[ltp] Wifi range: Cisco Aironet 350 vs IBM a/b/g combo

[linux-thinkpad@linux-thinkpad.org]

On Tue, 6 Jan 2004, