Originally Posted by Heartl3ss
what now u are talking about another device? cause i was indeed gonna ask u if there is a device that can obtain the main wifi signal and re-transmit it with higher strength in the rest of the house, but in the first post you told me that i need to connect it with ethernet to my router...and my router is pretty far from the place im gonna place my access point..
NKrader mentioned a device that can do either (it looks like it has an ethernet port, so presumably it can either be a WDS repeater, or can just be a plain access point by connecting it with ethernet - sorry nkrader, I didn't spot the ethernet port the first time I looked at your link).
You can also do either (plain AP, or WDS repeater) with a lot of different devices, but it depends on the hardware and firmware being capable. The reason I recommend a TL-WA901ND is because it's dirt cheap, quite fast and I know for a fact that the hardware supports all the things you'd want using OpenWRT, which is much better than using stock firmware IMO since it gives you more control. Here's the link to the page for the TL-WA901ND http://wiki.openwrt.org/toh/tp-link/tl-wa901nd
and there's a table of hardware at http://wiki.openwrt.org/toh/start
that tells you what devices are compatible and what features they have.
If you want to use ethernet cables (or powerlines to act like ethernet cables) to link your existing router to the new device, then you need an access point.
If you can't or don't want to use cables, you need a WDS repeater. That way it takes a wireless signal, and re-transmits it. WDS can (I have heard, never used it myself) be difficult, because different devices sometimes don't work properly together - the wiki article I linked mentions this: "WDS may be incompatible between different products (even occasionally from the same vendor) since the IEEE 802.11-1999 standard does not define how to construct any such implementations or how stations interact to arrange for exchanging frames of this format."
So if you use WDS, you run the risk that it just doesn't work for some reason, but I don't know how common that is. Also, as I said, WDS does reduce throughput. If all you're trying to do is make a crappy signal acceptable for stuff like web browsing and streaming internet videos etc. then you'd likely find it quite satisfactory, however if you have a very fast net connection, or local devices (like a NAS) to access over the wireless, the performance hit would be more noticable.
Incidentally, another device I've seen (but not tried) is the TP-Link TL-WPA281, which is a powerline plug with an access point in it. It doesn't do OpenWRT, but for your purposes it would probably work well - you'd have a single TL-PA211 (plain powerline) plugged in near the existing router and connected to it with a short ethernet cable, then anywhere else in the house you plug in a TL-WPA281 and that's it - it is an access point and powerline all-in-one. You'd set it's SSID, security mode and passphrase to the same as the existing network, but on a different channel, and devices would roam between that and the existing router.