PART 1/Differentiated needs of "Internet of Things (Internet of Things)" For a
long time, people have used network services through corresponding terminals (computers, mobile phones, tablets, etc.), and "individuals" have always been the main users of the network. Personal requirements for network quality are "high" and "unified": playing online games must require low latency, downloading files or watching online videos requires high bandwidth, calls need to have clear voices, and received text messages must not be missed.
For mobile communication networks, operators try their best to maintain low latency, high bandwidth, wide coverage, and on-demand network characteristics to ensure a good user experience and create a rich and diverse mobile application ecosystem.
For personal communication services, although users have high requirements, the overall requirements for network quality are consistent. Operators only need to establish a network quality standard system to construct and optimize the network, which can satisfy most people’s connection requirements. need.
As the growth of the number of user terminals (mobile phones, PADs, etc.) in the network has gradually slowed down, M2M applications have become the growth force for operators' network services, and a large number of M2M application terminals have become network users. M2M application terminals (sensing equipment, smart terminals) are essentially IoT terminals. They are connected to the operator's network by assembling wireless communication modules and SIM cards to build various centralized and digital industry applications.
Different from personal communication services, in the industry applications built by IoT terminals, the quality requirements of information collection, transmission, and calculation in various fields are very different; the environments for system and terminal deployment are also different, especially in the vastly different industrial environment In addition, when companies build applications, they also need to consider technical limitations (power supply issues, terminal volume, etc.) and cost control (including construction costs and operating costs). Therefore, various industrial applications have a "personalized" aspect, which makes the demand for connection develop in the direction of diversity.
1. The differentiation of IoT business requirements 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, upstream and downstream network bandwidth, mobility support, as well as the frequency of data transmission and reception (or periodicity), as well as 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-distance access and long-distance access. The "characteristics" and "quality" of the network are the main factors that reflect demand differentiation. For example, the "network characteristics" of sensor terminals may be: only "uplink data" sent to the cloud, but no "downlink data" received.
On the other hand, the network also needs to "take care" of terminal features that have not received much attention in order to adapt to various industry application requirements: control of "energy consumption" and "cost".
(1) Energy consumption.
Individual users spend most of their time in a livable environment. Smart terminals are often accompanied, and they can always find charging "power plugs" in the environment of human activities. Therefore, the manufacturers of these terminals are concerned about the battery The battery is not sensitive.
The working environment of IoT terminals is much more complicated than that of personal terminals. Some IoT terminals will be deployed in high-temperature and high-pressure industrial environments, some are far away from cities, placed in remote areas off the beaten track, and some may be embedded deep underground or settled in streams and lakes.
Many devices require long-term battery power to work, because the geographic location and working environment cannot provide them with external power, and the cost of battery replacement is also extremely high. So "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 a "lifetime" energy supply for a certain terminal.
(2) Cost
The terminal for personal use, whether it is a computer or a mobile phone, has rich functions, powerful computing capabilities, and a wide range of applications. The communication module is only a small part of all its electronic components and mechanical construction, and it accounts for a relatively large part of the total manufacturing cost. low.
Personal terminals are high-value products, and users and manufacturers are not particularly sensitive to the fixed cost of their communication units. The Internet of Things terminals are different. Many terminals that do not have networking functions are originally simple sensor devices with simple functions and low cost. Compared with sensor devices, the addition of expensive communication modules may cause a sharp increase in costs.
Deploying a large number of networked sensing devices in application scenarios often requires enterprises to make a determination to increase the cost of terminals. The contradiction to this is that the amount of data uploaded to the network by simple sensor terminals is usually very small; the period of their connection to the network is long (the frequency of network use is low); the value of each upload of information is very low. The terminal cost and the value of the information are out of proportion, making enterprises hesitate to make decisions about deploying a large number of IoT terminals. How to reduce the communication cost of these dumb terminals (single sensor terminals) is an urgent problem.
The previously mentioned energy consumption problem, if not properly resolved, will also affect the operating costs of IoT applications: If the terminal consumes too much power, it will need to be continuously redeployed or replaced.
2. Low power consumption and low cost are a major requirement for IoT communication. The
original network is not sensitive to applications. As long as it provides a unified high-quality network channel (the only standard), it can meet the needs of most users. No matter what kind of service users like to use, they can obtain communication services through high-quality network quality, and the network can meet most of the requirements of individual users.
