COMMISSION C: Radio Signals and Systems (November 2010 – October 2013)
Edited by Masahiro Morikura

C1. Mobile High Bit-Rate Transmission
In fourth-generation mobile communication systems, the maximum bit rate is aimed at 1 Gbps
[3GPP, 2011] and demand for higher bit-rate transmission has been rapidly growing. This section
surveys experiments for the mobile high bit-rate transmission.
First, 12×12 Multiple-Input Multiple-Output (MIMO) transmission with the signal bandwidth of 100
MHz achieved 5 Gbps [Taoka, 2008]. In addition, 10 Gbps transmissions using higher frequency bands
over 5 GHz were discussed at a 3GPP workshop focusing the post LTE-Advanced era [NTT
DOCOMO, 2012].
Moreover, 11 GHz band super high bit-rate mobile communications attaining over 30 Gbps havebeen investigated [Suzuki, 2010], [Umeda, 2010]. As experiments of the super high bit rate, a 10 Gbps
transmission experimental system using 8×16 MIMO-Orthogonal Frequency Division Multiplexing(OFDM) was developed [Suyama, 2012], [Suyama, 2013], and 10 Gbps transmission experiments
succeeded as the world’s first 10 Gbps experiment in outdoor mobile environments in December 2012
[Suyama, 2013]. On the other hand, in order to analyze a radio propagation mechanism, an 11 GHzband channel sounder that supports the maximum of 24×24 MIMO was developed [Konishi, 2012],
and channel measurement and analysis were performed in indoor and outdoor propagation experiments[Kim, 2013], [Chang, 2013]. The MIMO channel sounder shares 11 GHz band transmitter and receiverwith the transmission experimental system; however, the installed software packages are different.
Although 24×24 MIMO transmission is expected to achieve over 30 Gbps bit rate, an 11 GHz band 30
Gbps transmission experiment has not been carried out because high power amplifiers (HPAs) for only
8 transmitter antennas were available [Suyama, 2013]. Therefore, to verify the feasibility of the 30
Gbps transmission for future mobile communications, performance of 30 Gbps MIMO-OFDM
eigenmode transmission has been demonstrated by computer simulations using channel data that the 11
GHz band 24×24 MIMO channel sounder measured.
(K. Fukawa)
References
3GPP TR 36.913 V10.0. [2011], “Requirements for further advancements for E-UTRA(LTE-Advanced).”H. Taoka, K. Dai, K. Higuchi, and M. Sawahashi [2008], “Field experiments on MIMO multiplexing
with peak frequency efficiency of 50 bit/second/Hz using MLD based signal detection for OFDM
high-speed packet access,” IEEE J. Sel. Areas Commun., vol. 26, no. 6, pp. 845-856.
NTT DOCOMO [2012], “Requirements, candidate solutions & technology roadmap for LTE Rel-12
onward,” 3GPP RWS-120010.
S. Suzuki, S. Suyama, K. Fukawa [2010], “Research topics for super high bit-rate mobile
communication systems,” IEICE Society Conf., B-5-51 (in Japanese).
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S. Umeda, S. Suyama, S. Suzuki, and K. Fukawa [2010], “Low-complexity PAPR reduction method for
multiuser MIMO-OFDM systems with block diagonalization,” Inter. OFDM-Workshop, pp. 11-15.
S. Suyama, H. Fukuda, H. Suzuki, and K. Fukawa [2012], “10 Gbps 8×8 MIMO-OFDM broadband
experimental system for 11 GHz band super high bit-rate mobile communications,” Inter.
OFDM-Workshop 2012, pp. 115-120.
S. Suyama, J. Shen, Y. Oda, H. Suzuki, and K. Fukawa [2013], “11GHz band 8x16 MIMO-OFDM
outdoor transmission experiment for 10 Gbps super high bit rate mobile communications,” IEEE Inter.
Sympo. on Personal Indoor Mobile Radio Commun. (PIMRC).
