John Navas <(E-Mail Removed)> hath wroth:
>On 31 Jan 2007 06:55:31 -0800, "seaweedsteve" <(E-Mail Removed)>
>wrote in <(E-Mail Removed) .com>:
>
>>I just ran into this explanation. Don't know how accurate it is:
>>
>>http://stores.ebay.com/DataAlliance/...G-802-11A.html
It's totally wrong. There isn't one single correct statement anywhere
on that page.
My favorite is:
"G requires use of three different channels simultaneously,
and the network implementation may have a constraint to not
lock up three channels"
Amazing. B and G both use approximately 22MHz or about 5 channels.
The bandwidth requirements for both are intentionally identical. Only
at speeds above 54Mbits do *SOME* systems require more bandwidth.
>* B doesn't conserve battery life as compared to G. In fact newer G
>chipsets tend to have better power management than older B chipsets.
Yep. Battery life for B is much worse than G because:
1. For the same amount of data moved, the slower B is on the air
longer than G. That applies to both xmit and receive. It takes
longer to synchronize B (long preamble) and longer to sample receive
the data. With B, all management packets are sent at the slowest
1Mbit/sec (for compatibility), which also requires more airtime. If
one simply compared the current drain required to move an XX MByte
file using B versus G, the higher speed G would by far be more
efficient.
>* Speed is managed by the access point, not the wireless client.
Yep. The only exception is that in an ad-hoc network, the initiating
client can set the speed. However, we're talking infrastructure here,
not ad-hoc.
>* OFDM (G) tends to be more robust than BPSK (B).
Yep. OFDM has a really big advantage over B in that it is much more
immune to reflections and multipath. OFDM consists of 52
sub-carriers, all of which contain parts of the data. If one
disappears, the others still work. Frequency selective fading (as
caused by multipath) is the major enemy of wireless. Each of the 52
carriers are on slightly different frequencies, where frequency
selective fading might ruin one or two carriers, the rest will get
through. That's far more robust than 802.11b, where the loss of part
of the frequency spectra results in total loss of data.
Also, don't forget my previous comments about interference. Big slow
packets as found in B are a much bigger target for interference than
the smaller G packets (although fragmentation can help).
>* G doesn't have different channel requirements than B.
Yep.
>* G doesn't cost more than B.
Actually, G costs less because the chipsets tend to be more tightly
integrated than B.
>* Although B does interfere with G, it doesn't "nullify" it.
Yep. However, the author might be referring to the 802.11b
compatibility mode found on all access points. The presence of an
802.11b connection does slow things down considerably. However,
better algorithms have largely reduce the damage to the point where it
is easily tolerated.
>* Pentium processors don't operate in the 2.4 GHz band.
That might be in reference to 2.4GHz being a common CPU clock speed.
The RFI from the processor is fairly well scattered all over the
frequency spectrum. At one time, I was seriously worried that there
might be some interference from the processor. So far, I haven't seen
any. However, the digital circuitry and clock junk from the processor
on an access point or client radio creates far more interference than
the main CPU. Although lower power, the clock crud is physically far
closer to receiver than the CPU. Think inverse square law. Also, a
good rule is that wires radiate, while components generally do not.
There's lots more wrong with that web page, but I don't want to burn
any more time correcting them.
--
Jeff Liebermann
(E-Mail Removed)
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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