Marcus Grossmann

A measurement-based path loss model for wireless links in mobile ad-hoc networks (MANET) operating in the VHF and UHF band

For the development of future mobile-to-mobile communication systems, realistic channel models are required. Available models are aiming at broadcasting applications using high antenna towers and are therefore not applicable for mobile-to-mobile applications like mobile ad-hoc networks (MANET). In this paper, measurements of the path loss using car-mounted receiver and transmitter antennas are presented. Based on the measurement results, a new path loss model is proposed. It is shown that this model provides a more realistic prediction of the path loss for MANET systems in the VHF and UHF band than the widely used Okumura-Hata model.

Modeling shadow fading for mobile-to-mobile communications in the VHF and UHF band

Measurements of the shadow fading characteristics in tactical communication scenarios have been presented. New parameter sets for widely used shadow fading models have been proposed. Modeling the shadow fading using these parameter sets, rather than the parameters obtained through measurements with high antenna setups, will result in a more realistic representation of the phenomenon for communication systems with car-mounted Rx and Tx antennas.

Design and analysis of compressive antenna arrays for direction of arrival estimation

The design of compressive antenna arrays for direction of arrival (DOA) estimation has been investigated. The main aim is to provide a larger aperture with a reduced hardware complexity.The basic receiver architecture of such a compressive array is presented and a generic system model that includes different options for the hardware implementation is introduced.The design of the analog combining network that performs the receiver channel reduction is discussed and two design approaches are proposed.A comparison to sparse arrays and compressive arrays with randomly chosen combining kernels is presented, showing the superiority of the proposed designs. In this paper we investigate the design of compressive antenna arrays for narrow-band direction of arrival (DOA) estimation that aim to provide a larger aperture with a reduced hardware complexity and allowing reconfigurability, by a linear combination of the antenna outputs to a lower number of receiver channels. We present a basic receiver architecture of such a compressive array and introduce a generic system model that includes different options for the hardware implementation. We then discuss the design of the analog combining network that performs the receiver channel reduction, and propose two design approaches. The first approach is based on the spatial correlation function which is a low-complexity scheme that in certain cases admits a closed-form solution. The second approach is based on minimizing the Cramr-Rao Bound (CRB) with the constraint to limit the probability of false detection of paths to a pre-specified level. Our numerical simulations demonstrate the superiority of the proposed optimized compressive arrays compared to the sparse arrays of the same complexity and to compressive arrays with randomly chosen combining kernels.

Linear baseband precoding strategies for millimeter wave MIMO multi-X channels

This paper focuses on the design of linear baseband precoding and combining techniques for millimeter wave (mmWave) multiple input multiple output (MIMO) backhaul networks. We consider a scenario known as MIMO multi-X channel with L transmitter base stations and K receiver base stations, each equipped with multiple antennas, where each transmitter base station communicates simultaneously with all receiver base stations. The extremely short wavelength of mmWave requires the use of large antenna arrays at the base stations (BS) to combat the high path loss to achieve sufficiently high link gains, enabled by directional beamforming. As signal processing with large antenna arrays lead to implementations that are associated with high power consumption and high hardware complexity, hybrid (analog/digital) precoding/combining has been proposed recently to overcome these limitations. The design of such hybrid precoders/combiners is typically performed separately for the analog and the digital domains. In this work, we propose several novel low-complexity schemes suited for the digital part of such hybrid precoders/combiners. Our solutions are based on block-diagonalization and minimum mean squared error (MMSE) techniques and assume the availability of partial knowledge of CSI at each BS in the network. Finally the simulation results demonstrate the potential gains of the proposed algorithms.

Block diagonalization for interference mitigation in Ka-band backhaul networks

This paper considers the design of precoding and decoding techniques for backhaul networks at Ka band. In this frequency band, large antenna arrays must be employed with appropriate beamforming and precoding techniques to combat the high path loss. Traditional multi-antenna systems use digital baseband beamforming and precoding that is not economical for large antenna arrays due to its cost and power consumption. Recently, hybrid analog-digital solutions were suggested for millimeter wave multiple-input-multiple-output systems. They rely on two steps. The first step consists of an analog only beamforming which aims at the exploitation of the high antenna gain offered by the large-scale antenna array. The second step mitigates the multiuser interference by means of digital precoding. In this paper, we focus on the second step of the hybrid precoding. We propose a solution for interference mitigation in multi-base station scenarios. Our solution is based on a block diagonalization technique and requires full channel state information at each base station of a backhaul network. The performance of the algorithm is compared to a partial block diagonalization which was originally proposed for the single base station downlink scenario.

Setup and verification of a multi-GNSS over-the-air wave field synthesis testbed

In this paper, we describe the principle, hardware/software setup, calibration and verification measurement results of a wave field synthesis (WFS) over-the-air (OTA) testbed for global navigation satellite systems (GNSS). It represents a new approach that, in contrast to conventionally conducted and open-field tests, realistically emulates real world scenarios under controllable and repeatable conditions. This enables the realistic comparison of receivers and algorithms especially for multi/beamforming antenna receivers as well as for receivers with integrated antennas. Having outlined the architecture and hardware setup of the WFS OTA testbed together with the GNSS constellation simulator, we describe the current 2D setup and the upcoming 3D installation. Then we discuss and present results of two different ways of calibration and validation carried out in the 2D setup: firstly, using an electromagnetic field probe, and secondly, using a commercial geodetic GNSS antenna with reference receiver in a 2.5D emulation.