Y. Konishi, Y. Chang, M. Kim, Y. Maruichi, P. H. Van, and J. Takada [2012], “Multi-link indoor MIMO
measurements at 11 GHz using scalable wideband channel sounder,” Inter. Sympo. on Antennas andPropagation (ISAP 2012), pp. 335-338.
M. Kim, Y. Konishi, Y. Chang, and J. Takada [2013], “Characterization and modeling of indoor
wideband MIMO channels at 11 GHz,” European Conf. on Antennas and Propagation (EuCAP).
Y. Chang, V.H. Pham. M. Kim, J. Shen, Y. Oda, and J. Takada [2013], “Results of field measurementwith wideband MIMO sounder at 11 GHz for macrocell environments,” IEICE Tech. Rep., vol. 113,
no.8, RCS2013-2, pp. 7-12.

C2. Wireless Local Area Network (WLAN)(1) IEEE 802.11ac and DL MU-MIMO:
With the proliferation of IEEE 802.11 devices, wireless local area networks (WLANs) will play animportant role in future wireless service. One of the most significant challenges during 2010-2013 isthe development of the techniques for upcoming IEEE Gigabit Wireless LAN amendments, i.e. IEEE
802.11ac. Especially, downlink multi-user multiple-input and multiple-output (DL MU-MIMO)
transmission has been extensively investigated [Ishihara, 2013]. In MU-MIMO transmission, theestimation of channel state information (CSI) is also an important issue, and the efficient CSI
estimation scheme and CSI feedback method has been proposed [Kudo, 2012]. In addition, two frame
sequences with implicit CSI feedback mechanism for DL MU-MIMO system with massive antenna
was proposed [Murakami, 2013-1].
(2) Inter-Cell Interference under Overlapping BSS Environment:
Increase of the number of basic service set (BSS) causes overlapping cells where plural BSS
operating at the same channel are located close enough. In the overlapping cell environment, inter-cellinterference (ICI) severely degrades the throughput of WLANs. Since the available channel bandwidth
is expanded to enhance the highest throughput (e.g., maximum bandwidth in IEEE 802.11ac is 160
MHz), ICI will become more serious in the deployment scenarios of WLANs based on IEEE 802.11ac
std. As the countermeasures against this problem, interference-aware channel segregation based
dynamic channel assignment (IACS-DCA) was proposed, and a transmit power control wasadditionally introduced to reduce the ICI [Matsumura, 2013]. In addition, an interference-aware
multi-cell beamforming (IMB) technique was proposed [Murakami, 2013-2]. As an alternative way to
reduce the ICI while keeping higher throughput, multi-bandwidth channel selection scheme by2

coordinated access points (APs) was proposed [Hanada, 2013]. In this channel selection scheme,
through game-theoretic analysis, the coordinated APs dynamically select channels and the total
throughput at Nash equilibria is significantly improved.
(3) Medium Access Control (MAC) for Adavanced Radio Resource Management:
Medium access control (MAC) layer is responsible for coordinating the access of stations to theshared medium, and the MAC protocol is a key issue that determines the efficiency of sharing thelimited radio resource. A distributed dynamic resource allocation method that enables control offlexible bandwidth allocation to each specific station was proposed [Kishida, 2013]. The proposed
method controls the priority level and can coexist with conventional DCF (Distributed Coordination
Function) protocol. Centralized radio resource management (RRM) is another trend to improve thetransmission performance of WLANs. To enhance the throughput of WLANs using multi-user
diversity gain while keeping QoS requirements of each station, the centralized radio resource
management (RRM) strategy was introduced in WLAN [Miyamoto, 2013]. In the centralized RRM, AP
and associated stations form a cooperative group. Once the cooperative group reserves the radio
resource in a traditional DCF-manner, the central controller gathers the channel and traffic states
information (CTSI) and dynamically allocates the reserved radio resources to the stations. Of course,
the estimation of CTSI required for the centralized RRM causes the signaling overhead, and theexcessive signaling overhead due to centralized RRM can be overwhelming with the increase ofstations. As the countermeasures against this problem, two-stage DCF-based channel access protocol[Shimamoto, 2012] and station clustering scheme [Endo, 2013] were proposed.
