Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

What antenna configuration for a multi-building scenario?

I've been tasked with looking into wireless connectivity from our main campus to several buildings various distances away. I'm confused by the antenna choices when it comes to maximizing throughput to these locations.

The buildings that are "across the street" are the immediate candidates for wireless connectivity, but I've been asked to build the infrastructure with the idea of adding connectivity to buildings at greater distances later.


Immediate connectivity "across the street":

Buildings are roughly 2500' - 3000' from the campus building, but in different directions (one is SW of campus, one is N).

Possible later connectivity:

Several buildings up to 5-6 miles away, all in different directions.

"Would be nice" much later connectivity:

A building about 15 miles away.

Assuming 350 series bridges, would the root unit require an omni-directional antenna since the connecting buildings are in different directions? If so, does this introduce distance limitations that would hinder later connectivity to the buildings farther away (even if those locations used unidirectional antennas)? What are those distance limitations?

To connect to buildings in different directions can I even use unidirectional antennas?

Any ideas on an optimal solution for this situation?



Community Member

Re: What antenna configuration for a multi-building scenario?

You could start with an omni at the central building, but you will most likely want to end up with three or more directional antennas there, connected to multiple 350 bridges.

The reasons include both:

- RF factors (#1-without amplifiers your range from a directional to an omni is limited to 8.5 miles, then data rate and reliability have to drop. #2 an omni will pick up interference from all of the other WiFi users around you)

- Shared bandwidth limitations (the "11Mbps" rate yields an actual max of 6Mbps, which is shared AND it's half-duplex, so the average throughput is 3Mbps divided by the number of sites)

Three bridges at the central site will allow you to allocate different sites to each central bridge to better balance bandwidth demand. More than three will require some careful separation of antennas because you end up re-using channels. Directional antennas will give you up to 18 miles at the highest data rate - assuming you have a good line of sight.

And if you are thinking about 802.11a for building-to-building - fughedaboudit. It doesn't even go far enough for your 2500 foot across-the-street site.

Let me know if you need more detailed planning information.

Matthew Wheeler

Chief Wireless Architect

CreatePlease to create content