Introduction to NB-IoT of STM32

Narrow Band Internet of Things (NB-IoT), NB-IoT is built on the cellular network and only consumes about 180KHz of bandwidth. It uses the license frequency band and can be deployed in three ways: in-band, guard band, or independent carrier. Coexist with existing networks. It can be directly deployed on GSM network, UMTS network or LTE network to reduce deployment cost and achieve smooth upgrade.

Generally, we divide IoT devices into three categories:

　　① No need for mobility, large data volume (uplink), and a wider frequency band, such as city surveillance cameras.

　　② Strong mobility, frequent switching, small data volume, such as fleet tracking management.

　　③No mobility, small data volume, not sensitive to delay, such as smart meter reading.

NB-IoT was born to deal with the third type of IoT devices.

2. Features

(1) Advantages

Super coverage : Compared with GPRS, it increases the signal gain by 20db. Under the same frequency band, NB-IoT has a gain of 20dB compared with the existing network, which can better meet the needs of deep coverage such as factory areas, pipeline wells, and manhole covers.
Ultra-low power consumption : The goal for terminal power consumption is: based on AA (5000mAh) batteries, the service life can exceed 10 years. The module is in a dormant state at ordinary times, and can automatically wake up and upload data according to the program setting every day. If the requested command is not received, the module will automatically enter dormancy, and the standby time of the terminal module can be as long as 8 years.
Super-large connection : A sector can support tens of thousands of connections, supporting low latency sensitivity, ultra-low equipment cost, low equipment power consumption and optimized network architecture. The same base station can provide 50-100 times the number of accesses than existing wireless technologies.
Ultra-low cost : NB-IoT does not need to rebuild the network, and the radio frequency and antenna are basically multiplexed.

(2) Disadvantages

Transferring less data . Based on the mechanism of low power consumption, it is destined that NBIoT can only transmit a small amount of data to the remote end. Therefore, in formal application, either the number of bytes transmitted in a single transmission is small, or the interval between transmission data is long. For example, smart water meters and gas meters generally transmit data every 24 hours. This means that industry applications that rely on real-time data analysis are difficult to promote this technology. In addition, there is the hassle of battery replacement at the end of its life.
Communication costs are expensive . At present, NBIoT communication modules are still relatively expensive. Mainstream chip manufacturers include Ziguang Zhanrui, Huawei HiSilicon, and MediaTek. An NBIoT module costs about 20 to 50 yuan. In terms of communication traffic, Telecom is 20 yuan a year, which is relatively cheap for more than one year. The retail price of a water and electricity meter is only one or two hundred yuan, and the NBIoT module eats up a large part of the cost.
The technology is yet to mature . Although China's major operators claim to have invested a lot of manpower, material and financial resources in related construction, NBIoT technology is not yet very mature. It is true that behind the telecom cloud platform is Huawei as the technical support, and its strength is strong. It is presumed that the technology will mature and stabilize in the near future.
Platform docking is difficult . Telecom's IOT platform uses the CoPA protocol, and the CoPA protocol docking is complicated. Although the information on Huawei Telecom's IoT platform is complete, it still takes a lot of time to connect with the telecom open platform.

3. Current main applications

Public utilities: smart water meters, smart water services, smart gas meters, and smart heat meters.
Smart city: smart parking, smart street lights, smart trash cans, and smart cellar covers.
Consumer electronics: independent wearable devices, smart bicycles, chronic disease management systems, elderly and children management.
Equipment management: equipment status monitoring, white goods management, large public infrastructure, safety monitoring of pipeline gallery.
Intelligent buildings: environmental alarm system, central air-conditioning supervision, elevator Internet of Things, civil air defense space coverage.
Command logistics: cold chain logistics, container tracking, fixed asset tracking, financial asset tracking.
Agriculture and environment: Agricultural Internet of Things, animal husbandry, real-time monitoring of air, real-time monitoring of water quality.
Other applications: mobile payment, smart community, smart home, cultural relics protection

At present, the domestic NB-IoT frequency bands mainly operate in the B5 and B8 frequency bands.

2. NB-IOT deployment method

NB-IoT supports three deployment methods: in-band (In-Band), guard band (Guard Band) and (Stand-alone).