Besides the above mentioned areas, coexistence of different types of wireless networks operating in
unlicensed band is a critical issue for the design of WLANs. Distributed active channel reservation forcoexistence (DACROS) scheme was proposed to solve the coexistence of IEEE 802.11g-based
WLANs and IEEE 802.15.4-based wireless sensor networks [Inoue, 2013].
(S. Miyamoto)
References
K. Ishihara, Y. Asai, R. Kudo, T. Ichikawa, Y. Takatori, M. Mizoguchi [2013], “Development andExperimental Validation of Downlink Multiuser MIMO-OFDM in Gigabit Wireless LAN Systems,”
EURASIP Journal, vol. 123, pp. 1-10.
R. Kudo, J. McGeehan, S. Armour, M. Mizoguchi [2012], “A Channel State Information Feedback
Method for Massive MIMO OFDM,” Journal of Communications and Networks, vol. 15, no. 4, pp.
1-10.
T. Murakami, H. Fukuzono, Y. Takatori, M. Mizoguchi [2013-1], “Multiuser MIMO with Implicit
Channel Feedback in Massive Antenna Systems,” IEICE Commun. Express, vol. 2, no. 8, pp. 336-342.
Y. Matsumura, K. Temma, K. Ishihara, B. A. H. S. Abeysekera, T. Kumagai, F.Adachi, [2013],“Interference-aware Channel Segregation Based Dynamic Channel Assignment using SNR-based
Transmit Power Control,” Proc. of ISPACS 2013.
K. Hanada, K. Yamamoto, M. Morikura, K. Ishihara, R. Kudo [2013], “Game-theoretic Analysis ofMultibandwidth Channel Selection by Coordinated APs in WLANs,” IEICE Trans. on Commun., vol.
E96-B, no. 6, pp. 1277-1287.
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T. Murakami, R. Kudo, T. Ichikawa, N. Honma, M. Mizogichi [2013-2], “Performance Evaluation ofInterference-Aware Multi-Cell Beamforming for an Overlapping Cells Environment,” IEICE Trans. on
Commun., vol. E96-B, no. 6, pp. 1492-1501.
A. Kishida, M. Iwabuchi, T. Shintaku, T. Sakata, T. Hiraguri, K. Nishimori [2013], “User-Oriented
QoS Control Method Based on CSMA/CA for IEEE802.11 Wireless LAN System,” IEICE Trans. on
Commun., vol. E96-B, no. 2, pp. 419-429.
S. Miyamoto, S. Sampei, W. Jiang [2013], “Novel DCF-based Multi-User MAC Protocol forCentralized Radio Resource Management in OFDMA WLAN Systems,” IEICE Trans. on Commun,
Vol. E96-B, No. 9, pp. 2301-2312.
K. Shimamoto, S. Miyamoto, S. Sampei, W. Jiang [2012], “Two-Stage DCF-based Access Scheme for
Throughput Enhancement of OFDMA WLAN Systems,” Proc. of WPMC’12, pp. 584-588.
T. Endo, S. Miyamoto, S. Sampei, W. Jiang [2013], “Station Clustering Strategy for DCF-basedCentralized OFDMA WLAN Systems,” Proc. of ICCVE 2013.
F. Inoue, M. Morikura, T. Nishio, K. Yamamoto, F. Nuno, T. Sugiyama [2013], “Novel Coexistence
Scheme between Wireless Sensor Network and Wireless LAN for HEMS,” Proc. of IEEE
SmartGridComm 2013.

