K. Tsubouchi

Tohoku University, Miyagi, Japan

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Publications (213)111.97 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Low phase noise 5 GHz oscillator is designed with 90 nm silicon complementary metal oxide semiconductor (Si-CMOS) process. To achieve low phase noise, we used high Q value film bulk acoustic resonator (FBAR) instead of conventional LC resonant circuit. FBAR was mounted by using stud bump bonding instead of wire bonding to reduce parasitic inductance. This FBAR oscillator has phase noise of lower than -108dBc/Hz at 100 kHz offset.
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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 describes coverage estimates of an downlink 64 quadrature amplitude modulation (QAM) signal under the condition of constant base-station output power when the signal bandwidth is up to 20.48 MHz. The estimates are based on the field trial results of 1.28 MHz signal bandwidth. The coverage estimates based on a propagation model are also discussed. The estimation results show that wider signal bandwidth yields narrower coverage area. 64 QAM can be used within 90 %, 80 %, 65 %, and 50 % of the field trial area when the signal bandwidths are 2.56 MHz, 5.12 MHz, 10.24 MHz, and 20.48 MHz, respectively. We consider that the downlink 64 QAM signal is useful to provide a broadband wireless data communication service to users in an urban area even if the signal bandwidth is 20 MHz.
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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 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.
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    ABSTRACT: We have already proposed a hybrid single-carrier (SC) and multi-carrier (MC) system for next-generation mobile communication system. A SC signal has low peak-to-average power ratio (PAPR), which yields high power output for wide coverage. A MC signal is robust against frequency-selective fading and has high data rate with quadrature amplitude modulation (QAM). By appropriately selecting SC and MC signals, both high data rate and wide coverage system were attained in the proposed hybrid system. In this paper, uplink throughput of the proposed hybrid system was calculated using a computer simulation. Simulation results showed that the proposed system attained 20% higher throughput than conventional SC frequency division multiple access (FDMA) systems when the distance between the base station and a mobile station was 100 m. The proposed hybrid system also attained 52% wider coverage than conventional orthogonal frequency division multiple access (OFDMA) systems when throughput was 0.5 bit/s/Hz.
    Proceedings of the IEEE 21st International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2010, 26-29 September 2010, Istanbul, Turkey; 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.
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    ABSTRACT: With progression of scaling technique in silicon complementary metal-oxide semiconductor (Si-CMOS) process, it is available to produce radio frequency (RF) circuits using Si-CMOS for broadband wireless system, to reduce cost and size of devices. But in contrast, Si-CMOS RF circuit is deteriorated from circuits which use compound semiconductors. In order to reduce RF circuit's requirements, we propose a multi-carrier transmission with constant envelope modulation for high speed wireless system. Modulating method for sub-carrier is minimum shift keying. All sub-carriers are processed individually to reduce operating bandwidth requirement of intermediate frequency devices, and to keep envelope of input signal of power amplifier (PA) constant, so that the requirements of PAs can be reduced. Moreover, to reduce overall RF bandwidth, sub-carriers are allocated with overlaps. In the case of using 4 sub-carriers, we can get 375MHz baseband bandwidth and 2250MHz RF bandwidth, for 2Gbps system. Then the spectral efficiency is 0.89bit/s/Hz. The degradation of bit error rate is negligibly small.
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    ABSTRACT: In this paper, we propose a novel copper balls interconnection technology for 60 GHz band 3-D system-in-package (SiP) modules for 10 mm square 60 GHz band ultra-small wireless personal area network (WPAN) using organic substrates. Copper ball diameter of 350 μm is used for interconnection between the substrates. Ground copper balls placement is discussed showing electric field distribution. As a result, six ground copper balls around vertical signal line interconnection part are crucial for improvement of transmission characteristics. The six ground copper balls interconnection structure have similar results up to about 70 GHz for S21 compared with through CPW, hence copper balls interconnection technology is usable up to about 70 GHz.
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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: 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 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: 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: 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.
    IEICE Transactions on Fundamentals of Electronics Communications and Computer Sciences 07/2009; E92A(7). DOI:10.1587/transfun.E92.A.1642 · 0.23 Impact Factor
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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.
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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: 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: 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: 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

Publication Stats

1k Citations
111.97 Total Impact Points

Institutions

  • 1976–2013
    • Tohoku University
      • Research Institute of Electrical Communication
      Miyagi, Japan
  • 2011
    • Chiba University
      • Graduate School of Engineering
      Tiba, Chiba, Japan
  • 2008
    • Mitsubishi Corp.
      Kamakura, Kanagawa, Japan
  • 1996
    • Hitachi, Ltd.
      Edo, Tōkyō, Japan
  • 1980
    • Hiroshima University
      • Faculty of Engineering
      Hirosima, Hiroshima, Japan
  • 1976–1978
    • Osaka Prefecture University
      • School of Electrical and Electronic Engineering
      Sakai, Ōsaka, Japan