Ronald Raulefs

Location-Aware Communications for 5G Networks: How location information can improve scalability, latency, and robustness of 5G

Fifth-generation (5G) networks will be the first generation to benefit from location information that is sufficiently precise to be leveraged in wireless network design and optimization. We argue that location information can aid in addressing several of the key challenges in 5G, complementary to existing and planned technological developments. These challenges include an increase in traffic and number of devices, robustness for mission-critical services, and a reduction in total energy consumption and latency. This article gives a broad overview of the growing research area of location-aware communications across different layers of the protocol stack. We highlight several promising trends, tradeoffs, and pitfalls.

Beamforming in combination with space-time diversity for broadband OFDM systems

We investigate broadband OFDM systems which apply beamforming in combination with different space-time diversity techniques. Various beamforming scenarios with transmitter and/or receiver sided beamforming are considered. Space-time diversity is obtained by cyclic delay diversity (CDD) in order to artificially shape the spectrum of the received signal. Thus, an advantageous distribution of the errors before a Viterbi channel decoder is obtained. Simulation results for the bit error rate performance are presented and compared for OFDM systems applying different beamforming scenarios and CDD in a Rayleigh fading channel. Maximum ratio combining (MRC) of the signals received on multiple beams/antennas is also taken into account in the performance analysis.

Recent Advances in Indoor Localization: A Survey on Theoretical Approaches and Applications

The availability of location information has become a key factor in today’s communications systems allowing location based services. In outdoor scenarios, the mobile terminal position is obtained with high accuracy thanks to the global positioning system (GPS) or to the standalone cellular systems. However, the main problem of GPS and cellular systems resides in the indoor environment and in scenarios with deep shadowing effects where the satellite or cellular signals are broken. In this paper, we survey different technologies and methodologies for indoor and outdoor localization with an emphasis on indoor methodologies and concepts. Additionally, we discuss in this review different localization-based applications, where the location information is critical to estimate. Finally, a comprehensive discussion of the challenges in terms of accuracy, cost, complexity, security, scalability, etc. is given. The aim of this survey is to provide a comprehensive overview of existing efforts as well as auspicious and anticipated dimensions for future work in indoor localization techniques and applications.

Distance Dependent Model for the Delay Power Spectrum of In-room Radio Channels

A model based on experimental observations of the delay power spectrum in closed rooms is proposed. The model includes the distance between the transmitter and the receiver as a parameter which makes it suitable for range based radio localization. The experimental observations motivate the proposed model of the delay power spectrum with a primary (early) component and a reverberant component (tail). The primary component is modeled as a Dirac delta function weighted according to an inverse distance power law (d-n). The reverberant component is an exponentially decaying function with onset equal to the propagation time between transmitter and receiver. Its power decays exponentially with distance. The proposed model allows for the prediction of, e.g., the path loss, mean delay, root mean squared (rms) delay spread, and kurtosis versus the distance. The model predictions are validated by measurements: they show good agreement with respect to distance dependent trends.

Soft Cyclic Delay Diversity and its Performance for DVB-T in Ricean Channels

Cyclic delay diversity (CDD) provides additional diversity in Rayleigh fading channels, and therefore, improves the system performance. For line-of-sight (LOS) propagation, e.g., the additive white Gaussian noise channel, the implementation of CDD yields to a performance loss. The power distribution among the transmit (TX) antenna branches is a further parameter which can freely be chosen for optimizing the system performance and allows to switch on/off CDD softly. The idea is to feed different power levels into the multiple TX antenna branches rather than distributing the TX power uniformly among the TX antennas. We exemplarily implement the soft CDD principle to the terrestrial digital video broadcasting system (DVB-T). We consider a Ricean multipath fading channel, which allows to control the ratio of LOS and non-LOS propagation power via the Ricean factor for simulations. Simulation results for 2-TX and 4-TX antenna CDD show that antenna power weighting significantly reduces the SNR loss in LOS propagation by the cost of a slight degradation of the SNR gain in non-LOS scenarios.

Combining Wireless Communications and Navigation -The WHERE Project

Wireless communications and navigation have different constraints to cope with. On the one hand, communication systems traditionally aim at high spectral efficiency with specific requirements such as low latency and low power consumption. On the other hand, navigation is usually based on the transmission of known data signals at low data rates with fine synchronization capabilities for efficient signal acquisition and tracking. The ICT project WHERE (Wireless Hybrid Enhanced Mobile Radio Estimators) will focus on exploiting the positioning information to enhance communications -and vice versa- within heterogeneous and/or cooperative wireless systems. The paper gives an overview and outlines the upcoming goals of the FP7-ICT project WHERE. The WHERE project is an ICT STREP project involving 14 partners. It started in January 2008 and is running until June 2010.

Increasing time domain diversity in OFDM systems

Delay and Doppler spread of multipath fading channels have already been identified as sources of diversity in wireless communications systems. However, extensive delay- and Doppler spread may cause non-negligible intersymbol interference (ISI) and/or intercarrier interference (ICI) in OFDM systems. In this paper, we propose a method for increasing the Doppler spread of the multipath fading channel without causing additional ICI. The idea is to transmit the OFDM time domain signal predistorted via multiple transmit antennas. The proposed methods can be applied in addition to already existing OFDM systems without any modifications at the receiver, which makes them standards-compatible.

On prospects of positioning in 5G

Technologies envisaged for a 5G communications system provide interesting prospects which are beneficial for co-operative positioning. Since 5G development is in the early stages, there is a unique opportunity to develop and integrate mobile radio based positioning technology in 5G from the beginning. In this paper we discuss 5G concepts to ensure seamless positioning by cooperative positioning. In cooperative positioning, mobile terminals (MTs) collaborate to help each other to determine their own position. We address key 5G prospects like smaller cells, higher MT densities and the capability of device-to-device (D2D) communication to enable cooperative positioning. By using the Cramér-Rao lower bound we investigate cooperative positioning performance for signal propagation delay based pseudo ranging in an exemplary typical urban environment. Numerical results for an exemplary environment have shown that with MT densities D > 1100 MTs per square kilometer sub-meter positioning accuracy with outage probabilities converging to zero can be achieved.

A non-linear precoding technique for downlink MC-CDMA

Multiple-access interference is a major burden for MC-CDMA schemes. The possible complexity in the hardware of the mobile terminal is another major limitation. Both burdens can be answered in the downlink by preceding the signal with the knowledge of the channel state information. In this paper, we introduce a non-linear precoder to cancel the multiple-access interference motivated by the dirty-paper approach and by taking into account a non-linear modulo operation. The results show for a SISO system a significant improvement over recent proposed precoding schemes.

Cooperative and heterogeneous indoor localization experiments

In this paper we present the results of real-life localization experiments performed in an unprecedented cooperative and heterogeneous wireless context. These measurements are based on ZigBee and orthogonal frequency division multiplexing (OFDM) devices, respectively endowed with received signal strength indicator (RSSI) and round trip delay (RTD) estimation capabilities. More particularly we emulate a multi-standard terminal, moving in a typical indoor environment, while communicating with fixed OFDM-based femto-base stations (Femto-BSs) and with other mobiles or fixed anchor nodes (through peer-to-peer links) forming a wireless sensor network (WSN). We introduce the measurement functionalities and metrics, the scenario and set-up, providing realistic connectivity and obstruction conditions. Out of the experimental data, preliminary positioning results based on cooperative and geometric algorithms are finally discussed, showing benefits through mobile-to-mobile cooperation, selective hybrid data fusion and detection of unreliable nodes.