C3. Microwave Filters
With the growing demand for high-capacity and high-speed data transmission services, thefrequency bands allocated to mobile communication systems have been increasing. Future mobile
terminals should be equipped to deal with various frequencies and bandwidths in order to function
seamlessly in various mobile communication systems that have particular specifications such as theoperating frequency bands and the bandwidths. Additionally, from the standpoint of a wideband
transmission, future mobile terminals will be anticipated to use simultaneously the separated multiple
frequency bands that have been allocated to mobile communication systems. In recent microwave
filters, the following two topics are one of the most significant issues: One is to provide a reconfiguring
operation for the operating frequency band and bandwidth, and the other is to provide a multiband
simultaneous operation
There have been reports on the architecture to provide a reconfiguring operation for microwave
filters [Kawai, 2010], [Kawai, 2012-1], which describe a reconfigurable resonator and a bandpass filter
that provide independent tunability with regard to the resonant/center frequency and bandwidth while
maintaining symmetric transmission characteristics; and a tunable resonator that can tune its resonant
frequency and bandwidth independently using a single kind of MEMS variable device.
There have been reports on the filter architecture to provide multiband simultaneous operation for
microwave filters [Takagi, 2012], [Takagi, 2013], [Kawai, 2012-2]. A new approach for configuring aparallel-planar dual-band bandpass filter by employing multilayered LTCC technologies has been
proposed for the purpose of achieving frequency characteristics with an allowable deviation without
precise alignment between resonators [Takagi, 2012]. The group has also proposed dual-band bandpass
filter employing broad side coupling structure that provides flexibility in the sense of having a wide
range in selecting two center passband frequencies [Takagi, 2013]. With regard to the reconfiguring4

operation and multiband simultaneous operation, a tunable dual-band bandpass filter has been proposedthat can individually tune its center frequency and the bandwidth of its two passbands [Kawai, 2012-2].
Besides the above mentioned areas, high-performance microwave filters have been proposed byusing new methods for filter design such as an even- and odd-mode method for a microstrip
parallel-coupled dual-mode ring resonator [Ma, 2010], an optimization technique based on the genetic
algorithm [Kido, 2011], a parameter-extraction method for general Nth-order transversal resonatorarray filter with a direct source/load coupling [Ohira, 2013], and a synthesis scheme for a new class of
optimum Chevyshev-type ultra-wideband bandpass filters consisting of multistage stepped-impedance
resonators and two short-circuited stubs positioned at input- and output-ports [Chen, 2013].
(K. Satoh)
References
Kawai K., Okazaki H., and Narahashi S. [2010], “Tunable Bandpass Filter with Symmetric Attenuation
Characteristics,” Proceedings of Asia-Pacific Microwave Conference 2010 (APMC2010), pp. 143-146.
Kawai K., Okazaki H., and Narahashi S. [2012-1], “Resonant Frequency and Bandwidth Tunable Ring
Resonator Employing MEMS Tunable Capacitors,” Proceedings of Asia-Pacific Microwave
Conference 2012 (APMC2012), pp. 729-731.
Takagi Y., Satoh K., and Narahashi S. [2012], “New Approach for Configuring a Parallel-Planar
Dual-Band Bandpass Filter by Employing Multilayered LTCC Technologies,” Proceedings of 2012
IEEE Radio Wireless Symposium (RWS2012), pp. 147-150.
Takagi Y., Satoh K., Koizumi D., and Narahashi S. [2013], “Broadside Coupling High-Temperature
Superconducting Dual-Band Bandpass Filter,” IEICE Transactions on Electronics, Vol.J96-C, No.8,
pp.1033-1040.
Kawai K., Okazaki H., and Narahashi S. [2012-2], “5-GHz-Band Center Frequency and Bandwidth
Tunable Dual-Band Bandpass Filter,” Proceedings of the 42nd European Microwave Conference(EuMC2012), pp. 261-264.
Ma Z., Sasaki H., Chen C.-P., Anada T., and Kobayashi Y. [2010], “Design of a Wideband Bandpass
Filter Using Microstrip Parallel-Coupled Dual-Mode Ring Resonator,” Proceedings of Asia-PacificMicrowave Conference 2010 (APMC2010), pp. 21-24.
