BLE advertising : Minimum packet length ?

RE: BLE advertising : Minimum packet length ?

AmbystomaLabs — Mon, 02 Jul 2018 14:57:12 GMT

There is nothing on a smartphone that operates at that rate. Modern smartphones have BLE v4, maybe BLEv5, traditional bluetooth BR/EDR, some phones have ANT, most have NFC, 802.11b,g,a,an, ac (ie, WiFi). They also have 2G/3G/4G/LTE modems but you won't be able to access them. They just serve to provide a data path that you don't really control.

Anyway, nothing on a smartphone operates at 120kHz for the minimum basic time slot or packet length (as the case may be since these are a mix of random access and time division protocols).

If you really have to have 8usec bursts of data you will have to do some custom device that you hang off of the USB port on the smartphone. You will likely have to come up with your own protocol for the transmission or repurpose an existing one. Since it is custom you can probably do a wideband solution then you can send well formatted data in that 8usec burst with synchronization, channel equalization and FEC data.

But again this well be custom hardware at both ends. You can't get a stock SoC like nRF to do this.

I think if we had a better idea of your application we could assist. But your requirements are a little vague. Normally if you are sampling data at 120kHz you would just buffer and periodically broadcast en masse the accumulated data. That you actually can do with BLE.

RE: BLE advertising : Minimum packet length ?

Altron — Mon, 02 Jul 2018 07:20:01 GMT

Thanks :)

As i said i don't want to establish connection between 2 devices. Do you have a idea of how can i turn on a sensor with a perdiodical signal at 120KHz through the smartphone, no matter the communication protocol (WIFI or BLE) and the transmitted data frame ?

The receiver (sensor) can only detect this signal.

RE: BLE advertising : Minimum packet length ?

Kenneth — Wed, 27 Jun 2018 09:03:09 GMT

I understand what you want to do, but it is not possible. For any given packet there is typically this timing:

startup radio : 150us

preamble and address (2Mbps): 20us

packet content (2Mbps): (4us for each 8bit)

crc (2Mbps): 8us

Then you typically want to switch direction to receive an ack (not counting if there may be retransmissions due to packet loss).

So in total it may take around 500us putting it all together sending one data packet in a proprietary way (you can't do it this fast in BLE).

Best regards,
Kenneth

RE: BLE advertising : Minimum packet length ?

AmbystomaLabs — Tue, 26 Jun 2018 14:45:46 GMT

BLE broadcasts a preamble and sync word prior to the packets as do most wireless protocols.

These alone are longer than 8usec.

RE: BLE advertising : Minimum packet length ?

Altron — Tue, 26 Jun 2018 11:20:21 GMT

Thanks,

But i don't want to establish connection between 2 devices. I just need to make advertising during 7us or less and stop it after as a pulse signal.

RE: BLE advertising : Minimum packet length ?

Kenneth — Tue, 26 Jun 2018 11:11:16 GMT

Hi,

No, in BLE the minimum connection interval is 7.5ms. So you need to buffer up data into 7.5ms chunks.

Best regards,
Kenneth