Frequency bands above 6 GHz are being considered for future 5G wireless systems because of the larger bandwidth availability and of the smaller wavelength, which can ease the implementation of high-throughput massive MIMO schemes. However, great challenges are around the corner at each implementation level, including the achievement of a thorough multi-dimensional characterization of the mm-wave radio channel, which represents the base for the realization of reliable and high-performance radio interfaces and system architectures. The main properties of the indoor radio channel at 70 GHz, including angular and temporal dispersion as well as an assessment of the major interaction mechanisms, are investigated in this study by means of UWB directional measurements and ray tracing simulations in a reference, small-indoor office environment.

For multistatic radar networks in the upper mm-wave range with a large spacing between its radar sensor nodes, a coherent signal distribution is very complex and thus very costly. Hence, it is desirable to generate the mm-wave signals individually for each radar sensor node, i.e., non-coherently. However, multistatic radar networks using a non-coherent signal distribution for its radar sensor nodes are affected by systematic errors and uncorrelated phase noise, which reduces the resolution and the detection performance of these systems. In this article, a novel non-coherent signal synthesis concept based on the direct digital synthesis (DDS) principle is presented for multistatic radar networks. Compared to a signal synthesis using a phase-locked loop (PLL), it is shown that the different phase noise behavior of the DDS is beneficial for bistatic signal paths between the radar sensor nodes. The presented hardware concept is considered and analyzed for three different types of coherency regarding the signal distribution: coherent, quasi-coherent, and incoherent. Measurements with a multiple-input multiple-output (MIMO) radar at $150 \,\mathrm{G}\mathrm{Hz}$ prove that despite a non-coherent signal distribution, it is possible to achieve the same detection and imaging performance as with a fully coherent radar by using a DDS.

The vision of multi Gbit/s data rates in future mobile networks requires the change to millimeter wave (mm-Wave) frequencies for increasing bandwidth. As a consequence, new technologies have to be deployed to tackle the drawbacks of higher frequency bands, e.g. increased path loss. Development and verification of those novel technologies required an understanding of the propagation effects at mm-Wave which enabled by channel sounding measurements and analysis. Due to the variety of considered frequency bands and the necessity of spatial resolved measurements for e.g. testing of beamforming approaches, measurement duration and comparability becomes problematic. This paper presents multi-band channel sounder architectures, usable to measure up to four frequency bands simultaneously. Furthermore, we present a measurement campaign, featuring full polarimetric and directional resolved dual-band measurements, which comprises the microwave band at 10 GHz and the mm-Wave band at 30 GHz. Preliminary analysis results are presented.

Utilization of multiple input multiple output (MIMO) systems in radar and channel sounding has gained increased attention in recent years. Quite often, time-division multiplexing (TDM) is employed to realize orthogonal waveforms at the transmitter. Apart from its advantages, TDM has two severe drawbacks. First, motion-induced phase variations become indistinguishable from phase migration due to the signal's arrival direction. This is termed angle-Doppler coupling, which causes ambiguities in angle, and Doppler estimation. Second, the unambiguously resolvable Doppler, i.e., the Doppler bandwidth, is reduced. In this letter, a model-based estimation approach will be proposed, which compensates for angle-Doppler coupling, and restores the Doppler bandwidth. A data model for the MIMO observations is derived, which is exploited by a maximum likelihood estimator to infer angle, delay, and Doppler from the observations. The performance of the proposed approach will be testified by simulations.

Leakage in frequency-modulated continuous-wave (FMCW) radar with a homodyne receiver induces strong signal components in the lower frequency parts of the radar observations. There, the dynamic range of the observations has been reduced, such that close and weak targets are hard to detect. In this letter, a signal processing method is proposed to mitigate the leakage. First, background subtraction is applied to cancel the leakage. As the cancellation is imperfect, a noisy signal portion remains: the leakage noise. A statistical model is developed to describe the leakage noise as a colored noise process. This model is parameterized from measurements and used to whiten the observations. As a result, the dynamic range is improved, and the close targets become better detectable.

Antenna array calibration methods and narrowband direction finding (DF) techniques will be outlined and compared for a uniform circular array. DF is stated as an inverse problem, which solution requires a parametric model of the array itself. Because real arrays suffer from mechanical and electrical imperfections, analytic array models are per se not applicable. Mitigation of such disturbances by a global calibration matrix will be addressed, and methods to estimate this calibration matrix will be recapped from literature. Also, a novel method will be presented, which circumvents the problem of a changed noise statistic due to calibration. Furthermore, local calibration, where array calibration measurements are incorporated in the DF algorithm, is considered as well. Common DF algorithms will be outlined, their assumptions regarding array properties will be addressed, and required preprocessing steps such as the beam-space transformation will be presented. Also, two novel DF techniques will be proposed, based on the Capon beamformer, but with reduced computational effort and higher resolution for bearing estimation. Simulations are used to exemplary compare calibration and DF methods in conjunction with each other. Furthermore, measurements with a single and two coherent sources are considered. It turns out that global calibration enables computational efficient DF algorithms but causes biased estimates. Furthermore, resolution of two coherent sources necessitates array calibration.