L a b R e s e a r c h


Journal Papers
30. Proposal and Realistic Evaluation of a New Routing Algorithm for a Regional Protection System
H. Suzuki, S. Karasawa, D. Asano, Y. Fuwa, IEICE Transactions on Fundamentals, vol. E98-A, No. 8, pp. 1667-1670, 2015.
[Details]
  A regional protection system based on a wireless Ad-Hoc network has been in operation since 2008 in Shiojiri City, Japan. Wireless terminals transmit data packets to a server via transponders situated around the city. In this paper, a new routing algorithm that takes into account the level of congestion of the transponders is proposed. Using computer simulations, the proposed algorithm is shown to reduce the packet loss rate compared to the previous algorithm which is based on minimization of the number of hops to the server. Also, the proposed algorithm is shown be have almost the same packet loss rate as the best routing decisions obtained by an exhaustive search. Furthermore, the simulations used recreate the actual movement of terminals, so the results show what will happen in a realistic environment.


29. Performance Evaluation of a Serial UEP System with an AEPF-DFE for Fading Channels
S. Yamazaki, D.K. Asano, IEEJ Transactions on Electronics, Information and Systems, vol. 135, No. 2, pp. 191-196, 2015.
[ Details ]
  In our previous research, we proposed a serial unequal error protection (UEP) code system for use with information sources that contain a mixture of both important and less important data. Previously, theoretical analyses were presented, and the effectiveness and the validity of the system for additive white Gaussian noise (AWGN) channels were confirmed using theoretical analyses and computer simulations. On the other hand, we proposed an adaptive error prediction filter with a decision feedback equalizer (AEPF-DFE) to achieve faster convergence and lower computational cost during the tracking period. In this paper, we proposed our UEP system using AEPF-DFE for time and frequency selective fading channels. We confirmed the improvement in BER performance and the effectiveness of adaptive equalization for the proposed system in fading channels. Also, we confirmed the predominance of the proposed system by comparing the previous scheme, that is, the case using a simple DFE.


28. A PAPR Reduction Method for CPM-OFDM Systems using Initial Phase Randomization
K. Morioka, D. Asano, IEEJ Transactions on Electronics, Information and Systems, vol. 134, No. 8, pp. 1010-1015, 2014. (in Japanese)
[ PDF ]
  In this paper, CPM-OFDM systems which use CPM (Continuous Phase Modulation) as the first modulation scheme of OFDM (Orthogonal Frequency Division Multiplexing) are considered. As is the case for conventional OFDM systems, PAPR (Peak to Average Power Ratio) reduction is the most important task in CPM-OFDM systems. PAPR reduction by varying the initial phase of each sub-carrier with a fixed offset and a random offset are proposed. In the random offset method, the initial phase of each sub-carrier is not known at the receiver side, so we propose a demodulation algorithm using the phase continuity property of CPM and MLSD (Maximum Likelihood Sequence Detection). Simulation results show that the PAPR performance is improved if we use the random offset method. Also, we found that even though the initial phase is unknown at the receiver, the proposed algorithm can demodulate CPM-OFDM symbols as well as an algorithm where the initial phase is known.


27. A Pseudo-TDMA MAC Protocol using Randomly Determined Transmission Times for Landslide Prediction Wireless Sensor Networks
D. Asano, D. Kuroyanagi, H. Suzuki, E. Motoyama, Y. Fuwa, IEICE Transactions on Communications, vol. E97-B, No. 7, pp. 1449-1456, 2014.
[Details]
  Landslides during heavy rainfall cause a great amount of damage in terms of both property and human life. To predict landslide disasters, we designed and implemented a wireless sensor network using our existing highly fault tolerant ad-hoc network. Since many sensors \textcolor{red}{must} be used, we propose a new MAC protocol that allows the network to support more sensor terminals. Our protocol is a hybrid CSMA/{\color{red}Psuedo-}TDMA scheme which allows the terminals to decide their transmission timing independently in a random fashion. A timing beacon is not required, so power consumption can be reduced. Simulation results show that the number of terminals supported by the network can be greatly increased.


