論文

This paper reports the design, implementation and the result of real-world experiment of wireless modal testing with battery-free backscatter sensors. The battery-free backscatter sensor comprises a custom radio frequency integrated circuit (RFIC), a commodity micro electro-mechanical system (MEMS) accelerometer, and an antenna. Sensor data concurrency demanded in modal analysis is realized by allocating a dedicated subcarrier to each backscatter sensor. The orchestration of wireless communications in 920 MHz based on Gen2 protocol and the wireless power supply to the backscatter sensor are performed by a software defined interrogator built on Lab-VIEW communications and USRP. We developed an over the air (OTA) subcarrier frequency allocation with a sequence of WRITE commands of Gen2 protocol, and its performance was confirmed with the experiments in an indoor radio propagation. The accuracy of the proposed wireless structural modal testing was experimentally verified by comparing with a commercial modal test system with wired accelerometers. Although the phase characteristic measurement is disturbed by the instability of the clock source of RFIC, the gain characteristics of wireless modal testing matches well with that of a commercial wired modal testing system.

© 2018 The Institute of Electronics, Information and Communication Engineers. Multiple Subcarrier Multiple Access (MSMA) enables concurrent sensor data streamings from multiple wireless and batteryless sensors using the principle of subcarrier backscatter used extensively in passive RFID. Since the interference cancellation performance of MSMA depends on the Signal to Interference plus Noise Ratio of each subcarrier, the choice of channel allocation scheme is essential. Since the channel allocation is a combinatorial problem, obtaining the true optimal allocation requires a vast amount of examinations which is impracticable in a system where we have tens of sensor RF tags. It is particularly true when we have variable distance and variable bandwidth sensor RF tags. This paper proposes a channel allocation scheme in the variable distance and variable bandwidth MSMA system based on a newly introduced performance index, total contamination power, to prioritize indecision cases. The performance of the proposal is evaluated with existing methods in terms of average communication capacity and system fairness using MATLAB Monte Carlo simulation to reveal its advantage. The accuracy of the simulation is also verified with the result obtained from the brute force method.

© 2018 IEEE. This paper proposes a method to uniquely identify commercial products with an item level barcode, specifically JAN/EAN/UCC, with which we usually cannot distinguish individual products. This research is motivated by the industrial and consumer needs for first-in-first-out operations of their inventories in the environment, where serial level barcodes, such as GS1-128 and SGTIN, or RFID are still not available. The proposal, referred to as Barcode Fingerprinting, utilizes the microscopic features of printed barcode stripes to discriminate each other. We zoom in a particular portion of a barcode image and apply SURF Algorithms and RANSAC Algorithms, to extract the microscopic features. The features are stored with the barcode ID and the time stamp for the future comparisons. We examined the feasibility of the proposal method by processing 100 barcodes of single brand PET bottles. The experiment reveals that we can uniquely identify each of the 100 barcodes by using Barcode Fingerprinting with a proper preprocessing of images.

© 2018 IEEE. This poster presentation introduces a multi-subcarrier passive backscatter wireless communication which enables frequency efficient and perfectly synchronized sensor data streaming. The inevitable mutual interferences among sub-carriers are actively rejected with a sophisticated digital signal processing in the receiver. The performance of the method, in terms of the synchronization and the interference processing gain, are experimentally evaluated with two types of prototype sensors and a software defined receiver realized with USRP 2952R and LabVIEW communications. The results show that the proposed interference rejection method works both for analog and digital modulation.

© 2018 IEEE. Ultrasonic transducers (a pair of speaker and microphone) are extensively used in distance and wind speed measurements. The measurement of Time-of-Flight (TOF) between an ultrasonic speaker and a microphone dominates the accuracy. This paper presents a method to improve the TOF measurement accuracy using narrow-band commercial off-the-shelf (COTS) ultrasonic transducers. The method features the use of an experimentally captured waveform to correlate the transmitted and received signals and the use of a phase modulated ultrasonic signal. The method is experimentally evaluated to show that the proposal can significantly reduce the TOF measurement error, from 25.5% to 0.3%.

© 2018 IEEE. This paper proposes a multiple access method, referred to as Multiple Subcarrier Multiple Access (MSMA), for perfectly synchronized concurrent data collection from a group of passive backscatter wireless sensor tags and its experimental evaluation. By achieving less than 128 micro second synchronization error, backscatter communications can be applied to structural health monitoring of artifacts such as civil structures and machineries. In MSMA, each sensor tag uses a dedicated subcarrier frequency to produce a modulated backscatter. The sensor data is superposed onto the subcarrier either with an analog or a digital modulation. The inevitable harmonics among the subcarriers, stemming from the backscatter principle, can be rejected by numerically calculating the harmonic replicas and subtracting them from the observed signal in a software defined receiver. A frame based signal processing in the receiver results in no relative synchronization error among subcarriers even after the interference rejection. Since the interference rejection can be done before the demodulation and decoding, the concurrency can be secured irrespective to the choice of modulation method. We developed a prototype of MSMA using LabVIEW communications Software Defined Radio environment and prototype sensor tags using discrete electrical parts. The performances and limitation of MSMA using digitally modulated subcarriers are evaluated both in wired and wireless environments with up to four backscatter sensors.

