NB-IoT proposed by the former 3GPP also includes various technologies. It can currently be divided into two directions. One is developed by Nokia, Ericsson and Intel. NB-LTE (Narrowband-LTE) supported by other camps 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 used in the existing LTE environment. Can be reused in IoT applications.
Nowadays, wireless communications are developing rapidly. Global wireless communications are developing in full swing. People’s demand for mobile communications, audio and video transmission or terminal applications is increasing day by day. Networks are ubiquitous wherever they go, so even if 4G is still As the deployment continues to expand, the 5G generation is also announced to be coming, and the business opportunities contained in it are even more unlimited.
In order to welcome this huge blue ocean of communications, all countries are actively trying to seize the opportunity and investing a lot of resources and research into planning and developing the next generation of 5G communications, hoping to master the key technologies. and patents to improve the chances of being adopted by the 3rd Generation Partnership Project (3GPP) standards to help the future development of domestic communications-related industries.
5G communication performance is greatly improved
With the rapid development of the industry, various applications on the user side have also increased. In the face of global users’ demands for data transmission and network capacity, As demand is getting higher and higher, 5G networks have emerged to respond. 3GPP's 5G-related standard technology is expected to be finalized in 2016, and related products are expected to enter the commercial stage in 2020. In its future development, not only a large transmission rate is required, but also the number of connections is several times greater than today. The world will enter an era in which everything is connected to the Internet (Figure 1).
Figure 1 5G development trend
The well-known consulting firm McKinsey pointed out that the application output value of the Internet of Things (IoT) will reach 11.1 trillion US dollars in 2025. 5G proposes low latency, high transmission, low With characteristics such as energy consumption and large connections, 5G mobile communications are expected to have 50 billion terminal products worldwide with Internet access capabilities in 2020. The overall system capacity (Capacity) demand will also increase more than 1,000 times compared with 4G, and its transmission delay must be less than 1 millisecond. (ms), therefore the performance improvement and technical challenges of next-generation 5G communications are bound to be more severe than before.
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. In this regard, The demand for high-density connections and reduced terminal costs is becoming greater and greater, and new technologies are needed to meet such demands.
Analysis of 5G key technologies
In the future development of 5G, not only a large transmission rate will be required, but also the number of connections will be several times greater than today. The world will be connected to everything. In the era of 3GPP, Machine-to-Machine (M2M)/Machine Type Communication (MTC) was first proposed. Its design goals were mainly lower equipment cost, lower power consumption, greater coverage and support. A large number of devices are connected, but most outsiders believe that this is just a transitional version because its power consumption and construction cost are still too high. It is still not enough for applications that require lower power consumption and a larger number of connections. As a usable technology, 3GPP proposed a technology with lower transmission data volume, lower equipment cost and wider coverage in R13, called NB-IoT (Narrowband-Internet of Thing). Its largest transmission The data volume is 200kbit/s, the bandwidth is also reduced to 200kHz, and its coverage can be increased several times, so all mainstream telecom operators strongly support this technology (Table 1).
NB-IoT rushes into the blue ocean of the Internet of Things
The Internet of Things has been developing for many years, and various applications and technologies have been proposed one after another, such as LoRa and SIGFOX, both of which also emphasize low power consumption. and the need for broad coverage. However, because LoRa and SIGFOX use unlicensed spectrum, it means that anyone can use this frequency band, which also causes many uncontrollable interference problems. This becomes very unreliable in use, so all over the world Major telecom operators tend to support the NB-IoT technology proposed by 3GPP. Because it uses licensed frequency bands and can quickly deploy NB-IoT on original cellular network equipment, it can save money for operators. With the deployment cost and rapid integration of the original Long Range Evolution (LTE) network, it is foreseeable that NB-IoT will be promoted by mainstream telecommunications companies around the world in the future.
NB-IoT is a Low Power Wide Area (LPWA) technology. It is characterized by extremely low power consumption, wide coverage and a huge number of connections. Its devices The coverage can be improved by 20dB, and the battery life can exceed 10 years. Each NB-IoT carrier can support up to 200,000 connections, and according to capacity requirements, the scale can be expanded by adding more carriers, making a single base station It can support millions of IoT connections.
