In order to fulfill the demand of increasing data transmission rate, usage of THz band is attracting much attention. To overcome the high propagation loss in THz band, access points (APs) are supposed to be densely placed. In order to control radio resource usage of APs as well as supporting applications that require device positioning, it is highly desirable that symbol timings of the APs are synchronized. In this paper, as an alternative approach to use a synchronization master, network synchronization nor the synchronization using global navigation satellite system (GNSS), over-the-air (OTA) peer AP synchronization is proposed, where a pair of peer APs adjusts their symbol timings according to measured time of arrival (ToA) of each other's signal. By performing the peer AP synchronization with other surrounding peer APs, a whole group of APs can form a synchronized cluster. The results of computer simulations show that the maximum symbol timing difference of APs can be kept less than 10 ps for the case that the symbol duration is 100 ps, with which centimeter level device positioning can be supported.

The adoption of wireless communication in various fields has created the needs for easy wireless network construction and optimal wireless system selection, considering the coexistence of multiple wireless systems. In this paper, we propose two main contributions: a database that describes indoor building information and a wireless estimation method that uses deep learning. The first contribution involves digitizing indoor building information and creating the database for the building information, while the second utilizes the database to operate a deep learning model called RadioResUNet, which predicts the radio signal strength (RSS) of a 2.4 GHz Wi-Fi system in complex indoor environments with multiple walls and obstacles. By leveraging the building information database, the deep learning-based radio estimation method enables the estimation of RSS for a given building configuration and the position of the access point (AP). This method also allows for radio prediction in a desired area in advance, even when updating the indoor building information in the database. It can save time and expense while ensuring ongoing wireless connectivity support by comprehending the wireless situation of the new indoor building configuration,

In this paper, the received power calculated using ray-tracing simulations is compared with measurement data obtained in a factory environment. In order to reduce the errors of the ray-tracing received power at sub-6 GHz frequencies due to the wavelength being larger than many objects, a novel method to adjust the power of reflected and diffracted waves based on the wavelength and the dimensions of the objects is proposed. Through cross-validation of the proposed method at 922 MHz and 4.85 GHz frequency bands, the median absolute error of the ray-tracing received power value could be reduced from 9.7 dB and 4.1 dB to 4.6 dB and 2.2 dB for each frequency band respectively.

Bridge inspection using drones has become considerably more attractive owing to the ability of drones to gather information safely in lesser time and at a lower cost than traditional inspection methods. However, one of the critical issues in drone-based bridge inspection is ensuring stable communication between the operation base and inspection drones. The inspection drone easily loses sight of the operation base because bridges have intricate structures. Therefore, this study developed a radio map-based flight planning method of autonomous repeater drones for bridge inspection in order to ensure stable communication. Based on the inspection scenario, the repeater drone needs to ensure the communication with a minimum movement even under position deviations caused by winds. First, we generated a three-dimensional radio map of the bridge. Then, under the assumption that the inspection drone adopted a predetermined path, we developed a path planning method for a repeater drone based on the radio map. Some path planning examples demonstrated that the generated path reduces the moving distance and is also robust against the position error, in addition to ensuring stable communication.

In order to measure the propagation channel characteristics in a factory environment, measurements were performed in the 2.4 GHz and 5.2 GHz bands to obtain the received power and delay spread at various locations. The received power at several fixed locations was recorded simultaneously to measure the long-term power fluctuations caused by the dynamic factory environment. Power fluctuations were also recorded from a receiver placed on an Automatic Guided Vehicle (AGV) which frequently moved around a fixed area within the factory. The probability distribution of the received power was compared with several distribution models, and results show that they can be modelled using the stable distribution. Furthermore, analysis of the relationship between delay spread and received power between several transmitter and receiver locations in the factory suggested that they are inversely correlated, where the delay spread increased when the received power decreased.

This paper proposes a concept of large-scale emulation and evaluation environment of wireless communication systems. The environment can build radio nodes called virtual node by software in cyberspace and provide interaction among the virtual nodes and the reconfigurable physical radio devices that are connected to the environment from the outside. The environment therefore enables preliminary investigations and evaluations for the highly advanced and complicated wireless systems in the future. Moreover, in the radio interactive emulation, the radio propagation parameters based on the preliminary obtained models are suitably referred. The proposed wireless emulation environment enables wireless emulations required in the six typical wireless systems that are further developed and promoted in B5G/6G society. The paper shows evaluation and consideration of the fundamental performances for the proposed wireless emulation environment that includes numerical investigation for the interconnection performances between the virtual nodes and the reconfigurable physical radio devices, as well as fundamental operation for the wireless emulation with suitable visualization functions.

