Andreas Waadt

Combining Mimo with Network Coding: A Viable Means to Provide Multiplexing and Diversity in Wireless Relay Networks

In this paper, a two-step communication protocol combined with virtual MIMO (Multiple Input Multiple Output) and network coding technique is proposed. The protocol is therefore termed MINEC (MIMO Network Coding). A three nodes network with multi-antennas on relay node is taken as an illustrative example of MINEC. Theoretical and simulative analyses of the MINEC performance under the assumption of a binary symmetric relay channel model are carried out. It is found that MINEC performs equivalent to a 2x2 V- BLAST MIMO and a two 2x1 Alamouti MISO in transmitting phase and forwarding phase, respectively. Theoretical and simulative analyses prove that MINEC protocol facilitates more reliable transmission and higher throughput.

System implementation study on RSSI based positioning in UWB networks

The Ultra-Wideband Radio Technology (UWB-RT) enables accurate Location and Tracking (LT) applications. However, the required and sophisticated time of arrival (ToA) ranging procedure relies on accurate synchronizations and time measurements. Non-cooperative nodes, not supporting the ToA feature, cannot be localized with this LT approach. Other LT approaches exploit the received signal strength (RSS) or received signal strength difference (RSSD). Simulations of RSS based localization in UWB networks showed promising performance results. In this paper, the authors introduce a RSS based LT demonstrator, build up with conventional Certified Wireless USB (CWUSB) sticks, using multiband UWB-RT. Different LT algorithms are tested. In a small UWB network, measurements of the localization accuracy show a root mean square error (RMSE) of about 0.33 meters.

A DVB-T2 receiver realization based on a software-defined radio concept

When DVB-T (Digital Video Broadcasting - Terrestrial) was introduced in the 1990s, it was impossible to foresee the upcoming demand for HDTV devices. Thus, a revision of this broadcasting standard, namely DVB-T2, was necessary. Recently finalized, this standard is targeting to high-definition television (HDTV). To pave the way to commercialization, an appropriate implementation concept and its corresponding validation are of utmost importance. Without a doubt, the most challenging requirements introduced by the DVB-T2 specification are an FFT (Fast Fourier Transform) size of up to 32k samples, 256-QAM (Quadrature Amplitude Modulation) and LDPC (Low-Density Parity-Check) coding with a block size of 64800 bits. Within this manuscript, the authors present a software-defined radio based realization of a demonstrator platform. This platform employs a combined DSP (Digital Signal Processor) and FPGA (Field-Programmable Gate Array) solution being capable of meeting these requirements.

An overview of positioning systems and technologies

Applications requiring positioning in mobile networks gained importance in recent years. Examples are not only Location Based Services (LBSs), but also enhanced emergency call services such as the North American E911, or the newly defined eCall, which is planned to become a European standard as a part of the eSafety initiative of the European commission. Mobile network providers already offer LBS along with positioning, although the accuracies and reliabilities of the present techniques do not yet meet the requirements of the newly defined services in all cases. One of the most popular positioning systems in navigation is the GPS, which is satellite-based, quite accurate and widely available, as long as the receiver to be localized and the satellites have a LOS connection. In this presentation, an overview of positioning and tracking schemes will be given.

Positioning in multiband OFDM UWB utilizing received signal strength

Ultra-wideband (UWB) enables accurate Localization and Tracking (LT) applications. However, the required and sophisticated time of arrival (ToA) ranging procedure relies on accurate synchronization and time measurements. Today, only few UWB devices support the required ranging feature. Examples are pulse based low data rate (LDR) UWB devices. Conventional multiband OFDM based high data rate (HDR) UWB devices do not support the ToA ranging feature. But the ultra wide frequency bandwidth of UWB enables not only high resolution of space surrounding UWB transceivers and therefore accurate time measurements, its enormous frequency diversity also minimizes fading effects. This allows reliable distance measurements, based on measurements of the received signal strength (RSS). This paper shows, that RSS based localization can be as accurate as ToA based localization. For this purpose, measurement results of the RSS and a derived path-loss model are used to calibrate a Monte Carlo simulator for RSS based ranging and localization. The RSS measurements are done with conventional wireless USB sticks, using HDR UWB. For a small 2 × 2 meters network, the simulation results show mean localization errors between 0.1 and 0.2 meters.

