Texas Instruments | USING THE SIMPLELINK SUB-1 GHZ 15.4 STACK: CHOOSING BETWEEN SYNC/ASYNC MODE | Application notes | Texas Instruments USING THE SIMPLELINK SUB-1 GHZ 15.4 STACK: CHOOSING BETWEEN SYNC/ASYNC MODE Application notes

Texas Instruments USING THE SIMPLELINK SUB-1 GHZ 15.4 STACK: CHOOSING BETWEEN SYNC/ASYNC MODE Application notes
Application Report
SWRA614 – October 2018
Using the SimpleLink™ Sub-1 GHz 15.4-Stack: Choosing
Between Synchronous / Asynchronous Mode
Ben Gilboa/Nick Smith
.................................................................................................. Low Power RF
ABSTRACT
The SimpleLink™ Sub-1 GHz stack solution is built on the Texas Instruments SimpleLink MCU platform,
offering a single development environment with code portability to multiple connectivity protocols. It is a
complete solution for connecting long-range, low power sensors in the home, building, and city. The
SimpleLink Sub-1 GHz stack offers a standards-based, star-network that makes Sub-1 GHz connectivity
easy by providing all of the necessary components for a robust system. Benefits of the network solution
include:
• Sub-1 GHz ISM bands provide RF advantages such as long range, wall penetration, and low power
• Future proof deployments with scalable network features
• Standards based network solution with robust performance
• Lower development cost by providing an end-to-end solution
End nodes
Ultra-low power nodes with uplink
and downlink communication with
the collector/gateway
Collector/Gateway
Central node of the star network that
offers a bidirectional link between the
end nodes and the cloud
Visit ti.com/longrange to learn more about the key network features.
The SimpleLink Sub-1 GHz stack supports both synchronous and asynchronous mode for low power star
networks that incorporate two-way communication with acknowledgements.
SWRA614 – October 2018
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Using the SimpleLink™ Sub-1 GHz 15.4-Stack: Choosing Between
Synchronous / Asynchronous Mode
Copyright © 2018, Texas Instruments Incorporated
1
Operating in Synchronous Mode
1
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Operating in Synchronous Mode
Synchronous mode enables systems to have robust two-way communication with acknowledgements and
retransmissions while maintaining low latency and low-power consumption. End nodes in the network can
sleep for the majority of the time, waking up to listen for beacons from the coordinator, while maintaining
low latency responses to incoming downstream commands.
Receiving Data
From Collector
Polling Data
Beacon
Beacon
RX
Beacon
RX
TX
ACK
RX
ACK
Receiving
Broadcast
Beacon
RX
RX
RX
Beacon Interval
Beacons
The coordinator sends periodic beacons to the nodes, which contain network information and per node
notifications on pending incoming messages buffered at the coordinator. The time between beacons is the
dominant factor in the latency calculation, and is configurable by the system designer, allowing the
flexibility to trade latency vs power consumption.
Polling
Once a node receives an incoming message notification, the node polls the coordinator asking to receive
the message. Upon the coordinator receiving the poll, the buffered message is sent downlink to the node.
Asynchronous Messages
Uplink messages from the nodes to the coordinator, such as sensor data or status messages, can be sent
at any time to an “always on” coordinator or during the coordinator active period. This time interval is
configurable for power-sensitive coordinator applications.
2
Operating in Asynchronous Mode
Asynchronous mode is used when the downlink latency is not a critical parameter of the system and the
amount of expected downlink communication is significantly lower than the uplink. The coordinator is
always on and listens to transmissions coming from the nodes, allowing the nodes in the network to sleep
for long time intervals and consume very low power.
Send Data
Pull Command
TX
Poll Command
ACK
Poll Command
TX
Polling Period
ACK
TX
TX
ACK
ACK
TX
ACK
TX
ACK
Reporting Period
Uplink Messages
When the node is ready to transmit a message (sensor data update or other status messages), it sends
the data immediately and after receiving the data the coordinator responds with an acknowledgement.
2
Using the SimpleLink™ Sub-1 GHz 15.4-Stack: Choosing Between
Synchronous / Asynchronous Mode
Copyright © 2018, Texas Instruments Incorporated
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Operating in Asynchronous Mode
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Downlink Messages
Downlink messages from the coordinator to the sensor are buffered at the coordinator until the end node
sends a "poll" packet to get incoming messages. The frequency in which the node is sending poll
commands is a critical factor in the latency and power consumption tradeoff.
3
Choosing Between Synchronous and Asynchronous Mode
Synchronous Mode
Device Type
Optimized for actuator devices when downlink
commands to the end node are latency critical.
Optimized for sensors that report to the cloud
periodically.
Downlink messages are indicated by the
beacon.
Downlink messages are buffered at the gateway
and are delivered to the sensor node upon
request.
Battery Life
Over 3 years on 2 AAA batteries with a beacon
interval of 1.2 seconds.
Over 10 years on coin cell batteries when polling
for data every 10minutes and sending sensor
updates every 20minutes.
Typical Applications
Smart electronic door lock, smart fan, shades.
Motion detectors, door and window sensors,
temperature sensors.
Downlink Messages
4
Asynchronous Mode
Get Started With the SimpleLink™ Sub-1 GHz Network Solution:
1. Buy the LaunchPad™ Development Kit
2. Download the Software Development Kit (SDK)
3. Get started with the SimpleLink™ Academy
5
Trademarks
SimpleLink, LaunchPad are trademarks of Texas Instruments.
All other trademarks are the property of their respective owners.
SWRA614 – October 2018
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Using the SimpleLink™ Sub-1 GHz 15.4-Stack: Choosing Between
Synchronous / Asynchronous Mode
Copyright © 2018, Texas Instruments Incorporated
3
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