Recently, thin wave absorbers composed of a periodic structure of metal patches have been reported in order to reduce the radar cross section (RCS). A high value of permittivity of the substrate or a very thin substrate are required in order to achieve stable operation for absorbing frequency at oblique incident angles. This paper shows the RCS reduction characteristics of a metasurface absorber with 0.1-mm thickness. RCS reductions are found at 9.88 GHz when the incident angle is 0 deg. The experimental results indicate a 10-dB reduction at TE mode. In addition, the curved wave absorber shows similar RCS reduction characteristics to those of the flat one. This experiment yields that the proposal wave absorber is possible to be used on the body of which surface is curved.

A slim vertically polarized omni-directional feed circuit integrated loop slot antenna for mobile base station is proposed in this paper. Picocell antenna requires a compact and slim structure, because its installation space is limited in urban areas. The proposed antenna consists of loop slots and patches to improve omni-directional pattern and bandwidth. In order to enhance the directivity gain, we arrange two loop slot antennas to be excited out of phase by a microstrip line. The size of the antenna is only 0.17λ × 1.45λ. This antenna realizes more than 15% relative bandwidth, and an omni-directional pattern in both simulation and measurement results.

A double-band circularly polarized (CP) patch antenna is presented. It is a round patch antenna with a cross-shape slot. Furthermore, it radiates wide beam CP waves at two radio-frequency identification (RFID) bands: 920 MHz and 2.45 GHz. Slightly oblate round patch antennas generally radiate CP waves and have resonant frequencies at two or more harmonic bands. To radiate wide beam CP waves at two bands, a cross-shape slot was made on a round patch antenna in this study. As a result, the cross-shape slot has made it possible for a 920 MHz round patch antenna to simultaneously radiate wide beam CP waves at 2.45 GHz which is higher than a harmonic frequency.

This paper presents a super directive, beam switched antenna for mobile terminal application in satellite communication system. The antenna employs two inverted F elements mounted on a ground plane which is optimized to be as the same size as typical smartphones. The inverted F elements are fed alternatingly while the other one acting as parasitic element. A simple feeding circuit utilizing PIN diodes is used to switch the unidirectional radiation pattern in yz-plane into two opposite directions. This paper discusses the complete prototype antenna which is fabricated to demonstrate the switching of the beam patterns in vertical plane.

This letter proposes a constrained beam selection scheme for wireless local area network (WLAN) systems and elucidates its effectiveness by a ray-trace simulation in an indoor environment. In the proposed selection scheme, a control engine connected to multiple access points (APs) first winnows down the beam pattern candidate of each AP based on the received signal strength indicators (RSSIs) between AP-stations (STAs) and between AP-AP as inter-cell interference power. Then, each AP communicates with own desired STAs using the beam pattern selected so that the RSSI at each desired-STA is maximized under each constrained candidate. Computer simulation results clearly show that the proposed selection scheme can offer higher the signal to interference and noise ratio (SINR) than the conventional approach in the targeted area.

The transmission factor from a capsule dipole antenna placed in a digestive system of a human body to the outside was investigated using the FDTD analysis. It was found that the local maximum of the transmission factor was observed in the frequency range of 400–600 MHz in the cases when a capsule dipole antenna passes through the different organs of a digestive system. Also it is confirmed that high value of the received power was obtained when the capsule dipole antenna and the receiving antenna have the same polarization.

In this paper, 1D sampling which exploits the symmetry of the phaseless planar near-field distributions of antenna is presented to reduce sampling points and the measuring time of the phase retrieval method. Not only the accuracy of the estimation but also the tolerance of probe-positioning error of sampling points are necessary in high frequency measurements because of its short wavelength. Using 1D sampling including the probe-positioning error, the far-field pattern is estimated with sufficiently small error in the simulation. In the measurement, the far-field can also be estimated from 1D near-field including probe-positioning error.

In this paper, measurements of a dipole antenna in deionized water and human body equivalent liquid were performed, and the measured results are compared with the numerical analysis. The dispersive characteristics of relative permittivity and conductivity of human body equivalent liquid were considered in the FDTD analysis. To evaluate the antenna characteristics in the broadband frequency range, the S-parameter method was used. The input impedance and the transmission coefficient obtained in the numerical analysis and measurement were shown to be in good agreement. The reliability of both measurements and analysis were confirmed. These methods are useful to the design of capsule antennas.

