Differentiated requirements of "part 1 /" Internet of things "
For a long time, people use network services through corresponding terminals (computers, mobile phones, tablets, etc.), and "individual" has always been the main user of the network. Personal requirements for network quality are "high" and "unified": playing online games must require low delay, downloading files or watching online videos requires high bandwidth, calls need clear voice, and the received SMS must not be missed.
For mobile communication networks, operators try their best to maintain the network characteristics of low delay, high bandwidth, wide coverage and on-demand, so as to ensure a good user experience and create a rich and colorful mobile application ecology.
For personal communication services, although users have high requirements, the overall demand for network quality is consistent. Operators only need to establish a set of network quality standard system to build and optimize the network, which can meet the needs of most people for connection.
With the gradual slowdown in the growth of the number of user terminals (mobile phones, pads, etc.) in the network, M2M applications have become the driving force for the growth of network services of operators, and a large number of M2M application terminals have become network users. M2M application terminals (sensing devices and intelligent terminals) are essentially Internet of things terminals. They are connected to the operator network by assembling wireless communication modules and SIM cards, so as to build various centralized and digital industry applications.
Different from personal communication service, in the industrial application of Internet of things terminal construction, the quality requirements of information collection, transmission and calculation in various fields are very different; The environment of system and terminal deployment is also different, especially in the vastly different industrial environment; In addition, when building applications, enterprises also need to consider technical constraints (power supply, terminal volume, etc.) and cost control (including construction cost and operation cost). Therefore, various industrial applications have a "personalized" side, which makes the demand for connection develop in the direction of diversity.
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The differentiation of Internet of things business needs is reflected in two aspects
On the one hand, different terminals and applications have different requirements for network characteristics. Traditional network characteristics include: network access distance, uplink and downlink network bandwidth, mobility support, data sending and receiving frequency (or periodicity), security and data transmission quality (integrity, stability, timeliness, etc.).
These aspects can be condensed into three aspects, namely "access distance", "network characteristics" and "network quality"“ Access distance "is mainly divided into short-range access and long-range access. The "characteristics" and "quality" of the network are the main factors reflecting the demand differentiation. For example, the "network characteristics" of the sensor terminal may be: only the "uplink data" sent to the cloud, but not the "downlink data" received.
On the other hand, the network also needs to "take care of" the terminal characteristics that were not paid much attention to in order to meet the needs of various industrial applications: the control of "energy consumption" and "cost".
(1) Energy consumption
Individual users are in a livable environment most of the time, intelligent terminals are often accompanied around, and charging "power plugs" can always be found in the environment of human activities, so the manufacturers of these terminals are not sensitive to the power of the battery.
The working environment of IOT terminal is much more complex than that of personal terminal. Some IOT terminals will be deployed in high-temperature and high-pressure industrial environment, some will be far away from cities and placed in remote areas where people are rarely seen, and some may be embedded underground or settled in streams and lakes.
Many devices need long-term battery power to work, because the geographical location and working environment can not provide them with external power, and the cost of replacing the battery is extremely high. Therefore, "low power consumption" is a key requirement to ensure their continuous work. In many application scenarios, the power of a small battery needs to maintain the "lifetime" energy supply of a terminal.
(2) Cost
Terminals for personal use, whether computers or mobile phones, have rich functions, powerful computing power and wide applications. Communication modules are only a small part of all electronic components and mechanical construction, accounting for a relatively low proportion of the total manufacturing cost.
As a high-value product, users and manufacturers are not particularly sensitive to the fixed cost of their communication unit. Internet of things terminals are different. Many terminals without networking function are originally simple sensor devices, which have simple functions and low cost. Compared with sensor devices, the addition of expensive communication modules may cause a sharp rise in costs.
Deploying a large number of networked sensing devices in application scenarios often requires enterprises to make up their minds to increase the cost investment of terminals. The contradiction is that the amount of data uploaded to the network by simple sensor terminals is usually very small; They have a long period of connecting to the network (the frequency of network use is low); The value of each upload is very low. The terminal cost is out of proportion to the information value, which makes enterprises hesitate to deploy a large number of IOT terminals. How to reduce the communication cost of these dumb terminals (single sensor terminals) is an urgent problem.
