems are known to overcome the impairment of the wireless channel by splitting the given system-bandwidth into parallel sub-carriers, on which data-symbols can be transmitted simultaneously. This enables the possibility of enhancing the system's performance by deploying adaptive (dynamic) mechanisms, namely power and modulation adaption and(More)
Recently, a lot of research effort has been spent on cross-layer system design. It has been shown that cross-layer mechanisms (i.e., policies) potentially provide significant performance gains for various systems. In this article we review several aspects of cross-layer system optimization regarding wireless OFDM systems. We discuss basic optimization(More)
—Soft frequency reuse is a strong tool for co-channel interference mitigation in cellular OFDMA/LTE networks. The performance of such networks significantly depends on the configuration of the power masks that implement the soft frequency reuse patterns. In this paper, we investigate the performance of different power mask configurations against the optimal(More)
—One of the major challenges in designing cellular Cognitive Radio (CR) networks is the avoidance of Secondary User (SU) interference to so called Primary Users (PUs) operating in the licensed bands. Usually, SU operation has to be interrupted periodically in order to detect PU activity and avoid the respective frequencies. Recently, Dynamic Frequency(More)
— It is well known that applying dynamic resource allocation to down-link transmissions of OFDMA systems provides a significant performance increase, by taking advantage of diversity effects. In order to quantify the maximum possible gain achievable by applying dynamic mechanisms, several optimization problems have been suggested for studying a dynamic(More)
The fraction of voice over Internet Protocol (VoIP) based telephone calls among the totality of voice based communication acts has been significantly growing during the last years. In wired, as well as wireless communication applications , VoIP is expected to completely replace former circuit switched telephony approaches, and is, thus, a major factor to be(More)
— The usual approach to mitigate multiple access interference (MAI) in the uplink of cellular OFDMA based systems is to use relatively large cyclic prefixes as time domain guard periods. In this paper, we suggest to use a combination of short time domain guard periods and frequency domain guard bands to protect against MAI instead. Guard bands can be added(More)