BLE successful initial connection needs shorter distance

[nordicdev]

Hi,

I have 3 nrf51822 devices. Two of them act as peripheral and one acts as central. Each peripheral is used in a wheel and they are the 2 wheels of a cart. Central is in the remote that controls the cart with 2 wheels.

Min connection interval for peripherals: 7.5msec

Max connection interval for peripherals: 30msec

Advertisement interval of peripherals: 200msec.

What I have observed is that, when the central is very close (<5 meters) to the peripherals, the initial connection happens successfully. But, when the distance between the central and the peripherals >30 meters, initial connection does not happen successfully that often. But, once initial connection has established, the cart can be controlled by the remote even when the distance between the cart and the remote is >50 meters.

It might be because the advertisements for both wheels occur in only channels 37,38 and 39 - due to this there might be overlapping of the channels of both wheels . But, once connected, packets come through in random frequency hopped channels so there is less clogging between the remote with both wheels.

Please advice any ways to improve success rate of initial connection at a greater distance.

[run_ar]

Not sure there is a good way of improving this. I.e. you probably need a better link budget. This can be achived by using a PA, or swapping to a chip with better sensitivity and/or higer output power. I assume you are right in your assessment that channel 37,38 and 39 might be busy, but you also need to consider that at connectio esthablishement only one packet is sent that contains the connection request. If this fails there is no connection. In comparison you can lose many packetes while in a connection, the number depending on the supervision timeout and the connection interval you are using.