If the previously mentioned energy consumption problem is not properly solved, it will also affect the operating cost of Internet of things applications: if the terminal consumes too much power, it needs to constantly redeploy, put in or replace the battery.
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Low power consumption and low cost are a major demand for Internet of things communication
The original network is not sensitive to applications. As long as it provides a unified high-quality network channel (unique standard), it can meet the needs of most users. No matter what kind of business users like to use, they can obtain communication services through high-quality network quality. The network can meet most of the requirements of individual users.
However, with the deepening of industrial applications, network designers and builders must pay attention to the differences between applications and terminals, that is, the network needs to make corresponding adjustments and adaptations for terminals and applications.
Among the network characteristics and terminal characteristics mentioned earlier: "distance, quality, characteristics" and "energy consumption and cost", the two characteristics are closely related: the wider the signal coverage of the communication base station ("long distance"), the higher the power consumption of the base station and terminal ("high energy consumption"); In order to realize high-quality, safe and reliable network services ("high quality"), robust communication protocols are needed to realize error verification, authentication and retransmission mechanisms to establish end-to-end reliable connections. The guarantee is based on the fact that the configuration of communication modules cannot be low ("high cost")
Part2 / Nb IOT development history
When operators promote M2M services (Internet of things applications), they find that the business needs of enterprises for M2M are different from those of individual users. Enterprises hope to build a centralized information system and establish a long-term communication connection with their own assets for management and monitoring.
These assets are often distributed everywhere and in large quantities; The communication equipment equipped on the asset may not have external power supply conditions (i.e. battery power supply, and may be disposable, which can neither charge nor replace the battery); The amount of data to be reported by a single sensor terminal is small and the cycle is long; Enterprises need low communication costs (including communication charges and the cost of assembling communication modules).
The above application scenarios have strong unity at the network level, so organizations and enterprises in the communication field expect to optimize the existing communication network technology standards to meet the consistency requirements of such M2M services.
In 2013, Vodafone and Huawei jointly started the research on new communication standards. At first, they called the communication technology "nb-m2m (LTE for machine to machine)".
In May 2014, the GERAN group of 3GPP established a new research project: "Fs"_ IoT_ LC ", the project mainly studies new radio access network system," nb-m2m "has become one of the research directions of the project. Later, Qualcomm submitted the technical solution of "nb-ofdm" (narrow band orthogonal frequency division multiplexing).
(3GPP, "3rd Generation Partnership Project" standardization organization; Tsg-geran (GSM / EDGE radio access network): responsible for the formulation of technical specifications for GSM / EDGE radio access network)
In May 2015, "nb-m2m" scheme and "nb-ofdm scheme" merged into "Nb ciot" (narrow band cellular IOT). The convergence of this scheme mainly lies in that the communication uplink adopts FDMA multiple access mode and the downlink adopts OFDM multiple access mode.
In July 2015, Ericsson, together with ZTE, Nokia and other companies, put forward the technical scheme of "nb-lte" (narrow band LTE).
At the ran#69 plenary session in September 2015, after intense discussion and consultation, the leaders of each scheme integrated the two technical schemes ("nb-ciot" and "nb-lte"), and 3GPP approved the unified standard work. As a unified international standard, this standard is called "NB IOT (narrow band Internet of things based on cellular)". Since then, "nb-m2m", "nb-ofdm", "nb-ciot" and "nb-lte" have become history.
In June 2016, the core standard of Nb IOT was frozen in 3GPP rel-13 as a proprietary agreement for the Internet of things. In September of the same year, the standard formulation of Nb IOT performance was completed. In January 2017, the standard formulation of Nb IOT conformance test was completed.
In my opinion, the key to the "alliance" of these low-power cellular technologies is not only the growing business demands, but also the threat of other emerging (unauthorized frequency band) low-power access technologies. The emergence of new access technologies such as Lora, sigfox and RPMA has contributed to the group development of relevant member enterprises and organizations in 3pgg.