1. Stand alone operation (Stand alone operation) referred to as ST

It does not depend on LTE and can be completely decoupled from LTE.

It is not suitable for re-farming the GSM frequency band. The channel bandwidth of GSM is 200KHz, which just makes room for the 180KHz bandwidth of NB-IoT, and there is a 10KHz guard interval on both sides.

2. Guard band operation (Guard band operation) referred to as GB

Does not occupy LTE resources.

The resource block is obtained by using the unused 180KHz bandwidth in the LTE edge guard frequency band.

3. In-band operation (In-band operation) referred to as IB

Occupies 1 PRB resource of LTE.

It can be the same PCI as LTE, or it can be different from LTE. Generally speaking, if the IB method is used, it tends to be set to the same PCI as LTE (what is the problem? First, NB also has PCI, so the same frequency network is feasible. , different from GSM, the second is that there are also 504 PCIs, and the PCI planning of LTE can be reused, and the third is that the generation and functions of PCI are basically the same).

3. Working status

1. Connected (connected state, working state)

The module is in this state after registration and access to the network, and can send and receive data. After a period of time without data interaction, it will enter the Idle mode, and the time is configurable.

2. Idle (idle state, light sleep state)

It can send and receive data, and it will enter the Connected state when receiving downlink data, and it will enter the PSM mode when there is no data interaction for a period of time, and the time is configurable. The idle state can be configured to execute DRX or eDRX mode.

3. PSM (energy saving state, deep sleep state)

It cannot receive or send data. In this mode, the terminal turns off the transceiver and does not monitor the paging on the wireless side. Therefore, although it is still registered in the network, the signaling is unreachable, the downlink data cannot be received, and the power is very small. The duration is configured by the core network (T3412), and it will enter the Connected state when there is uplink data to be transmitted or when the TAU period ends.

4. There is a certain switching relationship between the three states

After knowing it, you will have a further understanding of the use of NB, which is summarized as follows:

(1) The terminal is in the Connected state after sending data, and starts the "inactivity timer", the default is 20 seconds, and the configurable range is 1s~3600s;

(2) When the "Inactivity Timer" expires, the terminal enters the Idle state, and the active-timer (Active-Timer [T3324]) is started, and the timeout time configuration range is 2 seconds to 186 minutes;

(3) When the Active-Timer times out, the terminal enters the PSM state, and enters the Connected state at the end of the TAU period. The configuration range of the TAU period [T3412] is 54 minutes to 310 hours.

(4) The TAU cycle refers to the period from Idle to the end of PSM mode.

4. Working mode (NB-IoT power saving technology)

1. DRX mode (discontinuous reception)

DRX (Discontinuous Reception) is discontinuous reception, which means that the terminal only turns on the receiver to enter the active state during the necessary time period to receive downlink data, and turns off the receiver to enter the sleep state during the remaining time period to stop receiving downlink data. A working mode that saves terminal power consumption.

DRX is a working mode that saves the power consumption of the terminal. Its basic principle is to let the module enter the sleep mode periodically; during the sleep period, the module will not monitor the PDCCH and turn off the transceiver unit to reduce its power consumption.
DRX works in Idle state, and reduces module power consumption by periodically monitoring paging in Idle state. However, the DRX parameters are determined by the network, and the module cannot modify or suggest network modification.

Notice:

(1) During the activation period, the UE will turn on the receiver, paging the channel, and judge whether there is downlink service.

(2) The value range of NB-IoT DRX cycle is: 1.28s, 2.56s, 5.12s or 10.24s.

(3) After the DRX cycle duration is determined:

The longer the activation period, the more timely the service processing, but the receiver works for a long time in the same cycle, and the UE consumes more power.
The shorter the activation period, the more power the UE (device) saves, but the longer the receiver remains off in the same cycle, the longer the service delay.

High latency requirements for downlink services, such as street lights.

2. eDRX mode (extended discontinuous reception)

In order to save terminal power consumption and meet certain downlink service delay requirements, 3GPP introduced the concept of extended DRX (extended DRX, eDRX).

The purpose of eDRX is the same as that of DRX, which is to reduce power consumption by letting the module enter the sleep state periodically.

