05/13/2021 at 06:22 •
RSSI(Received SignalStrength Indication) ranging is the strength indication of the received signal.A positioning technique that can be calculated by measuring the distance between the signal point and the receiver point by the signal strength and weakness received.
RSSI requires higher parameters for communication channels. The distance measurement theory is based on the principle that the signal power is attenuated by the distance transmitted by radio or sound waves.The distance between the nodes can be calculated by the attenuation model between the signal and distance based on the transmitting power of the beacon node and the signal power received by the node.However, due to distance and obstruction, the power intensity of the signal is attenuated, which indirectly affects the accuracy. It is important to understand that each distance measurement has its advantages and disadvantages.
- Advantages of RSSI Distance Measurement Mode
- The power consumption of RSSI distance measurement was lower.
- The cost of RSSI distance measurement is low compared with TOF distance measurement. It is not affected by transmitting delay and antenna delay. The hardware cost, software cost and time cost are relatively low.
Easy to use.In general, it is a function of commercial wireless transceiver chips to calculate receiving wireless signal strength.
2. Restrictions on RSSI Distance Measurement
- Environmental factors. The accuracy of distance measurement is influenced by obstacles, weather and non-range signals.For example, the energy of electromagnetic waves is attenuated if there are obstacles on both sides, especially metal ones.
- Signal energy instability due to radio channel multidiameter decline
- The measurement accuracy is influenced by antenna orientation and antenna gain.
In general, RSSI distance measurement is suitable for situations where the environment is empty and the environment is less disturbing. It is the only way to improve communication quality and reduce background noise.In practical environment, RSSI is mainly used in short distance measurement and indoor positioning.
TOF range measurement
TEF is called Time of Flight. TEF distance measurement is a method of flight time measurement. Traditional techniques include Two Way Ranging and one Way Ranging. The TOF distance measurement method is Two Way Rangin technology, which uses signal time between two transceivers to measure the distance between nodes.
Advantages of TOF Range
- The method of TOF distance measurement is two-way ranging, which reduces the error of distance measurement compared with one-way rang measurement.
- TOF distance measurement is dependent on flight time. Time measurement accuracy does not vary significantly with increasing test distance. The performance is more stable and the distance can be accurately measured is greater.
Error analysis of TOF distance measurement
1. The interval between wireless transceiver and wireless transmission is very short.In the TOF range measurement scheme, distance measurement depends on time measurement, but a small time error of up to 300,000 km/s can result in a larger distance error, so the exact distance required for the timing system of the transceiver and transceiver is also very high.
2. Time delay. Time delay includes sending delay, receiving delay, and antenna delay."When distance-measuring signals are processed and modulated by digital and analog signals, transmission and reception over the radio can result in some delay errors."Antenna transmitting/receiving signals may not be uniform because the delay in one radiation direction may be different from the other, and the delay time of different antennas may vary due to the quality of the antenna.
3. Multichannel refers to the phenomenon in which the transmitter is reflected and diffracted from the transmitter to the receiver.This effect becomes serious when there is an obstacle between the transmitter and the receiver....Read more »
05/11/2021 at 08:15 •
LoRaWAN is supported by the LoRa Alliance, an open non-profit association composed of more than 500 members. Its members work closely together and share experiences, promote and promote the success of the LoRaWAN protocol, and become the leading and open global standard for secure, carrier-grade Internet of Things LPWAN connections.
NB-IoT is supported by two telecommunications standards associations, 3GPP and GSMA, both of which have the same goal of promoting the interests of mobile networks and equipment.
LoRaWAN is optimized for ultra-low power consumption and remote applications. Therefore, network operators and equipment manufacturers can access the networks running on the license-free ISM Sub-1GHz spectrum for free.
NB-IoT uses a cellular spectrum network, which is optimized for spectrum efficiency. The licensing fee for frequency band usage is very high, and it is limited to a few operators.
3. Deployment status
According to the LoRa Alliance, 83 public network operators in 49 countries are currently using LoRaWAN, and more private companies are also using LoRaWAN networks.
GSMA is an organization representing the interests of NB-IoT, LTE and other mobile networks. According to it, 40 countries will launch NB-IoT networks in the future.
4. Deployment options
LoRaWAN network provides highly flexible deployment. It can be installed in a public, private, or mixed network, indoor or outdoor. LoRaWAN signals can penetrate into urban infrastructure, and each gateway can cover 30 miles (approximately 48.3 kilometers) in an open rural environment.
NB-IoT uses LTE cellular infrastructure, which is an outdoor public network and requires the deployment of 4G/LTE cellular towers. If the sensor exceeds the coverage area of the base station, the base station is not easy to move.
