IoT application cases of LoRa wireless technology in distance measurement and positioning

Introduction to LoRa wireless technology

LoRa wireless technology is an ultra-long-distance wireless transmission solution based on lora spread spectrum technology adopted and promoted by Semtech. It is one of the Low Power Wide Area Network (LPWAN) communication technologies. LoRa wireless technology is no longer limited by the trade-off between transmission distance and power consumption, and provides users with a system that can achieve long transmission distance, low power consumption, and multiple nodes to expand into a network.

As the audience for LoRa wireless technology grows and expands, it continues to develop. Semtech company then launched the SX1280 radio frequency chip lora solution, which means the advent of LoRa in the 2.4GHz frequency band. The chip has a built-in Ranging Engine, which is a Time Difference of Arrival (TDOA) fusion ranging engine, using the time-of-flight ranging method. Because of its low power consumption, long distance and ability to be used for precise ranging and positioning, more and more companies have followed up on this technology. For example, Chengdu Yibaite Electronic Technology Co., Ltd.’s SPI interface wireless modules E28-2G4M12S and E28-2G4M20S are based on SX1280.

Next, we briefly introduce the time-of-flight ranging method. This method is a two-way ranging technology that uses the flight time of the data signal to and from a pair of transceivers to measure the distance between two points. The time interval between the transmitter sending the data signal and receiving the receiving end's response signal is marked as Tt. The time interval between the receiving end receiving the transmitting end's data signal and sending the response signal is marked as Tr. The one-way signal between the pair of transceivers is Flight time Tf=(Tt-Tr)/2, then the distance between two points d=c*Tf, where c represents the propagation speed of electromagnetic waves.

The time-of-flight ranging method has two key constraints. The receiving end provides the length of signal transmission time, and the clocks of the transmitting end and the receiving end must be synchronized.

 Introduction to the principle of lora positioning technology

Next, we will briefly introduce the principle of LoRa positioning. LoRa technology uses the TDOA mentioned above to achieve geographical location positioning. The premise of LoRa positioning is that all LoRa gateways share the same time base, and at least 3 LoRa gateways are required to receive data signals. When a LoRaWAN terminal device transmits a data signal, all LoRa gateways within the network range will receive the signal and transmit it to the network server. The network server calculates the most likely location of the end device by comparing signal strength, arrival time, signal-to-noise ratio, and other parameters, as shown in the following figure:

Precisely because the LoRa geolocation function does not need to involve GPS positioning technology, it can achieve the smallest size, lowest power consumption, and lowest cost. At present, LoRa geolocation function is beginning to be applied to various industries and fields, such as logistics, animal husbandry, construction, insurance industry, etc. The following briefly introduces the application in animal husbandry.

The main current status of animal husbandry:

Cattle and sheep are mainly looked after manually, and labor investment costs are high;

There is no location for cattle and sheep, and cattle and sheep get lost to varying degrees every year;

Some GPS+GPRS positioning solutions are expensive and have short battery life.

Apply the LoRa geographical location function to animal husbandry to form a cattle and sheep positioning system. The cattle and sheep positioning system mainly consists of LoRa positioning module, LoRa gateway, and livestock management platform. The LoRa positioning module is mainly used for cattle and sheep, with one-to-one correspondence. Several LoRa gateways can meet the needs of large ranches. The LoRa positioning module regularly transmits data packets to several LoRa gateways, and the LoRa gateways transmit these data to the livestock management platform. The livestock management platform processes and analyzes these data through algorithms, and can view the specific location and health status of cattle and sheep. When cattle and sheep become sick, staff can rush to the location of the cattle and sheep in time to handle and treat them.

LoRa technology has been developing efficiently, which has brought about the improvement and maturity of LoRa distance measurement and positioning. I believe it will bring convenience to more fields in the future.