Thanks for the recommendation.
but the signal strength top up to 99 - 100% atm,

Now, I'm encountering this kind of problem.
Let's say I download something, about 1,000KB/s when starting.

After like 10-15 seconds, it would go down to 0KB/s, then goes back 1,000KB/s and revert back to 0KB/s after a few seconds again.

Of course, all this never occurred when using the net through cable/LAN.

Using this : TP-LINK 150Mbps High Power Wireless USB Adapter (TL-WN7200ND)