Massive multiple input multiple output (MIMO) improves transmission rate without increasing the complexity on signal processing by employing a large number of antennas at a base station. The effect of applying massive MIMO to small cells at the 2-GHz band has been reported. However, the primary targets of massive MIMO are small cells at a high-frequency band, because antenna size is considerably large when considering massive MIMO in a macro frequency band. In this study, measurements are performed for actual propagation channels using a wideband channel sounder with a horn antenna in the 20-GHz band in an actual indoor propagation environment. Moreover, the performance of interference rejection is evaluated using a virtual circular array antenna with 24 elements.

Technology of MIMO using multiple antennas and Carrier Aggregation operating multiple frequency bands are introduced in a mobile terminal to improve communication capacity. However, if plural MIMO antennas are installed closely, mutual coupling between the antennas must be reduced to suppress deterioration of radiation efficiency and increase of correlation coefficient. In this paper, we proposed a decoupling method for dual-band using trifurcation elements. Moreover, it is confirmed to be broadened decoupling bandwidth by optimizing branch width and length.

In this letter, we propose a near field wireless power transfer (WPT) system using reconfigurable transmitting/receiving antenna. The reconfigurable antenna is composed of parasitic elements with switches. Impedance of WPT system is changed by switching open/short termination and impedance matching condition can be improved when the misalignment of transmitting/receiving antenna are occurred. Therefore, the impedance mismatching loss is reduced, the power transmission efficiency is greatly increased. Result of numerical simulation shows the performance of the proposed system.

It is desirable for microstrip line/waveguide (MSL/WG) transitions to have low-loss, low-cost, and high-reliability. In order to suppress the unnecessary radiation which is a cause of loss, through-holes are provided in conventional transitions to surround the connection section. However, if through-holes are provided, manufacturing cost increases due to the greater complexity of the manufacturing process. In addition, since the dielectric expands and contracts due changes in temperature, problems arise involving decreased reliability, such as wire breakage due to application of tension to through-holes. Thus, this paper concerns a MSL/WG transition which simultaneously realizes low-loss, low-cost, and high-reliability by using a quarter-wavelength wavelength open stub instead of through-holes.

We present characteristics of a free access transmission line consisting of a paper substrate and foam for easy installation in body area network applications. The free access transmission line assists the communication between wireless devices. This paper shows the coupling characteristics between two dipole antennas with and without the transmission line. The coupling level on body propagation increase 30 dB by the assistance of transmission line.

In the development of intrabody communication systems, it is important to understand the effects of user’s posture on the communication channels. In this study, we conducted a statistical modeling of the dynamic intrabody communication channels in various grounding conditions of the transceivers. The proposed channel model was found to be useful to model the communication channels.

The finite difference time domain (FDTD) method is widely used for analyzing various electromagnetic problems including an interaction between antennas and human body. The FDTD method provides the accurate results in most cases, however, it is often encountered for obtaining the valid EM response that the number of FDTD iteration increases dramatically in low frequency range when finer mesh is used. This is due to the Courant stability condition. This paper studies a predicting technique of the steady state responses from the transient data by using the auto-regressive moving average (ARMA) algorithm. The effectiveness of this method is numerically confirmed by analyzing the electromagnetic fields due to loop antennas used for a MHz band wireless power transfer (WPT) system, which are placed near a rectangular human body phantom.

Scattering properties of meta-surfaces for plane wave incidences can successfully be analyzed using their own transmission line models (TLMs). The main idea of the TLM is the decomposition of a periodic structure into a frequency selective surface (FSS) or a meta-film and dielectric slab as a spacing medium between the FSS and a ground plane. Hence, how precisely obtain the scattering property of the FSS is one of essential points. This paper modifies a surface impedance expression of the FSS composed of square patch array so as to enable us to apply for general case, and incorporates it into the equivalent transmission line model of the meta-surface. The effectiveness of the proposed model is numerically confirmed by comparing with the FDTD calculation.

We study an analysis method for radiation characteristics of reflector antennas using measurement values from planar near-field antenna measurement (NFAM) of a primary feed. In planar NFAM, area truncation error (ATE) is an important error factor which must be considered. However, the effects of ATE are not clear in this analysis method. In this paper, we clarify the influence of area truncation level (ATL) on radiation characteristics for this analysis method by simulation. We use an offset parabola antenna, and compare the results using this analysis method and the physical optics method (PO), taking the edge level (EL) of the reflector and ATL as parameters.

