What is narrowband iot?
Narrowband Internet of Things or Narrowband IoT is NB-IoT, Narrowband IoT is built on the cellular network, consuming only about 180KHz bandwidth, using a License band, and can be deployed in three ways, such as in-band, protected band, or an independent carrier, to coexist with existing networks.
It can be directly deployed in GSM networks, UMTS networks, or LTE networks to reduce deployment costs and enable smooth upgrades.
Features of Narrowband IoT
Super coverage
Increase the signal gain by 20db relative to GPRS
Ultra-low power consumption
The goal for terminal power consumption is to have a service life of more than 10 years based on AA (5000mAh) batteries.
Ultra-large connection
One sector is capable of supporting tens of thousands of connections, supporting low latency sensitivity, ultra-low device cost, low device power consumption, and optimized network architecture.
Ultra-low-cost
Narrowband IoT eliminates the need to re-build the network, and RF and antennas are essentially reused.
Narrowband IoT Essentials Overview
To solve the problem that traditional 2G/3G/4G (GPRS) networks cannot meet the low power consumption and low cost of IoT terminal devices.
Compared to GPRS, some signaling is reduced, the paging period is lengthened, the PSM status is increased, and power consumption is reduced (real-time in exchange for range).
Terminal data is accessed to the core network through the operator’s base station, sinks into the operator’s IoT private network, and interacts with the user’s platform via the IoT platform for data.
Working status of Narrowband IoT
In the default state, there are three working states of Narrowband IoT, and the three states will be switched according to different configuration parameters.
I believe that these three states have profoundly influenced the characteristics of Narrowband IoT such as its low power consumption characteristics compared with traditional GPRS, which can be explained, and in the subsequent use of Narrowband IoT and the design of related programs, it is also necessary to develop these three working states according to the requirements and product characteristics.
The three operating states are as follows.
Connected state
After the module is registered to the network, it is in this state and can send and receive data, and will enter Idle mode after a period of no data interaction.
Idle state
The module can send and receive data, and will enter the connected state when receiving downlink data, and will enter the PSM mode after no data interaction for a period of time, the time is configurable.
PSM (Power Saving Mode)
In this mode, the terminal turns off the transceiver and does not listen to the paging on the wireless side, so although it is still registered in the network, the signaling is not reachable and no downlink data can be received, and the power is very small.
The duration is configured by the core network (T3412) and enters the Connected state when there is uplink data to be transmitted or at the end of the TAU cycle.
The transition process of the three operating states of NB-IoT, in general, can be summarized as follows.
The terminal is in the connected state when it finishes sending data and starts the inactivity timer, with a default of 20 seconds and a configurable range of 1s to 3600s.
The inactivity timer expires, the terminal enters the Idle state and starts the and/or timer (Active-Timer [T3324]), and the timeout time configuration range is 2 seconds to 186 minutes;
Active-Timer times out, the terminal enters the PSM state and enters the Connected state at the end of the TAU cycle, and the TAU cycle [T3412] is configured in the range of 54 minutes to 310 hours.
PS: TAU cycle refers to the period from the start of Idle to the end of PSM mode
NarrowBand-IoT terminal in different working status
The NarrowBand-IoT is in the active state when sending data and will enter the Idle state after exceeding the timeout configured by the inactivity counter.
The idle state introduces the eDRX mechanism, which contains several eDRX cycles in a complete Idle process. eDRX cycles can be configured by a timer in the range of 20.48 seconds to 2.92 hours, and each eDRX cycle contains several DRX paging cycles.
Several DRX paging cycles form a paging time window (PTW), the paging time window can be set by the timer, the range is 2.56s~40.96s, and the size of the value determines the size of the window and the number of paging.
After the Active Timer timeout, the NB-IoT terminal enters the PSM state from the idle state, in which the terminal does not page, does not accept downlink data, and is in a dormant state.
The TAU timer starts when the terminal enters the idle state, and when the timer times out, the terminal will exit from the PSM state, initiate TAU operation, and return to the active state.
When the terminal is in the PSM state, it can also return to the active state by actively sending uplink data.
Configuration of timer parameters
In the whole process of Narrowband IoT operation, there are some timer parameters that can be set to change the internal details and cycle ratio of each operating state, and these timer parameters need to be realized by signing APN on the device NB card.
Take the Telecom NB SIM card as an example, the default contracted APN is ctnb, which is automatically issued by the network when the terminal is in the network. Different APNs represent a different set of timer parameters, for example, the APN of ctnb is described as [monitor reporting class, activate timer=2s, turn on PSM, turn off eDRX].
If you use APN psmc.eDRXC.ctnb, the corresponding parameters are [turn on PSM, turn on eDRX, activate timer=180s, eDRX period=20.48s, paging window=10.48s].
APN also supports user customization, and the corresponding APN name is ue.prefer.ctnb. The switch and timer parameters of the working state are determined by the parameters reported by the terminal.