There are several goals in the design of NB-IoT. One is to improve the coverage rate. The reliability of the signal can be improved by reducing the coding rate, so that when the signal strength is weak, the It can correctly demodulate to achieve the purpose of improving coverage. In addition, in order to greatly increase the battery life cycle, the maximum energy it sends is 23dBm, about 200 milliwatts (mW). In addition, in order to reduce the complexity of the terminal, its modulation Using the Constant Envelope method can make the power amplifier (PA) operate in the saturation range, allowing the transmission end to have better usage efficiency. In terms of physical layer design, some components can also be simplified. To reduce complexity and reduce system bandwidth, the bandwidth is designed to be 200kHz. Because such a high transmission rate is not required on the Internet of Things, such a large spectrum is not needed and it can be used more flexibly. Allocation, and another important design goal is to significantly increase system capacity so that a large number of terminals can be connected at the same time. One method is to make the subcarrier interval smaller, making the spectrum resource allocation more flexible and cutting-edge. Allocate more subcarriers to more terminals.
NB-IoT has three deployment methods on the spectrum. The first is standalone deployment. This deployment method uses independent or Global System for Mobile Communications (GSM) spectrum, each other. It will not interfere with each other and is the simplest deployment method, but it requires its own spectrum. The second method is to use the Guard Band to deploy, using the guard band at the edge of the LTE spectrum to deploy in parts with weaker signal strength. The advantage is that it does not require a section of its own spectrum, but the disadvantage is that interference with the LTE system may occur. The third type is to deploy within the current operating frequency band (In Band). The deployment scenario is shown in Figure 2. The spectrum used is selected in the low frequency band, such as 700MHz, 800MHz, 900MHz, etc., because it can It has wider coverage, better transmission characteristics, and deeper penetration into indoor environments.
Figure 2 Three deployment scenarios of NB-IoT Picture source: NB-IoT enabling new business opportunities, Huawei
However, the NB-IoT currently proposed by 3GPP also includes various differences Technology can currently be divided into two directions. One is NB-LTE (Narrowband-LTE) supported by camps such as Nokia, Ericsson and Intel, and NB-LTE supported by Huawei and Vodafone. CIoT (Narrowband-Cellular IoT), the biggest difference between the two technologies for operators is how much of it can be reused in IoT applications in the existing LTE environment.
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 be higher. Improvement, equipment costs are also reduced, so the two technologies can be said to have their own merits. The following will give an overview of the two technologies.
NB-LTE is backward compatible and reduces costs
The bandwidth used in NB-LTE is 200KHz, and orthogonal frequency division multiplexing (Orthogonal Frequency Division) is used in the downlink. Multiple Access (OFDMA) technology, the subcarrier bandwidth is 15kHz, and in the interval of Orthogonal Frequency Division Multiplexing (OFDM) symbol (Symbol), time slot (Time Slot) and subframe (Subframe), it is different from the original The LTE specifications are the same.
NB-IoT uses Single-carrier Frequency-Division Multiple Access (SC-FDMA) for uplink. The sub-carrier bandwidth is 2.5kHz, which is the original LTE sub-carrier frequency. One-sixth of the width, and the range of symbols, time slots and sub-packets is six times that of the original LTE. NB-LTE mainly hopes to be able to use the old LTE physical layer part, and to a considerable extent be able to use the upper LTE network, so that operators can reduce the cost of equipment upgrades during deployment, and can also The original cellular network architecture is used to achieve rapid deployment.
Looking at the downstream part, the synchronization signals (PSS/SSS), physical broadcast channel (PBCH) and physical downlink control channel (PDCCH) need to be adjusted or redesigned, and some of the original controls need to be adjusted or redesigned. Channels, such as the Physical Control Format Indication Channel (PCFICH) and the Physical Hybrid Automatic Repeat Request Indication Channel (PHICH), are omitted to transmit data. In NB-LTE, in order to reduce the bandwidth to 200kHz, which is one-sixth of the original LTE minimum bandwidth of 1.4MHz, the transmission time period is lengthened, so a new time unit is defined in NB-LTE , called M-subframe, which is composed of six consecutive Subframes in the original LTE system, so its time length is 6 milliseconds, and six M-subframes constitute an M-frame (Figure 3). In an M-subframe, The smallest scheduling unit is a physical layer radio resource block (Physical Resource Block, PRB), which means that an M-subframe can support up to six terminals.
Figure 3 NB-LTE downlink packet design picture 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. Since each terminal needs to be time aligned with the base station, the time error must be smaller than the Cyclic prefix. Prefix, CP), so the CP design must be further stretched, so the subcarrier bandwidth is designed to be one-sixth of the original, to 2.5kHz. This can also allow the terminal equipment to do More flexible configuration.
