With the booming wave of the Internet of Things, the popularity of smart homes has also continued to heat up. Due to the safety, energy saving, comfort, convenience, and efficiency of smart homes, more and more customers are beginning to accept and develop smart home products and systems. In the past few years when Zigbee technology has been promoted in China, I have been fortunate to see manufacturers from China achieve "curving overtaking" in the field of Internet of Things and smart home. China’s smart home technology and market are developing extremely rapidly. Our products and systems can Said to be the world leader.
As the chairman of the Zigbee China Technology Group, I am very happy to have such an opportunity to talk about an important technical link in smart homes-wireless connection technology. Of course, I will not deliberately talk about Zigbee. On the contrary, I hope to reduce the technical barriers and talk about what kind of wireless connection is needed for a specific application area such as smart home. As the title of the article indicates, I hope to start from a technical point of view to explain the problem and answer the doubts. If there is another opportunity, my colleagues can talk about products and applications from a market perspective.
Please note that this article does not discuss technical details, but focuses on the common issues behind the technology. This is the consistent logic of this article.
The technical interface of the smart home systemTo analyze the wireless technology of the smart home, we must first clarify: What is the scope of the smart home? What is the system architecture? This is the basis of our discussion. Let's take a subsystem in the smart home—the smart lighting system as an example to illustrate the problem.
Figure 1 Home smart lighting system and technical interface
As shown in Figure 1, the home smart lighting system can be roughly divided into three technical interfaces: â‘ cloud-based applications and services; â‘¡ home-wide wireless control network; and â‘¢ the internal control software and drive circuit of smart lighting products.
Among the three technical interfaces, the most concerned, discussed and most confusing is the second interface: home wireless control network. Various product forms coexist on the market, and various opinions on the Internet are contending. It should be understood that the technology itself does not matter whether it is good or bad (bad technology is naturally eliminated in its development), only suitable or not. What we are thinking about is: What kind of wireless technology is more suitable for smart home networks? In other words, what unique requirements does the smart home system have for wireless interconnection technology?
How does the smart home system play?The acceptance of new things by individual consumers often exceeds the expectations of the industry, and smart home is also an example.
The scope of smart home is extremely wide, and there is no uniform definition. Its typical subsystem, smart lighting, can be as simple as a single controller (a mobile phone is also a controller) and a lamp, or as complex as a complete lighting system that integrates lighting equipment, sensors, smart switches, and control algorithms. As the first step for consumers to contact smart lighting, a light bulb that can be controlled by a mobile phone and is easy to install is a good product form. This light bulb may not be so perfect and not rich in functions, but it must be screwed on just like a normal light bulb. It can be operated in a few minutes. Therefore, for consumers, the first requirement for smart products is: low complexity and easy installation.
When consumers gradually got used to using their mobile phones to control the light bulbs at home, new demands emerged. At this time, switch devices that are seamlessly interconnected with light bulbs can provide more natural and intuitive services. If equipped with suitable sensors, such as motion, temperature and humidity, and light sensors, by setting specific rules, a small, automatically operating lighting system appears. This lighting subsystem can interact with other subsystems such as security, audio-visual, kitchen and bathroom, and sunshade systems. This constitutes a typical smart home wireless network.
Therefore, the wireless network of the smart home should be a large-scale, multi-device local area network. Speaking in technical language-it should be a mesh network.
We put aside the dazzling technical indicators and market publicity, and follow the thinking just now, what are the elements of a stable and reliable smart home wireless network.
1. Mesh network. The number of nodes in a smart home system can range from a few to dozens or even hundreds. This is completely different from the point-to-point control of smart items. The network is required to provide greater redundancy to facilitate load balancing and path selection. To achieve load balancing, it is necessary to work hard on routing protocols, reasonably create and select routes, and carry out continuous and dynamic optimization.
2. Robustness. In a network with a large number of nodes, robustness is crucial. Smart home systems are mostly deployed indoors, and the occlusion and reflection of the spatial structure and interference in the radio environment all put forward higher requirements for the robustness of the system. Reasonable creation of routes and reasonable maintenance of equipment, as well as different types of communication messages, all have a decisive impact on the robustness of the network.
3. Reusability of space. In a limited frequency spectrum, how to reasonably avoid and allocate with different technologies also puts forward a test of the stability of the wireless network. The space access mechanism, as well as the cooperation of software and protocols play a very important role in it.
Why does Zigbee bother to make a mesh network?Another IoT wireless technology that is also used to connect low-power resource-constrained devices-Low Power Wide Area Network (LPWAN) is a typical centralized network structure (ie, star network). It will be very interesting to compare the characteristics of these two technologies, and it will also help us deepen our understanding of IoT wireless connection technology.
LPWAN (such as NB-IoT and Lora) is an excellent wireless network. It connects IoT devices directly to base stations over long distances, and then connects to the cloud. This network topology determines that while obtaining low power consumption and long-distance connections, LPWAN has given up an extremely important feature for smart homes-local interaction of devices. Please see the example below.
This is a very simple device interaction-when the door is opened to light up the light bulb (of course it can also be a sensor). In a local mesh network, the door lock can be directly connected to the light bulb, and this function can be realized in one step through the logic binding of the application layer. Under the LPWAN architecture, the door lock must report the message to the base station. Generally, the base station does not implement application logic and needs to be further reported to the cloud. The cloud sends instructions to the light bulb through processing-turn on or turn off the light. For this application, this data path is obviously too complicated.
Of course, in practical applications, each message transmission of LPWAN also means a fee, but this is a matter of another level.
