In order to utilize higher frequency bands above 6GHz, which is an important technical challenge in fifth generation mobile systems, radio propagation channel properties in a large variety of deployment scenarios should be thoroughly investigated. The authors' group has been involved in a fundamental research project aimed at investigating multiple-input-multiple-output (MIMO) transmission performance and propagation channel properties at microwave frequency above 10GHz from 2009 to 2013, and since then they have been conducting measurement and modeling for high frequency bands. This paper aims at providing comprehensive tutorial of a whole procedure of channel modeling; multi-dimensional channel sounding, propagation channel measurement, analysis, and modeling, by introducing the developed MIMO channel sounders at high frequency bands of 11 and 60GHz and presenting some measurement results in a microcell environment at 11GHz. Furthermore, this paper identifies challenges in radio propagation measurements, and discusses current/future channel modeling issues as future works.

A multiple-input multiple-output software defined radio (MIMO-SDR) platform was developed for implementation of MIMO transmission and propagation measurement systems. This platform consists of multiple functional boards for baseband (BB) digital signal processing and frequency conversion of 5 GHz-band radio frequency (RF) signals. The BB boards have capability of arbitrary system implementation by rewriting software on reconfigurable devices such as field programmable gate arrays (FPGAs) and digital signal processors (DSPs). The MIMO-SDR platform employs hybrid implementation architecture by taking advantages of FPGA, DSP, and CPU, where functional blocks with the needs for real-time processing are implemented on the FPGAs/DSPs, and other blocks are processed off-line on the CPU. In order to realize the hybrid implementation, driver software was developed as an application program interface (API) of the MIMO-SDR platform. In this paper, hardware architecture of the developed MIMO-SDR platform and its software implementation architecture are explained. As an application example, implementation of a real-time MIMO channel measurement system and initial measurement results are presented.

This paper shows the applicability of the integral equation formulation of the measured equation of invariance (IE-MEI) to two-dimensional dielectric scatterers. That is, a relationship between the scattered electric and magnetic fields, which is derived from the new formulation of the IE-MEI, is applicable to lossless dielectric materials as well as perfect electric conductors (PEC). In addition, we show that the IE-MEI does not suffer from internal resonance problems. These two facts are validated by numerical examples for a circular cylinder and a square cylinder illuminated by Transverse Magnetic (TM) plane wave or a TM line source very close to the scatterers. The numerical results calculated by the IE-MEI agree well with the ones by moment methods that employ combined field formulations with exact boundary conditions.

This paper describes the measurement techniques of emissions from UWB devices discussed in ITU-R task group (TG) 1/8 to study the compatibility between ultra-wideband (UWB) devices and radiocommunication services. This paper also provides the background idea behind the measurement methods, as the final output of the discussion, i.e. ITU-R Recommendation, will not contain any citations to the references, nor any "educational" description of the theoretical background.

A proper design and analysis of future wideband wireless communication systems require an accurate radio channel model. This model is claimed to characterize both the spatial and temporal channel characteristics. This paper investigates the spatio-temporal channel modeling based on a ray-tracing approach. The temporal channels are characterized by a delay profile. The statistical median and fading-fluctuation range of delay profiles are predicted from ray tracing by incorporating the random phase approach. A high level of agreement between predicted results and measured ones is observed in the verification. The spatio-temporal channel impulse response (CIR) predicted from ray tracing is also transformed to have limited band-width and limited beam-width characteristics. The applicability of this transformation is also verified by the comparison with measurement. These verifications prepare the ground for the use of ray-tracing approaches to evaluate system performance in real environments.

Implementation of Multi-Input Multi-Output (MIMO) channel sounder is considered, taking hardware cost and realtime measurement into account. A remarkable difference between MIMO and conventional Single-Input Multi-Output (SIMO) channel sounding is that the MIMO sounder needs some kind of multiplexing to distinguish transmitting antennas. We compared three types of multiplexing TDM, FDM, and CDM for the sounding purpose, then we chose FDM based technique to achieve cost effectiveness and realtime measurement. In the framework of FDM, we have proposed an algorithm to estimate MIMO channel parameters. Furthermore the proposed algorithm was implemented into the hardware, and the validity of the proposed algorithm was evaluated through measurements in an anechoic chamber.

