C. Umit Bas

A real-time MIMO channel sounder for vehicle-to-vehicle propagation channel at 5.9 GHz

This paper introduces a real-time multiple input and multiple output (MIMO) channel sounder to measure the vehicle-to-vehicle (V2V) propagation channel at 5.9 GHz. Compared to the existing V2V channel sounders, our design emphasizes on improving the stability of the setup and increasing the MIMO snapshot rate. The system stability allows us to develop a high resolution parameter extraction algorithm for the data analysis, which jointly estimates parameters of multipath components such as time-of-arrival, direction of departure, direction of arrival and Doppler shift. The second emphasis increases the maximal absolute Doppler shift to 806 Hz, which the system can estimate without ambiguity. The increased snapshot rate also provides a more fluent representation of the channel dynamics. We verify the design of the channel sounder with actual V2V channel measurements. Results suggest that 80 percent of the sample snapshots have a diffuse power ratio less than 20 percent and the extracted dominant specular paths match well with the environment and dynamics of the measurement.

High-Resolution Parameter Estimation for Time-Varying Double Directional V2V Channel

This paper describes a high-resolution parameter estimation algorithm applied to the vehicle-to-vehicle (V2V) multi-dimensional channel measurements. The algorithm, which is based on a maximum likelihood estimator, jointly estimates parameters of multipath components, such as time-of-arrival, direction of departure, direction of arrival, and Doppler shift. It serves to provide a comprehensive understanding of the V2V propagation channel. We propose computationally attractive methods to initialize parameters in the global search and evaluate key components in the local optimization. We also apply the algorithm to actual V2V channel measurement data. The results suggest an overall good performance of the estimator, where 80% of the snapshots have a diffuse power ratio less than 20% and the dominant specular paths match well with the environment and dynamics of the measurement.

3D MIMO Outdoor-to-Indoor Propagation Channel Measurement

The 3-D multiple-input multiple-output (3-D MIMO) systems have received great interest recently because of the spatial diversity advantage and capability for full-dimensional beamforming, making them promising candidates for practical realization of massive MIMO. In this paper, we present a low-cost test equipment (channel sounder) and post-processing algorithms suitable for investigating the 3-D MIMO channels as well as the results from a measurement campaign for obtaining elevation and azimuth characteristics in an outdoor-to-indoor (O2I) environment. Due to limitations in available antenna switches, our channel sounder consists of a hybrid switched/virtual cylindrical array with effectively 480 antenna elements at the base station. The virtual setup increased the overall MIMO measurement duration, thereby introducing phase drift errors in the measurements. Using reference antenna measurements, we estimate and correct for the phase errors during post-processing. We provide the elevation and azimuth angular spreads for the measurements done in an urban macro-cellular and urban micro-cellular environments, and study their dependence on the user equipment (UE) height. Based on the measurements done with UE placed on different floors, we study the feasibility of separating users in the elevation domain. The measured channel impulse responses are also used to study the channel hardening aspects of the massive MIMO and the optimality of the maximum ratio combining receiver.

Real-time ultra-wideband frequency sweeping channel sounder for 3–18 GHz

This paper presents system concept, calibration and example measurements of a novel ultra-wideband, real-time channel sounder. The sounder operates in the frequency range from 3 GHz to 18 GHz thus providing a Fourier delay resolution of 66.7 ps. The developed sounder measures overlapping sub-bands of 1 GHz bandwidth to cover the whole frequency range. This allows us to use a waveform generator and a digitizer with relatively lower sample rates and significantly lowers the cost compared to sampling the whole band at once. With the transmit power of 40 dBm, the maximum measurable path loss is 132 dB without accounting possible antenna gains. In this work, we also describe the calibration procedure along with the method to patch sub-bands into a combined channel response. This approach is validated by comparing the results from vector network analyzer(VNA) measurements performed in the same static environment. In contrast to VNAs, however, our sounder is real-time and can measure in dynamic environments with maximum Doppler spreads up to 166.7 Hz. Additionally, we present sample results from the first measurement campaign performed in an urban cellular scenario covering 3–18 GHz.