Not sure if I'm asking the right question, but here goes...

WiFi reception upstairs is patchy. There is wired LAN. I'd like to add another access point. I would like it to be transparent. What do I need to Google for, or how do I do this? The existing router is running OpenWRT. I'm happy to spend a reasonable amount of money.

I did that just last year. I bought this TP-Link router. Cost me less than 40 euro. I then disabled its DHCP and ran an ethernet cable from my other, main router to one of the TP-Link's LAN ports. That was it.

It's been working perfectly for more than a year now. When I'm upstairs the main router is providing the wireless signal, when I go upstairs this switches to the TP-Link. Very transparant, and it was a lot cheaper than a 'real' access point too.

Oh, and this TP-link is compatible with DD-wrt and OpenWRT too. I didn't go through the trouble of flashing the router (the original firmware works fine for me - I've never even had to reboot it), but you could do that if you wanted to.

Use the same SSID, security setup, but a different channel. Wireless clients will pick the one with the better signal, and roam between them if the situation changes.

Got any old Airport Expresses lying around ? I use one for this, works well, nice small neat install (but my Ethernet jack is next to my power socket, which helps).

This sounds exactly like the setup that Mark Lord helped me do last year. I have a WRT54G wireless router connected to my cable modem, VOIP phone, a color laser printer, a couple of computers, etc. Another WRT54G on the deck downstairs picks up the signal from my primary router and rebroadcasts it to the floor below. It has worked perfectly, totally trouble-free for more than a year now.

tanstaafl.

This.

Thirded. What Tony and Tom said. To add to that, you should not need the same brand router or firmware. You can mix and match and do that just fine.

Doug: What you're referring to is a wireless repeater or wireless range extender. That would likely be the best option if he did not already have a wired network. I do this same thing in a concrete building where the primary router is on the third floor and I'm in the basement.

Fourth...ed? I do this all the time for my clients. It's a great way to expand wireless in the house.

Two things:

1- I don't believe what we're talking about is a repeater (someone correct me if I'm wrong, I probably am...). Commercial WiFi repeaters, IMO, are the devil, and when you make your own with WDS you're hobbling your wireless network. You're merely adding an additional hotspot to your network.

2- If you're reading this and you're like "darn, I'd like to do this but I don't have ethernet going through my house," I would suggest something like this product if you have coax in the rooms you need. I've used MoCA adapters like these to great effect, and the speeds are great, especially compared to powerline, which is a last resort. I prefer the Netgear MoCA adapters before, but they seem to have disappeared from Amazon, which stinks.

Except that they won't. The client will stay with the first adapter it sees until the signal gets sufficiently bad to warrant moving. Its idea of bad is more forgiving than mine.

How do I make roaming more aggressive?

I believe that in Windows, that's implemented in the WiFi adapter's driver. Go into the adapters settings in Device Manager and see if there's an option for that. I'm pretty sure that Intel adapters have such a setting. Yours may not.

Lowering the TX (transmit) power setting on the router may also help, especially if you used OpenWRT to boost it beyond defaults. Having it set higher may be allowing the adapter to still receive decent beacon packets from the router and not triggering the search for a better signal on another channel.

Locally, I reset my pair of wifi points to the same SSID and passphrase then lowered the tx power of both, and finally unlocked the frequencies on both.

I can roam around at will.

Edit: oh yeah, the two ap's are linked by cat5.