Maximum likelihood localization estimation based on received signal strength

This paper discusses a maximum likelihood (ML) estimator for the localization of mobile nodes in communication networks. The derived estimator is optimized for ranging measurements exploiting the received signal strength (RSS). For this purpose, the bias and uncertainties of the RSS based ranging procedure are analyzed, considering a path loss model of an indoor ultra-wideband (UWB) network under line of sight (LOS) conditions. The nonlinearity of the path loss model is first taken into account before the statistics of the observed RSS are approximated by a Taylor sequence of first order. The so found metrics describe a weighted least squares (WLS) method. The metrics of the estimator are analytically derived in closed-form. The performance of the derived estimator is investigated in Monte-Carlo simulations and compared with a simple least squares (LS) method and another method exploiting RSS fingerprints.

Applying Zero-Crossing Demodulation to the Bluetooth Enhanced Data Rate Mode

Short range communication systems such as Bluetooth and DECT (digital enhanced cordless telecommunications) require low-cost transceiver structures. Hence, the development of appropriate receiver techniques has been a major research topic. Particularly, analog limiter-discriminator with integrate and dump filtering (LDI) techniques have received considerable attention. With the availability of digital signal processing (DSP), the digital implementation of LDI techniques has become increasingly attractive. In order to make LDI receivers more accessible, zero-crossing detection was proposed. In this communication, the authors shall focus on a novel, yet promising, approach to digital zero-crossing detection in the intermediate frequency domain. Zero-crossing demodulation is an irregular sampling technique, which replaces the commonly employed regular, i.e. temporally equidistant sampling technique in the mentioned low-cost receivers. In this manuscript, the authors will present the theoretical aspects of zero-crossing demodulation with special focus on Bluetooth enhanced data rate (EDR). Next, the obtained performance results in terms of the bit error ratio (BER). Comparisons with theoretical bounds show the advantageous performance. Furthermore, a demonstrator concept termed HAWK shall be discussed and first measurement results will be presented

UWB coverage in public transport scenarios

In the near future, wireless connectivity will become a commodity in aircrafts. For the planning of the reliable network a detail analysis of the coverage is required. This paper studies the coverage in an AIRBUS A380 cabin for a OFDM UWB system based on the ECMA 368 standard. For this purpose, based on real measurement in an AIRBUS A380 airplane cabin, a Saleh-Valenzuela channel model and a path-loss model are presented. This models are used to obtain the block error rates and the throughput in an in-cabin environment.

Platform Based Design of Termninals and Infrastructure Components for Cognitive Wireless Networks

Cooperation in wireless networks will facilitate a new dimension in the evolution of multimedia communications, sCtting out from the todays situation with a multitude of communication standards and radio interfaces both in the licensed and thC unlicensed domain. In order to pave the way towards cooperative networks, the deployment of cognitive wireless solutions, which will form the communication platforms, will be a key asset. In the future, we expect to see an increasingly flexible, ad-hoc utilization of the available spectrum in the unlicensed domain and a co-existence of communication standards in the licensed bands. In this communication, the authors will illustrate a platform based approach towards cognitive wireless communications. Also, the authors will present three software defined radio concepts designed by the members of the Lehrstuhl für KommunikationsTechnik, namely the HAWK (Highly Adaptable Wireless Kit), the FALCON (Flxible Access Logic for COmmunication Networks), and the MUSTANG (MUlti-STAndard single chip transceiver for the Next Generation), finally, giving an outlook on their wireless optical communication device, termed ARGOS. HAWK, FALCON, MUSTANG and ARGOS form the basis of the cognitive wireless platform, developed by the authors, termed PROMETHEUS. The setup of PROMETHEUS and its functionality shall be illustrated together with selected measurement results.

Positioning framework for WLAN 802.11n utilizing Kalman filter on received signal strength

Location information has become crucial in many circumstances such as rescue operations, emergencies, navigation, and tracking. Furthermore, with the deployment of the wireless communication networks and the mobility that characterizes the wireless communication users, positioning information has become a great interest. Location tracking, based on received signal strength indicators (RSSI), is a cost efficient method to gather location information. However, RSSI suffers from estimation errors due to shadowing. In this paper, a positioning framework for location tracking in WLAN IEEE 802.11n networks has been proposed which is transparent to accuracy improvement technologies. Furthermore, a novel Kalman filter implementation is presented. The implementation brings advantages over the most common approach “extended Kalman filter” in terms of computational efforts and does not require the linearization steps. The positioning framework and the proposed implementation of the Kalman filter have been evaluated on experimental data using Monte Carlo simulation.