26. A Method to Construct Phase Spreading Sequences for CPM-CDMA Systems
K. Morioka, D. Asano, IEEJ Transactions on Electronics, Information and Systems, vol. 134, No. 4, pp. 534-542, 2014. (in Japanese)
[ PDF ]
  In this paper, a construction method for phase spreading sequences which is suitable for CPM-CDMA systems is proposed. Using these sequences, the performance of asynchronous CPM-CDMA systems with traditional BPSK/OQPSK-CDMA systems and the tradeoff between spreading factor and modulation parameters are considered. Numerical results show that the optimal modulation index for CPFSK-CDMA systems is h = 0.5 and the performance is better for lower values of BbTc in GMSK-CDMA systems. Also, we found that the user capacities of MSK-CDMA systems are 2.3 times larger than that of BPSK/OQPSK-CDMA systems.


25. An Automatic Modulation Classifier using a Frequency Discriminator for Intelligent Software Defined Radio
K. Morioka, D.K. Asano, IEEJ Transactions on Electronics, Information and Systems, vol. 133, No. 5, pp. 910-915, 2013. (in Japanese)
[ PDF ]
  In this paper, we propose a simple frequency discriminator based method to automatically identify PSK and M-ary FSK modulation schemes. This method is simpler than other methods based on statistical moments, neural networks and wavelet transforms. Also, this method can demodulate M-ary FSK signals using the classifier's output, resulting in a simple receiver structure. Results from a digital implementation are presented to show the validity of the proposed method.


24. On Improving the Tradeoff between Symbol Rate and Diversity Gain using Quasi-Orthogonal Space-Time Block Codes with Linear Receivers
K. Morioka, D.K. Asano, IEICE Transactions on Communications, vol. E95-B, No. 12, pp. 3763-3767, 2012.
[Details]
  In this letter, the tradeoff between symbol rate and diversity gain of Space-Time Block Codes (STBCs) with linear receivers is considered. It is known that Group Orthogonal-Toeplitz Codes (GOTCs) can achieve a good tradeoff with linear receivers. However, the symbol rate of GOTCs is limited to that of the base Orthogonal Space-Time Block Codes (OSTBCs). We propose to simply change the GOTC base codes from OSTBCs to Quasi-Orthogonal Space-Time Block Codes(Q-OSTBCs). Q-OSTBCs can improve the symbol rate of GOTCs at the expense of diversity gain. Simulation results show that Q-OSTBC based GOTCs can improve the tradeoff between symbol rate and diversity gain over that of the original GOTCs.


23. A Serial Unequal Error Protection Codes System Using MMSE-FDE for Fading Channels
S. Yamazaki, D.K. Asano, IEICE Transactions on Fundamentals, vol. E95-A, No. 7, pp. 1205-1210, 2012.
[Details]
  In our previous research, to achieve unequl error protection (UEP),we proposed a scheme which encodes the data by randomly switching between several codes which use different signal constellations and showed the effectiveness in AWGN channels. In this letter, we propose our UEP system using MMSE-FDE for fast and selective fading by using the fact that importance levels are changed every few symbols, i.e., every block, in the proposed system. We confirmed the improvement in BER performance and the effectiveness of adaptive equalization for the proposed systerm in fading channels. Moreover, in fading channels we confirmed the validity of the theoretical tradeoff shown in static conditions.


22. Progress of Digital Communication Technology -- Fading Phenomenon and Changes in Compensation Technology --
S. Yamazaki, D.K. Asano, IEEJ Transactions on Electronics, Information and Systems, vol. 132, No. 5, pp. 675-685, 2012. (in Japanese)
[ PDF ]
  In wireless communications, since transmitted signals are scattered from many objects, many propagation paths with different time delays are formed. When transmitting and receiving while moving in such an environment, received signals will be affected by intricate selective fading in both the frequency and time domains. In this technical note, first, the mechanism of fading phenomena is clarified, changes in previous phase compensation technology are surveyed, and a foundation for digital wireless-communications technology is provided.