Propagation characteristics have locality in a multipath fading environment. The locality is utilized for various applications using radio wave. Recently, on the other hand, new techniques to break the locality have been studied. In the techniques, received signals at arbitrary locations are estimated from remote receiving points. We present in this letter a new estimation technique of received signals utilizing Compressed Sensing (CS). In the technique, we estimate directions of arrival and each complex amplitude of arriving waves by CS, and calculate a received signal at a remote location based on the estimated results. We present the technique and evaluate the estimation performance through computer simulations.

The authors have proposed “Active Propagation Control” (APC) as a method to improve receiving transmission performance of a wireless communication channel. By APC, we can obtain better transmission performance by changing propagation characteristics actively in some ways, such as moving, rotating or transforming objects in the surrounding environment. In this paper, we evaluate the variation performance of the propagation characteristics of propagation control devices by indoor experiments and FDTD calculation to show the fundamental effectiveness of APC quantitatively.

Recently, the S-parameter method using a vector network analyzer was proposed whereby the differential input impedance of a balanced-fed antenna was obtained. To improve its measurement accuracy, the dependence on diameter of the semi-rigid cable used for the measurement jig is obtained from results of calculations using the FDTD method. Three jigs made from semi-rigid cables of differing diameter are fabricated; when coupled to a dipole antenna, the input impedances are measured as well as calculated using the S-parameter method. The impedances are also compared with those obtained from theories of King. Results from the S-parameter method indicate that using thinner-diameter coaxial cable produced very accurate measurements.

Recently, the increase in aged wanderers or the infant abduction is becoming the serious social problem. The practical use of the GPS function loadings shoes is advanced to prevent such incident occurring. The shoes mountable dual-band antenna that can correspond to the GPS signal reception, and the uplink into the wide area network is proposed in this report. The GPS-band of the proposal antenna is used to acquire the positional information on shoes. On the other hand, acquired shoes positional information is uplinked to the wide area network by Wi-Fi-band, and is used to inform the police or the nurse.

In order to realize a full-duplex wireless communication, the authors have proposed a spatial self-interference reduction technique with an end-fire array (EFA) which consumes only one degree of the multiple-input multiple-output (MIMO) freedom. However, this technique has a limited interference reduction performance due to an insufficient rank-degenerated interference channel because amplitude differences of the paths increase the rank of the channel in the EFA. In this letter, the authors propose a rotationally-symmetrical array (RSA) suitable for our conventionally proposing scenario to reduce the self-interference, where geometrical symmetry of the MIMO paths achieves a perfectly one-ranked channel and suppresses all of the self-interference in theory. Performance evaluation on the interference reduction level P_BF clarifies that the RSA reduces more interference than the EFA: P_BF = 47.3 dB (RSA), 23.0 dB (EFA) while array length of the transmitter (Tx), element spacing of the receiver (Rx), and distance between the Tx and Rx are 3.5 wavelengths, 0.5 wavelengths, and 5 wavelengths, respectively.

In this letter, we consider heterogeneous networks (HetNets) where interference alignment (IA), which is one of the promising interference management techniques, is applied. Using IA in HetNet has an issue that as the number of small-cells increases, small base stations (BSs) become more costly in terms of the number of antennas, because they require more spatial degrees of freedom (DoF) to align the inter-small-cell interference. To overcome this issue, we conduct clustering small-cells and aligning inter-small-cell interference only within each cluster, which reduces the number of required spatial DoF at each small BS. The effects of clustering small-cells are evaluated through the simulations and it is found that the achievable rate per transmit antenna increases by clustering small-cells.

To achieve cost-effective mobile fronthaul (MFH) with a time-division-multiplexing passive optical network (TDM-PON), we present a prototype optical-mobile cooperation interface, which converts mobile upstream scheduling information to transmission request information for the mobile upstream data that will arrive at each optical network unit (ONU). By basing bandwidth allocation on the request information converted by the interface, low-latency upstream transmission can be achieved on the MFH with the TDM-PON. We demonstrate the time spent for the conversion process in the prototype interface under various and practical conditions for the first time.