© 2019 IPSJ. Authors propose a method for improving channel reservations in multi-subcarrier multiple-access wireless communications schemes. This scheme is designed for use with wide-area synchronous sensing zones that use functionally extended multi-subcarrier multiple-access subcarrier communication schemes for passive radio-frequency identification (RFID). When the sensing target is larger than the communication distance of the sensor, the sensing zone must be divided. Overlapping zones invariably occur in this case. Sensors in overlapping zones transmit signals to their respective receivers over the same channels and interference follows. If three or more zones are placed side by side, middle zone's communication capacity is lower than else zones. Because, middle zone can not use nearly center frequency. However, the communication capacity and its variations have not been examined for how they are affected by the zones in which overlapping sensors are used. This study investigated communications between sensors in overlapping zones by assigning channels to receivers in odd zones. The channel reservation method and the conventional method were simulated in MATLAB an compared. By allocating channels to sensors in odd zones, communication capacity can be improved and variations suppressed.

Copyright c 2019 The Institute of Electronics, Information and Communication Engineers SUMMARY Backscatter wireless communications offer advantages such as batteryless operations, small form factor, and radio regulatory exemption sensors. The major challenge ahead of backscatter wireless communications is synchronized multicarrier data collection, which can be realized by rejecting mutual harmonics among backscatters. This paper analyzes the mutual interferences of digitally modulated multicarrier backscatter to find interferences from higher frequency subcarriers to lower frequency subcarriers, which do not take place in analog modulated multicarrier backscatters, is harmful for densely populated subcarriers. This reverse interference distorts the harmonics replica, deteriorating the performance of the existing method, which rejects mutual interference among subcarriers by 5 dB processing gain. To solve this problem, this paper analyzes the relationship between subcarrier spacing and reverse interference, and reveals that an alternate channel spacing, with channel separation twice the bandwidth of a subcarrier, can provide reasonably dense subcarrier allocation and can alleviate reverse interference. The idea is examined with prototype sensors in a wired experiment and in an indoor propagation experiment. The results reveal that with alternate channel spacing, the reverse interference practically becomes negligible, and the existing interference rejection method achieves the original processing gain of 5 dB with one hundredth packet error rate reduction.

© 2019 Information Processing Society of Japan. Software-defined radio (SDR) is used for R&D such as cognitive radio. Because sampling devices and personal computers configuring the SDR environment have fixed configurations, some reconfiguration is needed when the SDR application requires different data sources and computational resources. To enable reconfiguration, we present a cloud platform that has scalable computing resources and data sources deployed over a wide area. We use the existing SDR development environment (SDRDE) and implement it on the cloud platform. It is necessary to transfer the SDR environment to the cloud by separating the UI and data management from the existing SDRDE. In this study, we selected the GNU Radio Companion (GRC) as the base platform and implemented an SDRDE for an unspecified number of users by separating the UI. In addition, we used task parallel and distributed computing for the SDR application. In this study, we focus on compatibility with the base implementation and lifting the limits of computational resources. We confirmed the compatibility with GRC in terms of user skill sets and software assets and evaluated the system response time. Further, the relationship between CPU utilization and instructions per cycle during SDR application execution shows that in general, this approach is effective.

© 2019 IEEE. Backscatter communication is essential in applications where wireless and batteryless sensors are demanded. Backscatter communication system may suffer short communication range because its sensors transmit signals by means of the reflection of incident radio wave that is provided by counterpart interrogator. The use of multiple interrogators, forming multiple interrogation zones, is the usual practice to extend the range of backscatter communication system. However, if a sensor receives more than one radio waves-one from its counterpart interrogator and others from neighbor interrogators-the sensor produces modulated backscatters to all the interrogators, causing interference to neighbor interrogators. This inter-zone interference is particularly problematic when multiple sensors send stream data concurrently. This paper proposes a real-time separation of collided backscatter signals based on their statistical independence. The proposal uses a priori probability of backscatter signal to extract the independent carrier phase angles and the independent amplitudes from IQ signal observation. The measurement of channel state information with predefined symbol pattern in packet is not needed. The proposal is evaluated both in numerical simulations and a physical experiment using prototype backscatter sensors and a software-defined interrogator. The results show that collided backscatter signals can be separated in real-time without degrading the packet error rate of each signal.