21. Single-carrier Transmission Frequency-domain Equalization Based on a Wiener Filter for Broadband Wireless Communications
S. Yamazaki, D.K. Asano, IEEJ Transactions on Electronics, Information and Systems, vol. 131, No. 7, pp. 1384-1392, 2011.
[ PDF ]
  Recently, frequency-domain equalization for single-carrier transmission (SC-FDE) has been given much attention. For example, the enhanced mobile phone system, a SC-FDMA (Single-carrier frequency division multiple access) method using SC-FDE and multiple access will be adopted. However in previous research, there are many papers describing the features and advantages of SC-FDE based on a comparison of SC-FDE and orthogonal frequency-division multiplexing (OFDM) systems. In this technical note, we discuss single-carrier transmission equalization in the time-domain (SC-TDE) and SC-FDE in a unified way centered on the Wiener filter based on the minimum mean square error (MMSE) criterion. The reason to take up a Wiener Filter is that it is a basic filter based on the MMSE criterion. Also, we explain the basic principle of the SC-FDE and SC-FDMA in an organized and systematic way. Moreover, we point out the physical meaning of the Wiener solution in SC-FDE and relationship between SC-TDE and SC-FDE Wiener solutions. As a result, we show useful information and pointers, especially for when we want to replace existing SC-TDE technology with SC-FDE technology.


20. A Serial Unequal Error Protection Code System Using Multilevel Trellis Coded Modulation with Ring-type Signal Constellations for AWGN Channels
S. Yamazaki, D.K. Asano, IEEJ Transactions on Electrical and Electronic Engineering, vol. 5, No. 6, pp. 708-716, 2010.
[ PDF ]
  We propose a serial unequal error protection (UEP) code system for use with information sources that contain a mixture of both important and less important data. To achieve UEP, the proposed scheme uses a form of Trellis coded modulation (TCM) which encodes the data by switching between some codes that use different signal constellations. So we propose ring-type signal constellations with M levels of importance (MRING). Also, as no extra information about which code is used is added, the receiver estimates which code was used in the transmitter by examining the received signal points. In this paper, theoretical analyses of the 2RING signal constellations (that is, for M = 2) and TCM codes are presented, and the effectiveness and the validity of the system for additive white Gaussian noise (AWGN) channels are confirmed using theoretical analyses and computer simulations.


19. Field Experiments of an OFDMA/TDD System for Mobile WiMAX
S. Yamazaki, D.K. Asano, IEEJ Transactions on Electrical and Electronic Engineering, vol. 5, No. 4, pp. 501-503, 2010.
  Mobile worldwide interoperability for microwave access (WiMAX) is a technology that has received much attention for next-generation mobile broadband systems. In this paper, we focused on the physical layer of mobile WiMAX and performed field experiments. We show the performance of a WiMAX base station in the field using the error vector magnitude (EVM) performance measure experimentally and theoretically.


18. An Unequal Error Protection System Using Trellis Coded Modulation and an Adaptive Equalizer
S. Yamazaki, D. Asano, IEEJ Transactions on Electronics, Information and Systems, vol. 129, No. 1, pp. 147-148, 2009.
[ PDF ]
  We proposed an unequal error protection (UEP) scheme using trellis coded modulation and an adaptive equalizer for use in mobile fading channel communication environments. We proposed a signal constellation to realize unequal error protection and showed its performance using computer simulations.


17. Automatic Modulation Identification using a Frequency Discriminator
D. Asano, M. Ohara, IEICE Transactions on Communications, vol. E91-B, No. 2, pp. 575-578, 2008.
[Details]
  In this paper, an automatic identification method based on frequency discrimination is proposed. The proposed method can be used when the received signal is a constant envelope modulation scheme. To test the proposed method PSK and FSK are considered. Using computer simulations, the performance of the proposed method was evaluated and found to be able to distinguish between PSK and FSK well even in the presence of noise.


16. Development of an Experimental Noise Annoyance Meter
K. Furihata, T. Yanagisawa, D.K. Asano, K. Yamamoto, Acta Acustica united with Acustica, vol. 93, No. 1, pp. 73-83, 2007.
[ PDF ]
  The application of exposure effect relationships to transform a SLM to a noise annoyance meter is described. An annoyance scale using the most frequently used category descriptors related to noise for community noise assessment in Japan was developed. These descriptors were elicted from a listening experiment where the subjects listened to various kinds of noise sources for five minutes in or near their houses in and around Nagano city. As the equivalent continuous A-weighted sound pressure level (LAeq,(5min)) was measured for each of the sounds, it became possible to link the noise level to the annoyance descriptor. Thereby an experimental noise annoyance meter which can evaluate psychological effects on humans at the same time as (LAeq,(5min)) was developed. After having constructed the annoyance meter, it was validated using a separate sample of residents from other typical cities in Japan. They were presented to similar noise stimuli and both the measured noise levels and associated annoyance descriptors associated with the sounds. Through this process, the annoyance meter was shown to have face validity. It is therefore proposed that the noise annoyance meter cound be applied for combined noise exposure and noise impact rating in Japan.


