Osamu Takyu

Change of read range for UHF passive RFID tags in close proximity

In this paper, we discuss change of read range between a UHF passive RFID tag and reader when a tag is close to another tag. The read range is determined by the strength of forward link and reverse link, which are represented by received power at a tag and reader, respectively. Approaching of tags causes electromagnetic interference between antennas of tags and results in change in impedance matching condition between an antenna and IC of a tag. This change in impedance matching condition decreases in read range. Therefore, we measure the change in received power of a tag and reader experimentally so as to identify which link limits read range and to restrict the existence range of IC impedance. In addition, a technique for extending read range when tags are close is proposed.

High-speed LED driver for visible light communications with drawing-out of remaining carrier

The visible light communications that communicates by modulating the light of illumination, which is the existing infrastructure, attracts attention. So as to improve the speed, to increase the bandwidth, and to miniaturize hardware of this communication system, improvement in the transmission speed by a single LED for lighting is important. The transmission speed of an LED is greatly restricted by the carrier that remains in junction capacity. Therefore, the transmission speed can be increased by drawing out the remaining carrier. We proposed and applied the carrier drawing-out circuit to the driver circuit that drives a blue LED. An optical measurement shows that the fall time decreases from 56 to 10 ns (decreases to one fifth), and the horizontal eye opening ratio has been improved from 29% to 61% (increases to 213%) for 50 Mb/s PRBS.

Performance evaluation of decision directed channel estimation for single user IFDMA

Recently, an interleaved frequency division multiple access (IFDMA) has been attracting much attention. Accurate channel estimation is essential for both IFDMA demodulation and frequency domain equalization (FDE) at the receiver. In this paper, we propose a decision directed channel estimation (DD-CE) method to improve the tracking performance of fading fluctuation. In the proposed method, the frequency channel response over the entire frequency band is obtained by DD-CE and the frequency domain interpolation. After that, to reduce the effect of noise, delay time domain windowing is performed. We show by computer simulations the proposed method can reduce the channel estimation error and improve bit error rate (BER) performance compared to conventional channel estimation.

Analysis of read range for UHF passive RFID tags in close proximity with dynamic impedance measurement of tag ICs

In this paper, we discuss the change of read range between a UHF passive RFID tag and a reader when a tag is close to another tag. The read range is determined by the strength of the forward and reverse link. These links are identified by comparing the calculated received and reflected power with the measured dependence of the read range on the distance between close tags. We developed a system to measure the tag IC impedance in operation. The accuracy is assured by the short-open-load (SOL) one port calibration. The reader and tags change of received power is calculated according to the change of tag IC impedance due to the closeness of the tags. As a result, it becomes clear that the read range is determined by the reverse link finally.

Performance evaluation of effect of nonlinear distortion in SC-FDMA system

In up-link wireless access communication, the transmitter needs good linearity but low power efficiency power amplifier. If the nonlinear power amplifier is used for improving the power usage efficiency, the higher peak-to-average power ratio (PAPR) signal suffers from nonlinear distortion. The effect of nonlinear distortion to Single Carrier-Frequency Division Multiple Access (SC-FDMA) has not been evaluated yet. In this paper, the performance of effect of nonlinear distortion to SC-FDMA is evaluated in terms of PAPR, out-of-band radiation and bit error rate with computer simulation, where there are two types of access scheme in SC-FDMA, first one is interleaved frequency division multiple access (IFDMA) and second one is localized frequency division multiple access (LFDMA). From the simulation results, we clarify IFDMA or LFDMA has the higher robustness for nonlinear distortion.

Subcarrier assignment for achieving tradeoff between peak power and channel capacity in block transmission of multiuser OFDM

In this paper, the novel subcarrier assignment for achieving large channel capacity as well as small PAPR of transmitted signal is proposed in downlink multiuser OFDM system. In the proposed assignment, some resource blocks are acceptably assigned to the second-best mobile user. As a result, there are some candidates for assigning the resource block to mobile user. In the proposed technique, we choose the assignment pattern among the candidates as the peak to average power (PAPR) of transmitted signal becomes small. Even if the total channel capacity becomes smaller, PAPR becomes small. From the computer simulation, as the number of resource blocks assigned to the second best mobile station becomes larger, the PAPR reduction is more effective but the channel capacity decreases. Therefore, the proposed assignment establishes the PAPR — Channel Capacity trade off. However, as the number of mobile users increases, the base station has the more opportunities to find the mobile station having larger SNR. It is user diversity effect. Owing to user diversity, we also confirm that the PAPR — channel capacity trade off becomes better when the number of mobile users becomes larger.

On the ergodic performance of a simple closed-loop spatial multiplexing architecture

Cognitive radio system shares the frequency spectrum with the license system. As a result, the dramatic improvement of the frequency usage efficiency can be expected. Since the cognitive radio system is independent from the license system, it should recognize the wireless communication parameter of the license system, such as frequency, modulation scheme, and so on. Multiple-input multiple-output (MIMO) system, which can transmit multiple data signals with using single frequency spectrum, is applied to cognitive radio, and thus frequency use efficiency is more significantly improved. In MIMO-cognitive radio system, when new cognitive user tries to use the frequency resource, it is necessary that the new user should detect the number of parallel transmitted symbols which the license user transmit, because the new user should remove the interference signals whose number is the same as that of data symbol transmitted by the license user. In this paper, in MIMO-cognitive radio system, the novel method for recognizing the number of parallel data symbols is proposed.

Multi-target tracking based on features of sensing results and wireless parameters for physical wireless parameter conversion sensor networks

In wireless sensor network, in addition to long life operation and low complexity, small time delay and large traffic acceptance for supporting various machine-to-machine communications are required. Although physical wireless parameter conversion sensor network (PHY-C SN) achieves simultaneous data collection, the separation of mixed sensing results is a difficult problem. For separating each sequence of them, multi-target tracking technique is available, but failing when similar sequences are included in the sensing data. This paper proposes a novel data separation method based on multi-target tracking that uses both features of the sensing results and the wireless parameters. We show the accuracy of our method through computer simulations.

Performance evaluation of multi-target tracking for PhyC-SN

Physical conversion sensor networks (PhyC-SN) achieve simultaneous data collection in wireless sensor networks. Although the PhyC-SN can recognize the median and the outliers of all the sensing data simultaneously, their separation into each sensor data is a difficult task. To address this task, we have proposed a data separation method that utilizes multi-target tracking with use of the sensing data and the received spectrum power for the separation. Even if some of the sensor data are close to each other, the instantaneous power of the sensor data bearing signal is a useful feature for the separation. In this paper, we clarify the separation accuracy of our separation method under various wireless environments by computer simulation.

Highly efficient environment aware wireless sensor network

In this demonstration, we introduce a demonstration system of highly efficient environment aware wireless sensor network by considering characteristics of sensing information and spectrum efficiency. In this network, a suitable sensor system is selected from multiple wireless sensor systems by considering the demand of each sensor and surrounding wireless environment. In our demonstration system, we prepare 2.4GHz ZigBee, 920MHz small power wireless system and 460MHz wireless sensor network converting the sensing information to frequency called physical wireless parameter conversion sensor network (PHY-C SN). In order to understand the surrounding wireless environment, we also prepare a radio environment database based on the measurement data of each sensor. In CCNC 2016, we plan to introduce a video of the field test with more than 20 sensor nodes and to exhibit a small demonstration system based on multiple wireless sensor devices and USRPs.