Hello
We try to measure package loss if BLE Advertising & BLE Mesh is used in a congested environment.
(WLAN accesspoint has MIMO, 18dBm, heavy data transmitting with psping from/to an Notebook)
Is there a rule how near a (N)-WLAN Accesspoint is allowed to be placed to the BLE Scanner Device?
Or is there a calculation or table between distance to Accesspoint and signal/noise change inside the receiver (hope this is the right wording).
Thanks,
Lukas
Hello Kenneth
Sorry that i am not well trained in the right wording.
The background:
a)
We have a testsetup in our open space office. If we have holiday and no notebook is using WLAN then the reachable distance is measured and its good.
If we have a working day and many notebooks are active working with WLAN then the node which are reachable at a holiday are now no longer reachable. If we check then we see a reduction of the distance to 50% (!!)
We can`t understand why this happens...
b)
Next test:
From one Nordic node (software is casamib) to other Nordic node we transmit packages as fast as possible. In a clean environment (no other is sending on 2.4GHz) we see very less package drops (90 to 100%) of the package arrive at the receiver. The distance between the nodes is around 25m (but that is around the maximum bechause the node are inside a luminaire with plastic around and some metal in the near of the node.
If we now place an WLAN Accesspoint near the Nordic receiver device and start transfering WLAN data then the Packages which arrive the scanner Node drops dramatically. This is ok und understandable if the WLAN Frequency allocation (20MHz, OQFM, N-Type, fixed frequency) is overlapping the BLE Channel but we see the package drop on all selected wlan channels.
Eg. WLAN Cannel 1 is far away from 2480 MHz but wee see that only 35% packages arrive the receiver.
| Overview (Pakets OK in Percent) | |||||||
| WLAN -MHz | 2401 MHz | 2440 MHz | 2480 MHz | ||||
| 2412 | Kanal 1 | 41% | 38% | 35% | |||
| 2432 | Kanal 5 | 27% | 15% | 39% | |||
| 2442 | Kanal 7 | 35% | 38% | 35% | |||
| 2452 | Kanal 9 | 33% | 37% | 30% | |||
| 2472 | Kanal 13 | 30% | 25% | 15% | |||
| 33% | 31% | 31% | |||||
c)
Next test:
Now we measure how good is the Nordic nrf receiver (RX) in suppressing strong signals.
* Receiver develboard is reading background RSSI on Channel 19 (this should be 2440 MHz)
* Sender develboard is sending continuous carrier on one defined channel (we start with channel 12)
* Resulting RSSI on receiver board is identified
* Sender is changed to next channel (now channel 13)
* Resulting RSSI on receiver board is identified
* ... this is done for channel 12 to 26
Here is the result
Kanal / RSSI Wert
Develboard OFF / 101
Kanal 12 / 99
Kanal 13 / 98
Kanal 14 / 96
Kanal 15 / 96
Kanal 16 / 92
Kanal 17 / 90
Kanal 18 / 76
Kanal 19 / 36
Kanal 20 / 87
Kanal 21 / 88
Kanal 22 / 89
Kanal 23 / 91
Kanal 24 / 92
Kanal 25 / 92
Kanal 26 / 94
-----
Is my interpretation correct:
What i expect was that the RX "BandPassFilter" (what is the correct wording) is only 2 MHz wide. Any signal below or above that 2 MHz is filtered away.
What is now see is that the RX "BandPassFilter" is not selective enough to suppress strong wireless signals on other channels. This means that if a WLAN AP is in the near of an nrf device then this receiver "hears" a nois which is around 10dbm higher as without WLAN. This further means, that the resulting distance is reduced massively.
Thanks,
Lukas
