Nowadays, wireless communication is developing rapidly, and the application tentacles are beginning to expand to the connection of various objects and objects. Therefore, even if the 4G network continues to expand, the 5G standard war has long been filled with smoke, especially the narrow-band Internet of Things (NB-IoT) standard, which has become one of the main battlefields for all parties.
Nowadays, wireless communication is developing rapidly, and global wireless communication is in full swing. People's demand for mobile communication, audio and video transmission or terminal applications is increasing day by day. The network is everywhere, so even if 4G continues to expand, it will continue to expand. The 5G generation is also coming, and the business opportunities contained in it are even more unlimited.
In China, the Ministry of Economic Affairs expects that the output value of the domestic communication industry will reach 200 billion US dollars after 6 years. Therefore, in order to meet this huge blue ocean of communication, all countries are actively taking the lead in taking the lead and investing a lot of resources and research. The next generation of 5G communication is planned and developed, and it is necessary to master the key technologies and patents to enhance the adoption of the 3rd GeneraTIon Partnership Project (3GPP) standards and help the future development of domestic communication-related industries. .
5G communication performance is great
In the case of rapid industrial development, various applications at the user end have also increased. In the face of increasing global demand for data transmission and network capacity, 5G networks have emerged, 3GPP's 5G The relevant standard technologies are expected to be finalized in 2016, and the relevant products will be expected to enter the commercial phase by 2020. In its future development, it will not only require a large transmission rate, but also a number of connections that are several times larger than today. The world will enter the era when everything is connected (Figure 1).
Figure 1 5G development trend
Well-known consulting agency McKinsey pointed out that the application value of the Internet of Things (IoT) will reach 11.1 trillion US dollars in 2025. 5G proposes features such as low latency, high transmission, low energy consumption and large connectivity. 5G mobile communication is expected to have global coverage by 2020. 50 billion terminal products have Internet access, the overall system capacity (Capacity) demand is more than 1000 times more than 4G, and its transmission delay must be less than 1 millisecond (ms), so the performance and technical challenges of the next generation 5G communication will be more than before. More serious.
With the emergence of a large number of application terminals such as smart meters, smart home appliances, smart factories, and wearable devices, more and more work and life need to be solved through smart terminals. For this, high-density links and lower terminals Cost requirements are getting bigger and bigger, and new technologies are needed to meet such needs.
Analysis of 5G key technologies
In the future development of 5G, not only the large transmission rate is needed, but also the number of connections that are several times larger than today. The world will enter the era of Internet access. In 3GPP, machine-to-machine (M2M)/machine type communication is first proposed. Machine Type CommunicaTIon, MTC), which is designed with lower equipment costs, lower power consumption, greater coverage, and support for a large number of device connections, but most of them believe that this is only a transitional version. Because its power consumption and construction cost are still too high, it is not enough technology for applications that require lower power consumption and a larger number of connections. Therefore, 3GPP proposes a lower transmission data in R13. Amount, lower equipment cost, and wider coverage technology, called NB-IoT (Narrowband-Internet of Thing), its maximum transmission data volume is 200kbit/s, the bandwidth is also reduced to 200kHz, and its coverage It can be multiplied several times, so all major telecom operators are strongly supportive of this technology (Table 1).
NB-IoT grabs the Internet of Things blue ocean
The Internet of Things has been developed for many years, and various applications and technologies have been proposed. LoRa and SIGFOX also emphasize low power consumption and broad coverage. However, since LoRa and SIGFOX use unlicensed spectrum, they represent anyone. Both of these bands can be used, and many uncontrollable interference problems are formed, which becomes very unreliable in use. Therefore, the world's major telecom operators tend to support the NB-IoT technology proposed by 3GPP due to its use of licensed bands. And the NB-IoT deployment can be quickly deployed on the original cellular network equipment, which saves the deployment cost and quickly integrates the original Long-Range Evolution Project (LTE) network, so the future can be foreseen. NB-IoT will be the direction that mainstream telecom operators in the world will pursue.
NB-IoT is a low-power wide area wide area (LPWA) technology, which is characterized by extremely low power consumption, wide coverage and a large number of connections, and its device coverage can be increased by 20dB. Battery life can exceed 10 years, each NB-IoT carrier can support up to 200,000 connections, and according to capacity requirements, you can expand the scale by adding more carriers, so that a single base station can support millions of Internet of Things link.
