E-learning, which can be used anywhere and at any time, is very convenient and has been introduced to improve learning efficiency. However, securing a completion rate has been a major challenge. Recently, the learning forms of e-learning require learners to be introspective, deliberate, and logical and have proven to be incompatible with many learners with low completion rates. Thus, we developed an e-learning system that incorporates a fill-in-the-blank question-type concept map to deepen learners' understanding of learning contents while watching learning videos. The developed system promotes active learning reflectively and logically by allowing learners to answer blank question labels on concept maps from video content and labels associated with the blank question labels. We confirmed in the laboratory experiment by comparing with a conventional video-based learning system that the developed system encouraged a learner to do more system operations for rechecking the learning content and to better understand the learning contents while watching the learning video. As the next step, a field experiment is needed to investigate the usefulness and effectiveness of the developed system in actual environments in order to boost the practicality of the developed system. In this study, we introduced the developed system into the two class of the uviversity course and investigated the level of understanding to the learning contents, the system operations, and the usefulness of the developed system by comparing with those in the laboratory experiment. The results showed that the developed system provided to support the understanding to learning content and the usefulness of each function in the field experiment, as in the laboratory experiment. On the other hand, the students in the field experiment gave lower usefulness of the developed system than those in the lab experiment, suggesting that the students who attempted to thoroughly understand the learning contents in the field experiment were fewer than those in the lab experiment from their system operations during the learning.

This paper evaluates a variety of key 5G technologies such as base station (BS) massive multiple-input multiple-output (MIMO) antennas, beamforming and tracking, intra-baseband unit (BBU) hand over (HO), and coverage. This is done in different interesting 5G areas with a variety of radio conditions such as an indoor office building lobby, an outdoor parking area, and a realistic urban deployment of a 5G radio access system with BSs installed in buildings to deploy a 5G trial area in the Tokyo Odaiba waterfront area. Experimental results show that throughput exceeding 10Gbps is achieved in a 730MHz bandwidth using 8 component carriers, and distributed MIMO throughput gain is achieved in various transmission point deployments in the indoor office building lobby and outdoor parking area using two radio units (RUs). In particular, in the outdoor parking area, a distinct advantage from distributed MIMO is expected and the distributed MIMO gain in throughput of 60% is achieved. The experimental results also clarify the downlink performance in an urban deployment. The experimental results show that throughput exceeding 1.5Gbps is achieved in the area and approximately 200 Mbps is achieved at 500m away from the BS. We also confirm that the beam tracking and intra-BBU HO work well compensating for high path loss at 28-GHz, and achieve coverage 500m from the BS. On the other hand, line of sight (LoS) and non-line-of sight (N-LoS) conditions are critical to 5G performance in the 28-GHz band, and we observe that 5G connections are sometimes dropped behind trees, buildings, and under footbridges.

Fifth-generation mobile communication systems (5G) must offer significantly higher system capacity than 4G in order to accommodate the rapidly increasing mobile data traffic. Cell densification has been considered an effective way to increase system capacity. Unfortunately, each user equipment (UE) will be in line-of-sight to many more transmission points (TPs) and the resulting inter-cell interference will degrade system capacity. We propose large-scale coordinated multi-user multiple-input multiple-output (LSC-MU-MIMO), which combines MU-MIMO with joint transmission from all the TPs connected to a centralized baseband unit. We previously investigated the downlink performance of LSC-MU-MIMO by computer simulation and found that it can significantly reduce inter-TP interference and improve the system capacity of high-density small cells. In this paper, we investigate the throughput of LSC-MU-MIMO through an indoor trial where the number of coordinated TPs is up to sixteen by using an experimental system that can execute real-time channel estimation based on TDD reciprocity and real-time data transmission. To clarify the improvement in the system capacity of LSC-MU-MIMO, we compared the throughput measured in the same experimental area with and without coordinated transmission in 4-TP, 8-TP, and 16-TP configurations. The results show that with coordinated transmission the system capacity is almost directly proportional to the number of TPs.

