Designing for high-density Wi-Fi coverage

* Challenges in crowded Wi-Fi environments

Trapeze's recent announcement of an 802.11n access point priced for high-density environments got me to thinking. Equipment costs are just one challenge WLAN designers face when trying to cover crowded areas.

The piece that Trapeze is targeting is the capital expense (capex) associated with blanketing a conference room or lecture hall with enough APs to provide adequate capacity for many simultaneous user connections. Indeed, at $745, the Trapeze MP-82 dual-radio Draft 802.11n-capable device is 25% less expensive than the lowest-cost enterprise-class 11n-capable APs currently on the market and nearly 60% less than the most expensive ones.

So is the price tag where it ends? Of course not.

Designing for capacity usually means cramming a lot of radios into a small space to keep the aggregate amount of bandwidth shared by users respectable. This becomes a challenge in today’s commonly used 2.4GHz environment for traditional multi-cell architectures that place APs on alternate channels, because there are only three non-overlapping channels to use. Thus, the power of each AP must be tuned just so in order to avoid a collision free-for-all and insufferable co-channel interference.

Trapeze’s technical marketing manager, Rick Reid, maintains that its MP-82 has a smaller coverage footprint than the company’s primary .11n offering, the MP-432, which he says should help alleviate the collision/interference problem. Devin Akin, CTO at Wi-Fi training and certification company CWNP, cautions, though, that just because clients cannot successfully receive an AP’s transmission doesn’t mean that the transmitted RF energy stops at the cell border. Thus, the APs and clients in adjacent cells might sense the RF and refrain from transmitting, he says, so it’s important to make sure AP power levels are tuned just right.

There are other approaches to satisfying high-density environments that involve single-channel architectures and Wi-Fi radio arrays. We’ll take a look at those next time.

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