According to the relevant requirements of my country's radio management, it is clear that the base station of the NB-IoT system should go to the local radio management agency for the approval of the station establishment and obtain the radio station license. At the same time, according to the technical conditions of station coexistence, specific requirements are put forward for the setup of the base station of the NB-IoT system in the 800MHz and 900MHz frequency bands.
The frequency is 800MHz and 900MHz, see the picture to know the range of use. It is roughly equivalent to the frequency of a 3G signal. The frequency of a 4G signal must reach 2000MHz. The higher the frequency, the shorter the wavelength, and the shorter the transmission distance. That is why the mobile phone far away from the base station does not have a 4G signal but has a 2G signal.
Does NB-IoT support base station positioning? R13 does not support base station positioning, but the operator's network can make private solutions, such as cell ID-based positioning, which will not affect the terminal. It only requires the network to add a positioning server and contact the base station. R14 plans to do positioning enhancements to support E-CID, UTDOA or OTDOA. The positioning accuracy goal that operators hope is within 50 meters.
From the perspective of terminal complexity, UTDOA is better because it has almost no impact on the terminal, and in the case of coverage enhancement (164dB in the basement), UTDOA (uplink) power consumption is lower; if coverage enhancement is not required in most scenarios, from the network From a capacity point of view, OTDOA (downstream) will be better.
To effectively transmit radio waves, the frequency of the radio waves is required to have a certain relationship with the length of the transmitting antenna. The lower the frequency, the longer the transmitting antenna is required. The frequency of the sound is 20Hz～20kHz, the frequency of the audio signal converted from the sound by the microphone is also 20Hz～20kHz, and the frequency of the radio wave converted from the audio signal by the antenna is also 20Hz～20kHz. If you want to effectively transmit such low-frequency radio waves To go out, the length of the antenna is required to be several kilometers to several kilometers, which is extremely difficult.
800MHz is enough to use the current 2G/3G/4G base station antennas, so operators and shared bicycles are all engaged in NB-IoT.
Regarding the coverage of NB-IoT base stations:
NB-IoT has a gain of 20dB higher than LTE and GPRS base stations, and is expected to cover underground garages, basements, underground pipelines and other places where signals are difficult to reach. According to the simulation test data, in the independent deployment mode, the coverage of NB-IoT can reach 164dB, and the in-band deployment and guardband deployment have yet to be simulated and tested.
NB-IoT and LoRa communication distance comparison:
NB-IoT communication distance: The signal coverage of the mobile network depends on the base station density and link budget. NB-IoT has a link budget of 164dB, GPRS has a link budget of 144dB (TR 45.820), and LTE has a link budget of 142.7dB (TR 36.888).
Compared with GPRS and LTE, the NB-IoT link budget has been increased by 20dB, and the signal coverage of the open environment can be increased by seven times. 20dB is equivalent to the loss of the signal penetrating the outer wall of the building, and the signal coverage of the NB-IoT indoor environment is relatively good. Generally, the communication distance of NB-IoT is 15km.
LoRa communication distance: LoRa provides a maximum link budget of 168dB and a power output of +20dBm with its unique patented technology. Generally, the wireless distance range is 1~2 kilometers in the city, and the wireless distance can reach up to 20km in the suburbs.
What is the concept of the wireless distance up to 20km in the suburbs? I'll take a screenshot for everyone who is not very professional, probably from the city center to outside the Fifth Ring Road.
Relay of NB-IoT and LoRa
In the actual network deployment, the wireless network signals of NB-IoT and LoRa will have areas that cannot be covered, which can be called signal "blind areas". If the "blind areas" are covered by multiple base stations to achieve signal coverage, it will inevitably cause The cost of network construction is relatively high. This requires a low-cost "relay" product to expand and extend the network to complete the "blind zone" signal coverage.
It is understood that the China LoRa Application Alliance (CLAA) used MCU and SX1278 to make a relay to achieve low-cost signal coverage in "blind spots".
In fact, it is just a simple electromagnetic wave emission, or an old modulation and demodulation technology, but less data transmission and reception, low power consumption, nothing new. Noisy, but the standard is not set.
In addition, add other knowledge:
The process of loading low-frequency signals onto high-frequency signals is called modulation. There are two common modulation methods: amplitude modulation (AM) and frequency modulation (FM).
â‘ AM modulation. The low-frequency signal and the high-frequency carrier signal are processed in a certain way to obtain a high-frequency signal with the same frequency but with the amplitude changing with the low-frequency signal. This process is called amplitude modulation. This high-frequency signal whose amplitude changes with the low-frequency signal is called an amplitude-modulated signal.
â‘¡ FM modulation. The low-frequency signal and the high-frequency carrier signal are processed in a certain way to obtain a high-frequency signal whose amplitude is unchanged but the frequency changes with the audio signal. This process is called FM modulation. This high-frequency signal whose frequency changes with the audio signal is called a FM signal.
Modulation and demodulation technology adopted by NB-IoT:
The downlink adopts OFDMA, and the sub-carrier spacing is 15kHz. The uplink adopts SC-FDMA, Single-tone: 3.75kHz/15kHz, Multi-tone: 15kHz. Only need to support half-duplex, with a separate synchronization signal. The terminal supports instructions for Single-tone and MulTI-tone capabilities. The MAC/RLC/PDCP/RRC layer processing is based on the existing LTE procedures and protocols, and the physical layer is optimized.
Cellular Internet of Things (NB-IoT) has low power consumption and wide coverage, suitable for many IoT industry applications
2017 is called the first year of commercial use of narrowband IoT by the industry. With the strong support of the government, the cellular Internet of Things (NB-IoT) has become an important strategic industry direction in various regions.
NB-IoT advantages
1) Large link: In the case of the same base station, NB-IoT can provide 50-100 times the number of accesses than existing wireless technologies. One sector can support 100,000 connections.
2) In-depth coverage: NB-IoT has strong indoor coverage capabilities, with a gain of 20dB higher than that of LTE, which is equivalent to a 100-fold increase in coverage area capabilities. Not only can it meet the wide coverage needs in rural areas, but it is also suitable for applications that require deep coverage such as factories, underground garages, and manhole covers.
3) Low power consumption: NB-IoT can achieve longer standby time with PSM (Power Saving Mode) and eDRX. Among them, PSM technology is a newly added function in R12. In this mode, the terminal is still registered on the network but the signaling is unreachable, so that the terminal stays in deep sleep for a longer time to save power. eDRX is a newly added function in R13, which further extends the sleep period of the terminal in idle mode, reduces unnecessary startup of the receiving unit, and greatly improves the downlink reachability compared to PSM.
4) Low cost: Compared with LoRa, NBIoT does not need to rebuild the network, and the radio frequency and antenna are basically multiplexed. The simultaneous deployment of GSM/UMTS/LTE and NB-IoT can be carried out directly. The expected price of the module does not exceed $5.
Due to its outstanding characteristics such as wider coverage, more connections, lower cost, and less power consumption, this type of "smart parking, smart meter reading, smart street lights, smart buildings, smart buildings, etc., based on cellular Internet of Things (NB-IoT) technology" Agriculture..." and other smart applications will be more widely used in the field of Internet of Things, playing an increasingly important role in improving the efficiency and quality of the people's production and life.
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