Narrowband-IoT's power-saving technologies
DRX Mode
DRX (Discontinuous Reception), i.e. non-continuous reception, is an operating mode to save terminal power consumption by turning on the receiver into the active state for receiving downlink data only in the necessary time period and turning off the receiver into the dormant state to stop receiving downlink data in the remaining time period.
During the activation period, the UE will turn on the receiver and paging channel to determine whether there is a downlink service.
The DRX period of Narrowband IoT takes values from 1.28s, 2.56s, 5.12s, or 10.24s.
After the DRX period length is determined then.
The longer the activation period, the more timely service processing, but the longer the receiver works in the same cycle, the greater the UE power consumption.
The shorter the activation period, the more power the UE saves, but the longer the receiver stays off in the same cycle, the longer the service delay.
eDRX mode
In order to save terminal power and meet the requirement of a certain downlink service delay, 3GPP introduced the concept of extended DRX (extended DRX, eDRX).
In each eDRX cycle, there is a paging time window (PTW), the UE only listens to the paging channel in the PTW according to the DRX cycle, in order to receive downlink services, outside the PTW time in the sleep state, not listening to the paging channel, cannot receive downlink services.
The eDRX period length and PTW window length can be configured and negotiated between UE and operator, based on the value issued to UE by the operator.
The specific configuration of the eDRX period can be found in 3GPP TS 24.008.
PSM mode
The technical principle of PSM (Power Saving Mode) is very simple. In this state, the terminal RF is turned off, which is equivalent to the shutdown state, and the terminal is deeply dormant during the non-service period.
When the terminal enters the PSM state and the duration of residency in the PSM state is negotiated between the core network and the terminal.
When entering PSM mode, although the UE no longer receives paging messages and appears to be disconnected from the network, the device is still registered in the network so that when the UE wakes up from hibernation, it can send and receive data without re-registering with the network.
PSM wants to wake up can be woken up externally or by the cycle itself. External wake-up is commonly used to wake up by RTC interrupt (e.g. MT2625 uses external RTC wake-up), and the cycle of cycle wake-up is configured by the core network operator to the NB IoT card, which wakes up periodically.
The difference between PSM automatic wake-up and RTC_ENIT external wake-up
- In the PSM state, after waking up by RTC_EINT, if there is no other task in the system, the PSM state will be performed again immediately. If there are other tasks to be executed, the task will be executed. After the execution of the task, if the cycle has not yet reached auto wakeup, it will continue to re-enter PSM mode immediately.
- If the cycle has reached the automatic wake-up, it will maintain the Active time and then re-enter the PSM state. And Active Time can continue the service upstream and downstream.
The NarrowBand may be in deep sleep or deeper sleep when the MT2625 enters the PSM state, if the PSM cycle is a few minutes short, it will enter deep sleep, if the PSM cycle is more than ten hours long, it will enter deeper sleep. Other NB chips have not been verified by the author.
Narrowband IoT frequency band
Narrowband IoT technology is based on existing LTE standards, including OFDMA access (DL) and SC-FDMA access uplink (UL) channels used in the downlink, time-frequency structure, channel coding, etc. This significantly reduces the time specification development.
This significantly reduces the time to develop specifications and to develop and organize the production of network and client devices. All bands available in 3GPP Release 13 for NB-IoT deployment are frequency duplex bands (see table below).
Nevertheless, the M2M terminal (M2M-UE) can be used for reception or transmission at any time. The transition from transmit mode (UL) to receive mode (DL) is accompanied by the insertion of a protected subframe (SF), which allows the M2M-UE to switch between the transmitter and receiver chain. This type of access is called half-duplex with frequency division (HD-FDD – half-duplex FDD).
Frequency Band | UL/MHz | DL/MHz |
B1 | 1920 – 1980 | 2110 – 2170 |
B2 | 1850 – 1910 | 1930 – 1990 |
B3 | 1710 – 1785 | 1805 – 1880 |
B5 | 824 – 849 | 869 – 894 |
B8 | 880 – 915 | 925 – 960 |
B11 | 1427.9 – 1447.9 | 1475.9 – 1495.9 |
B12 | 699 – 716 | 729 – 746 |
B13 | 777 – 787 | 746 – 756 |
B17 | 704 – 716 | 734 – 746 |
B18 | 815 – 830 | 875 – 890 |
B19 | 830 – 845 | 875 – 890 |
B20 | 832 – 862 | 791 – 821 |
B25 | 1850 – 1915 | 1930 – 1995 |
B26 | 814 – 849 | 859 – 894 |
B28 | 703 – 748 | 758 – 803 |
B31 | 452.5 – 457.5 | 462.5 – 467.5 |
B66 | 1710 – 1780 | 2110 – 2200 |
B70 | 1695 – 1710 | 1995 – 2020 |
For the Russian market, this means in particular that it is possible to build an LTE network in the 31st range. The resources in this range are owned by Skylink (T2 Rus Holding).
For the China market, we use the B5 and B8 narrowband IoT frequency bands.
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