15. A three-dimensional sound intensity measurement system for sound source identification and sound power determination by ln models
S. Nagata, K. Furihata, T. Wada, D.K. Asano, T. Yanagisawa, Journal of the Acoustical Society of America, vol. 118, pp. 3691-3705, December 2005.
[ PDF ]
  This paper describes a full vector intensity probe which advances the field of sound intensity and sound source direction estimation using six matched rotating and variable directional microphones. The probe has three pairs of microphones at an equal spacing of 30 mm that are set up in each of the x, y, and z directions and share the same observation point. The calibration method using the rotating microphone system is effective to correct position errors in the y- and z-axes microphone pairs. Sound intensity measurements using the variable directional microphone method can locate with accuracy a sound source, i.e., the structure parts radiating most acoustic energy. The system can find the maximum sound intensity level and beamwidth of the major lobe, and the peak sound intensity levels of the minor lobes. Therefore, a procedure for sound power determination based on minimum measurement data is theoretically and experimentally discussed. Consequently, it is possible to reconstruct only parts of the system emitting the most noise and measure efficiently the sound power level.


14. Performance of GMSK and Reed-Solomon Code Combinations
L. Ma, D.K. Asano, IEICE Transactions on Fundamentals, vol. E88-A, pp. 2863-2868, Oct. 2005.
[Details]
  This paper examines a coded Gaussian Minimum Shift Keying (GMSK) system which uses Reed-Solomon (RS) codes both in Additive White Gaussian Noise (AWGN) channels and Rayleigh fading channels. The performance of GMSK and RS code combinations is compared with the constraint that the transmitted signal bandwidth is constant. The coding gains were obtained using simulations and the best combination of GMSK and RS codes was found. The optimal code rates over AWGN and Rayleigh fading channels were also compared.


13. Acoustic characteristics of an electrodynamic planar digital loudspeaker using noise shaping technology
A. Hayama, K. Furihata, D.K. Asano, T. Yanagisawa, Journal of the Acoustical Society of America, vol. 117, pp. 3636-3644, June 2005.
[ PDF ]   The present study extends our previous work [Furihata et al., J. Acoust. Soc. Am. 114, 174-184 (2003)] by investigating our electrodynamic planar loudspeaker when driven by a 12 bit digital signal with noise shaping. Changing the structure of the loudspeaker can lead to improvement, but in this paper improvements that can be made using signal processing are investigated. Results show that the digital loudspeaker demonstrated good linearity over its 84 dB dynamic range from 40 Hz to 10 kHz. This shows that a 12 bit digital loudspeaker which is equivalent to a 16 bit one is possible.


12. The acoustics of Japanese wooden drums called "mokugyo"
M. Sunohara, K. Furihata, D.K. Asano, T. Yanagisawa, A, Yuasa, Journal of the Acoustical Society of America, vol. 117, pp. 2247-2258, April 2005.
[ PDF ]   A drumlike traditional Japanese instrument, the mokugyo, is experimentally discussed. First, the acoustic characteristics of 176 mokugyos with diameters ranging from 7.5 to 120 cm and three drumsticks were measured. Results show that (a) the sound spectra consist of two common peaks [F1 (Hz): first peak frequency, F2 (Hz): second peak frequency] close together, with an average ratio (F2 /F1) of 1.15, and (b) a drumstick beating the mokugyo is translated into an impact force applied over a period of time from 1 to 6 ms related to the mass and stiffness of the material wrapped around the tip of the drumstick. Second, to evaluate the acoustic response of a mokugyo in the final tuning process, the mechanical and acoustical analogy between the mokugyo and a bass reflex loudspeaker is theoretically and experimentally discussed. Results show that the model can be estimated within a relative error of 0.52% from the mass of wood chips. Finally, from a psychological experiment, the timbre of the mokugyo shows higher scores on psychological scales when the ratio (F2 /F1) becomes 1.15.