Kido T., Deguchi T., and Tsuji M. [2011], “Compact Planar Bandpass Filters with Arbitrarily-Shaped
Conductor Patches and Slots,” IEICE Transactions on Electronics, Vol.J94-C, No.6, pp.1091-1097.
Ohira M. and Ma Z. [2013], “A Parameter-Extraction Method for Microwave Transversal Resonator
Array Bandpass Filters With Direct Source/Load Coupling,” IEEE Transactions on Microwave Theory
and Techniques, Vol.61, No.5, pp.1801-1811.
Chen C.-P., Oda J., and Anada T. [2013], “Synthesis of Optimum UWB Filters Composed of
One-Wavelength Parallel-Coupled SIRs and Shunt Short-Circuited Stubs,” IEICE Transactions on
Electronics, Vol.J96-C, No.10, pp.1281-1288.

5C4. Tunable Antenna Design for the Mobile Terminals
With the rapid growth of the communication industry, mobile terminals such as smart phones andtablet PCs are required to meet various wireless standards scattered over a wide frequency range. On
the other hand, a small form factor is desired for current and future mobile terminals. Multiple antennas,
wideband antennas and multiband antennas require a large antenna space and there is insufficient space
to place these antennas in the future mobile terminal. Tunable antenna is most promising candidate tocover many wireless communication bands without increasing antenna volume [Sorwar, 2010]. Somekinds of antenna design for mobile terminals that include tuning devices, such as MEMS switches,
MEMS capacitors, PIN diodes, varactor diodes and GaAs devices have been reported.
Compact tunable antenna using GaAs switch was proposed to cover 800 MHz, 1.7–2 GHz, and 1.5
GHz bands [Koga, 2013]. Since 2012, LTE (Long Term Evolution) service using band 21 (1.5 GHz)has been launched in Japan. This band includes the anti-resonant frequency of the 800 MHz band. It isa challenge to cover 800MHz band and 1.5GHz band with one antenna because anti-resonating antenna
is difficult to match to the 50 Ω line. To cover 1.5 GHz band and 800 MHz band with one antenna,reflection type GaAs switch is used to control the antenna element length.
Because of its low insertion loss and low power consumption over a wide frequency range, MEMS
device is most suitable for the tunable antenna to cover many frequency bands such as LTE (0.7-3.5
GHz), GPS (1.5 GHz) and WLAN (2.45 GHz and 5.1-5.7 GHz). Using MEMS switches, tunableantennas which cover wide frequency range have been proposed. It was demonstrated that effective
antenna length can be controlled by using two SPST (Single Pole Single Throw) MEMS switches[Koga, 2011]. The antenna operates with good matching and high efficiency from 0.67 to 6 GHz. The
volume of this antenna is 5.75 cm3. Using three SPST MEMS switches as the antenna matching circuit,the tunable antenna was designed and fabricated [Yamagajo, 2011]. The volume of the antenna
element is 4.94 cm3 and its operating frequency ranges from 0.64 to 5.85 GHz. Combining thetechniques mentioned above, compact planar tunable antenna was designed [Yamagajo, 2012]. In thisantenna, one MEMS switch is used to control the antenna length and other switches are used to match
antenna impedance to 50 Ω. The antenna area and the operating frequency range are 6.5 cm2 and
0.65-5.85 GHz, respectively.
Combination of the tunable device and meta-material antenna is one candidate for further size
reduction. A design of tunable inverted-L antenna with a SRR (Split-Ring Resonator) was proposed[Takemura, 2013]. A varactor diode is used in the antenna to control the resonant frequency of the SRR.
The antenna area is 5 cm2. Simulation and measurement results shows that the antenna covers LTE700(698-960 MHz), GSM850, GSM900 and LTE2600 (2.5-2.69 GHz) bands.
(T. Yamagajo)
References
M. G. Sorwar Hossain and T. Yamagajo [2010], “Reconfigurable printed antenna for a wideband
tuning,” Proceedings of the fourth European Conference on Antennas and Propagation (EuCap), pp.
