Set Up Single Wireless Network with Multiple WiFi Routers

First I add that some of these replies need clarification.

There are two kinds of overlap, one is channel overlap where the frequencies overlap, and the second being signal overlap.

You MUST have signal overlap for all devices to have coverage in all areas, or even most devices in most areas.

Secondly, there are various schools of thought for frequency overlap and some manufacturers even suggest putting all APs on a common channel. In the case of roaming IP phones this case becomes even stronger as a phone may hop across APs while in a call. This of course depends much on the hardwae of the phones and antenna placement and design.

Let us assume that we had a large open area that we wanted wifi coverage in. Now lets take a pole and place it in the middle of the area. Now we place 4 directional 90 degree antennas on the pole, each 90 degrees from the other . In this situation one may make a strong case for having all APs on the same channel to facilitate roaming. In theory there is little signal overlap but all frequencies overlap.

Now we have an open area with walls on four sides. and place an AP on each of the four walls. The signals WILL overlap from each of the 90 degree antennas , so we may want to consider using separate non overlapping channels on each AP , however there are only 3 non overlapping channels. 1, 6 , and 11. So instead we do the best we can in North America this might be 1, 4, 7, and 11 , each AP having SOME necessary frequency overlap. Of course in a perfect world this might be better accomplished with three APS in a triangular configuration.

In my home I have toyed with APs on Same channel and separate channels and in the end I see little coverage difference., I do see however that some devices such as wireless IP phones can more easily hop to another AP while in a phone call. I see that in most areas I do not have more than 2 overlapping signals and each on channel 4 at present. As I sit here I can launch wifi seeker on my android and see either of the 2 available APs and even connect to either. This of course is easier to test with separate SSIDs but more practical to use common SSIDs fopr everyday use.

While Oneiroi's answer starts to get you there. There are a few flaws that deserved more than a comment on his answer.

First, the bandwidth you are actually contending for isn't the back end ethernet link, but the wireless link speed. So on a 54 mbps router you would be contending for that 54 mbps. At 60 clients that would be about 900kbps each, not counting TCP overhead, counting TCP overhead you are already down to ~720kbps.

Secondly, you still have to deal with signal strength issues, which depending on your location could greatly effect throughput.

Thirdly, you have to deal with interference between those 60 radios all trying to broadcast. Years ago when I was working on planning an 802.11b wireless network the engineer we talked to said the rule of thumb was about 10-12 clients per AP for best performance, you can probably move that up to 20-25 (pure off the cuff number)with today's newer technologies. But that still doesn't get you to 60.

I would suggest that you take a look at some pure Wireless APs (not routers) and do a site survey to find the optimal placements for them.