In recent years, the importance of pre-verifying the status of wireless communications has increased for designing offices. Because wireless communication is used for various purposes in offices, this technology has become a basic infrastructure for business. Therefore, when building a new office or renovating an office, verifying the impact on radio waves while designing the workspace is paramount. However, no highly accurate simulation tools for radio waves are available that can be easily used by office planners, who do not possess expert knowledge of radio waves. To address this challenge, we propose smart office planning system that can be linked to a radio wave emulation system that can verify radio wave propagation and communication behavior with high accuracy and can be easily used by office planners. This paper presents the results of a usability evaluation of a smart office planning system. As a result, users could easily set simulation scenario by preparing a general-purpose template option and could evaluate the state of wireless communication by using 2 visualization strategies: a three-dimensional visualization that simultaneously presents the three-dimensional structure of the office space, radio propagation, and communication behavior, and a two-dimensional visualization that visualizes problems affecting the quality of work. Moreover, in the future, by integrating the smart office planning system with the radio wave emulation system, office planners will presumably be able to verify the effects of workspace design on radio waves in advance, thereby reducing the man-hours required for office construction and ensuring adequate communication quality in the workspace.

This paper presents measurement and analysis results of power delay profiles and fading characteristics for “Public Broadband Wireless Communication (PBB) System” in VHF band. The PBB system was proposed to utilize a portion of vacant spectrum in VHF band due to the frequency reallocation plan in Japan, and the system was standardized as ARIB STD-T103 as well as IEEE802.16n. The purpose of this study is to evaluate the applicability of the system for non-line-of-sight urban environment and characterize the 200 MHz band broad band radio channel. The measurement is conducted by using a developed device which is compliant with the ARIB STD-T103 as a transceiver, and received signal is captured as complex IQ signals by using a signal analyzer. In order to obtain the power delay profile, impulse responses are analyzed by calculating sliding correlation between reference signal and measured signals. For the evaluation of delay characteristics, RMS delay spread is calculated using the power delay profile. In addition, fading characteristics is also shown to confirm the behavior of VHF band mobile propagation channel.

In this paper, diversity receiver performance at base station for VHF-band broadband mobile communication systems is examined by using measurement results. Diversity gain of two RX antennas for link budget calculation has been calculated by using a selective combining and an equal gain combining schemes. By analyzing the diversity gain statistically, it is found that the diversity gain of selective combining and its variation are increased in larger antenna separation and shorter transmission range. On the other hand, the diversity gain of equal gain combining and its variation are decreased in larger antenna separation and in shorter transmission range. In addition, a path loss model has been developed for a link budget design. The path loss model parameters are extracted for over 1 km transmission range. By considering the path loss model with analytically-extracted constant diversity gains for BS antenna separation lengths of 1, 5, and 10 wavelengths, the system service coverage can be estimated.

This paper performs the world's first IEEE 802.11af based Wireless Local Area Networks (WLAN) operating in TV White Space (TVWS) indoor experiment in the Ofcom TVWS pilot program of the UK. The prototype system consists of TVWS Database (WSDB), Registered Location Secure Server (RLSS), and two prototype hardware for an Access Point (AP) and a Station (STA). The developed WSDB qualified by Ofcom TVWS pilot program of the UK. The prototype hardware meets to the transmission spectrum regulation of the European Telecommunication Standards Institute (ETSI). By using the developed system, a trial indoor experiment performed in the building of the King's College London (KCL), Denmark Hill Campus in London, UK. The prototype system and the experiment results show an effectiveness of the IEEE 802.11af and indicate the way to the practical application.

An IEEE 802.11af indoor trial experiment has been conducted in the Ofcom pilot program of the United Kingdom. This paper describes an indoor propagation characterization and throughput estimation method using prototype devices based on the IEEE 802.11af standard. Since the IEEE 802.11af is recent technology for TV white space (TVWS) spectrum sharing, indoor propagation measurements at TVWS band for WLAN usage are very seldom in the previous researches. Path loss model parameters has been extracted for each line-of-sight (LoS) and non-LoS (NLoS) situation on the same floor. Also a fluctuation of measured path loss is analyzed using the log-normal and the extreme value distributions. A developed path loss model is useful for the location design of access points and the interference risk estimation for IEEE 802.11af devices. As another modeling, a throughput estimation model has been developed using the exponential distribution derived from the cumulative probability distribution (CDF) of measured throughputs. By combination of the developed path loss model and the throughput estimation model, throughput can be estimated as a function in each LoS and NLoS situation.

In order to solve the problem of multi-Gbps transmission in 60 GHz band - communication interruption by human body crossing, this paper proposes a method to increase reflected waves by installing artificial reflector(s) in two-dimensional arrangement and shows a good improvement of disconnection probability reduction to 1/4 (by one artificial reflector) and to 1/16 (by two reflectors). The interruption by human crossing is modeled and locations of transmitters and receivers are set on any grid of sub-partitioned rooms by grid (room sizes are defined by IEEE 802.11ad) to get statistically meaningful data. The computer simulations have been carried out with various TX and RX antenna HPBWs (Half Power Beam Width), several receiver sensitivities corresponding to 3Gbps to 0.5Gbps transmissions and by assuming a fixed TX antenna direction and a beam-forming receiver antenna that can track the incoming reflected wave(s) in case of LOS (Line of sight) path interruption. The simulation results show that disconnection probability reduction from about 80% to 20-10% by setting an artificial reflector to generate an additional reflected path and a reduction to 5% by setting two artificial reflectors when the TX and RX antennas' HPBWs are 30degree and the receiver sensitivity is -55.0dBm. The improvements by the proposed method are generally applicable to similar indoor communications environments.

