QUOTE(crazyito @ Apr 20 2014, 04:38 PM)
A repeater will only solve my 1st problem (increase the strength of the signal for 2nd floor PCs), but won't solve my 2nd problem (connect 1st floor PC to it using ethernet cable) right? Or I can connect a secondary router to the repeater?
a typical standalone repeater, does provide one LAN port and you should be able to connect your second router to it if you need more ethernet ports. Otherwise, connect your PC straight to the repeater or get a cheap USB wifi adapter.
pros - no-brainer setup, simple and hassle free
cons - highly sensitive to positioning for signal strength with main router, only one LAN port, not flexible on network options, price
the option I use is WDS, with one TP-Link router upstairs on a 2nd wifi network.
pros - 4 LAN ports on a single power point, able to separate into 2 Wifi networks with different SSID, more flexible on positioning, stronger external antennae (upgradable as well), considered the more superior networking protocol to repeater, cheapest option
cons - WDS is non-standardised, it may or may not work with other branded routers, might be sensitive to positioning for signal strength with main router
you could also choose Homeplug option as mentioned by 'ihavenoidea', requiring two power points and two homeplugs one on each floor, and then connect a short LAN cable from the main router to the homeplug on groundfloor, then another LAN cable from homeplug on first floor, to your secondary router.
pros - best option when it works, packet loss between routers is reduced to almost nothing, streaming HD content and transferring files between 2 floors will be a joy
cons - most expensive option, takes up power points, might not work as good (or not at all) if both the power points are on a separate phase
all three options are perfectly fine on internet speed, surfing and downloading when they are successfully deployed.
GL