Armin Dammann

Standard conformable antenna diversity techniques for OFDM and its application to the DVB-T system

In this paper, we investigate different antenna diversity concepts, which can be easily applied to orthogonal frequency division multiplexing (OFDM) systems. The focus is to provide diversity schemes, which can be implemented to already existing OFDM systems without changing the standards. It is also possible to combine these techniques in a suitable manner. The introduced diversity techniques are applied to the DVB-T system for error performance investigations, which were done by simulation.

Transmit/Receive‐antenna diversity techniques for OFDM systems

In this paper, we investigate different antenna diversity concepts, which can be easily applied to orthogonal frequency division multiplexing (OFDM) systems. The focus is on standard compatibility, i.e. these schemes can be implemented to already existing OFDM systems without changing the standards. The introduced diversity techniques are applied exemplarily to the DVB-T system. Bit error performance investigations were done by simulation for different DVB-T and diversity parameter sets.

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.

Performance of Low Complex Antenna Diversity Techniques for Mobile OFDM Systems

In this paper, we investigate different antenna diversity concepts, which can be easily applied to orthogonal frequency division multiplexing (OFDM) systems. The focus is on standard compatibility, i.e. this schemes can be implemented to already existing OFDM systems without changing the standards. The introduced diversity techniques are applied exemplarily to the DVB-T system. Bit error performance investigations were done by simulation for different DVB-T and diversity parameter sets.

Particle filter based positioning with 3GPP-LTE in indoor environments

Global navigation satellite systems (GNSSs) can deliver very good position estimates under optimum conditions. However, especially in urban and indoor scenarios with severe multipath propagation and blocking of satellites by buildings the accuracy loss can be very large. Often, a position with GNSS is impossible in these scenarios. On the other hand, cellular wireless communication systems such as the third generation partnership project (3GPP) long-term evolution (LTE) provide excellent coverage in urban and most indoor environments. Thus, this paper researches timing based positioning algorithms, in this case time difference of arrival (TDoA), using 3GPP-LTE measurements. Several approaches and algorithms exist to solve the navigation equation for cellular systems, for instance Bayes filtering methods such as Kalman or particle filter. This paper specifically considers and develops a particle filter for 3GPP-LTE TDoA positioning. To obtain better positioning results, a 3GPP-LTE TDoA error model is derived. This error model is afterwards included in the likelihood function of the particle filter. The last part of this paper, evaluates the positioning performances of the developed particle filter in an indoor scenario. These evaluations show clearly the possibility of using 3GPP-LTE measurements for indoor positioning.

Synchronization Algorithms for Positioning with OFDM Communications Signals

This paper covers positioning techniques for cellular networks using orthogonal frequency division multiplexing (OFDM) communications signals. These methods are based on symbol-timing synchronization algorithms to find the starting point for the underlying OFDM symbols of the incident signals. Commonly used approaches are, e.g., the Schmidl-Cox algorithm and the Minn algorithm. These algorithms are investigated w.r.t. their positioning capabilities. Furthermore, they are extended to improve the performance in multipath environments and to achieve a sufficient accuracy with weak signals from neighboring out-of-cell base stations.

Hybrid Data Fusion and Tracking for Positioning with GNSS and 3GPP-LTE

Global navigation satellite systems (GNSSs) can provide reliable positioning information under optimum conditions, where at least four satellites can be accessed with sufficient quality. In critical situations, for example, urban canyons or indoor, due to blocking of satellites by buildings and severe multipath effects, the GNSS performance can be decreased substantially. To overcome this limitation, we propose to exploit additionally information from communications systems for positioning purposes, for example, by using time difference of arrival (TDOA) information. To optimize the performance, hybrid data fusion and tracking algorithms can combine both types of sources and further exploit the mobility of the user. Simulation results for different filter types show the ability of this approach to compensate the lack of satellites by additional TDOA measurements from a future 3GPP-LTE communications system. This paper analyzes the performance in a fairly realistic manner by taking into account ray-tracing simulations to generate a coherent environment for GNSS and 3GPP-LTE.

Interference-Aware Location Estimation in Cellular OFDM Communications Systems

In this paper, we consider location estimation algorithms using cellular orthogonal frequency division multiplexing (OFDM) communications systems. In the classical approach the mobile station (MS) determines time difference of arrival (TDOA) information from the received signals of at least three bases stations (BSs). With these TDOAs the location of the MS is estimated. However, only at the cell edge a good reception of several BSs is ensured. Especially for future systems targeting a frequency re-use of one, interference is a limiting factor. Hence, in the inner cell it is difficult to detect out-of-cell BSs with sufficient quality. Therefore, we propose an interference cancellation scheme to improve the performance in these critical situations for TDOA positioning. Simulation results for a 3GPP- LTE system show the ability of this approach to increase the accuracy and to extend the coverage of the overall location estimation.

Data-Aided Location Estimation in Cellular OFDM Communications Systems

In this paper, location estimation algorithms for cellular communications systems employing orthogonal frequency division multiplexing (OFDM) are investigated. To determine the location of a mobile station, usually time difference of arrival (TDOA) measurements are performed with at least three base stations using pilot symbols included in the signal streams. With these TDOAs then the location is estimated. However, the timing estimation process is faced by different effects that restrict the performance. For instance, limited number of pilot symbols, inter-cell interference, and multipath propagation decrease the accuracy of the timing estimates, and hence, position estimates. Therefore, we propose to feed back decided data symbols where particularly data-aided timing estimation and interference cancellation are considered in the location estimation context. Simulation results for a 3GPP-LTE system show the ability of these algorithms to increase the overall accuracy and reliability of location estimates.

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.