Next-generation wireless communication systems will incorporate millimeter wave (mmWave) as one of the key technologies to increase data rates. These forthcoming mmWave systems will integrate multiple-input multiple-output (MIMO) technology to ensure sufficient link margin and are expected to be deployed in conjunction with sub-6 GHz systems. Configuring a MIMO communication link usually relies on estimating channel state information (CSI), which is difficult to acquire at mmWave frequencies due to the low pre-beamforming signal-to-noise ratio (SNR). In this paper, we propose a novel approach to estimate mmWave MIMO channels by leveraging out-of-band information from a sub-6GHz band. Utilizing this approach, we develop three channel estimation methods and compare these methods with one using only in-band information. We investigate the influence of theK-factor, the SNR and the number of antennas on the performance of the proposed channel estimation methods through simulations. Additionally, we compare these methods in terms of their computational complexity. Finally, we validate the performance of the proposed methods through channel measurements conducted in an outdoor environment. The results demonstrate that the proposed methods outperform in-band mmWave channel estimation in terms of spectral efficiency, particularly in scenarios of low SNR and high K-factor.

Future vehicular communication systems will extend deployed frequency bands from sub-6 GHz to millimeter wave (mmWave). To investigate different propagation effects between sub-6 GHz and mmWave bands in high-mobility scenarios, we proposed a suitable testbed setup to compare these two bands in a fair manner. Experiments conducted using the proposed testbed provide realistic results, but they are only usable if they can be faithfully reproduced. To quantify the reproducibility of the proposed testbed, we perform channel measurements at center frequencies of 2.55 GHz and 25.5 GHz at a velocity of 50 km/h. We investigate the influence of antenna pattern, time between measurements, signal-to-interference-and-noise ratio (SINR) and signal bandwidth on the reproducibility in terms of the channel correlation.

In an operational mobile cellular network, measuring the mean mobile broadband performance at a certain place in a building within a short period of time (e.g., several minutes) is a challenging task as fading is position dependent and the overall network load changes throughout a day. In this work we derive a measurement methodology that allows for swift and repeatable measurements of the mean network performance by combining three techniques: Firstly, the instantaneous IP-throughput is derived within one second by using a novel packet pattern method on an Android cell-phone with external antennas. Secondly, the long-term trend in the IP performance, that is the slowly changing average network load, is removed. Thirdly, the scenario mean of the remaining small scale fading scenario with overlaid fast network fluctuations is obtained by statistical inference, namely, spatial systematic-sampling with an XY-positioning table. To assess the validity of our approach, we present the results of a seven day long live-network measurement campaign in Vienna, Austria. We show that, once the long term network trend is removed, a one minute long measurement is sufficient to determine the mean IP-throughput performance over the whole week with 10% accuracy at 90% level of confidence.

We introduce a novel directional channel sounding concept where we sweep a horn antenna around its phase center. Directional channel measurements are thus carried out at a fixed coordinate in space. To verify our concept, we conducted multi-carrier measurements with 2 GHz of measurement bandwidth. The directional broadband channel was sampled uniformly within a cube of three wavelengths side length. In this contribution, we compare narrowband measurements with spatial averaging to traditional broadband channel sounding. We saw that, spatial filtering through directional antennas leads to a limited number of propagation paths in the channel. We show the difference of both approaches and explain the deviation by spatial correlation. The spatial correlation is evaluated at several two-dimensional slices. We observed wavelength-periodic correlations.

In this paper, we derive closed-form capacity expressions for a low complexity bit-interleaved coded modulation system with uniform inputs in a Rayleigh fading channel with additive white Gaussian noise. Additionally, we include pilot-symbol assisted channel estimation in our considerations. Finding a closed-form solution is enabled by assuming quantization and that the decoder has no channel state information. The effects of these assumptions on the capacity are investigated separately. To verify our closed-form expressions and to show the applicability of our system model to real world physical channels, we perform measurements using the Vienna Wireless Testbed.

Long Term Evolution (LTE) is expected to substitute the Global System for Mobile Communications (GSM) as the radio access technology for railway communications. Recently, especial attention has been devoted to high-speed trains since this particular environment poses challenging problems in terms of performance simulation and measurement. In order to severely decrease the cost and complexity of high-speed measurement campaigns, we have proposed a technique to induce effects caused by highly-time varying channels on Orthogonal Frequency-Division Multiplexing (OFDM) signals while conducting measurements at low speeds. In this work, we evaluate this technique by comparing the results of LTE measurements at different velocities as well as by simulations. Additionally, we use this technique to show the performance of LTE for high-speed train scenarios up to 600 km/h. To accomplish this, we use both a controlled high-speed measurement setup as well as a channel model developed according to the guidelines of the ITU Radiocommunication Sector (ITU-R) for the evaluation of radio interface technologies for IMT- Advanced systems.

This paper has two major contributions. First, we present measured frequency selective wireless channels and show that there is only a small difference between mutual information and capacity. For single-antenna channels the maximum difference is about 0.15 bit/s/Hz, but typical differences are much smaller. These differences are increased with the number of transmit and receive antennas, achieving a maximum of about 0.4 bit/s/Hz for 2×2 MIMO channels and about 1.8 bit/s/Hz for 4×4 MIMO channels. The second contribution is a simple two-parameter channel model for frequency selective wireless channels, exhibiting the identical behavior in terms of capacity and mutual information than the measured channels. Due to its simplicity, this so-called poor-rich model is especially suitable for fast simulations and for analytical research in the field of information theory.

Modern wireless communication systems employ MIMO and feedback-two properties that make it especially difficult to measure the performance of such systems with reasonable effort in actual outdoor scenarios. In this paper, we will present a time, cost, and manpower efficient measurement approach to evaluate the throughput achieved by such systems. Summer/winter, large distance outdoor-toindoor/outdoor, urban/alpine measurements have been carried out to successfully test this approach. Exemplarily, we report on the throughput gains (over TX power and base-station-antennarotation) of standard compliant 2 × 2 MIMO HSDPA and IEEE 802.16-2004 WiMAX when for example employing improved channel coding methods.

In this work, we provide a new throughput-based antenna selection criterion that considers the entire system design rather than only the channel state information. The performance evaluation was carried out in a measurement campaign in a common outdoor urban scenario. We present our results in terms of physical layer throughput over transmit power. In addition to diversity gains, we also see gains due to the selection of differently polarized antennas. In terms of SNR, the results show a gain of several decibels depending on the number of antennas selected.

In this work, we report on results of MIMO High Speed Downlink Packet Access (HSDPA) throughput measurements. These measurements were carried out in an urban scenario. Besides the standard compliant SISO and two transmit antenna schemes, we defined and measured also a four antenna scheme. In all throughput measurements we used link adaptation, that is, adaptation of the channel coding rate and adaptive preceding. The measured throughput is compared to a so-called "achievable throughput" that is calculated based on the mutual information of the channel measured.

Various publications have drawn a precise picture on how correlation and capacity change when decreasing the receive-antenna distance of a 2 x 2 MIMO transmission to less than 0.1 lambda; however, little is known on how today's commonly employed coding schemes actually perform under such harsh conditions. In this paper, we evaluate - by measurements with a testbed - the uncoded BER over antenna distance performance of: spatial multiplexing, a linear dispersion code, the Golden Code, as well as Alamouti coding. We show, that even at very small antenna distances, a significant gain compared to an ordinary 1 x 2 SIMO transmission can be measured.