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Leveraging Single Channel Architecture for Multiple Channels

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Published on Nov 13, 2009

Meru Networks WLAN: Channel Layering

For more info visit: http://www.merunetworks.com

In this video, I'd like to talk to you about the architecture of layered channels and I'll start with how we leverage the single channel architecture in order to layer multiple channels and create Meru's multi-channel architecture. Before getting into the details of what we do and what the benefits are, I'd like to step back and start with how the legacy micro cell approach works. Now, the fundamental principal in providing coverage in any area is the following. You have access points that transmit, and signal decays over distance.

So here is a transmitter. On the Y access is signal strength, and on the X axis is distance. As you go further away, signal strength decays. So you want to make sure that access points are not placed so far away that there is a coverage hole. I hope you get the point. But at the same time, access points of the same channel can't be placed so close together that there is actually an overlap. So let's look at this in terms of circles, and I'm going to retain this picture because we come to this in a little bit. So the idea is you have one access point. On the same channel, the legacy micro cell architecture requires that you don't place access points so far away that there is a coverage gap, but if you place access points very close together, then in fact there will be co-channel interference.

The whole point of a micro cell architecture is to eliminate co-channel interference by design. In a companion video, we'll talk about how difficult that is to achieve in practice, but for the moment let's go along with that. And therefore, if you want to create a channel plan, here's what you would do. You would take multiple colors -- channels -- and you would create for yourself a channel plan. So notice that you need at least three colors, even in a simple two-dimensional picture, and obviously the world is three-dimensional and coverage is not nice circles so there are inherent limitations with the micro cell architecture from that perspective, or indeed any channel-planning architecture. But even assuming perfection, and a two-dimensional world, here's where you are. So you have access points, in this particular case all the blues are on one channel, all the oranges are on another channel, and all the reds are on a third channel. So notice here you actually needed, and I'll shade it here so you can see it more clearly. So notice here you actually need multiple colors just in order to get, essentially, one layer of coverage. So what do I mean by one layer? At any one point, there's exactly one channel that offers you coverage. And now in the 2.4GHz range, you have only three channels -- one, six and eleven -- that are non-overlapping. Therefore, if you want to provide a coverage in a 2.4GHz channel, you are essentially using up all your channels, all the available capacity, just to provide one layer of coverage. Now, in the 5GHz band you have a lot more channels, however once you start doing 40MHz, larger 802.11n channel plans, the number of channels comes down dramatically. And in a three-dimensional network, you actually need more channels. So fundamentally, with a micro cell approach, you get one layer worth and you're going to use pretty much all the available channels in order to create this one layer's worth of coverage.

So the idea is not that we force our customers or we require our customers to go the layered channel approach for any of the benefits that we've talked about in terms of redundancy or capacity or coordination or switch-like behavior, but that this layering allows the customer to selectively, in areas of interest, provide additional redundancy or capacity or the ability to separate traffic or users or introduce new technologies like 11n. Thank you.

......Please See Interactive Transcript For Full Text......

For more info visit: http://www.merunetworks.com

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