© 2019 IEEE. This paper proposes a carrier recovery method tailored to narrow-band multicarrier backscatter wireless links, which employ subcarrier modulation. Because backscattered subcarrier is usually produced by low accuracy and low rate internal clock in a low power consumption or batteryless, wireless sensor, the corresponding receiver needs to compensate the subcarrier frequency drift and fluctuation dynamically for demodulation and decoding. Although a backscattered subcarrier is produced by changing the antenna reflection coefficient of wireless sensor, the backscattered signal is usually converted to a zero-crossing signal to enhance signal resolution, and edge detection based demodulator is applied at the receiver. However, in a multicarrier backscatter system, the edges at symbol boundaries of each backscattered subcarrier become indistinct because of the narrow bandwidth. Consequently, subcarrier frequency estimation with existing carrier recovery technique may results in error. This paper solves the problem by removing outliers of temporal subcarrier frequency based on the statistical distribution and applying a feedback control. The statistical carrier recovery method is examined experimentally with a prototype wireless sensor and a software defined receiver to reveal the method can automatically compensate unstable subcarrier with about 10-2 order drift and outperforms the popular frequency doubler based carrier recovery. The optimal feedback gain, 1.0, is also revealed.

This paper presents a novel method to improve the subcarrier frequency accuracy of tag chip for UHF RFID sensing system based on EPC global Gen2 protocol. By changing the tag's response to the Write command, the tag returns the subcarrier before returning the response specified in the protocol. In this way, a frequency calibration loop will be established between reader and tag. This method not only enables a low-power oscillator with a precise frequency to be integrated into a tag chip, but also enables flexible configuration of the frequency. The tag chip containing this idea is fabricated in SMIC 0.18 μm CMOS process with a die size of 850 μm × 850 μm. Measurement results show that the proposed novel method can realize the calibration of the subcarrier frequency, and the subcarrier frequency deviation is less than ±0.385KHz in the range of 40KHz-640KHz. With this accuracy, the tag can be allocated up to 78 subcarrier communication channels.

This paper examines the practicality of concurrent sensor data streaming with backscatter communication applied to modal analysis, which demands accurate data synchronization among streams. The major synchronization error source in concurrent backscatter streaming system is the instability of backscatter sensor clock. Synchronization of the streams by resampling at receiver is necessary but careless implementation may produce artificial delay caused by the difference of anti-Alias filters tailored to the individual clock rates of backscatter sensors. In this paper, a set of signal processing to synchronize concurrent backscatter signals is designed and implemented in a prototype system. The prototype system comprises backscatter sensors, interrogators and modal analyzer, which takes care of the generation of transfer matrix. The signal processing in the modal analyzer features a recursive least square regression to recover instantaneous sampling rate of backscatter sensor and a zero-phase-filtering in overlap-And-Add approach. The proposal is evaluated by comparing the transfer matrices generated from the prototype system and a commercial modal analysis system where wired accelerometers are used. The experimental results show that the proposed signal processing can successfully synchronize concurrent backscatter streams by eliminating the artificial delay.

Radio frequency identification (RFID) technology is now widely used for tracking a great variety of objects in spatio-temporal dimensions. In the field of urban management and analysis, personal RFID is a powerful tool for tracing both individual pedestrians and crowd dynamics. In this research, we have focused our attention on how public services can use RFID technology, especially from the viewpoint of attractive and real-time visualization. In a trial demonstration, we installed nine RFID-reader gates in an urban district and provided hundreds of passive RFID-tags to pedestrians. Using this basic RFID-infrastructure, we developed a public display service which visualized and reported urban activities in the style of a real-time weather map. A large display shows the density of people at each location by using geometric contour lines and virtual clouds. Accumulated data is automatically updated and the 'weather' map quickly changes as time passes. The weather-like visualization helps the user understand the dynamics, flows, and trends of crowds, and promotes intuitive forecasting of urban activity.

UHF passive RFID has been already in practice. Industrial applications sometimes suffer insufficient tag readability. Engineering may be needed to enhance the readability, accordingly. One of the factor to deteriorate the readability is the multipath fading. Identification of principal reflecting paths is essential to improve the readability deterioration by, for example, using antenna diversity and usage of microwave absorbance materials to suppress reflections. In this paper, a path identification method for UHF RFID using the measured power profile is presented. The method only requires a series of the received power measurement at the position of the target tag. By applying the steepest gradient method, we can optimize the parameters that defines the reflecting plane and eventually identifies the path direction. Together with theoretical development of the method, numerical example shows the validity of the method. © 2007 IEEE.