Mitoshi Fujimoto

Channel capacity characteristics of multi-user MIMO systems in urban area

Multiple-Input Multiple-Output (MIMO) and Multi-User MIMO (MU-MIMO) systems have been expected to improve the channel capacity over a limited bandwidth of existing networks [1], [2]. The effects on channel capacity of Single-User MIMO (SU-MIMO) systems in urban scenarios have been previously studied [3]. It has been clarified that the larger number of antennas cannot contribute the improvement on the channel capacity in urban SU-MIMO scenarios due to very high spatial correlation. In this paper, we focus on the MU-MIMO transmission because it can discriminate multiple users by the difference of Angle of Arrival (AoA). We compare the Multi Access Channel (MAC) capacity in uplink with the channel capacity in SU-MIMO by setting the total numbers of transmitting and receiving antennas of SU-MIMO and MU-MIMO to be the same. When the same numbers of antenna elements are used, the better performance is obtained with MU-MIMO in urban scenarios, unlike identical independent distributed (i.i.d.) channels which are generally assumed in MIMO transmission. We also clarify an interesting relationship between the channel capacity improvement of MU-MIMO compared with SU-MIMO and a path visibility.

Mutual coupling reduction effects of EBG structure located on cylinder surface

EBG (Electromagnetic Band-Gap) structures composed of metal patches arranged at narrow intervals have been studied to apply to microwave components and antennas [1][2]. The EBG structures have the frequency-band-rejection characteristics and it can reduce the undesired radiation of electromagnetic waves [3]. In general, the EBG structure is made on the flat ground plane, and is not examined the design method when put on the curved surface. This paper describes the mutual coupling reduction effects of EBG structures located on cylindrical surface.

Effect of antenna element pattern on antenna pattern control of array antenna

There are some problems when spatial control schemes such as adaptive arrays and multi-input multi-output (MIMO) systems are applied to mobile terminals because they utilize several antenna elements on minute terminals. An analysis and evaluation of the effect of antenna element patterns on antenna pattern control of an array antenna is presented in this paper. The maximal ratio combining method is utilized as an example of a control method for MIMO systems. It is shown that interference can be adequately suppressed even if the antenna element pattern is not ideal and the element spacing is insufficient.

Variable reflection angle meta-surface using double layered patch type FSS

This paper proposes the variable reflection angle meta-surface using the double layered structure which can change the scatter pattern simply by sifting other layer. It is clarified that the gradients of the element vs. the reflection phase are changed by the relative position between two layers in double layered patch type FSS (Frequency Selective Surface). It is found that the reflection angle with range of about -34 deg. to -2 deg. is obtained in the proposed meta-surface.

Equivalent circuit analysis for double layer patch type AMC in consideration of mutual coupling between layers

This paper describes the equivalent circuit analysis of a double layer AMC (Artificial Magnetic Conductor) in consideration of mutual coupling between layers. The AMC with double layer patch type FSS (Frequency Selective Surface) is focused. This paper treats two type double layer structures. The one is stacked structure, and the other is alternated structure. It was shown that the calculated results by using the equivalent circuit well agreed with the results of the FDTD analysis. In addition, it was clarified that the stacked and alternated structures cause the common mode and the differential mode coupling, respectively. Moreover, it was shown that the miniaturization of the AMC is designed by setting the distance between the layers of double layer FSS as thin as possible.

Low-profile design of meta-surface by considering filtering characteristics of FSS

A FSS (Frequency Selective Surface) is composed of metal patches arranged in narrow intervals, and has frequency-band-rejection and frequency-band-pass characteristics. It is known that the FSS with the ground plane has PMC (Perfect Magnetic Conductor) characteristics in a specific frequency band. The surface is referred to as a meta-surface and it can control the phase of the wave which is reflected at the surface. This paper proposes a design method to realize a low-profile meta-surface. In the proposed method, the FSS which has low-pass or high-pass filtering characteristics is utilized. The effects of the filtering characteristics of a FSS on PMC characteristics of a meta-surface are described. Based on the calculated results, it is confirmed that the meta-surface can be obtained by using the FSS. In addition, it is found that the thinner and more wideband meta-surface can be achieved by using the FSS which has low-pass filtering characteristics.

DOA estimation without antenna characteristics calibration for UWB signal by using sub-band processing

In this paper, two types of sub-band technique to decrease the effect of antenna pattern distortion were proposed and evaluated; one was “Spectrum Averaging Method” and another was “Beam Averaging Method.” As the results, it was clarified that the estimation accuracy was greatly improved by “Spectrum Averaging Method”. It was also found that the accuracy of “Beam Averaging Method” was almost the same with “Spectrum Averaging Method” for phase error. Thus, the “Beam Averaging Method” is suitable for compensate the phase error of antenna elements.

Experimental study of adaptive array antenna system for ISDB-T high speed mobile reception

In this paper, we propose the system configuration in consideration of antenna directivity when four antennas are mounted on a vehicle and we experimentally demonstrate that the ISDB-T reception probability is improved while the vehicle moves at high speed.

Optimal tap interval in inverter noise suppression system

PCU (Power Control Unit) are installed in EV (Electric Vehicle) and HV (Hybrid Vehicle). Problems of inverter noise from the PCU become serious as popularization of the EV and H V. Especially, sound quality of AM radio is deteriorated due to the electrical noise because the AM radio utilizes relatively low frequency. As the countermeasure the authors proposed an inverter noise suppression system using a noise sensor and an adaptive filter. In this paper, the optimal tap interval of the adaptive filter in the proposed system is examined. As the result of examination, it is clarified that the optimal tap interval is 1/10 of the reciprocal of the frequency interval of the inverter noises.

Reflection Characteristics of Finite EBG Structures on Finite Ground Plane

In this paper, we take up mushroom type EBG structures and clarify the frequency-band-rejection characteristics of the finite EBG structures on the finite ground plane, and we also compare that with the infinite EBG structures and the semi-infinite EBG structures. Here, we analyze the reflection characteristics of a normal incidence plane wave.