Whenever I talk about IoT technology, it is nothing more than cost, battery life and transmission distance, but we often ignore the importance of network node capacity. However, because of the lack of actual data, we tend to over-reliance on theoretical values ​​and ignore many real life. The key factors that affect the capacity of network nodes.
The so-called network node capacity does not refer to the number of nodes connected at the same time, but also includes the average packet length, transmission time, transmission frequency channel, and the anti-interference ability of the system. The most basic factor affecting the network node capacity may depend on Use Ultra Narrow Band (UNB) or Wide Band for message transmission. Of course, ultra-narrowband and broadband each have their own advantages and disadvantages, as long as you can go to 芜å˜è can define the perfect Internet of Things technology.
Broadband and Extremely Narrowband Advantages Narrowband Technology for Multi-Node Systems
We will differentiate the market according to the width of the frequency band, which is ultra-narrowband, narrowband and wideband. These three are very different transmission methods in wireless network communication. If the network node capacity is used for discussion, the bandwidth limitations and transmission energy limits of the three in the ISM and SRD bands are very different. If you don't understand it very well, don't worry! Keep looking down.
The reason for choosing such a narrow bandwidth is to reduce the noise received by the receiver. Therefore, under the same power, the noise can be reduced not only, but also the transmission distance can be extended. It sounds perfect so far, but because the bandwidth is too narrow, the transmission rate is forced to decrease, so it is only suitable for small packets. . In combination with the above advantages and disadvantages, ultra-narrowband is more suitable for systems that do not require two-way communication, that is, QoS requirements are not so strict.
Broadband is another very common method. The bandwidth is usually 1MHz or more. Then the data is encoded with different codes to increase the transmission distance. The length of the code can be adjusted to change the effective transmission rate and distance. The disadvantage is that the rarity of the frequency band cannot satisfy both broadband and multi-channel, in other words, different systems will share the same frequency band. In design, such systems have very high requirements for time synchronization and power consumption control. Such a system will not be able to meet the sporadic and short-term transmission characteristics of the Internet of Things. Therefore, such communication technology will face great challenges in the construction of public networks or private networks.
Since both bands are too extreme, the most commonly used "sweet spot" is actually between the two. Whether it is QoS, cost, or efficiency, narrow frequency has excellent performance. A bandwidth of approximately 12.5 kHz provides optimal upload efficiency in a multi-node system.
Below we will discuss in detail how these variables will affect your IoT system, and then we will explore how Weightless technology configures these variables to meet demand.
IoT network node capacity must be carefully planned
Most of the low-power wide-area network (LPWAN) protocols are now rarely limited by the number of connections. In addition, most of the test data, such as transmission range and functionality, is based on the state of small nodes and linear transmission. under. Imagine if billions of nodes want to be online at the same time, how much change and challenge will the existing system and even the future be? The IoT base station will have to process hundreds of thousands of nodes at the same time. If there is no proper planning, the base station will exceed the load. Telecom operators are accustomed to defining the capacity of a cellular network in bits/Hz, that is, how many bits of data can be transmitted at a unit frequency (Hz), and each generation of humans is designing for better transmission efficiency. Good wireless transmission technology and better algorithms. When technology is temporarily unable to meet demand, telecom operators can only buy multiple frequency bands, or use a smaller base station to increase the capacity of the network with a denser layout. The latter is the main practice in the past decade, which means that telecom operators need more base stations and higher capital investment and operating expenses.
Whenever you design an IoT network, engineers often think of the design of the cellular network, but this is a mistake, because there are many Internet of Things features that are different, we will introduce them one by one:
Short message
Many IoT nodes only send a small amount of data. For example, the parking space detector only needs to return 1 bit to tell the base station whether the parking space is parked. The temperature sensor needs to transmit slightly more, about 8~16 bits. The positioning system has the most Need 8 bytes (Byte). The above is a typical feature of the Internet of Things - small amount of data. However, the amount of data is often negligible for a complete packet. For example, if the IPv6 protocol is used to transmit data, the length of the entire packet is 128 bits. An IoT terminal device only returns its identity but allows data. The amount is 10 times larger, and many applications encounter similar situations. Therefore, we must design a transmission method that conforms to the Internet of Things feature to greatly increase the network node capacity.
