LoRa Water Meter knowledge learning
LoRa is the abbreviation of "Long Range", which is a chirp spread spectrum modulation wireless communication technology dedicated to long distance and low power consumption.
This solution provides users with a simple means of long-distance, low-power wireless communication. At present, LoRa mainly operates in the ISM frequency band, mainly including 433, 868, 915 MHz, etc.
LoRa is the physical layer or wireless modulation used to establish long-distance communication links. Many conventional wireless systems use Frequency Shift Keying (FSK) modulation as the physical layer because it is a very efficient modulation that achieves low power consumption. LoRa® is based on chirp spread spectrum modulation, which maintains the same low power consumption characteristics as FSK modulation, but significantly increases the communication distance.
Features of LoRa: 1. Low power consumption 2. Long distance 3. Low speed
The reason why LoRa has a long communication distance lies in the spread spectrum technology, which can effectively resist the interference of various noises and other signals, and obtain a better signal-to-noise ratio gain.
Three basic parameters of LoRa: 1. Spreading factor (SF) 2. Signal bandwidth (BW) 3. Coding rate (CR)
1. Spreading factor (SF)
LoRa uses multiple information chips to represent each bit of the payload information. The transmission speed of the spreading information is called the symbol rate (Rs), and the ratio of the chip rate to the nominal Rs is the spreading factor (SF, SpreadingFactor ), indicating the number of symbols sent per information bit.
When spreading, each bit of data must be multiplied by the spreading factor. When the spreading factor is 8, each bit of data contains 8 bits of data to represent this bit of data after spreading, so the amount of data that needs to be transmitted will vary. Increase, but this can reduce the bit error rate, the larger the spreading factor, the lower the transmission rate, but the stronger the anti-interference ability.
2. Signal bandwidth (BW)
The signal bandwidth refers to the range of the upper frequency and lower frequency that the signal can pass through. It can be understood as a channel, and only frequency signals within the signal bandwidth are allowed to pass. In LoRa, increasing the BW can increase the effective data rate, but the sensitivity will be affected accordingly.
3. Code Rate (CR)
The coding rate refers to the proportion of useful signals in the data stream. If the coding rate is 4/5, for 4-bit valid data, the actual coding parameter will be 5 bits, and the extra bit is a redundant value. Interference ability. LoRa uses cyclic error correction codes for detection and error correction.