There are several goals in the design of NB-IoT. One is to improve the coverage rate. By reducing the coding rate (Coding Rate), the reliability of the signal can be improved, so that when the signal strength is weak, the signal can be correctly demodulated and improved. The purpose of coverage is to increase the battery life cycle by a maximum of 23dBm, which is about 200mW (mW). In order to reduce the complexity of the terminal, a constant envelope is used for modulation. Constant Envelope) allows the Power Amplifier (PA) to operate in the saturation range, allowing the transmitter to have better efficiency. In the physical layer design, it can also simplify some components and reduce the complexity. In order to reduce the system bandwidth, the bandwidth is designed at 200 kHz, because such a high transmission rate is not required on the Internet of Things, so that it does not need such a large spectrum, and it can be more flexibly allocated in use, and there is an important one. The design goal is to greatly increase the system capacity, so that a large number of terminals can be connected at the same time. One of the methods is to make the subcarrier interval smaller. On the spectrum allocation can be more resilient, cut out more subcarriers are assigned to more terminals.
NB-IoT has three deployment methods in the spectrum. The first one is Standalone. This deployment method uses the spectrum of independent or Global System for Mobile Communications (GSM), which does not interfere with each other. Simple deployment, but requires a spectrum of its own. The second is to use the Guard Band to build. The LTE spectrum edge protection frequency band is used, and the weak signal strength is deployed. The advantage is that it does not need a piece of its own spectrum. The disadvantage is that interference with the LTE system may occur.
The third is built in the current operating band (In Band), the deployment scenario is shown in Figure 2, the spectrum used is selected in the low frequency range, such as 700MHz, 800MHz, 900MHz, etc., because in the low frequency band It has wider coverage and better wave-transmission characteristics, and can have a deeper penetration rate for indoor environments.
Figure 2 NB-IoT three deployment scenarios Source: NB-IoT enabling new business opportuniTIes, Huawei
However, the current NB-IoT proposed by 3GPP also contains different technologies. Currently, it can be divided into two directions. One is NB supported by Nokia, Ericsson and Intel. - LTE (Narrowband-LTE) and NB-CIoT (Narrowband-Cellular IoT) supported by Huawei and Vodafone. The biggest difference between the two technologies for operators is how much they can be reused in the existing LTE environment. In a networked application.
NB-LTE is almost compatible with current LTE equipment, but NB-CIoT can be said to be a redesigned technology that requires the construction of new chips, but its coverage is expected to increase and equipment costs are even higher. Reduced, so the two technologies can be said to have their own advantages, the following will give an overview of the two technologies.
NB-LTE backward compatibility and cost reduction
The bandwidth used in NB-LTE is 200KHz, and the technology used in the downlink is Orthogonal Frequency Division MulTIple Access (OFDMA). The subcarrier bandwidth is 15 kHz, and the orthogonal frequency division is more. The division of the (OFDM) symbol (Symbol) and the time slot (Time Slot) and the sub-frame (Subframe) are the same as the original LTE specifications.
The NB-IoT uplink uses Single-Carrier Frequency-Division Multiple Access (SC-FDMA), and the sub-carrier bandwidth is 2.5 kHz, which is one-sixth of the bandwidth of the original LTE sub-carrier. The interval between the symbol and the slot and sub-packet is six times that of the original LTE. NB-LTE is mainly expected to be able to use the legacy LTE physical layer part, and to a considerable extent can use the upper LTE network, so that operators can reduce the cost of equipment upgrade during deployment, and can also be built The original cellular network architecture is used to achieve rapid deployment.
In the following line, the synchronization signal (PSS/SSS), physical broadcast channel (PBCH), and physical downlink control channel (PDCCH) need to be adjusted or redesigned, and some control channels, such as entity control format indication, are needed. The channel (PCFICH) and the entity hybrid automatic repeat request indication channel (PHICH) are omitted to transmit data. In NB-LTE, in order to reduce the bandwidth to 200 kHz, which is one-sixth of the original LTE minimum bandwidth of 1.4 MHz, the transmission time period is lengthened, so a new time unit is defined in NB-LTE. It is called M-subframe, which is composed of six consecutive Subframes of the original LTE system, so its length is 6 milliseconds, and six M-subframes form an M-frame (Fig. 3). In an M-subframe, The smallest scheduling unit is a physical layer physical resource block (PRB), which can support up to six terminals in an M-subframe.
Figure 3 NB-LTE downlink packet design image source: 3GPP TR 45.820
In the uplink part, SC-FDMA is used, and the terminal can flexibly use each single carrier resource. In the application of NB-IoT, the receiving end must be able to tolerate very weak signals, and the time delay may be large, because each time The terminal should be time aligned with the base station, and the error of the time is smaller than the Cyclic Prefix (CP). Therefore, the design of the CP must be extended, so the design of the subcarrier bandwidth is The original one-sixth, to 2.5kHz, can also make the terminal device more flexible in the spectrum configuration.
