In this paper, an Ultra-Wideband (UWB) double-directional channel sounding measurement and spatio-temporal analysis of UWB propagation based on the clusterization approach were reported. After separating the propagation paths and diffuse components both on the transmitter (Tx) antenna and receiver (Rx) antenna positions, the propagation paths both on Tx and Rx positions were observed for clusters separately, while coupling the clusters between Tx and Rx position based on similar time of arrivals, and ray tracing by utilizing high temporal and spatial resolution, respectively. The relation between direction of departure and direction of arrival will then be investigated. For cluster properties, parameters of model characteristics are discussed and compared to other earlier works.

In the urban area, buildings are the main scatterer which dominate the mobile propagation characteristics. However, reflection, diffraction, and scattering on the building surfaces in the radio environment induce undesirable multipath propagation. Multipath prediction with respect to a building surface has been conventionally based on an assumption that reflection from the surface has a substantial specular direction. However non-specular scattering from the building surface can affect the channel characteristics as well as specular scattering. This paper presents multipath characteristics of non-specular wave scattering from building surface roughness based on the experimental results. Superresolution method was applied as an approach to handle the signal parameters (DoA, ToA) of the individual incoming waves reflected from building surface roughness. The results show that the multipaths can be detected at many scatterers, such as ground, window's glass, window's frames and bricks surface, as well as directly from the transmitter. Most of the scattered waves are arriving closely from specular directions. The measured reflection coefficients were well bounded by reflection coefficients of the theoretically smooth and random rough surface. The Fresnel reflection coefficient formula, considering the finite thickness of the building surface and Gaussian scattering correction, give better prediction for glass and bricks reflection coefficient measurement.

Electronic Toll Collection (ETC), an application of Dedicated Short Range Wireless Communication (DSRC), had suffered from wrong operations due to multipath problems. To solve this problem, we proposed to apply a simple configured path determination scheme for the ETC system. The system consists of a vector network analyzer, low-noise amplifier, and X-Y positioner and achieves an automatic measurement of the spatial transfer function with emphasis on accurate measurement and reproducibility. For the reliable identification of the propagating paths, 3-D Unitary ESPRIT and SAGE algorithms were employed. Having developed the system, field experiments at the toll gate of the highway was carried out. In the measurements, we could determine many propagation paths so that the dominant propagation phenomena at the toll gate was identified. They included a ground-canopy twice reflected wave, which was a potential path that caused wrong operation. Consequently, their reflection coefficients and polarization characteristics were investigated. From the results, applicability of the path determination system for short range on-site measurement was confirmed.

Millimeter-wave (mm-wave) radio is attracting attention as one of the key enabling physical layer technologies for the fifth-generation (5G) mobile access and backhaul. This paper aims at clarifying possible roles of mm-wave radio in the 5G development and performing a comprehensive literature survey on mm-wave radio channel modeling essential for the feasibility study. Emphasis in the literature survey is laid on grasping the typical behavior of mm-wave channels, identifying missing features in the presently available channel models for the design and evaluation of the mm-wave radio links within the 5G context, and exemplifying different channel modeling activities through analyses performed in the authors' group. As a key technological element of the mm-wave radios, reduced complexity beamforming is also addressed. Design criteria of the beamforming are developed based on the spatial multipath characteristics of measured indoor mm-wave channels.

This paper introduces the concept of measuring double directional channels in ultra wideband (UWB) systems. Antenna-independent channel data were derived by doing the measurements in a wooden Japanese house. The data were useful for investigating the impact of UWB antennas and analyzing waveform distortion. Up to 100 ray paths were extracted using the SAGE algorithm and they were regarded as being dominant. The paths were then identified in a real environment, in which clusterization analyses were done using the directional information on both sides of the radio link. Propagating power was found to be concentrated around the specular directions of reflection and diffraction. This led to the observation that the spatio-temporal characteristics of extracted paths greatly reflected the structure and size of the environment. The power in the clusters indicated that the estimated 100 paths contained 73% of the total received power, while the rest existed as diffuse scattering, i.e., the accumulation of weaker paths. The practical limits of path extraction with SAGE were also discussed. Finally, we derived the scattering loss and intra-cluster properties for each reflection order, which were crucial for channel reconstrucion based on the deterministic approach.

This paper proposes a method for setting the threshold for ultra-wide-band (UWB) threshold-based ranging in indoor scenarios. The optimum threshold is derived based on the full analysis of the ranging error, which is equivalent to the probability of correct detection of first arriving signal in time-based ranging techniques. It is shown that the probability of correct detection is a function of first arriving signal, which has variations with two independent distributions. On the one hand, the first arriving signal varies in different positions with the same range due to multipath interference and on the other, it is a function of distance due to free space path-loss. These two distributions are considered in the derivation of the ranging error, based on which the optimum threshold is obtained. A practical method to derive this threshold is introduced based on the standard channel model. Extensive Monte Carlo simulations, ray-tracing simulations and ranging measurements confirm the analysis and the superior performance of the proposed threshold scheme.