Koichi Tsunekawa

Advanced LOS path-loss model in microcellular mobile communications

This paper proposes an advanced line-of-sight path-loss model incorporating characteristics of an actual urban environment. Accurate results are obtained by using a two-path model with shadowing caused by obstacles that would appear in an actual urban environment and rising reflection area caused by vehicular traffic. By applying the model in an urban environment, microcellular path loss can be predicted from ultra-high-frequency to microwave bands.

Measured path loss and multipath propagation characteristics in UHF and microwave frequency bands for urban mobile communications

This paper presents the frequency dependence of propagation loss and multipath propagation characteristics for urban mobile communications based on measurement results in Japanese urban areas. Path loss in reference frequencies from 457.2 MHz to 15.45 GHz increases according to the free space propagation power law in terms of frequency dependence for both macrocell and microcell environments. The standard deviation of each frequency band exhibits similar values. Wide-band propagation measurements show analogous characteristics among frequency bands from 3 to 15 GHz in urban multipath propagation. These measurement results show that the dominant difference among frequencies is found in only free space characteristics in terms of frequency dependence from the UHF to microwave frequency bands.

Performance Evaluation of 8×8 Multi-User MIMO-OFDM Testbed in an Actual Indoor Environment

Multiple input multiple output (MIMO) systems have attracted much attention as they can provide increased channel capacity within a limited frequency band. In some important applications, such as wireless LAN and cellular systems, MIMO systems will likely operate in environments for which a single base station should simultaneously communicate with many users. Such applications require development of multiuser(MU)-MIMO techniques. The prior work on MU-MIMO systems have resulted in derivation of the ideal channel capacity as well as various proposed schemes for transmission control and scheduling. In order to incorporate MU-MIMO technologies into commercial systems, extensive evaluations are needed, since the amount of system parameters in MU-MIMO is much larger as compared to the Signleuser(SU)-MIMO. Due to such a volume of system parameters, the performance of MU-MIMO in actual systems is still not well understood. This paper describes MU-MIMO testbed which can deal with 8times8 MIMO-OFDM transmission based on the IEEE 802.11a signal format. We have conducted experiments in an actual indoor environment in order to evaluate the frequency utilization for downlink scheme implemented in the MU-MIMO testbed. Finally, we discuss the effectiveness of MU-MIMO for SU-MIMO when the number of receiving antennas is changed

Low-voltage and broadband V-band InP HEMT frequency doubler MMIC

A broadband single-ended V-band InP HEMT frequency doubler MMIC is demonstrated. The fabricated frequency doubler MMIC was operated at 1 V drain supply voltage. The doubler consists of a fundamental input matching circuit and a (proposed herein) fundamental signal rejection filter that also operates as an output matching circuit. The fundamental signal rejection bandwidth of the proposed filtering circuit is more than four times wider than that of a conventional open stub circuit. The doubler MMIC realizes around 0 dB conversion gain and more than 22 dB isolation between the fundamental signal and 2nd harmonic signal over the output frequencies from 54 GHz to 70 GHz. The bandwidth over which both the 3-dB bandwidth and the isolation of 20 dB are satisfied is more than 26 %. The maximum conversion gain is 1.8 dB with 30.4 dB fundamental signal suppression at 60 GHz output frequency. The MMIC occupies just 0.89 mm 2 and consumes only 8 mW.

Geometrically based directional channel model for urban mobile communication systems

This paper proposes a geometrically based propagation model for an urban mobile environment that establishes a relationship between the angle-of-arrival and time-of-arrival of multipath components. The model is characterized by the geometric locations of a base station and mobile station among urban city structures. This model comprises three sets of propagation characteristics: the street-microcell propagation characteristics around mobile stations; the reflection and scattering characteristics around reflection areas; and the macrocell propagation characteristics from the reflection area to the base station. In particular, by using the propagation characteristics of a street-microcell around the mobile station, a more realistic model is established compared to previous models, which were based on circular or elliptic reflective areas.

Channel Capacity of TDD-OFDM-MIMO for Multiple Access Points in a Wireless Single-Frequency-Network

The multiple-input-multiple-output (MIMO) technique is the most attractive candidate to improve the spectrum efficiency in the next generation wireless communication systems. However, the efficiency of MIMO techniques reduces in the line of sight (LOS) environments. In this paper, we propose a new MIMO data transmission scheme, which combines Single-Frequency-Network (SFN) with TDD-OFDM-MIMO applied for wireless LAN networks. In our proposal, we advocate to use SFN for multiple access points (MAP) MIMO data transmission. The goal of this approach is to achieve very high channel capacity in both LOS and non line of sight (NLOS) environments. The channel capacity of the proposed method is derived for the direct path environments and it confirms the effectiveness of the proposed scheme in the LOS scenario. Moreover, solid computer simulation results confirm the effectiveness of the proposed method in both, single user and multiuser scenarios.

Novel microstrip antenna employing stacked rings on multi-layer ceramic substrate for mm-wave applications

This paper proposes a high-gain microstrip antenna employing stacked rings that uses a multi-layer high temperature co-fired ceramic (HTCC) substrate for a millimeter-wave system-on-package. The design and performance of the proposed antenna are described. The proposed antenna achieves the antenna gain of 15.7 dBi and its radiation efficiency is greater than 85.5%. This paper presents a 60-GHz band prototype antenna employing a multi-layer HTCC substrate that is well suited to achieving a low cost module. The measured performance of the prototype antenna is also described.

Frequency Correlation Characteristics Due to Antenna Configurations in Broadband MIMO Transmission

Recently, Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) has attracted much attention as a technology achieving high-speed wireless transmission with a limited bandwidth. However, since bit loading and adaptive modulation per sub-carrier should be employed according to the transmission quality of each sub-carrier in MIMO-OFDM, it is very important to understand the frequency correlation characteristics in broadband MIMO channels. This paper investigates the frequency correlation characteristics based on the antenna configuration for actual indoor MIMO channels. The results show that the frequency correlation of the channel capacity for the array antenna configured in the horizontal plane is significantly different compared to that configured in the vertical plane. Moreover, we propose a new cluster model that considers the antenna configuration in both the horizontal and vertical planes to estimate the frequency correlation in broadband MIMO channels.

Beamforming and antenna design techniques for realizing wideband MIMO-OFDM system

Multiple-input multiple-output (MIMO) techniques have emerged as a key technology for the next-generation wireless communication systems because these techniques enable very high data rate transmission using a limited frequency band. This paper proposed beamforming and antenna design techniques that improve hardware implementation, and described experimental equipment to actualize a wideband asymmetric MIMO-OFDM system.

Antenna selection method employing orthogonal polarization and radiation patterns for MIMO antenna

This paper proposes a simple antenna selection method that is suitable for the MIMO (Multi-Input Multi-Output) terminal antenna employing orthogonal polarizations and patterns. The combination of the antenna elements with the orthogonal polarizations and patterns is effective in reducing the antenna coupling and spatial correlation. As a basic consideration, a configuration of three orthogonal dipoles, which is the simplest configuration with orthogonal polarizations and patterns, is investigated to clarify the effectiveness of the antenna selection method. In this method, the vertical antennas, which tend to exhibit a high signal-to-noise ratio, are always used. This method allows the use of a fairly simple RF-switch circuit because the number of the antenna combinations is reduced. Based on numerical analysis, the proposed method provides channel capacity that is as high as that provided by the ideal antenna selection.