This paper presents a novel array configuration for high-resolution direction of arrival (DOA) estimation by extending the two-level nested array based on the concept of the Khatri-Rao product. We found that the proposed array configuration had larger aperture and higher degree of freedom in comparison with those of the two-level nested array, and also had a closed-form sensor position representation. Performance of the proposed array is evaluated through some computer simulation of DOA estimation.

This letter presents a low complexity cyclic autocorrelation function (CAF) computation technique for the spectrum sensing of orthogonal frequency division multiplexing (OFDM) signals in cognitive radio. Although CAFs are frequently employed in signal cyclostationarity detection (CD) based spectrum sensing, the computational complexity of CAFs is greater than that of signal energy. The presented technique computes the CAF by multiplying a received signal, delayed one and complex periodic function where these signals and function are thinned-out so that the sampling frequency becomes quadruple of a cyclic frequency. The employed function can only take the values ±1 and 0. Because the multiplication and addition can omit in the CAF computation, the computational complexity can be reduced. We numerically verify the effectiveness of the presented CAF computation technique.

Herein, we propose a novel scheme that combines information exchange and user activities in real-time so that those users can integrate their communications seamlessly with their daily lives. Called the Real-Spatial Information-Based Group Communication (r-Space) system, this scheme creates r-Space groups by considering personal and location information and enables users to share information within those groups. In a conventional message sharing scheme, when a user sends a data to other group members, multicast is normally used for the data delivery. However, because multicast does not have a mechanism to ensure the delivery of lost packets, the message may not be able to reach all of its intended recipients. With that point in mind, this paper proposes a reliable data delivery scheme that can improve packet delivery ratios and reduce transmission delays for r-Space communication. Later, we will evaluate this scheme via simulation.

Network monitoring for high-speed networks shared by an increasing amount of traffic has become a crucial issue. Especially, traffic anomaly detection technology for high-speed networks is one of the most important issues, because of the increasingly serious nature of cyber-attacks such as worms, port scans, and DDoS. This study focuses on the use of sketch schemes as data reduction methods for traffic anomaly detection. Previous studies on sketch schemes neglected to fully clarify the impact of the sketch parameters on the anomaly detection performance. This study verified the processing time and traffic anomaly detection accuracy with a sketch as a function of two sketch parameters: the number of hash functions and hash table size. The range of the two sketch parameters was clarified by determining the processing time and F-measure, which evaluates both the false positive and false negative rates.

A method is proposed for enhancing the transmission performance in a spatial division transmission system that utilizes the fading characteristics of two-ray ground reflection propagation. The method is tilting the elevation angle of antenna beams purposely towards out of the communicating peer. Using ray-tracing simulation, it is shown that the performance of the system is significantly improved when high-gain antennas with narrow beamwidth are used.

One significant problem of using discrete Fourier transform spreading-OFDM (DFTS-OFDM) is to produce the undesirable spectrum regrowth at the outside of allocated bandwidth due to the non-continuity between time domain symbols. To solve this problem, this paper proposes a simple spectrum regrowth reduction method for DFTS-OFDM by inserting interpolated samples for improving the continuity between symbols. This paper demonstrates the effectiveness of proposed method as comparing with conventional spectrum regrowth reduction methods by simulation results.

We propose use of the Functional Application Platform Interface mapped over Radio over Ethernet frames to develop a transport interface for the mobile fronthaul, i.e., the link between the baseband unit and remote radio heads for next generation cellular systems. We confirmed by numerical simulation that the statistical multiplexing effect was limited if the correlation between the streams was considered in the wireless system with the bandwidth of 600 Mb/s for 16 streams per access point. However we also confirmed that the required fronthaul capacity was suppressed to a few tens of Gb/s because the statistical multiplexing effect was still effective. Therefore, the fronthaul can be configured by a few links of cost-effective 10 Gb/s Ethernet.

Time fluctuation in mobile fronthaul (MFH) significantly degrades coordinated multi-point (CoMP) coherent joint transmission (JT). We examined the effect of time fluctuation on CoMP coherent JT by converting the time-fluctuation error into phase variation. We also investigated time-fluctuation requirements for MFH from the bit error rate characteristics using time-fluctuation as a parameter. On the basis of obtained results, we show that Ethernet based time synchronization technology can be applied and that CoMP performance is sufficiently achieved by a MFH with a layer 2 network.