You know, we (and especially I) throw the term performance around a lot. In networking, mentioning performance almost always implies throughput, and these two terms are frequently used interchangeably. Performance thus means how fast a given connection is in terms of bits per second.

Unfortunately, that definition is much too limited when we talk about wireless. As regular readers of this column know, the variable nature of the radio channel, and the consequential statistical behavior of wireless links, results in highly-variable throughput, which can range from just fine to nonexistent, and which, of course, can change on a moment-by-moment basis. This is perhaps the greatest frustration of any wireless user - after all, wired performance is highly predictable, especially when wired networks are carefully planned and overprovisioned, as is quite often the case today.

But the wireless environment is a lot tougher, so you never really know what you're going to get until you get it. The good news is that improvements in radio technology continue at what seems to be an accelerating pace, and lower costs allow us to overprovision in a manner analogous to that on wire (see my earlier article and whitepaper on dense deployments for more information). So wireless throughput continues to improve, but variability will almost always be with us as a fact of life.

But there's more to wireless performance than throughput alone. Let's consider some of the other dimensions of wireless performance, all of which influence throughput as well:

• Range: Those with limited experience in wireless always ask (right after the question about speed, of course) how far a given wireless connection will go, implying that more is better. Rarely, however, is more range better in wireless. The right amount of range is exactly that required to make a reliable connection at the desired level of throughput, but no more. Range beyond this means that we're using radio spectrum we don't need, and thus perhaps interfering with others nearby trying to use the same frequencies. This is especially true in the unlicensed bands used by wireless LANs and PANs. But sometimes more range is needed, especially indoors where the environment can quickly degrade a wireless link. Interestingly, MIMO technology (see my earlier article on the subject) is perhaps more valuable today for the improvements it brings to range than throughput. In yet another earlier article, I described how using MIMO can dramatically improve the quality of a wireless LAN connection when more range is required.
• Coverage: Especially when we talk about metro-area and wide-area wireless networks, coverage becomes a key element. I know of no one who's never suffered a dropped cell phone call, and the primary reason for this is that there aren't enough cellular base stations to cover a given area. This can sometimes also occur because all of the spectrum provisioned by a given base station is subscribed, leaving no room for new or roaming users, but that also basically means that there aren't enough base stations to
  

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