LoRa positioning, how LoRa achieves positioning

How does LoRa achieve positioning? As a narrowband wireless technology, LoRa uses Time Difference of Arrival (TDOA) to achieve geographical positioning. According to Machina Research, there will be more than 1.5 billion connected devices in the Internet of Things by the end of 2020. About one-third of these will rely heavily on geographic data, and 60% of applications will likely include geographic data. Especially some applications such as asset tracking. Let’s take a look at how it is implemented.

1. LoRa positioning principle

To understand how LoRa positioning works, it is necessary to look at the data transmission steps from the end node to the server. The premise of LoRa positioning is that all base stations or gateways share a common time base, which is very important.

When any LoRaWAN terminal device sends a data packet, it will be received by all gateways within the network range, and each packet will be reported to the network server. All gateways are the same, they receive signals at all data rates on all channels all the time. This means there is no overhead on LoRa end devices as they do not need to scan and connect to a specific gateway. The sensor simply wakes up, sends a packet, and all gateways within the network range can receive it.

All gateways send the same packets they receive to the network server, capturing high-precision arrival times using specialized hardware and software built into the latest generation of gateways. Algorithms on the network server side compare arrival time, signal strength, signal-to-noise ratio and other parameters to calculate the most likely location of the end node. In the future, we look forward to hybrid data fusion technology and map matching enhancement to improve arrival time differences and improve positioning accuracy.

In order for the geolocation to be more accurate, at least three gateways are required to receive the packets. More gateways and a denser network will improve positioning accuracy and capacity. This is because when more gateways receive the same packet, the server algorithm gets more information, thus improving geolocation accuracy.

A new generation of hardware is needed inside the LoRa gateway to calculate some parameters used in geolocation, such as high-precision arrival time. Semtech created a reference design for the new version of the gateway in early 2016, which was successfully implemented in many gateways. The reference design includes the required high-quality timestamping capabilities and is available to authorized gateway partners. This ensures that multiple vendor deployments work consistently to provide high-quality timestamps, enabling the highest quality geolocation services.

It’s important to note that geolocation relies entirely on gateway and network technology, so once the gateway is upgraded, geolocation functionality will be available to all devices

Semtech also provides a geolocation solver program. The general solver is not a dedicated application and is independent of the end node, which provides a good start for LoRa geolocation services. Additionally, an API has been defined that allows system integrators to use third-party solving algorithms that may improve the available position accuracy. Through this open model, Semtech encourages innovation and development of solution technology to ensure continuous improvement of LoRaWAN-based geolocation.

When a packet reaches the gateway, it does not know which end device the packet came from. Therefore, the gateway timestamps each received packet and forwards it to the server. Because access to geolocation services is valuable, these timestamps are protected via encryption in the gateway. The timestamp is transmitted to the network server and Semtech authorizes the decryption function to the network service provider. The web server provider can decrypt the data depending on the service level subscribed to.

One of the biggest difficulties in providing good location is reducing multipath transmission. As shown in the figure below, some data packets go directly to the gateway, some data packets do not but have a reflected signal, and other data packets have both situations. Reducing multipath transmission by using more packet transmissions can be through more channels, more gateways, more antennas, and using machine learning or statistical techniques.

2. Characteristics of LoRa positioning

LoRa Geolocation is a GPS-less solution for low power wide area networks. As a major enhancement to the LoRa wireless RF platform, Semtech’s LoRa geolocation solution will enable applications requiring location determination as part of an overall solution.

This new capability is supported by existing LoRa end nodes, eliminating additional costs and requiring no additional processing power while maintaining optimal security of data and location.

LoRaWAN™ sensors can now support tracking applications by using time difference of arrival technology to determine the location of proximity.

lowest power consumption

· No processing of position tasks in the sensor

· No “air time” required to send location data

· Possibility to use the smallest possible LoRaWAN packets for geolocation

lowest cost

· No GNSS or other hardware in the sensor

· Smaller battery since sensor power is not used to obtain position

· Minimum size, including electronics, battery, casing

minimal environmental impact

· Minimize sensor hardware (including electronic parts, battery, housing size, etc.)

· Many sensors come with a lifetime battery

3. Controllable parameters of LoRa positioning

Frequency Diversity: By repeating a message on all available channels, geolocation results are improved by 50% on average. A static end node working on an 8-channel network will improve its results by 50% by sending 8 packets on 8 different channels.

The shape of the deployment gateway mesh. The impact of gateway deployment grid is about 25%. A long fine mesh will perform 25% worse than a square mesh. Therefore, network deployment should focus as much as possible on deploying gateways in a square pattern.

Gateway Diversity: Generally speaking, the more gateways that receive the signal, the more accurate the results. However, beyond 6 gateways, the geolocation improvements start to become less noticeable. At 3 to 4 gateways, there is about a 25% improvement, and beyond 4 gateways the geographical location improvement starts to decrease.

Antenna diversity affects the weakest signals the most. So if a device is in a position with good reception on 3 gateways, adding a weak 4th gateway, the antenna diversity will usually change the packets received on the 4th gateway from unavailable to available. In this case, it can provide a 25% location improvement.

The above is the relevant introduction about ” LoRa Positioning “, I hope it will be helpful to you! LoRa is one of the LPWAN communication technologies. It is an ultra-long-distance wireless transmission solution based on spread spectrum technology adopted and promoted by the American Semtech Company. This solution changes the previous trade-off between transmission distance and power consumption, providing users with a simple system that can achieve long distance, long battery life, and large capacity, thereby expanding the sensor network. Currently, LoRa mainly operates in free frequency bands around the world, including 433, 868, 915 MHz, etc.