This paper presents a $24 imes24$ MIMO channel sounder that has been developed based on a scalable fully parallel MIMO architecture. It can be flexibly configured with 3 sub-transmitters and 3 sub-receivers, each of which consists of 8 RF ports. This flexibility allows the measurement for both purposes of double directional and multi-link MIMO channel measurements. Implementation issues related to the multi-link operation on the fully parallel architecture were successfully solved by appropriate system design and applying several calibration techniques. The performance of the developed system was validated by extensive test experiments. Finally, a multi-link channel measurement example in an indoor environment was presented demonstrating the capability of the proposed system.

This paper presents a spatial fading emulator for evaluating handset MIMO antennas in a cluster environment. The proposed emulator is based on Clarke's model and has the ability to control RF signals directly in spatial domain to generate an accurate radio propagation channel model, which includes both uniform and non-uniform angular power spectra (APS) in the horizontal plane. Characteristics of a propagation channel such as fading correlations, eigenvalues and MIMO channel capacities of handset antennas located in the vicinity of the emulator's ring can be evaluated. The measured results show that the fading emulator with 31 antenna probes is sufficient to evaluate fading correlation and MIMO channel capacity of handset antenna in the case of a narrow APS with the standard deviation of more than 20 degrees.

In this paper we propose a novel spatial fading simulator to evaluate the performance of an array antenna and show its spatial stochastic characteristics by computer simulation based on parameters verified by experimental data. We introduce a cavity-excited circular array (CECA) as a fading simulator that can simulate realistic mobile communication environments. To evaluate the antenna array, two stochastic characteristics are necessary. The first one is the fading phenomenon and the second is the angular spread (AS) of the incident wave. The computer simulation results with respect to fading and AS show that CECA works well as a spatial fading simulator for performance evaluation of an antenna array. We first present the basic structure, features and design methodology of CECA, and then show computer simulation results of the spatial stochastic characteristics. The results convince us that CECA is useful to evaluate performance of antenna arrays.

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.

A radial line slot antenna (RLSA) is a high gain and high efficiency planar array. A single-layered RLSA is much simple in structure but the slot length must be varied to synthesize uniform aperture illumination. These are now commercialized for 12GHz band DBS reception. In RLSAs, considerable power is dissipated in the termination as is common to other traveling wave antennas; the uniform aperture illumination is not the optimum condition for high gain in RLSAs. Authors proposed a theoretical method reducing the termination loss for further efficiency enhancement. This paper presents the measured performances of the SL-RLSAs of this design with non-uniform aperture illumination. The efficiency enhancement of about 10% is observed; the measured gain of 36.7dBi (87%) and 32.9dBi (81%) for a 0.6mφ and 0.4mφ antennas respectively verify this technique.

This paper experimentally studies and models the angular-delay power spectrum density at the mobile station based on the site-specific measurement in a macrocell in urban area of Tokyo. The authors first show the azimuth power spectral density at the mobile station. It is decomposed into the "classes" which represent specific contributions within limited azimuth range, as well as the residual. The site-specific propagation mechanism of the classes are next discussed. Finally, the angular-delay PSD models of both classes and residual are proposed and verified. The analysis and modeling in this paper are antenna independent with the full polarimetric information. Consequently, the results are useful to evaluate the performance of arbitrary array antennas with mixed polarization. Due to the rare number of antenna-independent and full-polarimetric measurements, the significant contribution of the angular-delay PSD channel model can be expected.

A waveform of an ultra wideband impulse radio (UWB-IR) system can be extremely distorted through a channel even for free-space transmission because of antenna dispersion. This highly degrades the link budget performance. Therefore, the understand of antenna characteristics, which effects on waveform distortion, is necessary. This paper studies the waveform distortion due to antenna in free space transmission in UWB-IR system. The link budget is usually evaluated by using the Friis' transmission formula. However, it is not directly applicable to the UWB-IR transmission system. The link budget evaluation formula attended from conventional Friis' transmission formula that takes into account the transmitted waveform, its distortion due to the antennas, the channel and the correlation receiver is proposed. Since the antenna is significant pulse-shaping filters in UWB-IR system, the example kind of the log-periodic dipole antenna (LPDA) is experimentally examined, especially focused on the effect of the template waveforms.

