Jiri Blumenstein

In-Vehicle mm-Wave Channel Model and Measurement

This contribution documents and discusses recent wideband radio channel measurements carried out in the intra-vehicle environment. Channels in the millimeter-wave (MMW) frequency band have been measured in 55-65 GHz using open-ended rectangular waveguides. We present a channel modeling approach based on a decomposition of spatially specific Channel Impulse Responses (CIRs) into the large and small scale fading. The decomposition is done by a Hodrick-Prescott filter. We parametrize the small scale fading utilizing Maximum-likelihood estimates for the parameters of a generalized extreme value (GEV) distribution. The large scale fading is described by a two dimensional polynomial curve. We also compare simulated results with our measurement exploiting two-sample Kolmogorov-Smirnov test.

Frequency-Domain In-Vehicle UWB Channel Modeling

This paper aims to present a simple but robust model characterizing the frequency-dependent transfer function of an in-vehicle ultrawideband (UWB) channel. A large number of transfer functions spanning the UWB (3–11 GHz) are recorded inside the passenger compartment of a four-seated sedan. It is found that the complex transfer function can be decomposed into two terms, the first term being a real-valued long-term trend that characterizes frequency dependence with a power law and the second term forming a complex correlative discrete series that may be represented via an autoregressive (AR) model. An exhaustive simulation framework is laid out based on empirical equations characterizing trend parameters and AR process coefficients. The simulation of the transfer function is straightforward as it involves only a handful of variables; however, it is in good agreement with the actual measured data. The proposed model is further validated by comparing different channel parameters, such as coherence bandwidth, power delay profile, and root-mean-square delay spread, obtained from raw and synthetic data sets. It is also shown how the model can be compared with existing time-domain Saleh–Valenzuela-influenced models and related IEEE standards.

The characteristics of the 2D spreading based communication systems

This paper deals with characteristics and theory of code division multiple access (CDMA), orthogonal frequency division multiplexing (OFDM) and variable spreading factor orthogonal ferquency and code division multiplexing (VSF-OFCDM) systems. As comparison and evaluation of VSF-OFCDM with various 2D spreading factor (SF) as frequency and time dispersive transmission channel according to ETSI standard (typical rural area and warehouse enviroment) is being done.

In-vehicle UWB channel measurement, model and spatial stationarity

This contribution documents an ultra-wide band (UWB) channel measurement performed in an in-vehicle environment for the frequency range 3-11 GHz. An emphasis is placed into an evaluation of a spatial consistency of measured channel characteristics in terms of Pearson correlation between measured channel impulse responses (CIRs). Moreover, the measured CIRs are reproducible via a two-part exponentially decaying envelope-delay profile (EDP). The small scale variation of received signal is parametrized utilizing a random process obeying the generalized extreme value (GEV) distribution. Validation of the channel model is demonstrated utilizing a two sample Kolmogorov-Smirnov (K-S) test.

CLEAN algorithms for intra-vehicular time-domain UWB channel sounding

A comparison of two variants of CLEAN, a time-domain serial subtractive deconvolution algorithm, is presented. Appropriate statistical metrics for assessing the relative merit of the deconvolution technique are identified in the context of intra vehicle ultra wide band transmission, and the better variant was selected based on its performance over a standard IEEE channel simulation testbed. The chosen method is then applied to extract important channel characteristics for a real-world channel sounding experiment performed inside a passenger car.

Intra-Vehicular Path Loss Comparison of UWB Channel for 3-11 GHz and 55-65 GHz

This paper provides a comparison of a real-world intra-vehicular radio channel measurements of the ultra-wide frequency bands, namely the 3-11 GHz and the 55-65 GHz. The measurement campaign was performed utilizing a vector network analyzer (VNA) and a frequency domain method ensuring a high dynamic range of 70 dB and a frequency resolution of 10 MHz. An inverse Fourier transform is exploited for a transition of the measured data into the time domain and to obtain a channel impulse response (CIR). A delay spread and a path loss are derived and compared. Measured data is freely available online: http://www.radio.feec.vutbr.cz/GACR-13-38735S/.

Comparative Study Of Time-Frequency Analysis Approaches With Application To Economic Indicators.