This paper describes the results of outdoor mobility measurements and high-speed vehicle tests that clarify the 4-by-8 multiple-input multiple-output (MIMO) throughput performance when applying distributed MIMO with narrow antenna-beam tracking in a 28-GHz frequency band in the downlink of a 5G cellular radio access system. To clarify suitable transmission point (TP) deployment for mobile stations (MS) moving at high speed, we examine two arrangements for 3TPs. The first sets all TPs in a line along the same side of the path traversed by the MS, and the other sets one TP on the other side of the path. The experiments in which the MS is installed on a moving wagon reveal that the latter deployment case enables a high peak data rate and high average throughput performance exhibiting the peak throughput of 15Gbps at the vehicle speed of 3km/h. Setting the MS in a vehicle travelling at 30km/h yielded the peak throughput of 13Gbps. The peak throughput of 11Gbps is achieved at the vehicle speed of 100km/h, and beam tracking and intra-baseband unit hand over operation are successfully demonstrated even at this high vehicle speed.

This paper presents outdoor field experimental results to clarify the 4-by-4 multiple-input multiple-output (MIMO) throughput performance when applying joint transmission (JT) and distributed MIMO to the 15-GHz frequency band in the downlink of a 5G cellular radio access system. Experimental results for JT in a 100m × 70m large-cell scenario show that throughput improvement of up to 10% is achieved in most of the area and the peak data rate is improved from 2.8Gbps to 3.7Gbps. Based on analysis of the reference signal received power (RSRP) and channel correlation, we find that the RSRP is improved in lower RSRP areas, and that the channel correlation is improved in higher RSRP areas. These improvements contribute to higher throughput performance. The advantage of distributed MIMO and JT are compared in a 20m × 20m small-cell scenario. The throughput improvement of 70% and throughput exceeding 5 Gbps were achieved when applying distributed MIMO due to the improvement in the channel correlation. When applying JT, the RSRP is improved; however the channel correlation is not. As a result, there is no improvement in the throughput performance in the area. Finally, the relationship between the transmission point (TP) allocation and the direction of user equipment (UE) antenna arrangement is investigated. Two TP positions at 90 and 180deg. from each other are shown to be advantageous in terms of the throughput performance with different direction of UE antenna arrangement. Thus, we conclude that JT and distributed MIMO are promising technologies for the 5G radio access system that can compensate for the propagation loss and channel correlation in high frequency bands.

This paper presents beamforming and beam tracking techniques and downlink performance results from field experiments using a Proof-of-Concept (PoC) system. The PoC implements a 5G mobile radio access system in the millimeter wave band and utilizes beamforming and beam tracking techniques. These techniques are realized with a dielectric lens antenna fed by a switched antenna feeder array. The half-power beamwidth of the antenna is 3° corresponding to massive MIMO using approximately 1000 antenna elements. The system bandwidth is 1GHz and the center frequency is 73.5GHz. Adaptive modulation and coding using four modulation and coding schemes is implemented. The field experiment is conducted in the following small cell environments: a courtyard, a shopping mall and a street canyon. The majority of the test area is Line-Of-Sight (LOS) however the shopping mall course contains 69% Non-LOS (NLOS) conditions. The results show that the maximum throughput of over 2Gbps using rate 7/8 coded 16QAM modulation is achieved in 87%, 34% and 28% of each of the respective environments. The beam tracking achieves high availability of coverage and seamless mobility not only in LOS environments but also under NLOS conditions through the reflected paths.

In multi user multiple input multiple output systems, spatial precoding is typically employed as an interference cancellation technique. This technique, however, requires accurate channel state information at the transmitter and limits the mobility of the mobile station (MS). Instead of spatial precoding, this letter implements collaborative interference cancellation (CIC) for interference suppression. In CIC, neighboring MSs share their received signals without decoding and equivalently increase the number of received antennas. The performance is evaluated through a field experiment using a vehicle that is equipped with seven MSs and moves around an urban area.

The performance in terms of the user separation of multi-user multiple-input multiple-output (MU-MIMO) depends on not only the spatial correlation but also the location of the mobile stations (MSs). In order to take into account the performance in terms of the user separation, we need to consider the granularity of the beam and null width of the precoded antenna pattern in addition to the spatial correlation to determine the base station (BS) antenna configuration. In this paper, we propose Smart Vertical MIMO (SV-MIMO) as the best antenna configuration that achieves both spatial correlation and granularity of the beam and null width of the precoded antenna pattern. We evaluate SV-MIMO in a field experiment using a downlink 4-by-2 MU-MIMO configuration focusing on the dependency of the location of the MSs in Yokosuka, Japan. The majority of the measurement course is under line-of-sight (LOS) conditions in a single cell environment. The MSs are almost uniformly set 30 to 60 degrees in azimuth and 12 to 30 degrees in elevation and the distance from the BS antennas is approximately 150m at maximum. We also evaluate the performance of 4-by-2 MU-MIMO using the conventional type of horizontal array antenna and show the difference. The field experimental results show that throughput of greater than 1Gbps is achieved at the Cumulative Distribution Function (CDF) of 14% by employing SV-MIMO for Rank-4 MU-MIMO. The throughput of SV-MIMO is 30% higher than that for the horizontal array antenna configuration at the CDF of 50%.

