CODEWITHSUNDEEP
bluetooth-lowenergycore-bluetoothandroid-bluetooth
MotiC
MotiC

Reputation: 63

Best approach for transfering large data chunks over BLE

I'm new to BLE and hope you will be able to point me towards the right implementation approach.

I'm working on an application in which the peripheral (battery operated) device continuously aggregate sensor readings. On the mobile side application there will be a "sync" button, upon button press, I would like to transfer all the sensor readings that were accumulated in the peripheral to the mobile application. The maximal duration between sync's can be several days, hence, the accumulated data can reach a size of 20Kbytes.

Now, I'm wondering what will be the best approach to perform the data transfer from the peripheral to the central application. I thought about creating an array of characteristics where each characteristic will contain a fixed amount of samples (e.g. representing 1hour of readings).

Then, upon sync, I will:

  1. Read the characteristics count (how many 1hours cells).
  2. Then read the characteristics (1hour cells) one by one.

However, I have no idea if this is a valid approach ?

  1. I'm not sure if this is the most "power efficient" way that I can use.
  2. I'm not sure if Characteristic READ is the way to go, or maybe I need to use indication instead.

Any help here will be highly appreciated :)

Thanks in advance, Moti.

Upvotes: 5

Views: 8348

Answers (1)

Emil
Emil

Reputation: 18442

I would simply use notifications.

Use one characteristic which you write something to in order to trigger the transfer start.

Then have another characteristic which you simply stream data over by sending 20 bytes at a time. Most SDKs for BLE system-on-a-chips have some way to control the flow of data so you don't send too fast. Normally by having a callback triggered when it is ready to take the next notification.

In order to know the size of the data being sent, you can for example let the first notification contain the size, and rest of them the data.

This is the most time and power efficient way since there can be sent many notifications per connection interval, compared if you do a lot of reads instead which normally requires two round trips each. Don't use indications since they also require basically two round trips per indication. They're also quite useless anyway.

You could possibly increase the speed also by some % by exchanging a larger MTU (which leads to lower L2CAP/ATT headers overhead).

Upvotes: 12

Related Questions