The four key features and implementation of NB-IoT tell you why NB

Abstract: IoT network is based on the evolution of 4G network, so it still uses 4G OFDMA and SC-FDMA in the uplink and downlink multiplexing technology.

This article is shared from the Huawei Cloud Community "The understands the four key features of NB-IoT and the implementation technology ", author: Wan Wanwan.

At the physical layer, NB-IoT is called narrow-band cellular Internet of Things, so where is its narrow-band embodied? This is 180KHz, which is only equivalent to the width of the 4G protection bandwidth. We know that the NB-IoT network is based on 4G network evolution, so it still uses 4G OFDMA and SC-FDMA in the uplink and downlink multiplexing technology. Although the design of NB-IoT is based on 4GLTE, the original intention is different, because 4G is designed for high-speed and high-bandwidth requirements, while NB-IoT is designed for low-speed.

Therefore, in terms of specific technical implementation, NB-IoT has also streamlined many unnecessary parts. For example, in terms of physical channels and physical signals, in order to reduce the complexity of implementation, NB-IoT has only two physical channels and one physical signal in the uplink, and only three physical channels and two physical signals in the downlink. The main purpose of streamlining channels and signals is to achieve wide coverage, low power consumption and low cost.

In the following content, the four key features of NB-IoT and the implementation technologies included in the features will be introduced.

Key feature one: ultra low cost

1.1 deployment method

As mentioned above, one of the characteristics of NB-IoT is that it can be directly deployed in the operator's existing network to achieve low cost. There are three deployment methods for NB-IoT. The first is independent deployment. Independent deployment means that NB-IoT can be completely independent without relying on the existing LTE network. Therefore, this method is suitable for re-cultivation of the GSM frequency band, because the channel bandwidth of GSM is 200KHz, which is more than enough to include the 180KHz bandwidth of NB-IoT.

Figure 1 Independent deployment

The second is called guardband deployment. As described above, how narrow is the narrowband of NB-IoT? It is narrow enough to be deployed on the protection bandwidth of the existing 4G frequency band, so that this part of the resources that were not used can be reused.

Figure 2 Protective belt deployment

The third type is in-band deployment, which can be directly deployed in the 4G frequency band. Readers who have studied communication should know that in a 4G network, the frequency domain and time domain are divided into small resource blocks. At the same time, because of NB The design of IoT is based on 4G, so it is completely compatible with 4G when designing the network. The bandwidth of each small resource block of 4G is 180KHz, which is why the system bandwidth of NB-IoT is 180KHz. Therefore, no matter which method is used for deployment, NB-IoT will not rely on the signal resources of any system.

Figure 3 In-band deployment

The above is one reason why NB-IoT achieves low cost in terms of deployment methods. In addition, readers need to understand that due to technical limitations, NB-IoT cannot be deployed in the band and protection band of the LTE system, so independent deployment is still the main deployment method for NB-IoT networks at this stage.

1.2 Chip design

In addition, in the design of the chip, a part of the function is simplified to achieve a low cost. Huawei designed the Boudica150 chip specifically for the Internet of Things through a series of single antenna and half-duplex and other processing, because for NB-IoT, a single antenna and FDD half-duplex are enough to meet the communication needs of the Internet of Things , Based on this design, for the NB-IoT module, it reduces a lot of costs.

Key feature two: ultra-low power consumption

For the needs of the scene, NB-IoT has designed two unique modes, one is eDRX and the other is PSM. Before describing the eDRX mode, readers first need to understand the DRX mode. DRX is a paging method widely used in mobile phones. You can think about it, if someone wants to call you in the most ideal situation, in what way can the phone be guaranteed to be able to listen to the paging information? It is equivalent to needing a mobile phone to be paged all the time, just like an attentive classmate in class, waiting for the teacher to call him to answer questions.

Figure 4 working principle of the mode

However, for mobile phones, if you have to wait to be paged all the time, it consumes a lot of power. Therefore, R&D personnel have developed DRX, a method of discontinuous reception (DiscontinuousReception). Its principle is shown in Figure 5-7. The blue pulse in the figure represents that the mobile phone is paging. After each paging, the mobile phone will take a break and enter the IDLE state. After entering the IDLE state, the mobile phone will turn off receiving The machine is equivalent to the classmates taking a nap during class. In DRX mode, the interval between each paging of the mobile phone is called the DRX cycle. This DRX cycle can be 1.28s, 2.56s, 5.12s or 10.24s.

Figure 5 Working principle of eDRX mode

But for IoT devices, this mode still cannot meet the low power consumption they need, because the DRX mode is a mode widely used on mobile phones. However, the power consumption of mobile phones is also relatively high. Even if you only use your mobile phone to make calls and send text messages, you have to charge it once a day or two or three days. But what the Internet of Things devices need is to charge them every few years or even more than ten years. Therefore, based on the DRX mode, the eDRX mode, which is extended discontinuous reception (ExtendedDRX), has been developed after continuous improvement.

As described in Figure 5-8, it designs a PTW paging time window on the basis of DRX. Within each window, the IoT device will page three times, and the interval between each paging is still the same as before. The DRX cycle is the same. But after every three paging, it will enter a long sleep, that is, the eDRX cycle, and this time can reach 2.92h at the longest. However, the specific duration will be set by the operator according to the actual situation of the Internet of Things equipment and the required data, so the flexibility of the model can also be reflected in this aspect.

