Nowadays, the IEEE 802.11n wireless local-area network (WLAN) has been extensively deployed around the world due to affordability, accessibility and expandability. As a result, a lot of access-points (APs) are closely allocated, which may cause radio interferences and degrade network performances. To solve this problem, we have studied the transmission power optimization method for concurrently communicating APs in WLAN. Either the maximum or minimum power is selected for each AP such that it gives the largest signal-to-noise ratio (SNR) of the receiving signal strength (RSS) through exhaustive measurements for the possible combinations. However, this method limits only two APs. In this paper, we present a generalization of this method for handling any number of APs in dense WLAN. To reduce SNR measurements, it sequentially selects the AP to the minimum power in descending order of the initial RSS where every AP has the maximum power. For evaluations, we conduct extensive experiments under various network topologies using Raspberry Pi for up to four APs. The results consistently show that the proposal can select the best transmission power combination for the APs, except for the cases where multiple APs are allocated in a small room. The improvements will be in future studies.