What Is a PSM(Power Saving Mode) in LTE Cat.M1 ?

LTE Cat.M1 (Cat.M1) is standardized by 3GPP which is International Standardization Organization and serviced nationwide through SKT. Also, Cat.M1 is a representative LPWAN (Low-Power Wide-Area Network) technology and specialized in IoT application development. Power consumption of battery-operated devices in IoT applications is directly related to device life cycle, so minimizing the power consumption is very critical. For this reason, Cat.M1 supports PSM and Enhanced DRX (eDRX) technology, which greatly reduces the power consumption. With PSM, you can reduce the power consumption by setting the active / sleep state of the device.

This guide explains how to configure the PSM functions using the Woori-net Cat.M1 module. The Cat.M1 module is typically controlled by AT commands that are available through the UART interface. PSM function can also be activated / deactivated using AT command.

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Step 1: Hardware Connection

2.1 Setting WM-N400MSE module

If you are using the WM-N400MSE module, use the IoT Starter Kit and it should be configured as follows:

2.2 Install UART Driver
After setting the hardware, Connect between board and PC using micro USB connector. PC operating system will confirm the COM port connected to the device. If the device is properly connected, you can check two COM ports, and send AT commands using Standard COM Port. Windows You can check the COM port in Device Manager in Control Panel.

If you can not verify the COM port in Device Manager, download and install the driver from the following link.
Link: CP210x USB to UART Bridge VCP Drivers

Step 2: AT Commands

3.1 AT+CPSMS

AT + CPSMS command is used to use PSM, and Active / Sleep cycle can be adjusted by parameter setting. You can adjust the Active / Sleep cycle by setting the value4 and value5 times of the command. Set 6-8 bits to set the unit of the period and 1-5 bits to set the value. For example, if value4 is set to 1010011, the unit is 1 minute since 6-8 bits is 101, so the value is 6 because it is set to 1-2 bit, so it is set to 6 minutes.


3.2 AT$$DBS

During the response of the AT $$ DBS command, the Active / Sleep time can be calculated using the PSM-ACTIVE and PSM-PERIODIC parameter values.


3.3 AT*SKT*RESET

If you use the above AT command to use PSM, you need to reboot to save the settings.

Step 3: Example

In order to determine the point of entry into the Active / Sleep state, AT commands should be periodically sent and acknowledged. This is the result of testing with PSM-ACTIVE set to 60 seconds and PSM-PERIODIC set to 180 seconds.

The Active / Sleep status can be determined through the LD3 of the IoT starter kit. If LD3 lights green, it is in the Active state. If it is off, it is in the Sleep state. Below is the result of testing with PSM-ACTIVE set to 60s and PSM-PERIODIC set to 180s. IoT starter kit is marked as Active Start when the light is on, and Sleep Start is indicated when the light is off.

The above results show that the active state is PSM-ACTIVE + 24-27 seconds, and the sleep state is PSM-PERIODIC-PSM-ACTIVE + 3-4 seconds.

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