The LoRaWAN protocol sends data asynchronously, and the data is sent only when needed. This can extend the battery life of the sensor device up to 10 years, and the battery replacement cost is low.
NB-IoT needs to maintain a synchronous connection to the cellular network, regardless of whether it needs to send data. For sensor devices, it consumes a long battery life, resulting in high battery replacement costs, which may be too costly in many applications.
6. Emission current
LoRaWAN provides 18 mA emission current at 10 dBm, and 84 mA emission current at 20 dBm. Modulation differences can enable LoRaWAN to support very low-cost batteries, including button batteries.
The NB-IoT sensor consumes ~220 mA at 23 dBm and 100 mA at 13 dBm, which means that it needs more power to operate and requires more frequent battery replacement or a larger capacity battery.
7. Receive current
LoRaWAN provides lower sensor BOM cost and battery life for remote sensors. The receiving current is about 5 mA, and the overall power consumption is reduced by 3-5 times.
The NB-IoT receiving current is about ~40 mA. The communication between the cellular network and the device consumes more than 110 mA on average, and a communication lasts for tens of seconds. The protocol overhead has a significant impact on the battery life of devices that need to work for 3, 5, or 10 years or more.
8. Data rate
LoRaWAN data rate is about 293 bps-50 kbps. The LoRaWAN protocol dynamically adjusts the data rate according to the distance between the sensor and the gateway, thereby optimizing the air time of the signal and reducing conflicts.
The peak data rate of NB-IoT is about 250 kbps, which is more suitable for use cases with higher power budget and higher data rate (above 50 kbps).
9. Link budget
LoRaWAN's MCL signal varies according to regional regulatory restrictions. The link budget is between 155 dB and 170 dB.
NB-IoT needs to repeat remote sensors at a low bit rate in order to be able to support remote sensors. The link budget is up to 164 dB.
LoRaWAN can support mobile sensors to track the...Read more »
05/11/2021 at 07:05 •
01 What is MCU?
MCU is a PC-like chip. It is not a chip that completes a certain logic function, but integrates a computer system into a chip; it is just not as powerful as a PC, but it can Embedded in other equipment to control it.
In a word: a chip becomes a computer The multi-computer application system of the single-chip microcomputer can be divided into a function collection system, a parallel multi-computer processing and a local network system.
It is small in size, light in weight, and cheap in price, which provides convenient conditions for learning, application and development.
At the same time, learning to use a single-chip microcomputer is the best choice to understand the principle and structure of the computer.
The use of MCU has been very extensive, such as smart meters, real-time industrial control, communication equipment, navigation systems, household appliances, etc.;
01 What is ARM
ARM is a well-known company in the microprocessor industry and has developed RISC processors, related skills and software.
ARM can be considered as the name of a company or as a general term for a class of microprocessors. This article mainly refers to the first RISC microprocessor designed for the low-computing market with the ARM architecture.
The ARM core is an embedded system. The instructions, registers and pipeline features of the RISC architecture make it very suitable for parallel computing
Low power consumption, energy saving, high functionality, 16-bit/32-bit dual instruction set, low price, and many partners; Rich embedded on-chip resources;
Most of the application areas are small household appliances and terminal equipment;
01 What is DSP
DSP is a unique microprocessor, a device that uses digital signals to process a large amount of information. It not only has programmability, but also runs at a speed of tens of millions of complex instruction programs per second, far exceeding general-purpose microprocessors. The device is an increasingly important computer chip in the digital electronic world.
Powerful data processing capability and high operating speed
At present, the main applications of DSP applications are graphics and images, instrumentation, automatic control, medical, household appliances, signal processing, communication, voice, etc.
01 What is wireless module?
Most of the modules involved in the Internet of Things are wireless communication modules, referred to as wireless modules. The principle of the wireless communication module is to send or receive electromagnetic wave signals and convert them into information that we can understand. The role of the wireless communication module is to connect things with things, so that all kinds of Internet of Things terminal devices can realize information transmission capabilities, and all kinds of smart devices have an Internet of Things information interface. Hardware integration and software design integrate a variety of communication methods.
Low cost, short construction project period, good adaptability and good scalability.
Agriculture, security, industry, smart home, mobile payment, smart community, industrial applications, etc.
Central Processing Unit: A very large-scale integrated circuit, which is the core and control unit of a computer. Mainly interpret computer instructions and process data in computer software. Just like the human brain, it processes thousands of data. The main frequency of the CPU, the number of cores, and the cache are the three major factors that determine the computing power of the CPU. The higher the CPU frequency, the more cores, and the larger the cache, the stronger its computing power.
From the perspective of realizing operations, single-chip microcomputer, ARM, DSP can all be called CPU.
Difference between...Read more »