Can BLE peripherals stays in RX mode and wait for scan request to start advertising?

[andyyau]

I am considering using BLE advertising for sensor devices as peripherals and using a mobile phone as receiving device.

Because the number of sensor devices can be more than 200 to 500, or even more, but they will be located at different floors and different location of the a building. So the nearby devices will be limited.

The requirement is users that does not want to have a lot of this Bluetooth signals everywhere. So it is possible for all sensor devices stay in RX mode and wait for Scan Request from mobile phone? Once Scan Request is received, the nearby sensor devices get the request and wake up for advertising? For those sensor devices not receiving the Scan Request, they can be ignored and process later with next Scan Request.

And will the sensor devices create radio signals in RX mode?

Thanks!

[Jørgen Holmefjord]

Hi,

This is not possible with BLE. The Bluetooth Low Energy specifications only allow you to send a scan request packet for a short period of time after receiving a advertising packet. The scan request packet indicate that the scanner have received the advertising packet, and request more information through the scan response packet.

You could implement a proprietary solution where the radio is in RX mode, waiting for some packet, but this would not be supported by phones. Another alternative if you do not want devices to advertise continuously, is to do advertising on the phone side and scanning on the sensor side. This would allow the sensors to start advertising when the advertising packet is detected from the phone, and the phone can scan for the advertising packets from sensors. Note that not all phones support advertising, and may not support concurrent advertising and scanning. This would also require you to write an application that could do this on the phones. Current consumption of sensors would also increase drastically compared to advertising only.

Best regards,
Jørgen

[cbd]

I would also like to add that scanning is very power hungry as you're running the BLE transceiver at full power.

Unless your sensors are hardwired I would seriously doubt that you would have the power budget for that.

What is the thinking behind your customer's preference in not having devices transmitting?