Wim Anton Theo Kotterman

60 GHz-Ultrawideband Real-Time Multi-Antenna Channel Sounding for Multi Giga-Bit/s Access

60 GHz technology has been proposed recently for multi-Giga-bit/s access within different application scenarios, e.g. in crowded multi-user public transportation (PT) environments. Hence, channel sounders that are used to investigate multipath propagation and multi-user access techniques including spatial diversity and beam-forming in time-variant shadowing environments require ultra-wideband (UWB) operation, multiple antennas, and real-time. This paper presents probably the first channel sounder architecture fulfilling these requirements. Moreover, an experimental study is described which is performed for planning purposes and deployment of 60 GHz WLAN/WPAN networks in PT scenarios. Coverage analysis based on different PHY channelization schemes, including multiple access point configurations and antennas is addressed for the Airbus 340 cabin. Additionally, distributions of time dispersion, coherent bandwidth, and Rice K-factor in the in-cabin coverage area are presented. Specifically, a brief analysis under dynamic channel conditions due to human activities is introduced. The suitability of the 60 GHz-UWB channels sounder for PT scenarios is demonstrated. Besides, some channel results for finding the most suitable system parameters for 60 GHz access deployment of in-flight-entertainment (IFE) systems are given.

Diversity properties of multiantenna small handheld terminals

Experimental data are presented on the viability of multiple antennas on small mobile handsets, based on extensive measurement campaigns at 2.14 GHz with multiple base stations, indoors, from outdoor to indoor, and outdoors. The results show medium to low correlation values between antenna branch signals despite small antenna separations down to. Amplitude distributions are mainly Rayleigh-like, but for early and late components steeper than Rayleigh. Test users handling the measurement handset caused larger delay spread, increased the variability of the channel, and induced rather large mean branch power differences of up to 10 dB. Positioning of multiple antennas on small terminals should therefore be done with care. The indoor channels were essentially flat fading within 7 MHz bandwidth (); the outdoor-to-indoor and outdoor channels, measured with 10 MHz bandwidth, were not. For outdoor-to-indoor and outdoor channels, we found that different taps in the same impulse response are uncorrelated.

Capacity of the mobile MIMO channel for a small wireless handset and user influence

We obtained results on the capacity of a mobile MIMO channel and on the influence of the user. Measurements were done in a configuration with three distributed transmitters equipped with single antennas and with a small wireless handset with four antennas, creating a 4Rx /spl times/ 3Tx configuration. We express the quality of the radio channel in terms of the effective degree of freedom (EDOF). From our measurement it follows that fitting a small handset with multiple antennas still makes sense in an outdoor-to-indoor mobile MIMO scenario. The channel capacity can be excellent, comparable with fully uncorrelated Rayleigh fading branch signals. However, on average the user should be satisfied with less favourable conditions amounting to a loss in EDOF of 0.16 at 50% complementary cumulative distribution function (CCDF) level. Systems operating without power control will suffer from an extra degradation in EDOF of 0.10 with an increased spread in channel quality both at the high and low end of the EDOF curve.

Correlation properties for radio channels from multiple base stations to two antennas on a small handheld terminal

It is generally understood that in Rayleigh fading radio channels, sufficient decorrelation for antenna diversity purposes is found at the mobile at antenna separations larger than about /spl lambda//2. However, it has been indicated that with dissimilar antennas with less separation on a small handset, still good diversity gain can be achieved(Pedersen et al. 1999). We present measurements of correlation properties with two similar antennas on our new small measurement handset (Kotterman et al. 2001) (connected by optic fibre, not by conducting cable) of indoor channels at 2140 MHz, including the user. The set-up is with three base stations (BS) simultaneously in order to simulate interference and macro diversity situations. We measured with two types of antennas, monopoles and patches (separation 0.29/spl lambda/ and 0.16/spl lambda/ resp.) in two buildings (old and modern construction) in two different BS configurations, each with up to twelve test users. At the smallest separation of 0.16/spl lambda/ the power correlation between branches remained below 0.83 for the fast fading (median values around 0.5). On the other hand, the slow fading can be strongly correlated between BSs (median value 0.8).

Quantification of Scenario Distance within Generic WINNER Channel Model

Starting from the premise that stochastic properties of a radio environment can be abstracted by defining scenarios, a generic MIMO channel model is built by the WINNER project. The parameter space of the WINNER model is, among others, described by normal probability distributions and correlation coefficients that provide a suitable space for scenario comparison. The possibility to quantify the distance between reference scenarios and measurements enables objective comparison and classification of measurements into scenario classes. In this paper we approximate the WINNER scenarios with multivariate normal distributions and then use the mean Kullback-Leibler divergence to quantify their divergence. The results show that the WINNER scenario groups (A, B, C, and D) or propagation classes (LoS, OLoS, and NLoS) do not necessarily ensure minimum separation within the groups/classes. Instead, the following grouping minimizes intragroup distances: (i) indoor-to-outdoor and outdoor-to-indoor scenarios (A2, B4, and C4), (ii) macrocell configurations for suburban, urban, and rural scenarios (C1, C2, and D1), and (iii) indoor/hotspot/microcellular scenarios (A1, B3, and B1). The computation of the divergence between Ilmenau and Dresden measurements and WINNER scenarios confirms that the parameters of the C2 scenario are a proper reference for a large variety of urban macrocell environments.