However, with the deepening of industry applications, network designers and builders must pay attention to the differences between applications and terminals, that is, networks need to make corresponding adjustments and adaptations to terminals and applications.
Among the network characteristics and terminal characteristics mentioned earlier: "distance, quality, characteristics" and "energy consumption, cost", the two types of characteristics are closely related: the wider the signal coverage of the communication base station ("long distance") , The higher the power consumption of base stations and terminals ("high energy consumption"); to achieve high-quality, safe and reliable network services ("high quality"), a robust communication protocol is required to implement error checking, identity verification, and retransmission mechanisms , To establish an end-to-end reliable connection, the basis of the guarantee is that the configuration of the communication module cannot be low ("high cost")
PART2 / NB-IoT development history When
operators are promoting M2M services (Internet of Things applications), they find that enterprises are The business needs of M2M are different from the needs of individual users. Enterprises hope to build a centralized information system and establish a long-term communication connection with their own assets for easy management and monitoring.
These assets are often distributed in various places and the number is huge; the communication equipment equipped on the assets may not have the conditions for external power supply (that is, battery-powered, and may be one-time, which can neither be charged nor replaced); a single sensor terminal needs to be reported The amount of data is small and the cycle is long; enterprises need low communication costs (including communication fees and the cost of assembling communication modules).
The above application scenarios have strong uniformity at the network level. Therefore, organizations and enterprises in the communication field expect to be able to perform a series of optimizations on the existing communication network technical standards to meet the consistent requirements of such M2M services.
In 2013, Vodafone and Huawei started research on a new communication standard. 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", which mainly studies a new type of radio access network system. "NB-M2M" has become one of the research directions of the project. Later, Qualcomm submitted a "NB-OFDM" (Narrow Band Orthogonal Frequency Division Multiplexing, narrowband orthogonal frequency division multiplexing) technical solution.
(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 networks)
May 2015, The "NB-M2M" solution and the "NB-OFDM solution" merge to form "NB-CIoT" (Narrow Band Cellular IoT). The main point of the integration of this scheme is: the communication uplink adopts FDMA multiple access mode, and the downlink adopts OFDM multiple access mode.
In July 2015, Ericsson, in conjunction with ZTE, Nokia and other companies, proposed the "NB-LTE" (Narrow Band LTE) technical solution.
At the RAN#69 plenary meeting in September 2015, after intense discussion and negotiation, the leaders of each solution merged the two technical solutions ("NB-CIoT" and "NB-LTE"). Subsequent standard work was established. As a unified international standard, this standard is called "NB-IoT (Narrow Band Internet of Things, cellular-based narrowband Internet of Things)". Since then, "NB-M2M", "NB-OFDM", "NB-CIoT" and "NB-LTE" have all become history.
In June 2016, the core standard of NB-IoT, as a proprietary protocol for the Internet of Things, was frozen in 3GPP Rel-13. In September of the same year, the standard formulation of the NB-IoT performance part was completed. In January 2017, the standard formulation of the NB-IoT conformance test part was completed.
In my opinion, the key to the "alignment" of these low-power cellular technologies is not only the growing business demands, but also the threat of other emerging (unlicensed frequency bands) low-power access technologies. The emergence of emerging access technologies such as LoRa, SIGFOX, and RPMA has promoted the group development of related member companies and organizations in 3PGG.
PART3/ NB-IoT Technical Features
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 small data volume and low frequency (low throughput) information upload. 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, low power wide area technology).
NB-IoT technology optimizes the original 4G network for the M2M communication scenario, and appropriately balances network characteristics and terminal characteristics to meet the needs of IoT applications.
In the "distance, quality, characteristics" and "energy consumption, cost", ensure the wide area coverage of the "distance" and reduce the "quality" to a certain extent (for example, the use of half-duplex communication mode, does not support high-bandwidth data Transmission), reduce "features" (for example, no handover is supported, that is, mobility management in the connected state).
The benefit 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 (low energy consumption and low cost) of some IoT terminals, the network has made a "compromise." NB-IoT "sacrifices" some network characteristics to meet the needs of different applications in the Internet of Things.
1. Deployment method
In order to facilitate the flexible use of operators according to the conditions of the free network, NB-IoT can be deployed on different wireless frequency bands. There are three situations: Stand alone, Guard band, In band deployment (In band).
