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802.11a vs. 802.11g

Two other topics that I've seen a range of claims and counter-claims on is the speed and range of 802.11a vs 11g. Let's look at the throughput issue first.

From what I can determine, all things being equal, the throughput of 802.11a and 802.11g products should be essentially the same. This is because they use the same modulation scheme (OFDM), which is the main thing that determines how fast the bits can go.

But since reviewers of draft-802.11g products, myself included, are finding slower-than-802.11a throughput, the question is what's not equal? As it turns out, there are a number of things - some temporary, and others permanent. Let's break them down:

  • Design maturity - In my opinion, this is the number one issue that is affecting current product performance. For the reasons I've outlined in previous sections, these products should come with big "Under Construction" stickers on them. There are new draft changes that need to be rolled into designs, and vendors are still tweaking their algorithms, and in some cases learning the additional challenges that OFDM can bring.

  • 802.11b compatibility - Also as I've shown, the 802.11b "protection" mechanism will cut throughput when it's enabled. But since the 11g spec doesn't mandate protection's use, vendors are including "no protection" modes that remove the additional overhead

  • Operating frequency - This is the big difference and the one that will give 11g the edge in anything other than "open field", i.e. no obstructions between stations, conditions. Ya can't change physics, and 5GHz signals will always have a higher signal loss going through walls, etc. than 2.4GHz signals.

The bottom line here is that there is a lot of FUD being generated and conclusions being jumped to based on products that are still very early in their development and low on their learning curves. As things get sorted out, the throughput of 11g equipment when used in a pure 11g environment should be essentially equal to that of 802.11a under best-case signal conditions.

As far as assertions that 11g products will have inferior range to either 11a or 11b products, neither my experience nor the underlying principles support them. First, since 11g operates in the 2.4GHz band, its signal will not suffer as much attenuation as 11a's 5GHz, and will travel better through the obstacles that most WLAN installations include.The 11a guys have long tried to argue that since they start at a higher throughput, their effective throughput at an equivalent range will still be higher than 11b's, but test results just haven't supported that assertion.

But how about 11g's range being better than 11b's? Although this article written by Intersil guys says that OFDM will have superior range because it can handle the signal reflections that are typical of indoor environments, my experience again tells me otherwise. In the end, superior design will probably provide one product's edge over another, and not the use of 11g vs. 11b.

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