Big Application of NB-CIoT New Design
In NB-CIoT, OFDMA is used in the downlink. Different from the previous LTE system, NB-CIoT uses forty-eight bandwidths of 3.75 kHz subcarrier and uses a 64-point Fast Fourier Transform (FFT) with a sampling frequency of 240kHz, which is also different from the old LTE system. In terms of time units, one NB-CIoT packet consists of eight sub-packets, and each sub-packet can be divided into thirty-two time slots, and each time slot is divided into seventeen symbols (Figure 4).
Figure 4 NB-CIoT downlink packet design picture source: 3GPP TR 45.820
It has also been redesigned in each signal channel, such as synchronization signal (PSS/SSS), although it is also like LTE The system uses a ZC sequence (Zadoff-Chu Sequence) with a fixed amplitude (Constant Amplitude), but it will copy the transmission twice in order to increase the reliability of detection. The physical downlink shared channel (PDSCH) originally uses a turbo code ( Turbo Coding) has also been changed to convolution coding (Convolution Coding) suitable for small data transmission, which can further simplify the system architecture and complexity and improve the system's ability to cope with the needs of the Internet of Things.
In the uplink part, the Frequency Division Multiple Access (FDMA) system is used. Compared with the OFDM system, there is no need for orthogonality between each sub-carrier, so precise Time and frequency calibration. In terms of frequency usage, NB-CIoT uses thirty-six 5kHz bandwidth sub-carriers, and it supports GMSK (Gaussian-shaped Minimum Shift Keying) modulation. GMSK is constant envelope modulation. It also has PSK (Phase Shift Keying) characteristics, which can provide higher spectrum efficiency and enable the PA to operate in the saturation range for more efficient performance.
It can be found that the overall design of NB-CIoT is very different from the previous LTE system. Not only the packet time architecture, but also the redesign of each channel used, so for operators , the chip module must be redesigned, and cost and construction speed are major issues that need to be taken into consideration.
NB-LTE and NB-CIoT have their own merits
The comparison of various technologies between NB-LTE and NB-CIoT is shown in Table 2. In NB-LTE, most of them are different from the original ones. There are LTE systems that are the same, such as the access technology used, FFT and sampling frequency, etc., but NB-CIoT has completely different design specifications.
For operators, NB-LTE can be directly applied to the old system without incurring too much cost, and can be quickly deployed in the original cellular network base station, while NB-LTE -CIoT is different from the original LTE in terms of packet design, sampling frequency or sub-carrier bandwidth size. However, because it is a redesigned specification specifically for the Internet of Things, it is used in various applications of the Internet of Things. In terms of characteristics, it will be more suitable than NB-LTE. For example, in terms of sampling frequency, NB-LTE is still 1.92MHz, which is still a major consideration in terms of equipment cost, while the sampling frequency of NB-CIoT is reduced to 240kHz. , which can significantly reduce equipment costs and power consumption.
The CP of NB-CIoT is also longer than that of NB-LTE, which makes it more resistant to time delays and enables longer transmission distances. Therefore, both NB-LTE and NB-CIoT have different advantages. and disadvantages, so the finalized technology and operating model may not be clear until the standards and specifications set by 3GPP.
The final version of NB-IoT may be one of these two versions, or the two technologies may be integrated into one version as much as possible, but several technical principles must exist, including: NB-IoT It is necessary to support the three deployment methods of Standalone, Guard Band and In Band at the same time; use 180kHz bandwidth; use OFDMA system in the downlink; use GMSK or SC-FDMA system in the uplink; technology and communication above L2 Specifications should be reused with the original LTE system as much as possible.
NB-IoT is imperative
In the future, entering the era of Internet of Everything, various back-end applications will be produced one after another. Therefore, how to fully realize these applications, as well as the operators How to get a piece of this pie? NB-IoT is undoubtedly a technology that must be promoted. Because SIGFOX or LoRa use unlicensed frequency bands, data reliability and security are a major consideration. The important thing is How operators gain benefits from it is also something that needs to be considered. NB-IoT uses the existing LTE network architecture and updates some of its equipment components to quickly enter the Internet of Things market. For the future rapid communication development and Demand, speed of construction and deployment are undoubtedly very critical considerations, and it uses authorized frequency bands, which greatly improves the security and reliability of data and can reduce many unnecessary interference problems. In this year (2016) ) is expected to finalize a version of the NB-IoT standard specification in the middle of the year, by which time we will be able to see the future development of narrow-band IoT.