Note: This article is reproduced from twowinter’s learning station.
This article is a popular science introduction to LoRaWAN. You may have seen countless superficial articles about LoRaWAN in your social circles, but it’s time for some real technical insights. We will first horizontally introduce the forces behind LoRaWAN and its network deployment, then vertically explain the network architecture and specific protocol content to help LoRa practitioners systematically understand the LoRaWAN protocol.
LoRaWAN is designed as a communication protocol and system architecture for long-distance communication networks based on LoRa.
Additionally, the official document provides a somewhat technical protocol hierarchy diagram for readers to get a general sense.
In the design of the protocol and network architecture, LoRaWAN fully considers several factors such as node power consumption, network capacity, QoS, security, and the diversity of network applications. The following content will provide a deeper understanding of the introductory section.
LoRa Alliance
The NB-IoT, which has a love-hate relationship with LoRa, comes from the global standardization organization 3GPP, composed of the well-known ETSI (European Telecommunications Standards Institute), Japan’s ARIB (Association of Radio Industries and Businesses), TTC (Telecommunication Technology Committee), CCSA (China Communications Standards Association), Korea’s TTA (Telecommunications Technology Association), and North America’s ATIS (Alliance for Telecommunications Industry Solutions), among others.
Compared to the well-established 3GPP, the LoRa Alliance behind LoRaWAN has a somewhat weaker influence. From the cover of the protocol, we can see that the authors come from three board member companies: N. Sornin (Semtech), M. Luis (Semtech), T. Eirich (IBM), T. Kramp (IBM), O.Hersent (Actility).
We know that the promotion of every technology is accompanied by the driving of interests. Although organizations and alliances are non-profit organizations, the member companies are not solely focused on public welfare. From a business perspective, spending $50,000 on an investment is inevitably aimed at leveraging at least $500,000 in returns.
The LoRa Alliance was founded in the first half of 2015 by several manufacturers including Cisco, IBM, and Semtech. As of now (April 2017), there are over 400 members, including many large enterprises among the board members, all working together to share the future low-power wide-area network cake. I have created a table collecting 19 board members willing to pay a $50,000 membership fee, and you can see their aspirations.
LoRaWAN Network Deployment Status
After binding with several major telecom operators, the network deployment situation is relatively promising. According to the current official statement (April 2017), the network deployment situation is as follows:
34 publicly declared deployed networks, with at least 150 ongoing city pilot deployments.
LoRaWAN Network Architecture
Having understood that LoRaWAN is quite popular, we will now look at it from a technical perspective. Below is the network architecture diagram from the official white paper of the LoRa Alliance.
We can see that a LoRaWAN network architecture includes four parts: terminals, base stations, NS (network server), and application servers. The topology between base stations and terminals adopts a star network due to the long-distance characteristics of LoRa, allowing single-hop transmission. In the terminal section, the official lists six typical applications, and a detail to note is that terminal nodes can simultaneously send data to multiple base stations. The base stations then forward the LoRaWAN protocol data between the NS and the terminals, carrying the LoRaWAN data over LoRa RF transmission and TCP/IP.
Next, combining with the industry ecosystem, we will take a closer look at this network architecture. The diagram comes from ST’s LoRa white paper “IoT Connectivity Made Easier STM32 MCUs & LoRa”.
Protocol Overview
5.1 Classification of Terminal Nodes
In the introduction, we see that the protocol specifies three types of terminal devices: Class A/B/C, which basically cover all application scenarios in the Internet of Things.
For convenience, I have also created a table.
5.2 Up and Down Link Transmission of Terminal Nodes
Now let’s look at some timing diagrams for a deeper understanding.
This is the timing diagram for Class A up and down links, where the RX1 receive window generally starts 1 second after the uplink, and the RX2 receive window starts 2 seconds after the uplink.
Class C is basically the same as Class A, except that during the sleep period of Class A, it opens the RX2 receive window.
Class B has a more complex timing, with a synchronization beacon slot and a fixed-period ping slot. In this example, the beacon period is 128 seconds, and the ping period is 32 seconds.
5.3 Network Joining of Terminal Nodes
After understanding the basic concepts, we can learn how nodes work. Before formally sending and receiving data, terminals must first join the network.
There are two ways to join the network: Over-the-Air Activation (OTAA) and Activation by Personalization (ABP).
Commercial LoRaWAN networks generally follow the OTAA activation process to ensure security. This method requires three parameters: DevEUI, AppEUI, and AppKey.
DevEUI is a globally unique ID similar to IEEE EUI64, identifying a unique terminal device, akin to the device’s MAC address.
AppEUI is a globally unique ID similar to IEEE EUI64, identifying a unique application provider. For instance, various garbage monitoring applications, smoke alarm applications, etc., all have their unique IDs.
AppKey is assigned to the terminal by the application owner.
After initiating the join process, the terminal sends a join command. If the NS (network server) confirms it is correct, it will reply to the terminal, assigning a network address DevAddr (32-bit ID). Both parties use the relevant information in the join reply and the AppKey to generate session keys NwkSKey and AppSKey for data encryption and verification.
If the second joining method, ABP activation, is used, it is relatively simple and straightforward. It directly configures the three final communication parameters for LoRaWAN: DevAddr, NwkSKey, and AppSKey, without needing the join process. In this case, the device can directly send application data.
5.4 Data Transmission
After joining the network, application data is encrypted.
LoRaWAN specifies two types of data frame: Confirmed and Unconfirmed, i.e., requiring acknowledgment and not requiring acknowledgment. Manufacturers can choose the appropriate type based on application needs.
Additionally, as mentioned in the introduction, one major consideration in the design of LoRaWAN from the outset was to support application diversity. Besides using AppEUI to categorize applications, during transmission, the FPort application port can also be used to handle data separately. The range of FPort values is (1~223), specified by the application layer.
5.5 ADR Mechanism
We know that there is a concept of spreading factor in LoRa modulation, and different spreading factors will have different transmission distances and rates, which do not affect each other.
To expand the capacity of the LoRaWAN network, the protocol has designed an Adaptive Data Rate (ADR) mechanism. Devices at different transmission distances will use the fastest data rate possible based on transmission conditions, thereby improving overall data transmission efficiency.
5.6 MAC Commands
To address network management needs, a series of MAC commands have been designed in the protocol to modify network-related parameters, such as the delay of receive windows and device rates. In practical applications, these are generally rarely involved and can be temporarily disregarded.
Regional Parameters
The LoRa Alliance has also released a supplementary document titled “LoRaWAN Regional Parameters” outside of the protocol. This document describes the specific parameters of LoRaWAN in different regions around the world. To avoid changes to the document due to the addition of new regions, the regional parameters section has been separated from the protocol specification.
This document mainly discusses the specific physical layer parameters of LoRaWAN in various regions globally. Not only are the frequency bands different, but it also details channel divisions, data rates, transmission power, maximum data lengths, etc., which all differ.
For convenience, I have created a table to summarize the overall situation.
In fact, this table also reveals an interesting point: why the parameters for South Korea are singled out, even though they are not much different from those of other Asian countries. If you recall the board member record mentioned earlier, you should know the position of SK Telecom in the LoRa Alliance. Such a high status with a little special treatment, would you say that’s too much?
Having finished introducing the above information, everyone should have a systematic understanding of LoRaWAN.
Source: twowinter’s learning station
Disclaimer: This article is a reproduced article. The purpose of reproducing this article is to share more information. The copyright belongs to the original author. If there is any infringement, please contact the editor for deletion (contact email: [email protected]).
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