The basic principle is to divide the Idle state into a paging period and a dormant period: in the paging period, the working mode of the module is consistent with LTE DRX; in the dormant period, the module does not monitor downlink paging. Compared with DRX, eDRX can support a longer paging cycle to further reduce power consumption.
In eDRX mode, the module only monitors downlink paging and receives downlink services according to the DRX cycle in PTW (turn on the receiver); if there is data sent to the module during the sleep period, the module cannot receive it in time, and can only wait until the current eDRX cycle is over Enter PTW again to monitor paging. Therefore, in eDRX mode, the reduction of module power consumption is at the "cost" of real-time performance. In actual application, it is necessary to determine the appropriate eDRX cycle and PTW value according to the business model to achieve a balance between power consumption and real-time performance.

There are high requirements for downlink service delay, and messages can be cached or sent immediately according to whether the device is in a dormant state, such as smart wearable devices.

3.PSM mode (power saving mode)

The technical principle of PSM (Power Saving Mode) is very simple. In this state of PSM, the terminal radio frequency is turned off, which is equivalent to the shutdown state. The terminal sleeps deeply during non-business hours and does not receive downlink data. Only when the terminal actively sends uplink data (MO Data) Can receive downlink data cached by the IoT platform.

The process of module entering PSM:

When the module establishes a connection with the network or Tracking Area Update (TAU), the network will send the T3324 and T3412 timer configurations to the module, and the UE will start the T3324 and T3412 timers after entering the Idle state. When the T3324 timer expires, the module enters PSM.
When the module is connecting to the network or initializing the PDN (Public Data Network) for emergency services, it cannot apply to enter the PSM.
When the module is in PSM mode, it will close the network connection activities, including search for cell information, cell reselection, etc. But the T3412 timer (related to the periodic TAU update) continues to work.

The module exits PSM (any of the following ways):

After T3412 timer expires, the module will exit PSM automatically.
When the module is in PSM mode, pull down PSM_EINT (falling edge) to wake up the module from PSM.

Notice:

(1) When the terminal enters the PSM state and the duration of staying in the PSM state is negotiated between the core network and the terminal.

(2) Enter PSM mode, although the UE no longer receives paging messages, it seems that the device and the network are out of contact, but the device is still registered in the network, so that when the UE wakes up from sleep, it can perform data without re-registering the network send and receive.

(3) If PSM wants to wake up, it can wake up through external wakeup or cycle itself. External wakeup is commonly used for RTC interrupt wakeup (for example: MT2625 uses external RTC wakeup). The period of periodic wakeup is configured by the core network operator for NB IoT card. Sexual arousal.

(4) The difference between PSM automatic wake-up and RTC_ENIT external wake-up:

In the PSM state, after waking up by RTC_EINT, if the system has no other tasks, it will resume the PSM state immediately. If there are other tasks to be executed, the task will be executed. After the execution of the task, if the automatic wake-up has not yet expired, it will continue to re-enter the PSM mode immediately.
If it wakes up automatically when the period is up, it will maintain the Active time and then re-enter the PSM state. And Active Time can continue the uplink and downlink of services.

The module consumes very low current at PSM (typical current consumption: 3.5μA) . Power Consumption Diagram:

4. The difference between the three modes of DRX, eDRX and PSM

(1) In DRX mode, the module monitors the paging channel once in each DRX cycle, and the power consumption is higher than that of eDRX and PSM.

(2) eDRX means that the module keeps turning on and off the receiver. Data can be received when the receiver is turned on, and data cannot be received when the receiver is turned off; the eDRX cycle consists of two complete periods of turning off the receiver and turning on the receiver, and the supported configuration duration is 20.48s ~ 2.92h. eDRX consumes less power than DRX.

(3) Compared with eDRX, PSM has a lower frequency of turning on and off the receiver, which can be as low as turning on the receiver once every few days. During the PSM cycle, the module can only receive data when the receiver is turned on, and cannot receive downlink data when the receiver is turned off. In PSM mode, the power consumption is only in the microampere level, and the terminal can achieve extremely low power consumption in this working mode.

reference connection

https://blog.csdn.net/Sanjay_Wu/article/details/83895259

https://blog.csdn.net/qq_44981039/article/details/116745796

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