Two radio-linked devices: Device A is a tiny hand-held cube with a single user knob which sleeps for months on a Coin-Cell. Device B, always on, powered by a wall adapter, drives a stepper motor that matches Device A's knob rotation angle.
Requirement 1: Device A while in deep sleep -- user twists knob, <30ms later the stepper moves on Device B.
Requirement 2 : With Device A awake and in use, User will rotate the knob wildly, which Device B's stepper must track with latency <20ms.
Assuming my other hardware and software designs are best practice, which radio protocol offers the best fit for my real-time critical application?