Stand alone mode: Use independent new frequency bands or idle frequency bands for deployment. The "GSM frequency band re-cultivation" mentioned by operators also belongs to this type of mode;
Guard band mode: Use the guard band at the edge of the LTE system. To adopt this mode, some additional technical requirements need to be met (for example, the original LTE frequency band bandwidth is greater than 5Mbit/s) to avoid signal interference between LTE and NB-IoT.
In band mode: Use a certain frequency band in the middle of the LTE carrier. In order to avoid interference, 3GPP requires that the signal power spectral density in this mode and the LTE signal power spectral density should not exceed 6dB.
In addition to the Stand alone mode, the other two deployment modes need to consider compatibility with the original LTE system. The technical difficulty of deployment is relatively high, and the network capacity is relatively low.
2. 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 to the terminal ("retransmission mechanism"), and then the terminal merges the repeatedly received data. Improve the quality of data communication.
This method can increase the signal coverage, but data retransmission will inevitably lead to an increase in time delay, thereby affecting the real-time nature of information transmission. In places with weak signal coverage, although NB-IoT can ensure the connectivity between the network and the terminal, it cannot guarantee some services that require high real-time performance.
On the uplink channel of NB-IoT, data retransmission on the wireless channel is also supported. In addition, the terminal signal is sent in a narrower LTE bandwidth, which can achieve signal enhancement on a unit spectrum, so that the PSD (Power Spectrum Density, power spectral density) gain is greater. By increasing the power spectrum density, it is more conducive to the signal demodulation at the receiving end of the network, and the penetration capability of the uplink wireless signal in the air is improved.
Through the optimized design of the uplink and downlink channels, the "coupling loss" of the NB-IoT signal can reach up to 164dB.
(Note: Coupling loss refers to the energy loss that occurs when energy propagates from one circuit system to another. Here is the energy loss of wireless signals propagating in the air)
In order to further utilize the signal coverage capability of the network system, NB-IoT also According to the strength of signal coverage, it has been classified (CE Level), and "paging optimization" is realized: PTW (Paging Transmission Window) is introduced, which allows the network to page the UE multiple times within a PTW, and adjust the number of paging according to the coverage level .
Normal coverage (Normal Coverage), its MCL (Maximum Coupling Loss, maximum coupling loss) is less than 144dB, consistent with the current GPRS coverage.
Extended coverage (Extended Coverage), its MCL is between 144dB and 154dB, relative to GPRS coverage with 10dB enhancement.
Extreme coverage (Extreme Coverage), its MCL up to 164dB, relative GPRS coverage strength increased by 20dB.
3. Realization of NB-IoT low power consumption
To run the terminal communication module with low power consumption, the best way is to "sleep" as much as possible. There are two modes of NB-IoT, which can make the communication module monitor the network's paging for a short period of time, and it will be closed at other times. The two "power saving" modes are: PSM (power saving mode) and eDRX (Extended Discontinuous Reception)
(1) PSM mode
In PSM mode, the communication module of the terminal device enters idle After a period of time, it will close its signal transmission and reception and related functions of the access layer. When the device is in this partial shutdown state, it enters the power saving mode-PSM. In this way, the terminal can reduce the energy consumption of communication components (antenna, radio frequency, etc.).
When the terminal enters the power saving mode, the network cannot access the terminal. From the perspective of voice calls, it means "cannot be called".
In most cases, terminals using PSM are dormant for more than 99% of the time. There are two main ways to activate their communication with the network:
when the terminal itself needs to connect to the network, it will exit the PSM state , And actively communicate with the network and upload business data.
In each periodic TAU (Tracking Area Update), there is a short period of time in the active state. In the active state, the terminal first enters the "connect state (Connect)", and interacts with the communication network its network and business data. After the communication is completed, the terminal will not enter the PSM state immediately, but will remain in the "idle state (IDLE)" for a period of time. In the idle state, the terminal can accept paging from the network.
In the operating mechanism of PSM, the "Active Timer (AT)" is used to control the duration of the idle state, and the activation timing is determined through negotiation between the network and the terminal when the network attaches (the terminal is first registered to the network) or TAU The duration of the device. When the AT timeout occurs in the idle state, the terminal enters the PSM state.
According to the standard, a TAU period of a terminal can reach up to 310H (hours); the duration of the "idle state" can reach up to 3.1 hours (11160s).