Presented paper deals with comparison of various methods for time-frequency representation of a signal with time-varying behavior. We choose methods such as wavelet analysis, multiple window method using Slepian sequences, time-frequency varying autoregressive process estimation and time-frequency Fourier transform representation (periodogram). We apply these methods first on the simple simulated artificial signal and we assess their performance. Then we proceed with application on the real data which is monthly data of the industry production index of European Union in the period 1990/M1-2011/M11. During the evaluation we focus on the results with respect to the time of global crisis. The results of the experiments are represented in the the graphical form and briefly discussed. INTRODUCTION The description of time-frequency structure of signal has wide range of usage. Its application can be seen in many scientific areas such as engineering (Xu et al., 2011), medicine (Xu et al., 1999), economy and many others. In last several years these techniques are in the front of economic researchers which analyze comovement of economic indicators. In this sense the papers of (Rua, 2010), (Yogo, 2008) or (Hallett and Richter, 2007) and many others were written. Estimation of spectrogram or scalogram of input signal or time series depends on used methods and their parameters. We investigate in this article four basic methods such as wavelet analysis (Jan, 2002), multiple window method using the slepian sequences (MWM) (Xu et al., 1999), time-frequency varying autoregressive (AR) process (Proakis et al., 2002) spectrum estimation and time-frequency Fourier transform estimation (periodogram) (Jan, 2002). On the basis of simulations on the artificial well-know signal we analyze behavior of each method and search for their advantages, disadvantages and recommendations for their usage. Consequently we compare obtained results with the aim to give recommendation for methods application. In order to practically demonstrate and evaluate the performance of the chosen methods we apply them to the analysis of the real data which is the monthly data of the industry production index of the European Union countries in the period 1990/M1-2011/M11. The paper is organized as follows: In the section Methodical Background we describe chosen methods of time-frequency analysis. Consequently, in the section Data, we briefly describe data used both for the simulation as well as for the practical application. After that, in the section Simulation, we show results of an application of chosen methods on simulated artificial data. The section Application presents results of real data analysis of the industry production index of the European Union and its brief economic interpretation. In both later sections results are graphically represented. The paper ends up with the conclusion and the list of used references. METHODICAL BACKGROUND Let us have a signal (a time series) y(n), n = 1, . . . , N . Under assumption that the time series contain a longterm trend, we can apply additive decomposition in the following form y(n) = g(n) + s(n) + c(n) + ε(n), n = 1, . . . , N, (1) where g(n) denotes a long-term trend, s(n) is the seasonal component, c(n) is the cyclical component and ε(n) is the irregular component (a random noise). Focusing on analysis of cyclical movements around its longterm trend it is necessary to remove the long-term trend applying some filtering methods. When the seasonally adjusted data are not available (in other words the analyzed series contains the seasonal component), the seasonality should be removed by applying some corresponding method. The spectrum of the signal (time series) y(n), n = 1, . . . , N can be written as a Fourier sum (Hamilton, 1994)

Impulse Noise Mitigation for OFDM by Time-Frequency Spreading

This paper deals with the impulse interferences in modern vehicles and assesses the suitability of establishing in-vehicle wireless links replacing standard data cable bundles. According to our experiments, the standard UMTS Long Term Evolution (LTE) is highly affected by impulse noise. We compare it with a novel 2D signal spreading method exploiting the orthogonal Walsh-Hadamard sequences in order to spread the transmitted signal in time and frequency. This method requires minor modification of the 3GPP LTE standard while no additional bandwidth nor noticeable computational power is required. In the presence of impulse noise, the novel 2D spreading method outperforms the standard compliant LTE significantly. As a system model, we used an open source LTE downlink simulator developed at Vienna University of Technology and the Middleton Class A impulse noise model.

Two Dimensional Signal Spreading in UMTS LTE: Exploiting Time-Frequency Diversity to Increase Throughput

This paper proposes a two-dimensional spreading method in UMTS Long Term Evolution (LTE). Such a method brings additional time-frequency diversity which is beneficial in terms of the ability to decode transmitted data at the receiver site under multipath fading. Additional diversity is provided due to the fact that chips of transmitted signals are spread using a Walsh-Hadamard spreading sequence over several subcarriers as well as over several time-slots simultaneously. A comparison with state-of-the-art LTE downlink transmission is provided. To enable reproducibility and to increase credibility of our results, an open source Vienna LTE simulator is utilized. LTE transmissions with the proposed 2D spreading are tested on several channel models. Simulations show that apart from an Additive White Gaussian Noise channel model, this 2D spreading based method outperforms the throughput performance of standard LTE. At high Signal to Noise Ratio (SNR), the throughput increase in most channel models is higher than 10 %.

PAPR and amplitude distribution in MC-CDMA system

This paper analyzes the crash factor (CF) for mul-ticarrier code division multiple access (MC-CDMA) communication system. The CF (or peak to average power ratio - PAPR) is critical in multicarrier orthogonal systems (based on orthogonal frequency division multiplex - OFDM). The amplitude statistics for system are computed and gamma distribution is considered for amplitude distribution modeling. The distribution parameters are estimated for different scenarios (different number of users in system). The usability for PAPR reduction is discussed.