H. Oguma

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

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Publications (46)0 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Heterogeneous wireless systems such as a combination of mobile broadband wireless access (MBWA) and wireless local area network (WLAN) are candidates to attain higher throughput and wide coverage in the next generation mobile communication systems. A multimode receiver to demodulate signals with multiple air interfaces is required in the heterogeneous systems. In this paper, we discuss an implementation of frequency domain equalizer (FDE) in the multimode receiver on an application specific integrated circuit (ASIC). The proposed multimode FDE could realize adaptively demodulate two systems (single carrier and multi carrier) depending on propagation environment. A multimode FDE ASIC is designed and implemented on 180-nm complementary metal-oxide semiconductor (CMOS). Core size of multimode FDE chip is 17.6 mm2. The experimental results show that the ASIC yields a throughput of 48.1 Mbit/s at a sampling rate of 100 MHz. The results also show that the power penalty of the measured bit error rate (BER) performance is only 1 dB at a BER of 10−3 in a 4-paths Rayleigh fading channel. We consider that the implemented ASIC is useful to demodulate signals with different air interfaces while optimally selecting an appropriate air interface in the heterogeneous wireless system.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on; 01/2013
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    ABSTRACT: For large scale disaster relief, we propose a location and short message system using the Quasi-Zenith Satellite System (QZSS). The target capacity of the proposed system is the transmission of 3 million message data (MD) or more within one hour. To control random access of mobile terminal (MT), Frame Slotted ALOHA is used. Frame Slotted ALOHA cannot provide optimum control, since the hub station (HUB) does not know the number of MTs. For realizing large capacity, we propose Frame Slotted ALOHA with Flag Method in which the HUB can estimate the number of MT quickly. The proposed Flag Method is divided into two modes. The send flag mode can estimate the number of MT within a short time. The send message data mode can control random packet access using estimated number of MD in send flag mode. Computer simulation shows that it is possible to accommodate 3 million MD by using the proposed Flag Method within 48m 19s.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on; 01/2013
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    ABSTRACT: As a result of the great east Japan earthquake, terrestrial communication infrastructure was seriously damaged. Thus the importance of secure satellite communication measures based on very small aperture antenna terminal (VSAT) systems has been recognized. In order to satisfy the various demands for urgent life line recovery, we have started an R&D project of “Satellite Communication Networks Valid for Disaster Recovery” as the next generation VSAT system. This project contains following three research topics. (1) multi-mode VSAT's based on software defined radio (SDR) technology, (2) low power consumption VSAT's and (3) emergency mode adaptive bandwidth control technique for HUB earth station.
    Microwave Conference (EuMC), 2013 European; 01/2013
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    ABSTRACT: We have proposed a hybrid single-carrier (SC) and multi-carrier (MC) system for next-generation mobile communication systems, where both high data rate and wide coverage system are attained by appropriately selecting SC or MC signal. We have confirmed effectiveness of the proposed hybrid system under single-cell environment. In this paper, the uplink throughput performance under multi-cell environment in the presence of inter-cell interference was calculated using computer simulation. The simulation results show that the hybrid system attains more than 10 times higher throughput than orthogonal frequency division multiple access (OFDMA) at a cumulative probability of 10% and 1.2 times higher throughput than SC-frequency division multiple access (FDMA) at a cumulative probability of 90%. The above result show that the proposed hybrid systems is useful in multi-cell environment as well as single-cell environment.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on; 01/2012
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    ABSTRACT: This paper proposes a heterogeneous wireless network with handover in the application layer. The proposed network requires no upgrade of wireless infrastructure and mobile terminals to convert the present homogeneous networks to the proposed heterogeneous network. Only installing application programs on the content server side and the mobile terminal side is required. The performance of the proposed network has been evaluated in a field trial using a mobile broadband wireless access (MBWA) air interface with wide coverage and a wireless local area network (WLAN) air interface with high throughput. The field trial results show that the maximum value of the handover outage time is only 170ms. The proposed heterogeneous wireless network is promising since both high throughput and wide coverage area are attained by a combination of the proposed handover scheme with the present homogeneous wireless networks.
    IEICE Transactions on Communications. 01/2012; E95.B(4):1152-1160.
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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). This paper describes coverage estimates of an uplink 64 quadrature amplitude modulation (QAM) signal under the condition of constant terminal output power when the signal bandwidth is up to 20 MHz. The estimates are based on the field trial results of 16 QAM and 1.28 MHz bandwidth. The estimation results show that wider signal bandwidth yields narrower coverage area. When the signal bandwidths are 10 MHz and 20 MHz, the coverage areas of 64 QAM are significantly shrunk to only 8% and 4% of the field trial area, respectively. One solution to the above coverage issue is a heterogeneous wireless network such as a combination of MBWA and wireless local area network (WLAN).
    14th International Symposium on Wireless Personal Multimedia Communications, WPMC 2011, Brest, France, October 3-7, 2011; 01/2011
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    ABSTRACT: We have proposed a hybrid single-carrier (SC) and multi-carrier (MC) system for next-generation mobile communication systems. By appropriately selecting SC or MC signal, both high data rate and wide coverage system are attained in the hybrid system. In this paper, we discuss multi-antenna technology for the hybrid system. When space division multiplexing (SDM) is applied to the hybrid system, the maximum throughput is increased by SDM; however, the uplink coverage is narrowed under the condition of constant total output power. To widen the coverage, we propose adaptive multi-antenna transmission scheme that optimally selects SDM or joint detection of frequency-domain equalization (FDE) with antenna diversity. A computer simulation is carried out to estimate the uplink throughput performance of the proposed hybrid system. The simulation results show that wider coverage is attained by 41 % than SDM when the uplink throughput at a cell edge is 0.5 bit/s/Hz, while keeping the same maximum throughput as that of SDM.
    14th International Symposium on Wireless Personal Multimedia Communications, WPMC 2011, Brest, France, October 3-7, 2011; 01/2011
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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 uplink 16 quadrature amplitude modulation (QAM) signal under the condition of constant terminal output power when the bandwidths are from 2.56 MHz to 20.48 MHz. The estimates are based on the field trial results of 1.28 MHz bandwidth. The results show that wider bandwidth yields narrower coverage area. 16 QAM can be used within 55 %, 45 %, 35 %, and 25 % 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 16 QAM is useful even if the signal bandwidth is wider than that 10 MHz.
    Wireless Communications and Networking Conference (WCNC), 2010 IEEE; 05/2010
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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 uplink transmission with the maximum modulation level of 64 QAM, using the measured uplink throughput performances when the maximum modulation levels are quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (QAM). The field trial results show that 64 QAM improves the uplink throughput performance in 30% of the field trial area. It is considered that the maximum modulation level of 64 QAM is feasible to provide a mobile broadband data communication service with a higher throughput in uplink as well as downlink.
    GLOBECOM Workshops, 2009 IEEE; 01/2010
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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: 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.
    01/2010;
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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.
    01/2010;
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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.
    01/2010;
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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: 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 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;