Yuusuke Kawakita

Method for estimation of distance between objects and its application for finding lost objects

In this paper, we propose a method to estimate the distance between objects attached with radio-frequency identification (RFID) tags that are used for finding lost objects. Many systems for finding lost objects adopt real-time location systems (RTLSs) using received signal strength indication (RSSI). The fundamental structure of a general method for an RTLS using RSSI involves the creation of a number of reference nodes whose locations are known in advance. Crowded objects often form a group; hence, it is very helpful to find some object members of the group in a certain place so as to find the lost object belonging to the group. However, an RTLS is not required to know the objects located in a certain place or to estimate the distance between these objects. Hence, we propose a method to estimate the distance between objects rather than the individual object locations without using a method to obtain location-dependant information.

Controlling of communication connection range using acoustic waves emitted from smartphones

The development of smartphones and other portable devices has expanded new ways of communication and collaboration both in private and business settings where there are used e.g. for sharing files and other information. However, this communication is not always secure and can be intercepted by a third party in the vicinity. This paper proposes an intelligent communication control mechanism where the shared information is accessible only within a physically limited space. Normally, existing communication methods based on radio waves (Wi-Fi or Bluetooth) are accessible to anyone within a specific range; thus, they are susceptible to breach and communication eavesdrop beyond walls. Our proposed method is based on an association scheme whereby the sending smartphone can restrict the communication range by controlling an acoustic wave’s magnitude and frequency. Thus, unlike radio waves, it is possible to send the signal to devices located in a specific range, where the client devices exist, after recognizing the distance and angle between devices. Our experiments by sharing signals among smartphones indicate that it is possible to unidirectionally control the sharing range while sharply reducing any possibility to eavesdrop on the communication.

Remote implementation of GNU radio-based SDR development environment

Software-defined radio (SDR) is used in several areas, such as the verification and implementation of radio prototypes. The SDR environment is generally configured with an analog-to-digital converter (ADC) and a personal computer (PC). However, since ADCs and PCs are fixed configurations, reconfigurations are needed in order to respond to different data sources and computing environments when the radio protocol or SDR are indefinite. To enable this reconfiguration, we present a cloud platform that has scalable computing resources and data sources deployed in a wide area, using an existing SDR development environment. In order to apply the existing SDR development environment to the cloud platform, UI separation and data management are required. In this manuscript, we implement an SDR environment for many unspecified users through UI separation by selecting the GNU Radio Companion (GRC) as the platform. We focused on compatibility and flexibility with regard to the configuration, in order to allow the user to adjust the resources consumed by the PC. The results show that one particular implementation of the remote SDR execution and development is suitable. In addition, we confirmed the compatibility with GRC in terms of user skills and software assets, and achieved distributed processing to allocate resources between the client and cloud according to the users discretion, by dividing the processing of the SDR on the basis of the function unit.

Active RFID attached object clustering method based on RSSI series for finding lost objects

An active radio frequency identifier (RFID) tag that can communicate with smartphones using Bluetooth Low Energy technology has recently received widespread attention. Indeed, many products have been released that aim to find lost objects using the received signal strength indication (RSSI). However, these products do not provide sufficiently accurate location information to find objects. In this paper, we propose an active RFID attached object clustering method based on RSSI series for finding lost objects. This approach to find lost objects does not execute existing localization methods. We hypothesize that users can deduce the location of a lost object from information about surrounding objects in an environment where RFID tags are attached to all personal belongings. To help find lost objects from the proximity between RFID tags, the system calculates the proximity between a pair of RFID tags from the RSSI series, and estimates the groups of objects in the neighborhood. We present a method for calculating the proximity of the lost object to those around it using a distance function between RSSI series and estimating the group by hierarchical clustering. We confirm the validity of the proposed method, and determine the most appropriate pairs of four distance functions and four clustering algorithms. From the experimental results, it is apparent that our method provides a clear advantage in finding lost objects at low financial and installation cost, and can estimate groups accurately even if the smartphone or RSSI sensor is moving quickly.

