CSIRO RTI Series (4): Device Application and Scheduling Design

Device Application Design for RTI

There are two firmware roles in this RTI system:

1. Normal node: broadcasts packets and measures RSSI.
2. Master node: schedules nodes and collects raw RSSI data.

The master sends command packets to control each node’s broadcast interval and iteration count.

A key challenge is radio interference. RTI heavily relies on RSSI quality, so simultaneous transmissions can corrupt measurements. To avoid this, I introduced a time-slot schedule where only one node broadcasts in each slot.

Example schedule (N=5 nodes, iteration=3):

In each slot:

• The master issues a command (control plane)
• The selected node broadcasts 3 times (data plane)
• Payload includes RSSI summaries from the previous cycle

Example payload:

N 3 -46 -45 -43 0 -43

Meaning:

• N: normal packet type
• 3: node ID
• Remaining values: average RSSI from each peer
• 0: self-link placeholder (node3 → node3)

Source code (original project):

• Normal node: https://github.com/generousRocky/radioTomography/tree/master/contiki-examples/radio_tomography
• Master node: https://github.com/generousRocky/radioTomography/tree/master/contiki-examples/rti_mater

2026 Update Note

• Migrated and language-polished in 2026.
• The time-slot scheduling design is still the key practical lesson: measurement quality collapses when concurrent transmissions are not controlled.
• This approach can be generalized to other low-power sensing networks where signal quality is central to inference.