Figure 6 PSM mode working principle

Perhaps, this mode of eDRX is still not low enough for some IoT devices, so there is another mode called PSM (Power Saving Mode, power saving mode). To put it simply, the period of dormancy is extended longer. From Figure 5-9, it can be seen that the dormant state can be extended to 310 hours at the longest, which is about 13 days. Although the sleep time that can be achieved in PSM mode is very long, there are some disadvantages: in PSM mode, if the application layer business platform issues instructions to the terminal, the terminal will not receive these instructions, and these instructions will temporarily It is stored in the IoT platform and is sent out after waiting for the terminal to be awakened. That is to say, when the device enters the sleep state of PSM mode, the instruction issued by the platform layer cannot wake up the device. Only when the device wakes up after the time is up, the platform side knows that the device is online, can the command be issued Issued.

So these different modes correspond to different scenarios in the Internet of Things. For example, the application scenario of shared bicycles should use DRX mode, because if it is eDRX mode, it may require users to stand in front of the bicycle and wait for five minutes. Automatically unlock. The eDRX mode can be used in scenarios such as logistics monitoring, because the goods do not need to be monitored in real time during transportation, as long as the location is determined at intervals. The PSM mode can be used on remote water meters and electricity meters, because the data on these meters does not need to be copied once a day. It may be enough to check the data in about half a month. Therefore, the different modes of NB-IoT low power consumption are different from The scene is closely related. Developers need to flexibly choose different low power consumption modes according to different application scenarios.

Key feature three: super coverage

The design goal of NB-IoT in terms of coverage is to increase the coverage by 20dB on the basis of GPRS. If this data is presented from another angle, the coverage of NB-IoT will be three times that of GPRS, and it can wear more than GPRS. Through two walls. What is the principle of NB-IoT to achieve super coverage? The uplink and downlink will be described separately. From the downlink point of view, it is mainly to increase the reliability of the transmission by repeating the transmission to obtain greater gains.

Figure 7 Power spectral density increase

As far as the uplink is concerned, it is mainly divided into two aspects, one of which is the same as the downlink, which is to expand the gain through repeated transmission. On the other hand, it is a feature of NB-IoT: the technology can use a single sub-carrier for transmission, that is, a 15KHz sub-carrier. This is different from 4G. The 4G network divides the spectrum resources in the time domain and the frequency domain, and at least 180KHz is required for each transmission. As shown in Figure 5-10, when the transmission power is the same, the gain of data transmission in a narrow band is greater. The above is the reason why NB-IoT has achieved wide coverage.

Key feature 4: Super connection

The last feature is super large connection, so what is its principle? Readers can think about the difference between the traffic model of the Internet of Things terminal and the mobile phone? In fact, there are many terminals in the Internet of Things, but the data packets sent by each terminal are very small, and they are not sensitive to delay requirements. But for mobile phones, the reason it can only have a limited number of users in a base station area is that the 4G base station used by the mobile phone needs to ensure the communication quality of all users within the base station range, so every device must be of high quality. Communication for access. But for IoT devices, it does not have such high requirements for the quality of communication, so this means that it can access more terminals within the same base station range, so that 50k IoT devices can be accommodated. Within the range of a base station, because there are a large number of devices in the dormant state.

The figure below shows the overall architecture of the NB-IoT solution, which can be linked to the IoT architecture. First, the perception layer is the NB-IoT terminal, and then the network layer is the access network, such as the NB-IoT base station, then to the core network, then to the IoT platform at the platform layer, and then upload to the application layer. application.

Figure 1 NB-IoT solution architecture

Based on the overall architecture of this solution, what follows is the actual application of the NB-IoT network.

Figure 2 Smart parking solution

The above is a case diagram of smart parking. In the matter of parking, parking lot managers have also received a lot of challenges. Parking is divided into on-street parking and indoor parking according to different scenarios. The challenge here is that it is difficult to locate parking spaces due to signal problems. At the same time, the price of each vehicle inspection device is relatively high due to the high price of communication modules, and the power consumption of the equipment is relatively high.

Based on these issues, Huawei provides an NB-IoT network for module replacement. Because the NB-IoT modules and base stations can be used together in other scenarios in the city, the equipment in the entire city can be connected to the same network, which is convenient for maintenance and management. At the same time, because of the characteristics of NB-IoT, its power consumption is relatively low, so the service life is also effectively extended.

Figure 3 Bike sharing solution

In addition, there are cases of shared bicycles. Before using the NB-IoT module, the locks on the shared bicycles will use mechanical locks and GPRS electronic locks, but these two methods are not particularly easy to use. Because there is no way to change the password of a mechanically locked shared bicycle, when someone knows the password, they can use the bicycle unlimited times, which will cause a very large cost loss for the enterprise. The same is true for electronic locks using GPRS, because the cost of GPRS electronic locks is very high, and the difficulty of charging is also greater, so the user experience is not particularly good.

Therefore, the solution provided by Huawei uses the NB-IoT method for communication to achieve low power consumption and reduce costs.

Figure 4 Smart street lamp solution

In addition to the two cases of smart parking and shared bicycles, there are also two cases of smart street lights and smart meter reading. So in these two cases, it is the same. The advantage of using NB-IoT to enterprises or companies is that it can reduce the cost of their solutions and increase the efficiency of use, and it can also facilitate their unified management. .

Figure 5 Smart meter reading solution

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