Multiple-input multiple-output (MIMO) systems with antenna selection are practical in that they can alleviate the computational complexity at the receiver and achieve good reception performance. Channel correlation, not just carrier-to-noise ratio (CNR), has a great impact on reception performance in MIMO channels. We propose a practical receive antenna subset selection algorithm with reduced complexity that uses the condition number of the partial channel matrix and a predetermined CNR threshold. This paper describes the algorithm and its performance evaluation by both computer simulation and indoor experiments using a prototype receiver and received signals obtained in an actual mobile outdoor experiment. The results confirm that our proposed method provides good bit error rate performance by setting the CNR threshold properly.

The present paper introduces a prototype design and experimental results for a multi-user MIMO linear precoding system. A base station and two mobile stations are implemented by taking full advantage of the software-defined radio. The base station consists of general purpose signal analyzers and signal generators controlled by a personal computer. Universal software radio peripherals are used as mobile stations. Linear spatial precoding and a simple two-way channel estimation technique are adopted in this experimental system. In-lab and field transmission experiments are carried out, and the bit error rate performance is evaluated. The impact of the channel estimation error under average channel gain discrepancy between two mobile stations is analyzed through computer simulations. Channel estimation error is shown to have a greater influence on the mobile station with the greater average channel gain.

The IEEE802.11ac task group has announced the use of a wider channel that extends the channel bandwidth to more than 80 MHz. We present an experimental platform consisting of a baseband and a RF unit in a 22 MIMO-OFDM system for the wider channel and report its system performance results from a field experiment. The MIMO-OFDM transceiver in the baseband unit has been designed to detect real-time MIMO and provides a maximum data rate of 600 Mbps. OFDM tends to cause high peak PAPR for wider channels and distorts the power amplifier performance in the RF unit. We have improved the non-linear distortion by optimizing the OFDM preamble and evaluated its performance by conducting a simulation integrated with baseband processing and a RF. In the field experiment, our platform tested the communication performance in a farm and a passage environment.

Long Term Evolution (LTE) system, which is specified in the 3rd Generation Partnership Project (3GPP) Release 8 and employs downlink multiple input multiple output (MIMO) transmission, is drawing attention as a promising next generation cellular mobile radio system due to its high spectral efficiency compared to the current High-Speed Packet Access (HSPA) system. The authors performed a field trial of an LTE system that complies with 3GPP Release 8 in Kitakyushu-city, Fukuoka, Japan, as a specified ubiquitous district project promoted by the Ministry of Internal Affairs and Communications of Japan. This paper first summarizes the field trial. Next, it describes the overview of the field trial system and reports the field experiment results on the downlink 22 MIMO wireless transmission. Finally, it compares the field experimental results to laboratory experimental results obtained with a hardware channel simulator using the channel model based on Recommendation ITU-R P.1816.

Motivated by the deployment of post-disaster MANEMO (MANET for NEMO) composed of mobile routers and stations, we evaluate two candidate routing protocols through network simulation, theoretical performance analysis, and field experiments. The first protocol is the widely adopted Optimized Link State Routing protocol (OLSR) and the second is the combination of the Tree Discovery Protocol (TDP) with Network In Node Advertisement (NINA). To the best of our knowledge, this is the first time that these two protocols are compared in both theoretical and practical terms. We focus on the control overhead generated when mobile routers perform a handover. Our results confirm the correctness and operational robustness of both protocols. More interestingly, although in the general case OLSR leads to better results, TDP/NINA outperforms OLSR both in the case of sparse networks and in highly mobile networks, which correspond to the operation point of a large set of post-disaster scenarios.

