According to the two-ray ground model, the signal power strength p at the receiver has the relation with the distance between the sender and receiver: d to the 4. P1 to p3 is the power strength that receiver received at different time. Ps is the signal  strength threshold at the receiver. So the t is the link breakage time for node A and B. From above equation, we can calculate the t. When node B is receiving unicast packets from A, it uses sliding window to calculate the link breakage time, and only calculate the decreased signal power strength.
	The conditions for the prediction algorithm are:
	at least three unicast packets are needed to obtain correct prediction time.
	And during the time we make prediction and link breaks, we assume two nodes will maintain their speed and direction.
	So if one of them changes movement pattern, the prediction will not be accurate unless receiving another three packets.