It can be seen from the technical principles that PSM is suitable for applications that have almost no downstream data traffic. The interaction between cloud applications and terminals mainly depends on the terminal's autonomous connection with the network. In most cases, cloud applications cannot "contact" the terminal in real time.
(2) PSM mode
In PSM mode, the network can only page to the terminal within the first time period of each TAU (paging in the idle state after the connected state). The operation of eDRX mode is different from that of PSM. It introduces the eDRX mechanism to improve the accessibility of the service downlink.
(Remarks: DRX (Discontinuous Reception), that is, discontinuous reception. eDRX is extended discontinuous reception.)
eDRX mode, in a TAU cycle, contains multiple eDRX cycles, so that the network can establish communication with it in a more real-time manner Connect (paging).
A TAU of eDRX includes a connected state period and an idle state period, and the idle state period includes multiple eDRX paging periods, and each eDRX paging period includes a PTW period and a PSM period. The states of PTW and PSM will alternately appear in a TAU periodically, so that the terminal can be in a standby state intermittently, waiting for a call from the network.
In the eDRX mode, the network and terminal establish communication in the same way: the terminal actively connects to the network; the terminal accepts paging from the network within the PTW in each eDRX cycle.
In TAU, the smallest eDRX cycle is 20.48 seconds and the maximum cycle is 2.91 hours.
In eDRX, the smallest PTW cycle is 2.56 seconds and the maximum cycle is 40.96 seconds.
In PTW, the smallest DRX cycle 1.28 seconds, the maximum period is 10.24 seconds
Generally speaking, when the TAU is consistent, the eDRX mode has a higher idle state distribution density than the PSM mode, and the terminal responds to paging more timely. The services applicable to eDRX mode generally require relatively more downlink data transmission, but allow terminals to receive messages with a certain delay (for example, the cloud needs to perform terminal configuration management and log collection from time to time). According to technical differences, eDRX mode consumes more power than PSM mode in most cases.
4. Terminal simplification brings low cost
. For applications that do not require high data transmission quality, NB-IoT has low-speed, low-bandwidth, and non-real-time network characteristics. These features make NB-IoT terminals not as complicated as personal user terminals. The simple structure and simplified module circuit can still meet the needs of IoT communication.
NB-IoT adopts a half-duplex communication mode, and the terminal cannot send or receive signal data at the same time. Compared with a full-duplex terminal, it reduces the configuration of components and saves costs.
The low-speed data traffic of the business makes the communication module do not need to configure a large-capacity buffer. Low bandwidth reduces the requirements for equalization algorithms and reduces the requirements for equalizer performance. (The equalizer is mainly used to counteract wireless channel interference through calculation) The
NB-IoT communication protocol stack is based on LTE design, but it systematically simplifies the protocol stack, so that the software and hardware of the communication unit can also be reduced accordingly: the terminal can be used Low-cost application-specific integrated circuits replace high-cost general-purpose computing chips to realize the simplified functions of the protocol. This can also reduce the overall power consumption of the communication unit and extend the battery life.
5. Business simplification
in the core network In the NB-IoT core network (EPC- Evolved Packet Core, 4G core network), according to the demand characteristics of the Internet of Things business, the cellular Internet of Things (CIoT) defines two optimization solutions :
CIoT EPS user plane function optimization (User Plane CIoT EPS optimisation)
CIoT EPS control plane function optimization (Control Plane CIoT EPS optimisation)
(1) User plane function optimization
"User plane function optimization" is not much different from the original LTE business. Its main feature is the introduction of RRC (Radio Resource Control). Suspend/Resume (Suspend/Resume) process" reduces the signaling overhead of repeated network access by the terminal.
When there is no data traffic between the terminal and the network, the network puts the terminal into a suspended state (Suspend), but the original connection configuration data is still retained in the terminal and the network.
When the terminal re-initiates the service, the original configuration data can immediately resume the communication connection (Resume), which subtracts the procedures of re-rRC reconfiguration and security verification, and reduces the amount of signaling interaction on the wireless air interface.
(2) Control plane function optimization
"Control plane function optimization" includes two implementation methods (message transmission path). Through these two methods, the terminal does not need to establish a service bearer with the network on the wireless air interface, and can directly transmit service data to the network.
