And how to do it for digital agriculture step by step.

We discussed about different communication options for digital agriculture in the previous article. Among few choices we have selected LoRa LPWAN.

What is the difference between GPRS and LoRa from point of view of the end user and company? Well, everything is different.

Switching from GPRS to LoRa means almost complete redevelopment of the product line. But more important is the changing of business concept.

GPRS installation is relatively plug and play and can be done by customer. LoRa needs installation of gateway, authorization of every device and adjusting of radio communication. Big network needs planning of topology. How many gateways and where need to be installed. This needs special installation engineers or education of customers. Quality of radio signal can be changed by time because of appearance of different natural and artificial obstacles such as plants or constructions.

In case of GPRS, GSM technology has taken care of all these problems.

The need of gateway
Gateway is one of the most complex and expensive parts of LoRa network. In fact it replaces GSM tower if we compare to GPRS based system. Price of industrial grade outdoor gateways easily reach 1000 USD. In agriculture, LoRa network is relatively sparse meaning we have few devices scattered over big area. This allows to use fewer gateways with less power. Assuming 2 gateways cover 10km in rural areas, it would require 2 gateways per 30000 Ha. Let’s round up and take 2 gateways per 20000 Ha.

The need of Internet connection
Gateway needs permanent Internet connection. It could be landline, 4G or WiFi. In many cases, 4G is the only available option. Many gateways already have built in 4G connectivity. I would prefer to use separate 4G router to have better control and stability. It’s very hard to beat the price and performance of Huawei 4G router.

Security considerations
One of the biggest problem of home-made wireless solutions is security. Often, data is sent totally insecurely over internet between the end devices and web platform. It is very vulnerable to any kind of attack, such as DoS or impersonating the end devices. Data of such systems cannot be considered reliable.

LoRa implements 128-bit AES1 encryption between the end device and application server, so called end to end encryption. It means data cannot be read and tampered, even if someone gains access to the gateway. This is enough for the most of cases. It is still possible to launch DoS attack on server (less likely on gateway) but this can be protected by standard means and has no relation to LoRa itself. For very demanding data or customers, VPN between LoRa gateway and server can be installed.

The need of power
Permanent Internet connection requires lot of power. Most of gateways are designed to work with power lines and not optimized for power consumption.

Typical 4G gateway would consist of LoRa gateway and 4G router.

The need of LoRa server
Contrary to what you might think, having the end device and gateway still not enough. Software of the gateway is very simple. Basically it can only forward the packets between Web server and end device converting from LoRa protocol to HTTP and back. All intelligence takes place at the servers side in a special tier called LoRa server. LoRa server has many functions to control the whole network and pass data to our application server. Among other functions, LoRa server removes duplicate packets, decides about communication channels and sending power of the nodes, stores data packets from network and server. In other words, gateway is a dummy packet forwarder between the end devices and LoRa server. This design solution has its advantages and disadvantages. It should keep the gateways simple, compatible and economical. Yet the former isn’t true by some reason. Hopefully price will drop when more products appear on market.

Because server software is very complex and not easily available, in many cases it might be better to use 3rd party commercial servers as service. There are quite many offers on market such as The Things Network and Loriot. Many new are coming. They may charge per number of gateways or end devices per months and offer different services. user application may communicate with 3rd party LoRa server via HTTP API or MQTT.

The need of MQTT

Another new player on the LoRa scene is MQTT (Message Queue Telemetry Transport). Strictly speaking it’s not a standard part of LoRa protocol and is optional. MQTT is a lite weight message broker with very small code footprint. It can be used in any system to allow message exchange between devices and software modules. Module can subscribe to MQTT broker to receive the messages from other modules as well as publish its own messages.

All existing implementations of LoRa server can exchange data with user applications via HTTP API and / or MQTT. So, what is wrong with the HTTP API and why we need MQTT? The problem is that HTTP is a server API and application must be querying it regularly to check for the arrival of the new data. This is very ineffective. We want LoRa server to push data to the user applications immediately upon arrival. This is exactly what message broker can do much more effective than HTTP API. Application subscribers for certain types of message and broker will push these messages automatically using message queue. As mentioned above, LoRa server already supports MQTT. We need to add MQTT client to our application.

Resume

This is the todo list of walking from GPRS to LoRa.

From development point of view

  1. Develop the end device with LoRa class C communication
  2. Choose a gateway suitable for your application
  3. Install LoRa server or buy subscription from 3rd party server
  4. Add MQTT support to your application

From business point of view.

  1. Add the hardware and installation cost of 1-2 gateways for every 5 km
  2. Prepare technical support department for installation and maintenance of LoRa network
  3. Find solution for permanent Internet connection. It could be, for example, 4G router with Ethernet port.
  4. Find solution for power of gateway and 4G router. In most of the cases gateway can be installed at nearest building that has power line. In special cases solar panel and rechargeable battery could be used. It should provide at least 3-10 Watt depending on gateway and router
  5. Reclaim your connectivity

Seems hard? But once the job is done it is paid back multiple times, as having our own network infrastructure allows us to deploy any kind of customized solutions quickly and with little resources.