11. Preparation and properties of polypyrrole
H. Masuda, D.K. Asano, Journal of Synthetic Metals, vol. 135-136, pp. 43-44, 2003.
[ PDF ]   Optimal conditions and improvement methods for electrochemical polymerization of pyrrole (Py) in the presence of sodium p-toluenesulfonate (PTS) as a dopant in water were studied. The electrical and spectral properties of poly-Py (PPy) doped with PTS were compared with those of PPy doped with sodium alkylbenzenesulfonates such as sodium benzenesulfonate (BS), sodium 4-ethylbenzenesulfonate (EBS), sodium 4-n-octylbenzenesulfonate (OBS), sodium dodecylbenzenesulfonate (DBS) and tetraethylammonium p-toluenesulfonate (Et4NPTS), prepared under the same polymerization conditions. UV-Vis-NIR absorption spectra were independent of the electrolytes used.


10. Acoustic characteristics of an electrodynamic planar digital loudspeaker
K. Furihata, A. Hayama, D. K. Asano and T. Yanagisawa, Journal of the Acoustical Society of America, vol. 114 (1), pp. 174-184, July 2003.
[ PDF ]   In this paper, an electrodynamic planar loudspeaker driven by a digital signal is experimentally discussed. The digital loudspeaker consists of 22 voice coils, 11 permanent magnets, a diaphragm with streamlined sections molded in plastic, and a suspension made of handmade Japanese paper between the diaphragm and the frame. First, the acoustic responses are affected by the arrangement of the voice coils, so an asymmetric arrangement is studied. This asymmetric arrangement is designed to obtain as flat a frequency response to an analog signal as possible. This arrangement is compared with a symmetric one and results show that the flatness of the frequency response around 1 kHz and 4 kHz is improved and that the sound reproduction band is from 40 Hz to 10 kHz. Second, to evaluate the acoustic responses to a digital signal, the digital loudspeaker is driven with a pulse code modulation signal. Results show that the digital loudspeaker can reproduce pure sound with a total harmonic distortion of less than 5 value only in a narrow frequency band near 4 kHz. This digital loudspeaker was demonstrated to have good linearity over its dynamic range of 84 dB.


9. Optimization of coded GMSK systems
D. K. Asano and S. Pasupathy, IEEE Transactions on Information Theory, vol. 48, pp. 2768-2773, Oct. 2002.
[ PDF ]   In this paper, block and convolutional coding for Gaussian Minimum Shift Keying in additive white Gaussian noise channels is investigated. The performance improvement that can be obtained without an increase in bandwidth is found for block and convolutional codes with various block lengths and constraint lengths, respectively, when a simple suboptimal demodulation scheme is used. For a fixed system transmission bandwidth, the tradeoff between the percentage of bandwidth to use for coding and the percentage to use for modulation is examined and optimized for various values of bandwidth.


8. Preparation and Properties of Polythiophene Derivatives
H. Masuda, D. K. Asano and K. Kaeriyama, Journal of Synthetic Metals, vol. 119, pp. 167-168, 2001.
[ PDF ]   Chemically prepared poly(3-alky1-2,2'-bithiophene)s (poly-ArBT) are found to be highly soluble and electrochemically prepared ones less soluble. The salts of copper (II) and iron (III) ions are found to be effective oxidants for the chemical polymerization of poly-ArBT, due to the low oxidation potential of the bithiophene derivatives. The conductivities of electrochemically prepared polymers are found to be lower than those of chemically prepared polymers and near to the conductivity of poly(2,2'-bithiophene).


7. Coding and Modulation Tradeoffs for Limiter-Discriminator based CPM Transceivers in a Rayleigh Fading Channel
D. K. Asano, S. Pasupathy and R. Kohno, IEICE Transactions on Communications, vol. E83-B, pp. 1896-1899, August 2000.
[ PDF ]   Coding and modulation tradeoffs for limiter-discriminator based CPM transceivers are examined in Rayleigh, fast fading environments. Comparisons are made on the basis of a fixed bandwidth to information rate ratio, so coded schemes and uncoded schemes can be compared fairly. It is shown that using the proper balance of modulation and coding is important to achieve good performance. It is found that combining bandwidth efficient modulation with convolutional coding achieves better performance than trellis coded modulation (TCM). The increase in performance as the code complexity is increased is also found to be larger for convolutional coding than for TCM.