Note: One of the characteristics of the communication system is the separation of control and bearer (service). Intuitively speaking, the control messages of the service (establish service, release service, modify service) and service data themselves are not mixed and transmitted on the same link. The optimization of NB-IoT control plane functions simplifies this usual information business architecture.
There are two ways to realize the CP mode, that is, two data transmission paths:
A. In the core network, MME and SCEF network elements are responsible for the transfer of business data.
In this way, NB-IoT introduces a new network element: SCEF (Service Capability Exposure Function, Service Capability Exposure Function). The Internet of Things terminal receives or sends service data through wireless signaling links, not wireless service links.
When the terminal needs to upload data, the service data is carried by wireless signaling messages, and is directly transmitted to the core network element MME (Mobility Management Entity, mobility management entity in the 4G core network), and then the MME passes through the newly added SCEF network The meta is forwarded to the CIoT service platform (CIoT Services, also known as AP-application service). The direction in which the cloud sends business data to the terminal is the opposite of the upload direction.
Path: UE (terminal)-MME-SCEF-CIoT Services
B. In the core network, the service data is exchanged with the service plane through the MME.
In this way, the terminal also sends and receives service data through the wireless signaling link. For the upload of service data, the MME equipment sends the service data of the terminal to the service plane network element SGW of the core network, and then enters the Internet platform through the PGW; for the downstream service data, the SGW transmits it to the MME, and then the MME passes it through The wireless signaling message is sent to the terminal. The paths for uploading and downloading business data are also the same.
Path: UE (terminal)-MME-SGW-PGW-CIoT Services.
According to the traditional process (including user plane optimization scheme), the terminal needs to establish SRB (Signaling Radio Bearer) and then DRB (Data Radio Bearer) with the network before it can Data is transmitted on the wireless channel. With the control plane optimization scheme (CP mode), only the establishment of SRB can realize the sending and receiving of business data.
(3) Summary of function optimization mode The
CP mode draws on some design ideas of short-distance communication, and is very suitable for uploading services of low frequency and small data packets, similar to the SMS service. However, the bandwidth of the "signaling plane" in the network is limited, so the CP method is not suitable for transmitting larger service data packets. The UP mode can meet the delivery of big data services.
Regardless of the UP mode or the CP mode, the simplification of the wireless communication process essentially saves the communication calculation and energy consumption of the terminal, and improves the data transmission efficiency.
6. Mobility management in connected state
Initially, the NB-IoT specification was designed and formulated for static application scenarios (such as smart meter reading), so in the Rel-13 version (June 2016), it does not support mobility management in the connected state. That is, "wireless switching" is not supported. In the subsequent version of Rel-14, NB-IoT will support handover between base station cells to ensure the continuity of services in the mobile state.
PART4/ NB-IoT technical characteristics summary
It can be seen from the characteristics of NB-IoT that it has strengthened the depth of communication coverage through "signal enhancement" and "paging optimization". Mainly through three aspects, to "take care" of the terminal's requirements for low power consumption and low cost:
1. Low power consumption "sleep" mode (PSM, eDRX) is introduced;
2. The requirements for communication quality are reduced and simplified Terminal design (half-duplex mode, protocol stack simplification, etc.);
3. Simplify the process through two functional optimization modes (CP mode, UP mode), reducing the amount of interaction between the terminal and the network.
These "optimized" designs for wide-area mobile communication technologies make NB-IoT more suitable for some scenarios of the Internet of Things, that is, LPWA (low-power wide area network) applications. And due to the introduction of the sleep mode, the communication quality requirements (mainly real-time requirements) are reduced, so that NB-IoT base stations can access more terminals (carrying LPWA services) than traditional base stations.
Terminals using NB-IoT can be used for high-density deployment and low-frequency data collection applications (including meter reading in fixed locations, warehousing and logistics management, information collection in urban public settings, etc.) while meeting the needs of low power consumption , Or low-density deployment, long-distance communication connection applications (including agricultural monitoring, geological and hydrological monitoring, etc.).
Of course, as a LPWAN technology, NB-IoT has its inherent limitations. It is obviously not suitable for services that require low latency and high reliability (Internet of Vehicles, telemedicine), and services with medium demand (smart wearables). , Smart home) is also a bit "difficult" for it.
In the IoT technology ecosystem, no communication access technology can "take everything" in all application scenarios. There are certain complementary effects between various access technologies. NB-IoT can rely on its technical characteristics in the IoT field Occupy a place.
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