This paper proposes a dual-band dual-rectangular-loop circular polarization antenna for Global Navigation Satellite Systems (GNSSs). The proposed antenna combines two large outer rectangular loops with two small inner loops. Each large outer loop is connected to its corresponding small inner rectangular loop. Each loop has gaps located symmetrically with respect to a feed point to produce Right Handed Circular Polarization (RHCP). The gap position and the shape of the rectangular loops are very important to adjust both the impedance matching and circular polarization characteristics. The proposed antenna offers dual-band Voltage Standing Wave Ratio (VSWR) and Axial Ratio (AR) frequency characteristics that include the L1 (1575.42 MHz) and L2 (1227.60 MHz) bands. The antenna gains exceed 8.7 dBi. Broad AR elevation patterns are obtained. These antenna characteristics are well suited to precise positioning.

This paper presents the analysis of the impedance characteristics of a sectoral cylindrical cavity-backed axial slot antenna excited by a probe. The integral equations are derived based on boundary conditions of the proposed structure and they are expressed in terms of dyadic Green functions and unknown current densities. The dyadic Green functions are obtained by using the eigenfunction expansion method together with application of scattering superposition techniques. The unknown current densities are solved by the Method of Moments. The input impedance is subsequently determined from the unknown electric current density at the probe. Numerical results of input impedance and return loss are demonstrated as functions of frequency for various parameters such as cavity length, cavity radius ratio, slot location in φ direction, slot length and probe length. Calculated results are validated by the measurements. At the operating frequency, it is found that the result is sufficiently accurate. The results from this study are very useful for the design of a sectoral cylindrical cavity-backed axial slot array antenna excited by a probe with omnidirectional beam radiation.

Automatic modulation classification (AMC) involves extracting a set of unique features from the received signal. Accuracy and uniqueness of the features along with the appropriate classification algorithm determine the overall performance of AMC systems. Accuracy of any modulation feature is usually limited by the blindness of the signal information such as carrier frequency, symbol rate etc. Most papers do not sufficiently consider these impairments and so do not directly target practical applications. The AMC system proposed herein is trained with probable input signals, and the appropriate decision tree should be chosen to achieve robust classification. Six unique features are used to classify eight analog and digital modulation schemes which are widely used by low frequency mobile emergency radios around the globe. The Proposed algorithm improves the classification performance of AMC especially for the low SNR regime.

In this paper, a novel approach of a human motion classification system in wireless body area network (WBAN) using received radio signal strength was developed. This method enables us to classify human motions in WBAN using only the radio signal strength during communication without additional tools such as an accelerometer. The proposed human motion classification system has a potential to be used for improving communication quality in WBAN as well as recording daily-life activities for self-awareness tool. To construct the classification system, a numerical simulation was used to generate WBAN propagation channel in various motions at frequency band of 403.5MHz and 2.45GHz. In the classification system, a feature vector representing a characteristic of human motions was computed from time-series received signal levels. The proposed human motion classification using the radio signal strength based on WBAN simulation can classify 3-5 human motions with the accuracy rate of 63.8-95.7 percent, and it can classify the human motions regardless of frequency band. In order to confirm that the human motion classification using radio signal strength can be used in practice, the applicability of the classification system was evaluated by WBAN measurement data.

A field trial, within a suburban macro-cell environment, of a space-time (ST) equalizer for TDMA mobile communication systems is described. The ST equalizer was a cascade connection of two array processors for a four-antenna array and a two-branch-metric-combining maximum-likelihood sequence estimation (MLSE) that was designed to obtain full space- and path-diversity gains from first-arrival and one-symbol-delayed signals while suppressing excessively long-delayed inter-symbol interference (ISI). The radio frequency was 3.35 GHz, the transmission rate was 4.096 Mb/s, and the modulation was QPSK. The long-delayed ISI reduction and the space-path diversity effect of the ST equalizer was validated by Eb/N0 vs. bit-error-rate (BER) curves with respect to delay spread and antenna spacing as compared with the case of an array processor alone being used.

This paper describes a method for evaluating the performance of a small magnetic core loop antenna used for radio controlled watches. Recently, amorphous metal core loop antennas are used as built-in small antennas inside a metal case. It is difficult to perform electromagnetic simulation for amorphous core loop antennas because of the complicated laminate structure. Therefore, we modeled the amorphous metal core loop antenna as an equivalent bulk structure having anisotropic permeability property that we can simulate. We analyzed the receiving sensitivity of the amorphous antenna by calculating the antenna factor. The receiving sensitivity degrades remarkably when an antenna is inside a metal case. We performed further simulation to investigate eddy current losses that cause deterioration.