The data rate it uses is a function of the data rate used for the uplink transmission. ![]() The frequency used for Rx1 is a function of the uplink frequency. The second receive window following the last transmission is complete.It has received a downlink message during Rx1, or.Note: A device will not try to send another uplink message until either: This means that RECEIVE_DELAY2 = RECEIVE_DELAY1 + one second. The end device then waits one second after Rx1 closes before opening Rx2. The default delay may be region-specific, and can be changed by the network operator through the MAC command RxTimingSetupReq. The default delay for Rx1 ( RECEIVE_DELAY1) is a network parameter found in the LoRaWAN Regional Parameters document from the LoRa Alliance®. The following diagrams illustrate the different receive window state possibilities. Rx2 typically begins two seconds after the end of the uplink transmission, though this duration is also configurable. Typically, this delay is one second, however this duration is configurable. The start time of Rx1 begins after a fixed amount of time following the end of the uplink transmission. Receive Windowsįollowing an uplink, a Class A end device opens a short receive window (Rx1) and, if no downlink is received during that period, it opens a second receive window (Rx2). This design is specifically geared toward applications that require downlink communication in response to an uplink, or that can schedule downlinks ahead of time with fairly loose latency requirements. The key characteristic of Class A is that communication is initiated only by the end device.ĭownlink messages from the network server are queued until the next time an uplink message is received from the end device and a receive window (Rx) is opened. In this type of network, end devices are allowed to transmit arbitrarily. The LoRaWAN protocol relies on an Aloha-type network. In this paper, we take an in-depth look at Class A end devices. ![]() To illustrate the different levels of power consumption for each of the different end-device classes, see Figure 3.įigure 3: Energy Consumption by Device Class These devices are more energy-intensive, and usually require a constant power source, rather than relying on a battery. They constantly listen for downlink messages from the network, except when transmitting data in response to a sensor event. A periodic beacon signal transmitted by the network allows those end devices to synchronize their internal clocks with the network server.įinally, Class C (“Continuous”) end devices never go to sleep. In contrast, rather than only waiting for one of its sensors to notice a change in the environment or fire a timer, Class B end devices also wake up and open a receive window to listen for a downlink according to a configurable, network-defined schedule. Class A is the most energy efficient and results in the longest battery life. After the device sends an uplink, it “listens” for a message from the network one and two seconds after the uplink ( receive windows) before going back to sleep. ![]() Basically, they can wake up and talk to the server at any moment. Because LoRaWAN is not a “slotted” protocol, end devices can communicate with the network server any time there is a change in a sensor reading or when a timer fires. Class A end devices spend most of their time in sleep mode. The more energy efficient a device, the longer the battery life.Īll end devices must support Class A (“Aloha”) communications. ![]() The class also determines a device’s energy efficiency. While end devices can always send uplinks at will, the device’s class determines when it can receive downlinks. End devices send data to gateways ( uplinks), and the gateways pass it on to the network server, which, in turn, passes it on to the application server as necessary.Īdditionally, the network server can send messages (either for network management, or on behalf of the application server) through the gateways to the end devices ( downlinks).Įnd devices in a LoRaWAN network come in three classes: Class A, Class B and Class C. An In-depth look at LoRaWAN® Class A Devices IntroductionĪ LoRaWAN®-based network is made up of end devices, gateways, a network server, and application servers.
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