Randomness
Most mobile communications are random--when someone calls or the Apps are using the network, the phone starts communicating with the base station, and then the phone enters the "random access" mode until the next The second event occurred. This is very convenient for mobile phone users, but it is not an efficient network architecture. For a network, the more users mean the greater the chance that these users will use the network at the same time, the more packets will be transmitted over the air, thus increasing the probability of packet collisions. The greater the chance of packet loss. When the packet is lost, the mobile phone can only transmit the packet repeatedly. Such a process is discussed in detail in the "Aloha Access" theory. The conclusion is that the success rate of communication is only about 30%. There are many conflicts in message transmission, conflicts will lead to more conflicts, and finally only rely on the system. Reset to solve this problem.
It is worth mentioning that in the world of cellular networks, because "random access" only accounts for a small part of the data transmission, this problem is not obvious; but in the world of the Internet of Things, the data is packaged into very small The packet means that all messages are transmitted as random access. After the actual test, the transmission efficiency is reduced by at least 3 times under the best conditions. The conclusion is that if the node can be told when to send the message next time, for example, the temperature sensor will be able to increase its performance by at least 3 times every time it returns.
Power control
In the cellular communication system, the handheld device tends to adjust to the optimal modulation system and signal strength according to the current situation. However, in the IoT system, the transmission time is often short-lived and there is no way to fine-tune the time of the two. The device often uses a stronger method than the required energy to transmit, and thus creates more interference. In design we have to find a more efficient way, and we can rely on different data like the node is still or the characteristics of other networks.
Multiple coverage network
Since the telecom operators of the cellular network have their own frequency bands, they are not designed to worry about interference from other parties; on the contrary, most IoT operators use unlicensed frequency bands, so interference cannot be avoided. This has not been an important factor so far, but with the rapid growth of the Internet of Things, the impact will become more and more obvious sooner or later. Some technologies, such as CDMA, must be suitable under certain conditions. If multiple networks overlap in the same frequency band, the technology will often fail, and the technology instead, such as frequency hopping or Message Acknowledgement, etc. Gradually rising.
The freedom of channel allocation is also greatly increased by the ability to reuse channels and adjustable transmission rates in large networks. In addition, if the system is time-synchronized, resource scheduling can be used to optimize performance. For the above reasons, the performance of the Internet of Things is not suitable to be measured in the existing way. A system that uses poor modulation is likely to make the actual performance 10 times faster because of the small transmission of information.
There are many systems on the market that are not designed for multiple nodes. It is very likely that there will be serious consequences due to the large number of nodes. For example, the ultra-narrowband typical approach is to use the same message several times to increase the probability of successful reception, which is obviously not suitable for use on the Internet of Things. The broadband band mentioned above, if the verticality of the signal is overlapped to other systems in the same frequency band, the consequences are unimaginable. Although the 3GPP solution is not yet fully defined, the packet will be too large. Many problems can't be revealed in the test, because the network size of the test is not large, but in fact, as the number of nodes increases, it will gradually emerge. When the base station has been built, the cost of changing the system architecture is often very expensive.
For the above reasons, it is not difficult to find that the narrow frequency provides the advantages of integrated ultra-narrowband and wideband. It is very suitable for the transmission of IoT packets. If properly designed, the node amount of the whole system will be greatly improved. The Weightless technology uses narrow bands. With the new technology of industrial IoT, developers only need a set of Weightless IgniTIon Pack with a complete network suite, a base station and four nodes to start development.
A most optimized system should have a very short message length, frequency hopping mechanism, debuggable transmission parameters, group or MulTIcast transmission, and flexible scheduling to reduce the number of random reads. Even if there is no significant difference in transmission speed with other systems, the network node capacity it supports may vary greatly. If the IoT device replaces a round like a smart phone every two years, it may not matter, but the IoT system usually takes years or even decades. It is best to consider it at the beginning of the design because of the replacement cost. It will be very high.
(The author of this article is Chairman of the Marketing Working Group of the Weightless Technology Alliance)
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