Furthermore, if hundreds of devices are operated in this way, the performance difference of the system will be very obvious.
Figure 2 Device interaction between local mesh network and LPWAN architecture
Some people may wonder, why can't local communication be realized on LPWAN, such as NB-IoT devices? It's not surprising to ask this question, and it's even taken for granted. I once met an IoT practitioner at a seminar, and he described his new application on NB-IoT in a large length, which was based on this idea.
In fact, think about it, whether it is NB-IoT or Zigbee (the name is not important), almost all (almost to avoid absolute, in fact, all) low-power wireless technologies have adopted a common technology-device sleep. Common technologies such as Zigbee, Thread, BLE, NB-IoT, Lora, and Z-wave are without exception. Think about this question-how to establish long-term, stable communication between two sleeping devices (more technically, they are asynchronous)? This is impossible.
Therefore, this also confirms the fact that Zigbee's end devices cannot communicate directly but must be routed; LPWAN devices cannot communicate directly but must rely on the base station. The two are not coincidences, they have common ideas and communication mechanisms behind them.
This example also explains why Zigbee (and Thread and other technologies) spend a lot of energy in formulating mesh network standards, and why Bluetooth technology must develop network technology with mesh functions when it enters smart homes.
Can Zigbee guarantee the interoperability of certified products?Due to space limitations, I will talk about one more issue-product interoperability.
First, the Zigbee Alliance claims that certified products can guarantee interoperability. The issue of interoperability of proprietary protocols (which exist a lot in practice) is not discussed.
Some people may raise objections: "Why does Zigbee need to be certified? Other technologies don't need it?"
(Who can say this? You stand up! I will talk to you about life...)
This is completely false. As far as I know, all technologies for the purpose of "interoperability" have strict testing and certification requirements. The most common Wi-Fi, Bluetooth, and Zigbee all require product certification. Before the Thread technology was fully standardized, the Thread Alliance proposed a strict certification program (original: rigorous certificaTIon program). I was at the scene and I still remember it.
Not only does wireless interconnection technology require certification, but even the smart home ecosystem will formulate certification links to ensure interoperability between products. You can search for "Huawei Hilink Certified Products" by yourself.
So, does Zigbee’s “guaranteed interoperability between products†have any specific scope or conditions?
First answer: yes. There is a distinction between the interoperability that Zigbee claims and the interoperability that consumers feel.
The following is a further answer to the interoperability brought about by Zigbee's standards and testing, as well as the differences in the "non-interoperability" that everyone complains about in the market. Understanding these requires a basic understanding of Zigbee's standards and testing procedures. You can consult our Zigbee authorized laboratories (CESI, TuV Rheinland, Element, UL, NTS).
As an open standard for the Internet of Things, Zigbee is defined from the standard to the method and process of testing. Its goal is the specification and interoperability of device communication and behavior, and does not involve the performance of the product itself. In other words, the standard itself defines the format and specification of communication levels (OSI 7-layer model or simplified 4-layer model); and the test itself focuses on the compliance of over-the-air packets. The performance difference of the equipment itself is left to the manufacturers and the market, which is also a reasonable result of balancing "standardization" and "differentiation".
For example, the following items are part of the Zigbee test, and their interoperability is guaranteed by the Zigbee standard:
1. The basic behavior of the device network layer, including network discovery, joining/leaving the network, interacting network parameters, etc.
2. The security behavior of the device, including the support of the security mode, the generation and distribution of the key, the dynamic update of the key, etc.
3. The functional behavior of the device, including testing all the Datary and Optional behaviors listed in the PICS file.
The following items do not belong to the content of Zigbee testing, nor do they belong to the scope of product interoperability guaranteed by Zigbee:
1. The consistency of function parameters in product expression. For example, the optical expression of the same brightness and color parameters in different products is inconsistent (chromaticity difference).
2. Subtle differences in the execution of commands. For example, when the device executes the "OFF" command, the disconnection time of the device is inconsistent (fast or slow).
3. Differences in equipment RF performance. For example, the performance of products of different companies in the network is inconsistent, and different products have different signal strengths and effective propagation distances.
4. The performance and stability of the equipment itself. For example, some products can exist in the network stably for a long time, and some products have a higher probability of disconnection.
At the same time, in a large-scale network, the difference in network behavior caused by a large number of devices due to inconsistent network parameters is also frequently mentioned. For example, the carrying capacity of the routing device, the data cache time and the frequency of data requests (Data Poll Rate), the frequency and number of broadcast messages, the trigger conditions for initiating a new network access request after the device is offline, and the selection of a variety of parameter windows There are many differences in behavior.
It should be noted that the consistency of product performance is not the requirement of the Zigbee Alliance, nor should it be the responsibility of an IoT international open standard. While the industry is pursuing interconnected technologies, it also needs enough space to pursue product differentiation and brand added value.
The Zigbee Alliance always faces up to the needs from the industry and actively provides solutions to meet consumer requirements for interoperability. Some of the current work of the alliance includes:
1) Add new test content during the certification process to improve product interoperability;
2) Sort out and optimize the existing optional functions (opTIonal cluster);
3) Enhance and expand existing functions;
Concluding remarksIn the past two years as the chairman of the Zigbee China member group, I am deeply proud of the vigorous development of the Internet of Things and smart home in my country. Excellent products and systems lead the development of the global IoT industry, and the speed of China has surprised and admired international businessmen time and time again. I hope that through this platform, I can communicate more with you about the technology, products, market, and ecology of the smart home industry. I also look forward to your feedback!
Dongguan Guancheng Precision Plastic Manufacturing Co., Ltd. , https://www.dpowergo.com