How to extend the communication distance of ESB in nRF52832

Hi,

I am developing the proprietary protocol by using ESB function in nRF52832.

If the linear distance between the two devices is less than 10 cm, normal communication is possible.
When the distance between two devices is greater than 1 meter, the RF signal will not be communicated even if I set the output power to "4dBm".

How can I solve it's problem?

Thank you

Chianglin