1-4.
Y. Koga, A. S. Andrenko, T. Yamagajo and M. Shimizu [2013], “Compact frequency-tunable antenna
with a GaAs switch for mobile handset,” Proceedings of IEEE Antennas and Propagation in WirelessCommunications (APWC) 2013, pp.736-739.

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Y. Koga, T. Yamagajo and M. Shimizu [2011], “Frequency tunable antenna design technique with
MEMS switches for mobile phone,” Proceedings of 2011 Asia-Pacific Microwave Conference (APMC),
pp. 441-444.
T. Yamagajo and Y. Koga [2011], “Frequency reconfigurable antenna with MEMS switches for mobile
terminals,” Proceedings of IEEE Antennas and Propagation in Wireless Communications (APWC)
2011, pp. 1213-1216.
T. Yamagajo, Y. Koga and M. Shimizu [2012], “Planer frequency reconfigurable antenna for mobile
terminals,” Proceedings of 2012 Asia-Pacific Microwave Conference (APMC), pp. 1166-1168.
N. Takemura [2013], “Tunable Inverted-L Antenna With Split-Ring Resonator Structure for Mobile
Phones,” IEEE Trans. Antennas Propag., vol.61, no.4, pp.1891-1897.

C5. Antenna Measurement(1) S-Paramenter Method:
The S-parameter method using a standard network analyzer was proposed by Meys in 1998 tomeasure the input impedance of a balanced-fed antenna like a dipole antenna or a mobile terminal
antenna. Several remarkable researches on the S-parameter method have been executed in Japan.
Four compensating methods using cascade matrices were adopted to reduce the influence of a jig for
the S-parameter method by Konya. The results of the proposed methods were presented and comparedwith a calculated result using the moment method and the measured result of a monopole antenna on a
ground plane [Konya, 2011]. Sasamori examined a jig fabricated by microstrip line for the S-parameter
method in order to improve the measurement precision. The measured result of S-parameter method
was examined after the SOLT calibration and the TRL calibration had been performed. In case of the
SOLT calibration, three compensating methods using ABCD-matrix, called open-correction,short-correction, and open-short-correction were applied to eliminate the influence of the jig for the
S-parameter method [Sasamori, 2013-1, 2013-2].
Radiation characteristics can be also measured by using the S-parameter method. Fukasawa
proposed an extended S-parameter method that can be applied to radiation pattern measurements ofamplitude and phase. In this method, two cables are connected to an antenna, and the excitation
coefficients of the two cables are obtained from the S-parameters under the condition where theunbalanced current of the coaxial cables is reduced. From array patterns generated with these excitation
coefficients, the radiation patterns with a reduced unbalanced current of the coaxial cables can beobtained [Fukasawa, 2012]. Yanagi proposed an S-parameter method including radiation characteristics
and mutual coupling of antennas on a small ground plane. They showed also that accurate measurement
results can be obtained using the proposed method [Yanagi, 2012].
(2) OTA (Over-the-Air) Measurement:
Multi-Input Multi-Output (MIMO) is one of the hottest technologies for mobile radio systems. In
order to evaluate the performance of MIMO antennas accurately, actual antennas mounted on themobile terminal or the base station must be used in actual multipath-rich propagation environments.
MIMO-OTA (Over-the-air) measurement methods for mobile terminals and base stations have been
recently studied and developed for mobile communications. Some researches on the topics in Japan arereported as follows.
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Spatial correlation function in spatial channel emulator (fading emulator) for MIMO-OTA wasformulated taking probe antenna configuration into consideration. It was qualitatively andquantitatively clarified that fundamental estimation error of spatial correlation depends on installation
range and interval between probe antennas. Criteria for estimating the required installation range andinterval between probe antennas were derived from formulated equation of spatial correlation
coefficient. Spatial correlation characteristics depending on probe antenna configuration were validated
from experiment [Imai, 2010]. A spatial fading emulator for the evaluation of a handset MIMO antenna
was also developed by Yamamoto. The MIMO channel capacities obtained from the propagation test
are good agreement with those of the OTA measurement both at 776 MHz and 2.35 GHz. The
comparison of the MIMO performances between 2-by-2 handset MIMO arrays under a multipath
fading environment with a uniform power distribution using a spatial fading emulator was presented[Yamamoto, 2010].
