microcontroller - Cheapest way to wirelessly synchronize two MCUs

I have two battery powered MCUs about 30cm apart, one will be the master, and one the slave. Each MCU has several LEDs connected which flash in a sequence.

All I want to do is synchronize the two MCUs so that the sequences don't drift out of phase.

Is there some super easy way to send a simple RF pulse from one MCU to the other?

Added:

• The sequence lasts for approx 1 second, and repeats forever.


• If the slave misses some sync pulses, it's not the end of the world, because it would take many cycles to drift noticeably out of phase.



• For personal / religious / aesthetic reasons which I am not allowed to discuss, I do not wish to use IR, capacitive, acoustic means to transmit this pulse.


• The range is very short, less than 30cm.


• The signal will need to travel through open air. No concrete or metal in the way.


• RF-like inductive coupling would be OK too.


• Since the signal consists of only a single pulse, I imagine there must be a smaller, cheaper solution than those involving packet transmission (Xbee, etc.)


• Ideally the solution would consist of some kind of PCB trace antenna, and a simple oscillator for the transmitter, and simple circuit (demodulator?) to detect the pulse at the receiver.