LPWAN stands for Low Power Wide Area Network and it is a quite suitable communication technology in IoT field. Representative technologies are Sigfox, LoRa NB-IoT, and LTE Cat.M1. These are all low power long distance communication technology. In general, the LPWAN has low data rate due to its characteristics of low power and long distance communication. In the table below, the maximum transmission speed of LPWAN technology is 12Bytes ~ 375Kbps.
LTE Cat.M1 has a higher maximum transmission rate than others, so it is appropriate for medium-sized and real-time applications such as photo transmission, biometric authentication and real-time tracking service. In this article, we will use LTE Cat.M1 among LPWAN technologies to check if the pictures can be transferred and verify the actual LTE Cat.M1 speed.
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Step 1: Project Overview
There are two ways to use Woori-net's LTE Cat.M1 external modem. First, you can control an external modem with the AT command via the UART interface. Second way is using as RNDIS mode. When using the AT command, the UART interface (Baud Rate: 115200) is used, so the LTE Cat.M1 maximum transmission rate of 375 kbps is not available. Therefore, I select a second way that is using as RNDIS mode. In addition, when you want to use this mode, you must be set ‘RNDISMODE = 1’ using AT command.
configuring this way, Raspberry pie can use an external modem in RNDIS mode, which allows you to use LTE Cat.M1 communication. Hardware connection will be explained in STEP 3.
Step 2: Pre-requisitions
Step 3: Hardware Connection
If you set RNDIS mode in STEP 1, connect to Raspberry Pi as below.
If the Internet connection is established, you can check that mark as shown below.
Step 4: Source Code Links and Descriptions
Raspberry Pi – Client Source
Python 2.72 version is installed in Raspberry Pi. And the external modem uses IPv6, so you need to convert the server's IPv4 address as follows. This Conversion rule is negotiated by SK Telecom and Woori-Net.
Briefly, take a picture using Raspberry Pi Camera and transfer the file to the server of that IP.
Please check the link at the bottom for the full source code.
PC – Server Source
The server that receives the photo is developed with pyQT that is GUI programming tool.
A progress bar was inserted to check the transfer progress and when it received all, you can also check the image.
The TCP server runs as a thread.
We used the Signal-pyqtSlot () function to refresh the image and progress bar.
Step 5: Project Video and Verifying LTE Cat.M1 Speed
5-1. Project Video
Please refer to Youtube
5-2. verifying LTE Cat.M1 speed
A total of 50th tests were conducted in the form shown in the table below. The average data rate was 298.37 bps. We confirm that we can send data about 80% of the LTE Cat.M1 maximum transmission rate.
Step 6: Finish
With the IoT field is expanding, and the application range of LPWAN technology is increasing. For example, there are photo transmission, real-time tracking service not just send or monitoring a sensor data. In this article, I checked that pictures can be transferred using LTE Cat.M1 and verify the actual LTE Cat.M1 speed. (Please note that usage may different from country to country and LTE Cat.M1 module manufacturer.)
I hope this article will help you to take advantage of developing LTE Cat.M1 applications in the new IoT field.
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