This work presents an alternative wearable tracking system based on a low-power wide area network. A complete GPS receiver was integrated with a textile substrate, and the latitude and longitude coordinates were sent to the cloud by means of the SIM-less SIGFOX network. To send the coordinates over SIGFOX protocol, a specific codification algorithm was used and a customized UHF antenna on jeans fabric was designed, simulated and tested.
Moreover, to guarantee the compliance to international regulations for human body exposure to electromagnetic radiation, the electromagnetic specific absorption rate of this antenna was analyzed. A specific remote server was developed to decode the latitude and longitude coordinates. Once the coordinates have been decoded, the remote server sends this information to the open source data viewer SENTILO to show the location of the sensor node in a map.
The functionality of this system has been demonstrated experimentally. The results guarantee the utility and wearability of the proposed tracking system for the development of sensor nodes and point out that it can be a low cost alternative to other commercial products based on GSM networks.
MATERIALS AND METHODS
As it is shown in Figure 2, the system architecture interconnection uses an LPWAN to transport data from sensor nodes to the final communication end-point hosted on the Internet. Specifically, in this system, the SIGFOX Network Operator has been used. SIGFOX is a leading operator of LPWAN with proprietary technology that offers an end-to-end connectivity solution, and has an extensive deployment in the Spanish territory. This operat or deploys the proprietary base stations and connects them to the backend servers using an IP-based network.
Figure 3 illustrates the block diagram of the proposed wireless wearab le sensor node (WWSN). The main part (core) of the WWSN is the microcontroller. This block receives the location data from the GPS receiver by means of the NMEA0183 frame. This information is codified into the microcontroller and transmitted to the cloud by using the SIGFOX transmitter, which is connected to a specific textile antenna to efficiently radiate the information.
Figure 14 shows a photograph of the proposed wireless wearable sensor node. As can be observed, the prototype has been implemented on the right leg of usual jean trousers. The electrical connections between the different modules (GPS receiver, microcontroller and SIGFOX transmitter) have been implemented by stitching conductor yarn on the jeans.
As it is observed, each minute a message with the latitude codifications is sent by the wearable sensor node and received in the SIGFOX backend. The message is directly forwarded to the developed remote server to decode the latitude and longitude and additional information. Once the information is decoded, it is transmitted to SENTILO, as depicted in Figure 16.
DISCUSSION AND CONCLUSIONS
In this work, an alternative wearable tracking system based on the low-power wide area network has been developed. The system consists of a GPS receiver and SIGFOX transmitter integrated with a textile substrate. In order to use the SIGFOX network to transmit the latitude and longitude coordinates, a specific codification algorithm has been used. In order to enhance the wearability of the system, a customized UHF antenna on jeans fabric has been designed and developed.
The impact of the electromagnetic radiation absorbed by the human body has been evaluated and it is under the limits defined in the electromagnetic exposure international regulations, guaranteeing the health safety of the system. The coded coordinates have been decoded in a specific developed remote server and sent to the open source data viewer SENTILO. The functionality of the system has been experimentally evaluated by means of a field test in Terrassa.
The proposed system enhances the wearability and reduces the cost with regard to other alternatives. However, in order to increase the wearability of future nodes even more, work is in progress to integrate all the electronic components in a single wearable PCB and develop an additional GPS textile antenna. Moreover, other aspects such as the washing process and wear-out impact should be addressed.
Source: Catalonia Agency for Management of University
Authors: Raul Fernandez-Garcia | Ignacio Gil