An orthogonal polarization based MIMO transmission scheme is proposed to achieve over 10Gbps transmission for advanced 60GHz WLAN. As the proposed MIMO transmission scheme uses V(Vertical)/H(Horizontal) polarization directional antennas, stable 2×2 MIMO transmission is enabled even in LOS (line-of-sight) environment. A ray-tracing method is employed for computer simulation to evaluate channel capacity and BER performance of the proposed scheme in indoor conference room environments. The simulation results confirm that the proposed orthogonal polarization based MIMO transmission scheme achieves higher channel capacity than the conventional MIMO transmission using the same polarization antenna. Furthermore, this paper shows that BER performance depends on the location of transmitter and receiver as well as the beam-width of the directional antenna. BER performance is significantly degraded when the antenna height of the transmitter is the same as that of the receiver. On the other hand, better BER performance can be achieved when the antenna height difference is large.

In order to realize very high throughput wireless local area network (WLAN) systems, which demand multi Gbps capacities/bitrates, the IEEE802.11.TGad (Next generation WLAN standard at 60GHz band) is in the standardization process. To evaluate and select the proposed physical layer modulation and coding schemes in the standardization process, channel models for each specified usage model are required. In this paper, suitable impulse channel models for that purpose are proposed. Propagation measurements are carried out in a living room environment in the 60GHz band. To cover various usage cases, line-of-sight (LOS) and non-line-of-site (NLOS) scenarios and three different signal transmission polarization types are examined, and each channel model's parameters are extracted by statistical analysis. These channel models are useful in designing systems for millimeter-wave wireless communications.

In order to clarify the dual antenna offset channel model needed to transmit multi gigabit/sec streams with directional Tx and Rx antennas at 60 GHz, the paper describes the measurement results of vertical, horizontal and circular polarized signal transmission using co-polarized and cross-polarized directional antennas. Measurement results show that the number of strong reflection waves depends on the polarization type and that the power of cross-polarized wave transmission is very small. These results are useful for developing the novel indoor millimeter-wave channel model that considers AoD, AoA and polarization type.

In order to realize intra-car multimedia communications systems composed of entertainment which requires several hundred Mbps to 1 Gbps capacity and monitoring signal transmission between many parts of the car which requires high reliability and low latency, this paper proposes a millimeter wave system which has high capacity and low latency transmission capability. To clarify the feasibility of millimeter wave systems applications to intra-car multimedia communications, propagation characteristics inside a car have been extensively measured and analyzed. The proposed system sets a car navigator as the center of Intra-car multimedia communications with an Omni antenna and receivers are assumed at front seats, back seats and the luggage space behind the back seats in a typical SUV (Sports Utility Vehicle). The measured results show i. Front seat communications are no worry with simple single carrier (SC) modems without any equalizer, ii. Back seats communications may need beam forming capability for better receive signal power (an Omni antenna system still works with a simple SC modem with a simple rake receiver but without any equalizer, iii. "Luggage space communications may require a directive / beam forming antenna for better receive signal power. The maximum delay spread observed is 6 to 7 ns and no equalizer necessity has been found for Omni antenna receivers inside a car. Further advancement to beam forming antenna will have only 1 - 2 ns maximum delay spread inside a car. Thus, this paper has proved the feasibility of millimeter wave intra-car multimedia communications system by employing a simple single carrier modem without any equalizers but with simple rake receivers.

In order to realize a vehicle area network for multimedia entertainment systems, which demand capacities of up to 1 Gbps, and vehicle control links between many parts of the car, which demand high reliability and low latency, this paper proposes a millimeter-wave system that offers high capacity and low latency transmission. Propagation measurement results show the maximum delay spread of 6 - 7 ns can be achieved with omni antennas without complicated equalizers. Feasible advances in beam forming antenna performance will reduce the maximum delay spread inside the car to only 1 - 2 ns. This paper proves that millimeter-wave vehicle area networks can support multimedia communications as well as control links by employing a basic single carrier modem with simple rake receivers; no equalization is needed.

Proposed PHY layer schemes are evaluated using the channel model that corresponds to each usage model in IEEE802.15.3c standardization process. NICT has contributed TSV model to the IEEE802.15.3c channel model subgroup. The model developed by NICT has been selected as the model for the evaluation of mandatory simulations. This paper describes the channel model for millimeter-wave band developed for the TG3c.