Tobias Felhauer

A novel algorithm for channel segmentation based on a Lloyd-Max quantization

Signal detection and bandwidth estimation, also known as channel segmentation or information channel estimation, is a perpetual topic in communication systems. In the field of radio monitoring this issue is extremely challenging, since unforeseeable effects like fading occur accidentally. In addition, most radio monitoring devices normally scan a wide frequency range of several hundred MHz and have to detect a multitude of different signals, varying in signal power, bandwidth and spectral shape. Since narrowband sensing techniques cannot be directly applied, most radio monitoring devices use Nyquist wideband sensing to discover the huge frequency range. In practice, sensing is normally conducted by an FFT sweep spectrum analyzer that delivers the power spectral density (PSD) values to the radio monitoring system. The channel segmentation is the initial step of a comprehensive signal analysis in a radio monitoring system based on the PSD values. In this paper, a novel approach for channel segmentation is presented that is based on a quantization and a histogram evaluation of the measured PSD. It will be shown that only the combination of both evaluations will lead to an successful automatic channel segmentation. The performance of the proposed algorithm is shown in a real radio monitoring szenario.

Combining automatic radio monitoring and license databases for future spectrum management

Several radio monitoring campaigns have been carried out in the past at different locations to determine the degree to which radio spectrum is currently used. The purpose of these measurement campaigns is to show if the radio spectrum, which is a non-expandable and non-importable national resource, is efficiently used at a certain place. Although all of these campaigns follow the similar approach, they are not comparable due to a lack of common measurement setups and evaluation methodologies. Moreover, none of these monitoring campaigns compare their measurement results with the corresponding spectrum management data. This work presents a novel evaluation methodology by taking the a priori data of the spectrum management into account. Starting with a precise description of the measurement setup and a definition of a newly defined threshold for signal detection, this study presents an evaluation methodology that automatically compares the measurement results with the corresponding spectrum management data in the frequency bands UHF IV and V. With this approach the monitoring system delivers beside the common spectrum occupancy value a novel signal identification index that indicates if the detected emission is listed in the spectrum management database. The spectrum management data used in this measurement campaign is a public transmitter database of the German regulator and the signal identification is based on the evaluation of the center frequency, bandwidth and spectral shape of the emission.

Data clustering algorithm for channel segmentation in a radio monitoring system

The detection of signals and the estimation of signal bandwidth is a perpetual topic in radio communication systems. Both issues are extremely challenging, since the wireless channel is unreliable in nature. A radio monitoring system faces the most difficult conditions in this task; it normally scans a wide frequency range of several hundred MHz and has to detect a multitude of different signals. Owing to the computational costs, the radio monitoring systems use nowadays mainly energy detectors based on fast Fourier transform spectrum analysers and a static threshold, defined by a previous noise estimation. A refined algorithm based on the self-splitting competitive learning (SSCL) clustering is presented that quantises the power spectral density (PSD) according to the present signal power levels. The quantisation of the PSD results in a promising channel segmentation. In contrast to the traditional threshold evaluation, this approach is independent of a previously assumed noise estimation and therefore more robust against noise level and noise distribution changes. The presented definition of the essential cluster validity criterion is key for a successful channel segmentation. Furthermore, the novel postprocessing of the clustering result introduced in this study evaluates the progression of the PSD data and significantly improves the channel segmentation.

Wireless Network Coding with Cooperative Diversity

In this paper we integrate the ideas of network coding and relays into an existing practical network architecture used in a wireless network scenario. Specifically, we use the COPE architecture to test our ideas. Since previous works have focused on the communication aspect at the physical layer level, we attempt to take it one step further by including the MAC layer. Our idea is based on information theoretic concepts developed by Shannon in order to reliably apply network coding to increase the net throughput.

Beam Forming and Steering with INS for Cellular Phones to Reduce EM Radiation Exposure

Cellular phone antennas are generally designed to have radiation patterns that are as omnidirectional as possible. Omnidirectional antennas allow a phone’s radio to work well for many orientations of the phone with respect to the cellular base station. Recent studies, however, are generating uncertainty about the health effects of prolonged exposure to electromagnetic (EM) radiation from cellular phones. In this paper, an antenna array is designed primarily to minimize users’ exposure to EM radiation. The antenna comprises a beamforming 4 by 3 array of microstrip patch antennas that is controlled by an accelerometer-only inertial navigation system. The proposed design reduces radiated power directed toward the user to below 10% of the total in the worst case.

Application of wireless technology for IP-based aircraft in-flight entertainment

Since cabling is very complex and often causes reliability problems in aircrafts new approaches which base on wireless technologies are highly desired. In this paper an innovative communication system is proposed that uses the essential elements of the airframe for data transfer. The communication is based on the wireless standard for Digital Video Broadcasting (DVB) and enables high data rates, which are required for the in-flight entertainment system as an example of use.