On the other hand, the OTA method for base station antennas has not been reported. Yamaguchi
proposed a novel fading generator that was based on a near-field modified Jakes scattering model.
Although metal patches on the dielectric disc as scattering objects are used to obtain fading waves in
the conventional method, slots on the metal disc are newly adopted as scattering objects in order to get
the same waves. The validity of the proposed generator was clarified by experiments using a prototype[Yamaguchi, 2011].
(R. Yamaguchi)
References
S. Konya, T. Sasamori, T. Tobana, Y. Isota [2011], “Wideband impedance measurement of balanced
antenna using the S-Parameter method,” Proc. Asia-Pacific Microwave Conf. 2011, 7-WE2P-30, pp.
717-720.
T. Sasamori, T. Tobana, Y. Isota [2013-1], “Input Impedance Measurement for Balanced Antenna by
S-parameter Method,” PIERS Proceedings, pp. 276-279.
T. Sasamori, T. Tobana, Y. Isota [2013-2], “Broadband Measurement of Input Impedance Using
S-Parameter Method,” (in Japanese), IEICE Trans. on Comm., vol. J96-B, no. 9, pp. 1067-1075.
T. Fukasawa, T. Yanagi, H. Miyashita, Y. Konishi [2012], “Extended S-Parameter Method Including
Radiation Pattern Measurements of an Antenna,” IEEE Trans. Antennas Propagat., vol. 60, no. 12, pp.
5645-5653.
T. Yanagi, T. Fukasawa, H. Miyashita, Y. Konishi [2012], “Measurement Using the S-Parameter
Method for Radiation Characteristics and Mutual Coupling of Multiport Antennas on a Small Ground,”Proc. of ISAP2012, pp. 1003-1006.
T. Imai, Y. Okano [2010], “Spatial Correlation Characteristics to be observed in Spatial Channel
Emulator for MIMO-OTA Testing,” Proc. of APMC2010, WS1D-2.
A. Yamamoto [2010], “Effectiveness of a Fading Emulator Using a Dual-Band Handset MIMO
Antenna by Comparison with a Propagation Test,” Proc. of APMC2010, WS1D-4.
R. Yamaguchi [2011], “A Fading Generator Using Rotated Scattering Slots,” Proc. of URSI XXXthGA 2011.
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C6. MIMO Systems
The growing popularity of smart phones and wireless LANs has set the demand for achieving
broadband wireless transmission within a limited frequency band. Multiple input multiple
output-orthogonal frequency division multiplexing (MIMO-OFDM) systems have been developed
because they promise to increase the channel capacity compared to single input single output (SISO)
systems. Moreover, multi-user MIMO (MU-MIMO) systems have recently attracted much attention asa technology that enhances the total system capacity by generating a large virtual MIMO channel
between a base station and multiple user terminals (UTs).
In this period, the following topics have been attracted much attention. The detailed topics are shownas follows:(1) Short Range MIMO
Since the distance between two array antennas that face each other is comparable to the size of thearray antenna aperture in short range MIMO, the propagation characteristics are greatly different fromthose in conventional MIMO. Unlike conventional MIMO, the optimal element spacing, which
maximizes channel capacity, exists in short range MIMO. Moreover, the channel capacity with optimalantenna spacing exceeds the Ergodic capacity of independent identically distributed (i.i.d.) channels
since optimal eigenvalue distribution, which can maximize channel capacity, is obtained in the shortrange MIMO. When the optimal element spacing is obtained, the channel capacity obtained whenemploying ZF is almost the same as that obtained when using EM-BF [Nishimori, 2011]. From a pointof view in simplification on signal processing part, the use of orthogonal polarized SR-MIMO wasproposed and its effectiveness in an actual scenario was shown [Hiraga, 2013].
