NRF51 - iOS BLE advertising interval - Increase speed of connection

Question

I am looking at speeding up the connection time between my iOS application and the peripheral. I have looked up Apples Documentation on the subject: https://developer.apple.com/library/content/qa/qa1931/_index.html

Originally (prior to reading the doc above) I had the advertising interval set to 2 seconds to, what I had thought would be, a good compromise between power consumption and connection time. Having read the documentation further I have changed the interval to 1285 ms . #define ADVERTISING_INTERVAL 2056 ble_obj.setAdvertisingInterval(ADVERTISING_INTERVAL); The device is always discovered quickly by the app but the problem comes when trying to connect.

However, I have seen no increase in speed in connection time between my application and the peripheral device. Connections between the devices can take anything from 3-4 seconds up to 30+ seconds.

Is there something I am missing? Either on the peripheral or the central side?

Peripheral BT chip is the Nordic Semiconductor NRF51822. On examining the devices advertisement packet on the Nordic Semiconductor app I can see that the advertisement interval normally varies from 1275 ms to about 1295 ms (as expected? due to the random time added to the advertisement packet)

NOTE Have also tried with an advertising interval of 152.5 ms and am still not seeing any major improvement in connection speed. I am , obviously, seeing a marked improvement in speed of discovery

Answer 1

What you observe is normal. Don't expect fast connection setup with an advertising interval of more than a second.

Core Bluetooth uses a high duty scan window/interval for the initiation the first seconds. If it doesn't connect then it continues to scan with much more power restrictive parameters.