K. Tsubouchi

Tohoku University, Sendai-shi, Miyagi-ken, Japan

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Publications (209)109.72 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we report on a mobile broadband wireless access (MBWA) system field trial with Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing (FLASH-OFDM), which was carried out in a suburban area of Sendai city. This paper focuses on coverage and downlink throughput performance, which are the most important criteria for assessing broadband wireless data communication systems. The field trial results show that the measured downlink throughputs are higher than 1.2 Mbit/s and 300 kbit/s within coverages of 3 km and 6 km, respectively, under the condition that the sector antenna height is 58 m. We consider that the MBWA system is suitable to provide a mobile broadband data communication service to subscribers in a suburban area as well as in an urban area.
    01/2010;
  • Ieice Electronic Express. 01/2010; 7(3):165-169.
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    ABSTRACT: This paper estimates a received signal level variation in a mobile broadband wireless access system using the Institute of Electrical and Electronics Engineers (IEEE) 802.20 vehicular-A delay profile model through a computer simulation. The simulation results show that wider signal bandwidth yields a narrower variation range of the received signal level when the bandwidth is narrower than 3 MHz. When the signal bandwidth is wider than 3 MHz, the variation range of the received signal level is not decreased with an increase of the bandwidth since the channel transfer function is quasi-periodical. We consider that the IEEE 802.20 vehicular-A delay profile model is appropriate to calculate the received signal level variation when the signal bandwidth is narrower than 3 MHz.
    01/2010;
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    ABSTRACT: A planar slot antenna is designed and fabricated for 10mm square 60-GHz-band ultra-small wireless personal area network (WPAN) modules using low-cost organic substrates. Effects of ground and connector are discussed using computer simulation. As for planar slot antenna, it is proved that multilayered large grounds structure is most effective for gain enhancement, however, influence of the connector is very little. From measurement results, relative bandwidth of over 26.3%, radiation efficiency of 66% at 60-GHz, and maximum actual gain of 7.1 dBi at 60-GHz are obtained. Organic substrates have enough potential for being used as materials of substrates for low-cost 60-GHz-band planar antenna.
    01/2010;
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    ABSTRACT: For realizing over 2 Gbit/s transmission rate at portable terminals, we propose Advanced Kiosk Model (AKM) of 60 GHz band indoor multipath condition with hand tremor. In the AKM, coverage and bit error rate (BER) are defined as 10 m and 1 × 10-5 or less, respectively. Environment of multipath with Doppler effect by hand tremor causes serious inter-symbol interference (ISI). In this paper, we evaluate influence of hand tremor at 60 GHz communication systems. Measurements of relative amplitude with 2 path environment are well matched to simulation results. Simulation results show hand tremor cause serious ISI. Due to ISI, large degradation of BER performance is occurred every 1 ms periodically. Therefore, it is strongly necessary to consider influence of hand tremor with multipath environment for designing of 60 GHz-band wireless communication system.
    01/2010;
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    ABSTRACT: We discuss millimeter-wave film bulk acoustic resonator (FBAR) with very thin aluminium nitride (AlN) film fabricated using metal organic chemical vapor deposition (MOCVD) method. In previous works, we have successfully grown c-axis oriented AlN film using MOCVD method on Ru/Ta/SiO<sub>2</sub>/Si substrate. In this paper, we grew excellent orientation films of AlN and Ru electrodes in MOCVD, although their film thickness were very thin. Experimental results show that full width at half maximum (FWHM) is 1.3° at AlN thickness of 30 nm. In calculating analysis, when both top and bottom electrode thicknesses were 20 nm and AlN thickness was 30 nm, we obtained that resonant frequency was higher than 50 GHz. Therefore, FBAR is possible to apply to millimeter-wave bands devices, also contribute to small-size, low power consumption and low cost for millimeter-wave terminals.
    Ultrasonics Symposium (IUS), 2009 IEEE International; 10/2009
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    ABSTRACT: In this paper, we report on a mobile broadband wireless access (MBWA) system field trial with Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing (FLASH-OFDM), which was carried out at Sendai city in Japan. In this paper, the uplink throughput improvement effect of 16 quadrature amplitude modulation (QAM) is estimated by using the measured throughput and received signal level of quadrature phase shift keying (QPSK). The estimation results show that 16 QAM yields a higher uplink throughput than QPSK within coverage of 700 m when the base-station antenna height is 58 m. The results are validated by evaluating the uplink throughput performance of 16 QAM measured in the field trial. We consider that 16 QAM is useful to provide a mobile broadband data communication service to subscribers in uplink as well as downlink.
    Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
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    ABSTRACT: Multi-carrier (MC) transmission is attractive in next-generation mobile communication systems because of yielding high data rate and robustness against frequency-selective fading. An issue of the MC signal is high peak power. The MC signal is not effective for long distance transmission since longer distance requires higher output power. On the other hand, single-carrier (SC) transmission is effective for keeping a wide coverage area because of low peak power. To obtain both the merits of MC and SC, we consider a hybrid method that uses SC or MC. In this paper, an issue of the SC/MC hybrid system is discussed. We estimate an effect of carrier frequency offset on bit error rate (BER) performance by using computer simulation. The results show that SC is more sensitive to frequency offset than MC. To mitigate effects of the frequency offset, we propose an interference reduction method that removes head and tail symbols of block in the SC transmission. The simulated results show that the proposed method significantly improves the BER performance, and is effective to realize the SC/MC hybrid system.
    Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
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    ABSTRACT: In this work, a fully integrated 5 GHz Voltage Controlled Oscillator (VCO) is presented. The VCO is designed with 0.18 mum mixed signal Complementary Metal Oxide Semiconductor (CMOS) process of Taiwan Semiconductor Manufactuning Company (TSMC), Limited. To achieve low phase noise, a varactor circuit is designed to cancel effects of 1/f noise and fluctuation of capacitance due to harmonics. The proposed VCO has tuning range from 5.1 GHz to 6.1 GHz (17.9%) and phase noise of lower than -110.8 dBc/Hz at 1MHz offset over the full tuning range. Figure-of-merit-with-tuning-range (FOMT) of the proposed VCO is -182dBc/Hz.
    Radio Frequency Integrated Circuits Symposium, 2009. RFIC 2009. IEEE; 07/2009
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    ABSTRACT: In this paper, we report on a mobile broadband wireless access (MBWA) system field trial with fast low-latency access with seamless handoff orthogonal frequency division multiplexing (FLASH-OFDM), which was carried out at Sendai city in Japan. Downlink throughput distributions in multiple-cells environment with a sectored cell layout are discussed when the frequency reuse factors are one and three. The field trial results show that the reuse factors of one and three yield the median downlink throughputs of 3.2 Mbit/s and 2.1 Mbit/s, respectively, within 3.84 MHz system bandwidth. It is considered that the MBWA system with the reuse factor of one has higher median throughput by 50% than that with the reuse factor of three in multiple-cells environment.
    Wireless Pervasive Computing, 2009. ISWPC 2009. 4th International Symposium on; 03/2009
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    ABSTRACT: In this paper, we report on a mobile broadband wireless access (MBWA) system field trial with Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing (FLASH-OFDM), which was carried out at Sendai city in Japan. This paper discusses the feasibility of downlink transmission with the maximum modulation level of 256 quadrature amplitude modulation (QAM), using the received signal level and throughput under the measurement condition of the maximum modulation level of 64 QAM. The feasibility study results show that 256 QAM yields a higher downlink throughput than 64 QAM within coverage of 1.2 km when the base-station antenna height is 84 m. The results are validated by evaluating the downlink throughput performance in the field trial under the measurement condition of the maximum modulation level of 256 QAM. It is considered that 256 QAM is feasible to provide a mobile broadband data communication service to subscribers in an urban area.
    01/2009;
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    ABSTRACT: The self-timed pipeline (STP) is one of the most promising VLSI/SoC architectures. It achieves efficient utilization of tens of billions of transistors, consumes ultra low power, and is easy-to-design because of its signal integrity and low electro-magnetic interference. These basic features of the STP have been proven by the development of self-timed data-driven multimedia processors, DDMP's. This paper proposes a novel scheme of interacting self-timed (clockless) pipelines by which the various distributed and interconnected pipelines can achieve highly functional stream processing in future giga-transistor chips. The paper also proposes a set of elementary coupling control modules that facilitate various combinations of flow-thru processing between pipelines, and then discusses the practicality of the proposed scheme through the LSI design of application modules such as a priority-based queue, a mutual interconnection network, and a pipelined sorter.
    01/2009;
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    ABSTRACT: We have successfully fabricated 5 GHz band FBAR using aluminium nitride (AlN) film by metal organic chemical vapor deposition (MOCVD) method on SiO<sub>2</sub>/Si substrate. However, large spurious existed between resonant frequency and antiresonant frequency on admittance characteristics of prototype FBAR. We analyzed spurious vibration mechanism using three-dimensional (3-D) simulation. Spurious vibration mode was longitudinal thickness mode by simulation results. Therefore, we completely suppressed the spurious vibration by designing film thickness.
    Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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    ABSTRACT: In this paper, we report on a mobile broadband wireless access(MBWA) system field trial with fast low-latency access with seamless handoff orthogonal frequency division multiplexing (FLASH-OFDM), which was carried out at Sendai city in Japan. This paper focuses on coverage and downlink throughput performance, which are the most important criteria for assessing wireless data communication systems. The field trial results show that the base-station can communicate to a subscriber at a cell edge with a throughput of 1.5 Mbit/s assuming circular cells of 0.4 km<sup>2</sup>, 0.6 km<sup>2</sup>, and 1.7 km<sup>2</sup> when the sector antenna heights are 19 m, 58 m, and 84 m, respectively. Therefore, it is considered that the MBWA system is suitable to provide a broadband mobile data communication service to subscribers in an urban area.
    Wireless Communication Systems. 2008. ISWCS '08. IEEE International Symposium on; 11/2008