SDR processing delay estimation applying correlation detection for structure health monitoring using multi-subcarrier multiple access

Wireless and battery-less structural health monitoring (SHM) that detect structural damage at low cost are required. To achieve this, the use of multi-subcarrier multiple access (MSMA) communication method is being considered. In MSMA, time synchronization of sensing data is shifted owing to software defined radio (SDR) processing. Therefore, when an SHM monitoring method requiring time synchronization of sensing data is used, time synchronization taking SDR processing delay into account is necessary. In this study, we propose a system that estimates SDR processing delay by correlation detection and acquires time synchronization of sensing data. We measured SDR delay estimation with time accuracy by installing this system on an experimental object. Results showed that the error of the allowable processing delay estimation was different, and time synchronization can be achieved by performing sensing once by the SDR processing delay estimation method using correlation detection.

Inter-zone interference avoidance using channel reservation in multiple subcarrier multiple access scheme

Interest in structural health monitoring for which sensors are used to detect structural damage has increased. For low-cost installation, these sensors are required to be batteryless and wireless. The objective of this study is to realize structural health monitoring for large-scale structures using a multiple subcarrier multiple access scheme that functionally enhances sub-carrier methods in radio-frequency identification (RFID) communication. When the target structure is of large scale, it is necessary to divide the structure into several zones because of communication distance restrictions. In this case, some wireless sensor nodes are located in zones where adjacent transceiver ranges overlap, thereby transmitting their sensing signals to both zones; thus, the problem of inter-zone interference due to unintended subcarriers arises. Therefore, we propose a method of inter-zone interference avoidance in which channels are reserved for wireless sensors overlapping adjacent zones. Evaluation via simulation reveals that the average communication capacity reduction can be suppressed compared with the case without channel reservation.

Monopulse switching to cancel phase offset in array antenna comprising multiple COTS SDRs

This paper proposes a phase offset canceler for an array antenna, which comprises multiple low-cost commercial of the shelf (COTS) software defined radio (SDR) devices. The main challenge is the phase synchronization of SDR devices because each SDR devices has its own phase offset when it produces IQ stream. We devise a simple yet effective method to cancel the phase offset of individual SDR device using a double-pole, double-throw (DPDT) switch which is implemented between antenna and SDR device. The DPDT switch is controlled according to the frame timing of each IQ stream to produce two set of measurements, from which we can compute angle of arrival (AoA) with a simple signal processing. We refer this mechanism as “Monopulse Switching”. We evaluated the working principle experimentally to reveal Monopulse switching successfully cancel phase offset to detect AoA without any initial calibration and achieves 2.8 degree measurement accuracy.

Improvement in multiple access channel allocation for sensor node configuration based on RFID communication

Wireless sensors are expected to be low cost and to reduce their power consumption so that a large number of sensors can be installed for collecting real-world information. Passive radio-frequency identification (RFID) is proposed to assign communication channels to sensors that only send analog sensing signals for their multiple access control. In this method, the RFID reader-writer assigns channels to all sensors by writing channel numbers to the RFIDs attached to the sensors. We propose a method that more efficiently assigns a multiple access channel to the controlled sensor by using passive RFID. We determine the channel by using the electronic product code (EPC) of the RF tags. This approach results in a large reduction in the number of writes. However, it is shown that there is a tradeoff between the reduction in the number of writes and the total number of channels. In addition, our method has a tradeoff between the reduction in the number of writes and the spectral efficiency.

A Method to Assign Spread Codes Based on Passive RFID Communication for Energy Harvesting Wireless Sensors Using Spread Spectrum Transmission

Considerable research has been conducted on systems that collect real-world information by using numerous energy harvesting wireless sensors. The sensors need to be tiny, cheap, and consume ultra-low energy. However, such sensors have some functional limits, including being restricted to wireless communication transmission. Therefore, when more than one sensor simultaneously transmits information in these systems, the receiver may not be able to demodulate if the sensors cannot accommodate multiple access. To solve this problem, a number of proposals have been made based on spread spectrum technologies for resistance to interference. In this paper, we point out some problems regarding the application of such sensors, and explain the assumption of spread codes assignment based on passive radio frequency identification (RFID) communication. During the spread codes assignment, the system cannot work. Hence, efficient assignment method is more appropriate. We consider two assignment methods and assessed them in terms of total assignment time through an experiment. The results show the total assignment time in case of Electronic Product Code (EPC) Global Class-1 Generation-2 which is an international standard for wireless protocols and the relationship between the ratio of the time taken by the read/write command and the ratio of total assignment time by the two methods. This implies that more efficient methods are obtained by considering the time ratio of read/write command.