SDN-Based Centralized Downlink Scheduling with Multiple APs Cooperation in WLANs

Algorithm 2

Maintaining and updating RL and TL.

	Require: This algorithm runs all the time.
	Input: U, sender U [i], receiver U [j]
	Update: Set TL and RL store the transmission and receiving status of nodes in U
	Temporary variables: RL and TL
(1)	initialize RL = RL [0]  |U| and TL = TL [0]  |U|
(2)	when status changing event arrives do
(3)	if SDN controller receives a data transmission start instruction then
(4)	TL [i] ⟵ 1
(5)	RL [j] ⟵ 1
(6)	else if SDN controller receives a data transmission end instruction then
(7)	TL [i] ⟵ 0
(8)	RL [j] ⟵ 0
(9)	end if
(10)	update the TL and RL stored in SDN controller