This paper presents a realization of a simple antenna system for land vehicle satellite communication that is tested in experiments conducted on the Engineering Test Satellite-VIII (ETS-VIII). The developed antenna system which was mounted onto a vehicle roof is compact, light weight with simple satellite-tracking operation. In order to realize compact antennas, an onboard-power divider and switching circuit for antenna feeding control are mounted under the array antenna. A Global Positioning System (GPS) module is used to provide accurate information on the vehicle's position and bearing during travelling. A personal computer (PC) is used as the control unit and data logger, which was specifically designed for this application, allow the switching circuit control as well as the retrieving of the received power levels and error rate. The field tests reported in this paper mainly address the tracking performance of the proposed antenna system. Satisfactory results were obtained. Good received power levels and bit error rate (BER) for tracking the ETS-VIII satellite were confirmed. Furthermore, in order to grasp the environmental factors that impact the quality of land vehicle communications, we carefully captured data at obstacles such as buildings, foliages, utility poles and highway overpasses. The results showed blockage and shadowing was confirmed. Additionally, when the antenna was tested at the inclined-road for simple propagation characteristics in elevation direction, stable reception of the satellite signals was realized.

This paper presents throughput performance along with power profiles in the time and frequency domains over 100 Mbps based on field experiments using the implemented Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) transceiver with a 100-MHz bandwidth in a real multipath fading channel. We conducted field experiments in which a base station (BS) employs a 120-degree sectored beam antenna with the antenna height of 50 m and a van equipped with a mobile station (MS) is driven at the average speed of 30 km/h along measurement courses that are approximately 800 to 1000 m away from the BS, where most of the locations along the courses are under non-line-of-sight conditions. Field experimental results show that, by applying 16QAM data modulation and Turbo coding with the coding rate of R = 1/2 to a shared data channel together with two-branch antenna diversity reception, throughput over 100 and 200 Mbps is achieved when the average received signal-to-interference plus noise power ratio (SINR) is approximately 6.0 and 14.0 dB, respectively in a broadband channel bandwidth where a large number of paths such as more than 20 are observed. Furthermore, the location probability for achieving throughput over 100 and 200 Mbps becomes approximately 90 and 20% in these measurement courses, which experience a large number of paths, when the transmission power of the BS is 10 W with a 120-degree sectored beam transmission.

This paper gives laboratory as well as the results of field experiment and describes the implementation of a system developed to evaluate and demonstrate multimedia multimode time division multiple access (MTDMA). The equipment has been developed with the radio transmission technology for future public land mobile telecommunication systems (FPLMTS/IMT-2000) in mind. To meet FPLMTS/IMT-2000 requirements the system employs the following techniques: a hybrid multiplex modulation system consisting of quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM), a high data transmission bit rate of 2 Mbit/sec for QPSK, 4 Mbit/sec for 16QAM, and diversity combining and adaptive equalization technique. For the diversity adaptive equalization technique, we used a decision feedback equalizer (DFE) consisting of one feedback (FB) transversal filter and two feed-forward transversal (FF) filters. The output signals from two branches of space diversity reception antennas are then fed to the two FF filters of the DFE. For middle-speed mobile radio communication for a micro-cellular pedestrian environment, a QPSK modulation system is selected to obtain wide coverage, while for a pico-cellular indoor office environment, the delay spread is small, and a 16QAM modulation system is selected to achieve a high bit rate. The results given here of laboratory and field experiments show the technical feasibility of MTDMA for future public land mobile telecommunication systems.

Many efforts are currently underway to design wideband mobile communication systems. In this letter, we clarify the received signal level characteristics for wideband mobile radio channels in line-of-sight (LOS) microcells. We conduct several urban-area field experiments to measure the received signal levels for various receiver bandwidths from 300 kHz to 30 MHz and the power delay profile. The experimental results show that the fading depth of the received signal decreases as the normalized rms delay spread, defined as the product of receiver bandwidth and rms delay spread, increases. These results are useful in designing wideband microcell systems for urban areas.

This paper gives field experimental results on 16-ary quadrature amplitude modulation/time division multiple access (16QAM/TDMA) and trellis coded 16QAM/TDMA systems for land mobile communications in order to evaluate its capability of achieving large capacity and high quality data transmission. Pilot symbol aided space diversity and symbol timing synchronization based on maximum likelihood (ML) estimation are applied to both 16QAM/TDMA and trellis coded 16QAM/TDMA to improve transmission quality. For the trellis coded 16QAM/TDMA, trellis coding with Viterbi decoding and 2-frame symbol interleaving are further employed. The field experiments were conducted in the Tokyo metropolitan area of Japan. The results show that 16QAM/TDMA and trellis coded 16QAM/TDMA are practical modulation/access schemes for land mobile communication systems.