LoRa Network Architecture: LoRaWAN

LoRa Network Architecture: LoRaWAN

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The LoRa network utilises a telecommunications network called LoRaWAN that provides the routing of the data from the end node via a LoRaWAN gateway to the required entities. LoRaWAN also defiens the way in which data is sent around the network, detailing the responses of the LoRaWAN gateways, and the LoRa network server.

In the same way that a cellular network has a wired network or core network, so too does LoRa which is often referred to as LoRaWAN.

LoRa network architecture

A LoRa network consists of several elements:

  • End points: The endpoints are the elements of the LoRa network where the sensing or control is undertaken. They are normally remotely located.
  • LoRa gateway : The gateway receives the communications from the LoRa endpoints and then transfers them onto the backhaul system. This part of the LoRa network can be Ethernet, cellular or any other telecommunications link wired or wireless. The gateways are connected to the network server using standard IP connections. On this way the data uses a standard protocol, but can be connected to any telecommunications network, whether public or private. In view of the similarity of a LoRa network to that of a cellular one, LoRaWAN gateways may often be co-located with a cellular base station. In this way they are able to use spare capacity on the backhaul network.
  • LoRa Network Server: The LoRa network server manages the network and as part of its function it acts to eliminate duplicate packets, schedules acknowledgement, and adapts data rates. In view of the way in which it can be deployed and connected, makes it very easy to deploy a LoRa network.
  • Remote computer: a remote computer can then control the actions of the endpoints or collect data from them - the LoRa network being almost transparent.

In terms of the actual architecture for the LoRa network, the nodes are typically in a star-of-stars topology with gateways forming a transparent bridge. These relay messages between end-devices and a central network server in the backend.

Communication to end point nodes is generally bi-directional, but it is also possible to support multicast operation, and this is useful for features such as software upgrades and the like or other mass distribution messages.

LoRaWAN endpoint classes

There are many different needs to LoRa endpoints. Accordingly the LoRaWAN supports three classes of endpoints:

  • Class A - bi-directional end-devices:LoRaWAN class A endpoint devices provide bidirectional communications. To achieve this, each endpoint transmission is followed by two short downlink receive windows. The transmission slot scheduled by the particular endpoint is based upon the needs of the end point and also there is a small variation determined using a random time basis.

    LoRa Class A operation provides the lowest power option for end points that only require downlink communication from the server shortly after the end-device has sent an uplink transmission. Downlink communications from the server at any other time wait until the next scheduled uplink time.

  • Class B - bi-directional end-devices with scheduled receive slots:LoRa Class B devices provide the Class A functionality and in addition to this they open extra receive windows at scheduled times. To achieve the required synchronisation from the network, the endpoint receives a time synchronized Beacon from the gateway. This allows the server to know when the end-device is listening.
  • Class C - bi-directional end-devices with maximal receive slots:LoRa Class C devices provide nearly continuously open receive windows. They only closed when the endpoint is transmitting. This type of endpoint is suitable where large amounts of data are needed to be received rather than transmitted.

LoRa messaging

When messages are transmitted over the LoRaWAN network by an end devices, it is received by all LoRa base stations that are in range. This capability enhances the resilience of the network, improving the number of messages that are successfully received.

Although having multiple LoRa base stations in an area increases the deployment capital expenditure, it does improve performance and when planning a network a trade-off needs to be made between performance and cost.

The redundant or multiple reception instances are filtered in the network by the LoRa server, and this also provides message security checking.

The LoRa server also sends acknowledgments to the end device, as well as sending the message to the corresponding application server.

In addition to all of this, the LoRa server is also able to provide location information about the end devices. It uses a technique called TDOA, time difference of arrival and this can be achieved because there is very accurate time synchronisation between the different base stations.

The capability of the LoRa network to accommodate the multiple reception of the same messages by different base stations also aids in handover between base stations if the node is mobile.

LoRa network security

The issue of network security is becoming increasingly important. As such LoRa networks require high levels of security to prevent disruption of any systems.

To achieve the required levels of security for LoRa networks, several layers of encryption have been employed:

  • Unique Network key (EUI64) and ensure security on network level
  • Unique Application key (EUI64) ensure end to end security on application level
  • Device specific key (EUI128)

Employing these layers of encryption ensures that the LoRa network remains sufficiently secure.

The LoRaWAN network provides the required connectivity, enabling the LoRa end points to pass data over the wireless interface to the gateway and then on to the required destination.

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