What is RSSI
RSSI, Received signal strength Indication, is an important parameter in radio signals.RSSI indicates how weak the signal is at the receiving end, and it is a measure of radio energy. In the mobile network, we will measure the RSSI value of the base station or AP to calculate the distance of the cell phone, RSSI is generally expressed as a negative number, and the size of its value directly reflects the current level of signal strength.
dBm as an indicator of signal strength (reception)
On the receiving end, signal strength is usually understood as the sensitivity of the signal to the receiver. In this case, we need to remember a few basic concepts about dBm values:
This is always a negative number: we are not talking about quantity here, but about metrics. This is because 0 dBm (1 mW) means the sensitivity of the 100% - an impossible level. The actual signal level is always below 0 dBm.
Signal sensitivity ranges from 0 dBm to -128 dBm. the closer the number is to zero, the stronger the signal. For example, -30 dBm is stronger than -60 dBm.
Again, since dB and dBm don't scale like most measurements (weight, length, etc.) - they are non-linear and increasing: the difference between 30 dBm and -60 dBm may be no greater than the difference between -60 dBm and -65 dBm.
Typically, the effective dBm values on the receiving end range from -10 (strongest signal) to -90 (weakest signal).
The formula for RSSI
Received Signal (dBm) = Transmit Power (dBm) + Transmit Gain (dBi) - Free Space Path Loss + Receive Gain (dBi)
How RSSI is used for ranging
In RSSI localization, two main features are utilized:
- Signal strength decays with distance. That is, in general, when the receiving end is farther away from the transmitting end, the received signal strength attenuates. If the signal strength of a number of transmitters adjacent to the current location can be measured, the current location can be inferred from the degree of attenuation of these signal strengths.
- Wireless signals spread spherically under unobstructed conditions. Therefore, the current position can be calculated by solving the equation by measuring the signal strength of a number of transmitters adjacent to the current position.
The RSSI positioning method is more suitable for occasions that do not require a high degree of accuracy, because its positioning accuracy can generally only reach within a few tens of meters.
Positioning technology of Hainan Shidian
ZIGBEE localization technology and application of WorldTech
Label Ranging Formula
BTS accepts tag field strength as a function of distance
Measurement of the wireless signal field strength of the tag to calculate the distance between the tag and the antenna, distance and wireless signal strength for the exponential curve relationship between
There are 3 values that we need to measure and calibrate over and over again
1, L0: the signal strength when the distance between the tag and the reader is 0 cm, the measured value is -8dBm.
2、 L1: The signal strength when the distance between the tag and the reader is 40 centimeters, the measured value is -20dBm.
3, L2: label and reader distance of 100 cm when the signal strength, measured value of -30dBm
Based on these three values, the derived equation is as follows.
Due to chart size limitations, only correspondences within a distance of 6 meters are shown
Label Positioning Principle
Approximate location for installing base station measurement tags
In the warehouse, the workshop's surroundings installs the good localization base station (reads the card) to be able to measure the label's approximate position. In the effective range of each base station will get the electronic label and their own distance, according to the 2 ~ 3 closest to the electronic label of the base station's test value, may get the electronic label in the space of the approximate position. Positioning accuracy 1~3 meters
Typical Application Block Diagram
Device Access Method
Access to 32 485 readers
Access to 16 wireless card readers
Personnel positioning connection method
Motion Detection Improves Label Life
Selects "the movement detects" the working mode electronic label, the label long time does not have the movement (the default 10 minutes), the label automatically stops working. This can effectively save power, greatly prolongs the label to use the time. When the label is used as the personnel, the vehicle localization, the recommendation chooses "the movement detects" the working mode electronic label. Tag from the motion state to the stationary state of the detection time default for ten minutes (can be customized to 1 ~ 60 minutes). Stationary state tag default does not work (can be customized to work slowly, 1 ~ 60 seconds to send a). Need to customize and our customer service contact after the order!
Find labels directly with handhelds
Without a locator system installed, it is still possible to find a tag using only the handheld. Directly in the handheld enter the label ID, or use inventory software to send the label ID of the item to the handheld, the handheld to start looking for, you can confirm that the label is in the vicinity of the label to confirm the initial location of the label, so that the handheld to send commands to activate the label, through the sound and light reminder can be easily find the label. Methods are as follows:
Turn on the handheld, enter the "Find" page, enter the corresponding label code, click the "Start" button, you can find whether the label is nearby. If you find the label in the vicinity, the handheld will display the actual distance between the label and the handheld, you can judge the distance value of the label near and far, to quickly determine the label in which area, to improve the efficiency of the search for items.
The found tag glows (blinks continuously) to remind the user of the tag's location. If you still can't find it, you can click the horn button at the bottom right, the tag will beep, beep, beep, beep, beep, beep, beep to make you find the tag more conveniently.
Products
Card reader and base station
ZigBee Base Station
RFID Location Tag/Reader Module
RFID Location Tag/Reader Module
ZigBee
ZigBee Base Station
ZigBee Base Station
ZigBee Base Station
ZigBee Base Station
Provide card readers and base stations adapted to different industries, coverage radius: 100m; average power consumption: <5W; power supply: 12V
tab (of a window) (computing)
AOA Labeling
AOA Labeling
AOA Labeling
AOA Labeling
AOA Labeling
AOA Labeling
With different sizes of labels to suit different needs, low power consumption, long distance, sound effects, LED brightness, tamper-proof, waterproof and other different features
software and interfaces
Free software; Win7 /Win 10/Win Server 2012 R2; and open interfaces for your applications to call
Industry Application Notes
Production management system call tags
The label positioning function is implanted into the production management system, the management system can not only know the location of the label, if necessary, you can directly call the label, so that the label luminous, sound, through the sound and light reminder to easily determine the location of the items, the production process is more accurate and efficient.
The production management system sends the call command to the tag positioning system, the tag positioning system according to the current location of the tag, the closest base station (reader) to the tag to send call commands, the called tag sends sound and light reminders.
Hospital equipment asset management
Hospital asset management includes: ① general office equipment, refers to commonly used office and business equipment; ② special equipment, refers to all the equipment belonging to the hospital specifically for a particular job; ③ medicines and displays and other management. These items are many and varied, manual management is time-consuming and laborious, and each inventory is prone to errors!
The use of ZIGBEE locator tags and readers from WorldTech, combined with the software process can be paired with a complete system.
More information
Personnel time and attendance clocking system
Many factories and enterprises for security needs, the requirements of the work period shoulder allowed to carry a cell phone into the workplace, but also need information timely and accurate sent to the staff; World Power customers developed LCD tags, specifically for personnel attendance and smart clocking function; the whole system can provide senseless clocking, track replay, personnel call, danger notification; and provide data interfaces, the customer can be realized and WeChat data interoperability; so that users can receive SMS messages from WeChat on the label.
Warehouse Management System
Warehousing goods 3 meters accurate positioning system using zigbee networking technology, based on zigbee technology to achieve precise positioning of personnel card, positioning accuracy of up to 1-5 m. System coverage, a single base station can achieve 100m signal coverage, and can support infinite base station cascade, to adapt to a variety of warehouse conditions layout requirements
More information
Tunnel Site Management System
During the construction of tunnel projects, safety management is always a great concern for all construction units; based on its own ZIGBEE positioning technology and UWB positioning technology, World Power provides a variety of cost-effective solutions for tunnel projects; the implemented cases have been fully verified and have received good feedback from customers in terms of personnel clocking, statistics of personnel figures, and process monitoring.
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