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FAQ: transmission frequency
Dennis German edited this page Nov 22, 2020
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The frequency, inverse of the the interval, for the distributed firmware is different for each mode,
version | raw (highres) ms |
URL ms |
|
coded | measured | ||
2.2.2 | 1000 | ||
1.2.12 | 1000 | 500 | 508 |
1.0.1 | 1000 | 500 |
This seemingly very rapid transmission is an attempt to remediate the inherent poor percentage of sucessful packet reception of the BLE packets.
Here is a sample of packet reception times as seen by a raspberry pi zero Nothing was moving, the ruuvi and the pi were 4 meters apart, indoors. Notice the missing samples.
>hcidump -t|\ grep --line-buffered --before-context=3 --after-context=4 'addr C7:10:3C:68:24:C2'|\ egrep --line-buffered '2018|RSSI' 2018-11-07 22:54:05.340086 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -65 2018-11-07 22:54:05.840114 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -84 2018-11-07 22:54:06.342644 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -85 2018-11-07 22:54:06.850133 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -85 2018-11-07 22:54:07.355129 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -79 2018-11-07 22:54:08.364490 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -84 2018-11-07 22:54:08.866807 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -83 2018-11-07 22:54:09.376688 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -84 2018-11-07 22:54:09.880479 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -83 2018-11-07 22:54:10.385499 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -78 2018-11-07 22:54:10.884945 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -84 2018-11-07 22:54:11.891446 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -85 2018-11-07 22:54:12.393816 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -79 2018-11-07 22:54:12.900664 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -79 2018-11-07 22:54:13.402499 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -89 2018-11-07 22:54:15.421055 > HCI Event: LE Meta Event (0x3e) plen 43 RSSI: -79
Reducing the frequency has some effect on the battery lifetime, especially in harsh environments.
- Changing the frequency: As of 11/22/20 firmware version 2.5.9 stable and 3.28.13 beta the only way to vary the frequency of transmission is to modify the source (see https://github.com/ruuvi/ruuvi.firmware.c/issues/172 for ideas on that).
- Reducing the frequency to more than 5 seconds has minimal, if any, effect on battery life as it approaches self life.
- As the number of bluetooth devices in a given environment increases, it may be beneficial to reduce the frequency to avoid collisions.
- Bluetooth advertising does not provide for retransmission in the event that the receiver detects an error or misses a packet. Increasing the frequency may mitigate this by transmitting the same data multiple times.
- Ruuvi tags "radiolocially" near the receiver have a better chance of being received without error so the frequency might be reduced.
- Too many devices transmitting at a high frequency can overwhelm the gateway or other downstream facilities (for example the database).
- Some sensors, in particular humidity, have an settling time and increasing the frequency will only report the same values.
- Some conditions being observed change very slowly so decreasing the frequency may not effect the data even if some packets are lost.
- Some conditions, for example orientation (Z-axis), may change to a new value then back to a previous value and if the frequency is too slow the change will go unreported.