NB-CIoT new design application
In NB-CIoT, the downlink uses OFDMA. Unlike the previous LTE system, NB-CIoT uses forty-eight subcarriers with a bandwidth of 3.75 kHz and uses sixty-four-point Fast Fourier Transform (FFT) to sample it. The frequency is 240kHz, which is also different from the old LTE system. In the time unit, one packet of NB-CIoT is composed of eight sub-packets, and each sub-packet can be divided into thirty-two time slots, and each time slot is further divided into seventeen symbols (Fig. 4).
Figure 4 NB-CIoT downlink packet design image source: 3GPP TR 45.820
It is also redesigned in each signal channel, such as the sync signal (PSS/SSS). Although it uses the ZC sequence (Zadoff-Chu Sequence) of the Constant Amplitude like the LTE system, it will duplicate the transmission twice. It is to increase the reliability of detection. In the physical downlink shared channel (PDSCH), the Turbo Coding code is originally used, and the Convolution Coding for small data transmission is also changed, which simplifies the system architecture and Complexity, improving the system's ability to respond to the needs of the Internet of Things.
In the uplink part, a Frequency Division Multiple Access (FDMA) system is used. Compared with the OFDM system, no orthogonality is required between each subcarrier, so accurate time and frequency calibration is not required. For frequency use, NB-CIoT uses thirty-six subcarriers of 5 kHz bandwidth, while it supports GMSK (Gaussian-shaped Minimum Shift Keying) modulation, GMSK is constant envelope modulation and has PSK (Phase Shift Keying) The characteristics of the spectrum provide high spectral efficiency and allow the PA to operate in a saturated range for more efficient performance.
It can be found that the overall design of NB-CIoT is very different from that of the previous LTE system. Not only in the architecture of the packet time, but also in the channels used for each use, it is necessary for the operator to redesign the chip module. Group, for the cost and speed of construction is a big need to take care of.
NB-LTE and NB-CIoT have their own advantages
The comparison between NB-LTE and NB-CIoT technologies is shown in Table 2. In NB-LTE, most of them are the same as the original LTE system, such as the access technology used and the size of the FFT and sampling frequency, but NB. -CIoT, but it is a very different design specification.
For operators, NB-LTE can be applied directly to the old system without cost, and can be quickly deployed in the original cellular base station, while in NB-CIoT, regardless of the packet The design, sampling frequency or subcarrier bandwidth is different from the original LTE, but because it is a redesigned specification for the Internet of Things, it is better than NB- in all kinds of features applied to the Internet of Things. LTE is more suitable. For example, at the sampling frequency, NB-LTE is still 1.92MHz, which is still a big consideration in the cost of the equipment, and the sampling frequency of NB-CIoT is reduced to 240kHz, which can greatly reduce the equipment cost. And power consumption.
The CP of NB-CIoT is also longer than NB-LTE, so it can resist the delay of time and make the transmission distance farther. Therefore, NB-LTE and NB-CIoT have different advantages and disadvantages, so the final decision is made. Technology and operational models may not be clear until the standard specifications set by 3GPP.
The final version of NB-IoT may be one of the two versions, or the two technologies should be merged into one version, but there are several technical principles that must exist, including: NB-IoT supports both Standalone and Guard Band. And In Band's three deployment methods; use 180kHz bandwidth; use OFDMA system in the downlink; use GMSK or SC-FDMA system in the uplink; technology and communication specifications above L2, try to be as original as possible LTE system reuse.
NB-IoT is imperative
In the era of entering the Internet of Things, various back-end applications have been produced one after another. Therefore, how to make these applications completely realized, and how operators should get one of them in this, NB-IoT is undoubtedly a necessary implementation. Technology, due to the use of unlicensed bands, such as SIGFOX or LoRa, is a major consideration for data reliability and security. It is important that operators get the benefits in it, and the NB-IoT is owned by the existing The LTE network architecture, by updating some of its device components, will be able to quickly enter the IoT market. For the future development and demand of communication, the speed of implementation and deployment is undoubtedly a critical consideration, and it uses authorization. In the frequency band, the security and reliability of the data will be greatly improved, and many unnecessary interference problems can be reduced. It is expected that a standard version of the NB-IoT will be finalized in the middle of this year (2016), and then it will be visible. The development of future narrow-band IoT.
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