Dirk Hampicke

Identification of time-variant directional mobile radio channels

For the identification of the time-variant, directional structure of the mobile radio channel impulse response, a broadband vector channel sounder is described. The measurement procedure relies on periodic multifrequency excitation signals, correlation processing and joint delay-azimuth superresolution based on the ESPRIT algorithm. Problems of imperfect receiver and antenna performance and antenna array calibration methods are discussed. Results of multidimensional correlation analyses of various channel scenarios in the time-frequency-spatial domain and the corresponding Doppler-delay-angular domain are represented.

MIMO vector channel sounder measurement for smart antenna system evaluation

For the simulation and design of smart antenna transmission principles in mobile radio, precise knowledge of the time-variant directional multipath structure in various radio environments is required. In this paper, a new real-time multiple-input-multiple-output (MIMO) vector radio channel sounder is described, which uses multiple antennas at the transmitter as well as at the receiver position. The proposed MIMO measurement principle can be effectively exploited to estimate the propagation direction at both ends of the wireless link simultaneously, and thus, dramatically enhance overall resolution of the multiple path parameters. Applying a proper antenna architecture and the multidimensional unitary ESPRIT algorithm, joint superresolution estimation of the direction of departure (DOD), time- delay of arrival (TDOA), Doppler shift, and direction of arrival (DOA) of the propagating waves becomes possible. The measured results can also be used directly for the simulation of combined transmit-receive diversity (MIMO) transmission principles and space-time (ST) adaptive receivers in a multi-user scenario. Results based on measurements in different locations are referenced, including a complicated indoor environment as is typical for industrial WLAN applications.

Array measurement of the double-directional mobile radio channel

We describe a novel technique to measure the double-directional mobile radio channel. The channel is called double-directional since it includes directional spreading at both link ends, namely the base station and the mobile station. We use a double-array multiplexing technique consisting of a switched linear array at the receiver and a virtual array at the transmitter site. The measured microcellular scenarios are an open and a closed courtyard with different transmitter positions. The data are evaluated with an alternating estimation and beamforming technique that relies on (Unitary) ESPRIT estimation of positional parameters and subsequent beamforming for complex weight extraction. Usage of a two-axis crossed array at the transmitter site avoids forward-backward ambiguity. The presented exemplary results show a good agreement of the extracted directional information with the physical environment and give an indication of its scattering properties.

Joint estimation of DoD, time-delay, and DoA for high-resolution channel sounding

The detailed knowledge of the directional characteristics of the mobile radio channel is required to develop directional channel models and to design efficient smart antenna concepts for future mobile radio systems. In this paper, we present a high-resolution estimation scheme for the directional channel parameters from dual antenna array based channel sounding measurements. Since 360/spl deg/ azimuth coverage seems reasonable at the mobile station (MS), the utilization of a circular uniform beam antenna array at this place is proposed. Moreover, a transformation is described making this array suitable for high resolution angle estimation with ESPRIT. With this approach, the joint estimation of direction of departure, time-delay, and direction of arrival using 3-D Unitary ESPRIT is derived. Finally, we propose a procedure for the model order estimation and discuss some calibration issues.

Characterization of the directional mobile radio channel in industrial scenarios, based on wideband propagation measurements

The object of this paper is to provide data from wideband directional channel measurements carried out at 5.2 GHz in two different industrial scenarios. The channel is characterized by the temporal, azimuthal and Doppler characteristics under LOS and non-LOS situations. The results give insight into the propagation behavior for this type of environment and reveal that the installation of wireless LANs in industrial scenarios imposes important requirements on the system design.

MIMO capacities for different antenna array structures based on double directional wide-band channel measurements

We present an approach for investigating the performance of generic multiple-input multiple-output (MIMO) wireless systems in a realistic way using wideband real-time propagation measurements of the double-directional radio channel. Applying a multidimensional high-resolution channel parameter estimation procedure the descriptive parameters for any relevant propagation path including the path weights, time-delay, Doppler shift and the propagation directions at both ends of the wireless link are extracted simultaneously from the measurement data. from the estimated parameter sets then a local reconstruction of the multidimensional wave fields in the vicinity of the measured aperture volumes in time, space and frequency is possible. Since this way the measurement antenna properties are excluded from the channel, the influence of a variety of application specific array architectures can be investigated. Here, we use this synthesis approach to analyze the performance of given target systems with smart antennas in terms of the resulting channel capacities and eigenvalue distributions.

MIMO measurement and joint M-D parameter estimation of mobile radio channels

We describe a measurement and parameter identification procedure for the mobile radio propagation channel which includes the azimuth directions of the propagating waves at both link ends, elevation at the base station, time delay, and Doppler shift. The measurement is based on a broadband, real-time multiple-input-multiple-output radio channel sounder. At the mobile station a circular uniform beam array (CUBA) is used which covers 360/spl deg/ viewing angle whereas at the base station a uniform rectangular array (URA) is deployed. We derive the underlying data model and propose a multidimensional joint parameter estimation procedure from measurements which is based on the M-D ESPRIT algorithm. The resolution of coherent paths by subspace smoothing and the reduction of measurement errors by device calibration procedures is addressed.

Results of double-directional channel sounding measurements

In this paper a new channel sounding concept for double-directional and time-delay resolved channel measurements is proposed. It is based on the RUSK ATM vector channel sounder with a uniform linear array at the receiver. Using a switched multibeam antenna instead of an omni-directional antenna at the transmitter site the measurement device became a MIMO system. The sounder has been employed during a measurement campaign in a court yard within the 5.2 GHz HIPERLAN band. The collected measurement data were processed using parameter estimation algorithms. Combining a joint 2-D unitary ESPRIT algorithm and a 1-D unitary ESPRIT algorithm the DoDs, the time-delays, and the DoAs have been estimated. The estimation results demonstrate the suitability of the proposed measurement approach.

Performance of space-time processing for ISI- and CCI-suppression in industrial scenarios

This paper shows simulation results of the performance of linear and decision-feedback space-time equalizers for a single carrier system with 24 Msym/s data rate at 5.2 GHz carrier frequency. Thereby the radio channel is realistically modeled by using measurement data of a vector channel sounder gathered in two industrial scenarios. A comparison is given for a variety of equalizer complexities, various channel conditions and different numbers of co-channel interferers. For a proper selection of the complexity good performance values can be obtained under the presence of strong multipath propagation.

Reduction of DoA Estimation Errors Caused by Antenna Array Imperfections

Antenna arrays are expected to be widely used for future mobile radio applications. Therefore implementation issues are a matter of concern. Since real antenna arrays suffer from different impairments, sophisticated calibration procedures are required in order to enhance the performance. For that aim a promising calibration approach is described Its performance has been verified by simulations and measurements. Especially, the application for the direction of arrival estimation in wideband radio vector channel sounders is addressed.