(2) MIMO Sensor
Intruder detection method by utilizing a time variation of Multiple Input Multiple Output (MIMO)
channel (MIMO Sensor) has been proposed. Although the channel capacity on the MIMO transmission
is severely degraded in time variant channels, we can take advantage of this feature in MIMO Sensor
applications. It is shown that the detection probability by 4x1 SIMO sensor might be degraded due tosingle antenna at the transmitter site while 2x2 MIMO sensor obtains the high detection probability byboth transmit and receive diversity effect [Ushiki, 2003]. The antenna arrangement which is suitable for
2x2 MIMO sensor was proposed and this arrangement can enhance the detection probability comparedto the conventional antenna arrangement which is used in W-LAN systems [Honma, 2013].
(K. Nishimori)
References
K. Nishimori, N. Honma, T. Seki and K. Hiraga [2011], “On the Transmission Method for Short Range
MIMO Communication,” IEEE Trans. Vehicular Tech. Vol.60, no.3, pp.1247-1251.
K. Hiraga, K. Sakamoto, K. Nishimori, T. Seki, T. Nakagawa, and K. Uehara [2013], “Study ofshort-range MIMO transmission utilizing polarization multiplexing for the simplification of decoding,”
IEICE Trans. Commun., Vol.E97-B, pp459-468.
N. Honma, K. Nishimori, H. Sato and Y. Tsunekawa [2013], “Compact Antenna Arrangement for
MIMO Sensor in Indoor Environment,” IEICE Trans. Commun., Vol.E96-B, pp2491-2498.
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K. Ushiki, K. Nishimori, N. Honma and H. Makino [2013], “Intruder Detection Performance of SIMO
and MIMO Sensors with Same Number of Channel Responses,” IICE Trans. Commun., Vol.E96-B,
pp.2499-2505.
C7. Terahertz Technology
In a wide range of fields, including materials, bio-imaging/sensing, medical measurement, safety,
and security through to telecommunications, developments related to terahertz (THz) frequencies havebeen attracting a lot of attention recently [Tonouchi, 2007] [Davies, 2008] [Siegel, 2004]. THz
frequencies are electromagnetic waves within the ITU-designed band frequencies from 300 GHz to 3
THz. They are called “unexplored radio wave” previously and there is an engineering term of “THzgap” because practical technologies had not been existing in the THz region between radio waves andinfrared light. However, in addition to the radiation of THz frequency using the quantum cascade laser(QCL) [Köhler, 2002], a variety of THz sources have been gradually filling the THz gap in recent years.
Approaches for developing THz sources are optical generation, QCL, and solid-state electronic devices[Orihashi, 2005]. For THz detectors, bolometers, SBDs, and SIS junctions are widely used. The
principle applications for THz technology are divided into two categories; sensing and communications.
In order to realize a wide range of applications, higher-power THz sources, more sensitive THz sensors,and more functional devices and materials are necessary.
(K. Washio)
References
Tonouchi, M [2007], “Cutting-edge terahertz technology,” Nat. Photon., vol. 1, pp. 97–105.
Davies, A.G., et al. [2008], “Terahertz spectroscopy of explosives and drugs,” Mater. Today, vol. 11,
pp. 18–26.
Siegel, P. H. [2004], “Terahertz Technology in Biology and Medicine,” IEEE Trans. Microwave
Theory Tech., vol. 52, pp. 2438-2447.
Köhler, R., Tredicucci, A., et al. [2002], “Terahertz semiconductor-heterostructure laser,” Nature, vol.
417, pp. 156.
Orihashi, N., Suzuki, S. and Asada, M. [2005], “One THz harmonic oscillation of resonant tunneling,”
diodes. Appl. Phys. Lett. vol. 87, 233501.

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