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    ABSTRACT: Single-carrier (SC) transmission using frequency domain equalization (FDE) based on the minimum mean square error (MMSE) criterion is an efficient way to combat the effects of frequency selective fading. In this paper, we discuss several key aspects concerning the implementation of a frequency domain equalizer and propose a feasible design. One of the problems is the implementation of the division operator used to compute the equalization weights. The CORDIC algorithm was employed for this as it reduces the hardware overhead. The proposed design was implemented in a FPGA and the performance was evaluated through experimental data.
    Wireless Communications, Networking and Mobile Computing, 2008. WiCOM '08. 4th International Conference on; 11/2008
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    ABSTRACT: Single-carrier (SC) transmission using frequency domain equalization (FDE) is one of the candidates for the next generation mobile communication systems expected to deliver high-speed and high-quality packet data services. Fast synchronization is critical for the performance of packet transmission systems. In this paper, a robust timing synchronization scheme for SC-FDE packet transmission is presented and its implementation is discussed. The proposed scheme uses an integration process to find the optimum timing of the guard interval (GI). An SC-FDE packet transmission system is implemented on a FPGA and its performance is analyzed through experimental data.
    Vehicular Technology Conference, 2008. VTC 2008-Fall. IEEE 68th; 10/2008
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    ABSTRACT: This paper discusses results of a MBWA system field trial with fast low-latency access with seamless handoff orthogonal frequency division multiplexing (FLASH-OFDM). The results of the trial show that the downlink throughput performance is significantly impaired by inter-sector interference. To clarify the reasons of the impairment, we carry out a computer simulation on inter-sector interference reduction capability of frequency hopping orthogonal frequency division multiple access (FH-OFDMA), which is used as a multiple access scheme in FLASH-OFDM. The results are summarized as follows: (1) the interference reduction capability of FH-OFDMA is almost the same as that of direct sequence code division multiple access (DS-CDMA), which allocate the same frequency band to all sectors, and (2) in FH-OFDMA, a long hopping-pattern length yields no site diversity effect to reduce inter-sector interference. Additionally, a cumulative distribution of measured signal to noise and interference ratio (SNIR) shows that pilot signals in the neighboring sectors mainly impair the throughput performance. Since a sectored cell layout is mandatory for deployment of the MBWA systems in a high traffic area, inter-sector interference reduction is a key issue for these systems.
    Vehicular Technology Conference, 2008. VTC 2008-Fall. IEEE 68th; 10/2008
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    ABSTRACT: We developed a high speed wireless LAN prototype in 5 GHz frequency band. Maximum transmission rate of the developed WLAN system is 324 Mbit/sec using 6 multi-channels of the IEEE802.11a. We propose a SINR estimation scheme using the correlation of long training fields, and implemented it in closed-loop link adaptation. We compared the proposed link adaptation schemes with the legacy ACK-based link adaptation schemes by computerized simulation. It was found that the performances of legacy ACK-based link adaptation schemes depended largely on the parameter choices. The proposed link adaptation scheme achieved higher throughput than the legacy ACK-based link adaptation schemes. We also found that the proposed link adaptation scheme selected the optimal MCS on the developed WLAN system in both AWGN and fading conditions.
    Personal, Indoor and Mobile Radio Communications, 2008. PIMRC 2008. IEEE 19th International Symposium on; 10/2008
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    ABSTRACT: High speed wireless LAN prototype of 324 Mbit/sec has been developed. Six channel binding of 802.11 a signal on frequency domain was employed for increasing PHY data rate. Frame aggregation was employed to improve MAC-SAP throughput. Individual adaptive data rate setting on each channel, so called adaptive dynamic channel assign was implemented in order to achieve maximum MAC-SAP throughput at any channel condition. In this paper, multiple channel interleaving over all frequency channels for randomization of burst error was presented. Interleaving can be carried out over all channels or inside individual channel. Bit and packet error rate were measured using implemented WLAN equipements with/without multiple channel interleaving. It was confirmed that improvement using multiple channel interleaving were measured to be 2 dB.
    Personal, Indoor and Mobile Radio Communications, 2008. PIMRC 2008. IEEE 19th International Symposium on; 10/2008
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    ABSTRACT: This study has designed a planar dipole antenna for 10 mm square 60 GHz band ultra-small and low-cost modules using any layer interstitial via hole (ALIVH) substrate. The planar dipole antenna is patterned on the top layer of the module. Simulated results show that bandwidth and gain of the proposed module are sufficient for 60 GHz wireless personal area network (WPAN) system. The proposed module is fabricated with a planar dipole antenna. Maximum actual gain of the fabricated module of 6.0 dBi at 63 GHz is measured. Proposed antenna patterned on ALIVH substrate for 60 GHz band module has enough potential for being used as a compact antenna for 60 GHz band WPAN modules.
    Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE; 08/2008

Publication Stats

720 Citations
109.72 Total Impact Points

Institutions

  • 1976–2011
    • Tohoku University
      • Research Institute of Electrical Communication
      Sendai-shi, Miyagi-ken, Japan
  • 2007–2008
    • Mitsubishi Corp.
      Kamakura, Kanagawa, Japan
  • 1996
    • Hitachi, Ltd.
      Edo, Tōkyō, Japan
  • 1976–1978
    • Osaka Prefecture University
      • School of Electrical and Electronic Engineering
      Sakai, Ōsaka, Japan