Part3 / Nb IOT technical characteristics
Like its competitors, Nb IOT focuses on communication applications with low power consumption and wide area coverage. The communication mechanism of the terminal is relatively simple, and the power consumption of wireless communication is relatively low. It is suitable for information upload with small amount of data and low frequency (low throughput). The signal coverage is basically the same as that of ordinary mobile network technology. Such technologies are collectively referred to as "lpwan technology" (low power wide area) in the industry.
NB IOT optimizes the original 4G network for the M2M communication scenario, and appropriately balances the network characteristics and terminal characteristics to meet the needs of Internet of things applications.
In "distance, quality, characteristics" and "energy consumption and cost", ensure wide area coverage on "distance", reduce "quality" to a certain extent (for example, adopt half duplex communication mode, do not support high bandwidth data transmission), and reduce "characteristics" (for example, do not support switching, that is, mobility management in connection state).
The advantage of "shrinking" network characteristics is that it also reduces the communication "energy consumption" of the terminal, and can reduce the "cost" by simplifying the complexity of the communication module (for example, simplifying the processing algorithm of the communication link layer).
Therefore, in order to meet the individual requirements of some IOT terminals (low energy consumption and low cost), the network has made a "compromise". NB IOT "sacrifices" some network features to meet the needs of different previous applications in the Internet of things.
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Deployment mode
In order to facilitate operators to flexibly use according to the conditions of free network, Nb IOT can be deployed in different wireless bands, which can be divided into three cases: stand alone deployment, guard band deployment and in band deployment.
Stand alone mode: deploy with independent new frequency band or idle frequency band, and the "GSM frequency band re ploughing" proposed by the operator also belongs to this mode;
Guard band mode: use the edge protection frequency band in LTE system. With this mode, it is necessary to meet some additional technical requirements (for example, the bandwidth of the original LTE band should be greater than 5mbit / s) to avoid signal interference between LTE and Nb IOT.
In band mode: use a certain band in the middle of LTE carrier. In order to avoid interference, 3GPP requires that the signal power spectral density and LTE signal power spectral density in this mode shall not exceed 6dB.
In addition to the stand alone mode, the other two deployment modes need to consider the compatibility with the original LTE system. The technical difficulty of deployment is relatively high and the network capacity is relatively low.
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Coverage enhancement
In order to enhance signal coverage, on the downlink wireless channel of Nb IOT, the network system repeatedly sends control and service messages ("retransmission mechanism") to the terminal, and then the terminal combines the repeatedly received data to improve the quality of data communication.
This method can increase the signal coverage, but the data retransmission potential will lead to the increase of time delay, which will affect the real-time performance of information transmission. In places with weak signal coverage, although NB IOT can ensure the connectivity between the network and the terminal, some services with high real-time requirements cannot be guaranteed.
On the uplink channel of Nb IOT, data retransmission on the wireless channel is also supported. In addition, when the terminal signal is transmitted in a narrower LTE bandwidth, the signal enhancement on the unit spectrum can be realized, so that the PSD (power spectrum density) gain is greater. By increasing the power spectral density, it is more conducive to the signal demodulation at the receiving end of the network, and improves the penetration ability of the uplink wireless signal in the air.
Through the optimal design of uplink and downlink channels, the "coupling loss" of Nb IOT signal can reach 164db at most.
(Note: coupling loss refers to the energy loss when energy is transmitted from one circuit system to another. Here refers to the energy loss of wireless signal propagation in the air)
In order to further utilize the signal coverage capability of the network system, Nb IOT also carries out classification (CE level) according to the strength of signal coverage and realizes "paging optimization": PTW (paging transmission window) is introduced to allow the network to page UE multiple times in one PTW, and the paging times are adjusted according to the coverage level.
For normal coverage, its MCL (maximum coupling loss) is less than 144db, which is consistent with the current GPRS coverage.
The MCL of extended coverage is between 144db and 154db, with 10dB enhancement compared with GPRS coverage
For extreme coverage, its MCL is up to 164db, which is 20dB higher than GPRS coverage.
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