6. Synthesis of poly (3-alkoxymethylthiophenes)
H. Masuda, D. K. Asano and K. Kaeriyama, Journal of Synthetic Metals, vol. 101, pp. 73-74, 1999.
[ PDF ]   The reaction of 3-lithiothiophene with alkyl chloromethyl ether yielded 3-alkoxymethylthiophenes, which were electrochemically polymerized to give conducting polymer films. The conductivity of poly(3-ethoxymethylthiophene) was higher than that of poly(3-methoxymethylthiophene), indicating that a longer side chain homologue exceptionally shows higher conductivity.


5. Serial Unequal Error Protection Codes based on Trellis Coded Modulation
D. K. Asano and R. Kohno, IEEE Transactions on Communications, vol. 45, pp. 633-636 , June 1997.
[ PDF ]   Unequal error protection codes that are designed using trellis coded modulation are proposed for use with a single data stream consisting of information with two levels of importance. To achieve unequal error protection, the proposed scheme encodes the data according to the importance of the information by switching between two codes which use different signal constellations. Using simple trellis codes, it is shown that the error rate of the important information is lower than the error rate for an equivalent equal error protection scheme.


4. Stability of poly (3-alkylthiophene) doped with copper(II)perchlorate
H. Masuda, D. K. Asano and K. Kaeriyama, Journal of Synthetic Metals, vol. 84, pp. 209-210, 1997.
[ PDF ]   Poly (3-dodecyl-2,2'-bithiophene)(PDBT), Poly(3-dodecylthiophene)(PDT), and poly(3,4-dibutoxythiophene)(PDBOT) were chemically prepared and doped with copper(II) perchlorate. The conductivity, stability and spectral change of the doped polymers during storage in air were compared. The results suggest that copper(II) perchlorate is an effective oxidant.


3. Improved Post-Detection Processing for Limiter-Discriminator Detection of CPM in a Rayleigh, Fast Fading Channel
D.K. Asano, S. Pasupathy, IEEE Transactions on Vehicular Technology, vol. 44, pp. 729-734, November 1995.
[ PDF ]   A simple, robust processing strategy, called the Fading Magnitude-Integrate, Sample and Dump (FM-ISD) processor, is proposed for use with Limiter-Discriminator detection of CPM signals in Rayleigh, fast fading channels. The FM-ISD processor is introduced as a simplification of an optimal estimator-correlator receiver. The performance is compared to a standard integrator processor and found to provide an improvement in performance for all values of signal-to-noise ratio. The FM-ISD processor is also shown to be robust to changes in modulation format, channel fading rate and pre-detection filter type.


2. Phase Smoothing Functions for Continuous Phase Modulation
D.K. Asano, H. Leib, S. Pasupathy, IEEE Transactions on Communications, vol. 42, pp. 1040-1049, February/March/April 1994.
[ PDF ]   In this paper, the problem of signal design for continuous phase modulation is examined. Using the performance measures of effective bandwidth and minimum distance, "optimal" signal shapes are calculated for various receiver observation intervals for full and partial response signalling. For the partial response case, the optimization could only be done for a receiver observation interval of one symbol due to the difficulty of the optimization. Therefore, a family of signals based on previously calculated optimal signals is introduced. The tradeoffs that result between bandwidth and bit error rate are then compared as a function of the receiver observation interval and as a function of the memory length of the signalling scheme. Then, the signals introduced in this paper are compared to well known signals in terms of their effective bandwidth-minimum distance tradeoffs, power spectra and percent-in-band-power. The signals obtained by the optimization process are found to have good spectral properties in relation to well known signals.


1. Photon Emission in Self-Quenching Streamer Chambers
M. Salomon, D. Webster, D. Asano, IEEE Transactions on Nuclear Science, vol. NS-31(1), pp. 87-88, February 1984.
[ PDF ]   We have studied the properties of photons emitted by self-quenching streamer chambers. In particular the timing, intensity and wavelength distribution of these light pulses was measured with several gas mixtures.