| In industrial application scenarios,such as large-scale factory storage system,unmanned warehouses,supermarket and supply chain management system,the automatic identification and unmanned management of objects has become a requirement.Information system needs to identify and manage large-scale and densely distributed objects.In order to complete the whole automatic controlling of the object,we not only need to obtain the attribute information of the objects,but also the real-time location of them.To sum up,with the extensive and wide deployment of the Io T system in the mentioned scenarios above,an identification and location system for largescale and densely distributed goods is being expected.At present,the identification and location technology of objects is mainly based on two carriers: radio frequency and optical.As we know,the RFID is the identification and location technology which was most widely used and also the mainstream solution adopted by the industry.RFID modulates the information of objects on the received electromagnetic wave and transmit it in reverse by backscattering wireless communication,so does it achieve the purpose of passive object identification.In addition,by using the strength information,arrival time and channel state information of the wireless signal,the relative position between the transmitter and the receiver can be calculated.However,RFID uses ALOHA protocol for access control which collision will inevitably happened,and it would make the probability of tag identification greatly reduced with the increase of the items' quantity.In the aspect of localization,because the object location is obtained by analyzing the RF signal,the complexity of whole calculation process is large,and the energy consumption to achieve high accuracy is too high,hence it's not appropriate in the case of high label density.In optical tag,optical coding(QR code or barcode label)technology is widely used.With the help of image processing technology,the recognition function can also be realized,but the operating distance is short(?50cm),and it cannot read multiple tags at the same time,hence the throughput is pretty insufficient.Secondly,the optical tag cannot localize the object,so it cannot server the identification and location task of large-scale and densely distributed objects.To solve the problem of identification and location of large-scale and densely distributed objects,we've designed an indoor location and communication system which was based on coded image sequence detection.The transmitter broadcasts a set of Gray coded image sequence to all objects through the visible light modulation device(DMD).The objects(tags)in different spatial regions receive unique position coding through simple light and dark detection.The accurate position information of the labels can be obtained without analyzing the characteristics of the signal itself.In addition,because of utilizing solar cell as receiver.The tag can harvest energy from the visible light signal which could be used to power up the whole working process.Because of unique position code,the receiver can get its relative position in the projection area.There will be no collision happened when the attribute information was transmitted back through TDM protocol.Compared to RFID's multi tag recognition,proposed system effectively avoids the problem of collision in the process of information gathering.Compared with the optical coding tags recognition,proposed system realizes the multi label recognition.In addition,the system also achieves accurate positioning and low power consumption.Experiments show that the system can provide positioning services of 1024 tags with localization error less than 10 cm. |
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