Over-the-air testing of Car-to-Car and car-to-infrastructure communication in a virtual electromagnetic environment

This paper provides an overview of over-the-air (OTA) testing for next generation communication devices with special consideration of Car-to-Car (C2C) and Car-to-Infrastructure (C2I) communication. Existing state-of-the-art techniques, their merits, and limitations are discussed. We identify the requirements for the OTA test in virtual electromagnetic environment (OTAinVEE) for the C2C/C2I communication scenario, where interference emulation becomes a highly challenging task. We propose systematic test procedure and closed-loop OTA set-up applicable for such scenario. Since the main test challenge in C2C/C2I communication is the modeling of highly time variant channel, we discuss channel modeling concepts and propose a framework appropriate for such communication. The ongoing activities in Ilmenau towards simulation and testing for C2C/C2I communication is also briefly discussed.

High time-resolution spectrum occupancy model for testing of cognitive radio devices

The ubiquitous problem of radio spectrum scarcity caused by ever-increasing traffic, e.g. in mobile communications, demands measures. One approach would be secondary use of spectrum by radio devices with cognitive abilities employing dynamic spectrum access. In order to avoid interference with the primary use of the spectrum, such cognitive devices must be thoroughly tested. In this paper, we present a high time-resolution model of spectrum occupancy, stemming from the activity of primary users, for testing purposes. The proposed model is based on a few statistical parameters and includes a novel parameter adaptation procedure that improves the accuracy of current models significantly. The intended use of the model is over-the-air testing of cognitive devices, for instance for prototyping purposes, e.g. evaluation of the achievable performance, or for conformance testing. The model parameters are extracted from measurement data in the GSM 900 downlink band obtained at the Ilmenau University of Technology campus. However, the modeling approach is not restricted to GSM 900 but lends itself to other bands and radio technologies, too.

Using software defined radios for baseband phase measurement and frequency standard calibration

We devise a novel phase and time error measurement technique for 10 MHz and 1 PPS reference signals, based on Software Defined Radios (SDR) and Digital Signal Processing (DSP). The proposed measurement setup allows us to employ two synchronized type N210 Universal Software Radio Peripheral (USRP) devices with LFRX daughterboards to realize an economically priced and easy-to-use quad-channel measurement setup. Our real-time C++ DSP software is based on the USRP Hardware Driver and enables flexible long-term measurements with verified sub-nanosecond precision. We demonstrate our intended use case, the calibration of two off-the-shelf rubidium standards (SRS FS725) against each other, using their RS 232 interface. By means of two 120 hour long-term measurements with a power cycle and cold start in between, we verify it is possible to reproducibly maintain a relative drift of ±5 parts-per-trillion, which is an order of magnitude better than specified by the FS725 data sheet. Additionally, we investigate the influence of the ambient temperature on short-term stability.

Virtual electromagnetic environment for over-the-air testing of car-to-car and car-to-infrastructure communication

This paper provides an overview of over-the-air (OTA) testing for Car-to-Car (C2C) and Car-to-Infrastructure (C2I) communication. We identify the requirements for OTA tests in virtual electromagnetic environments (OTAinVEE) for C2C/C2I communication scenarios, where emulation of known and unknown interference in addition to multipath becomes a highly challenging task. We propose a systematic test procedure and closed-loop OTA set-up applicable for such scenario. We discuss channel modeling concepts applicable to C2C/C2I communication scenario and propose an appropriate framework. The ongoing activities in Ilmenau towards simulation and testing for C2C/C2I communication are also briefly discussed.

Accuracy of an OTA system emulating a realistic 3D environment for GNSS and multi-satellite receiver testing

In satellite-based systems, such as global navigation satellite systems (GNSS), the use of antenna arrays is becoming increasingly common, as it allows various applications, such as jammer/spoofer suppression or improving the positioning accuracy in multipath-environments. Testing such equipment under realistic and reproducible conditions is often not feasible, for example in the case of a not fully deployed system (e. g., Galileo satellites) or testing of classified transmission technologies (e. g., Galileo public regulated service (PRS) receivers). For tests under reproducible and realistic conditions, we propose 3D wave-field synthesis (WFS) in an over-the-air testbed. This allows a realistic emulation of the radio environment under laboratory conditions. In this paper, a feasibility study for such a testbed is presented. Possible antenna setups for a 3D WFS laboratory environment are proposed. For these setups, the 3D WFS accuracy is investigated for emulating different polarization types and multipath reflections with arbitrary source directions. The results show that with presently available hardware for channel emulation and 3D WFS, a virtual electromagnetic environment can be created for testing receivers with (beamforming) antenna arrays of typical size (120 mm-300mm diameter).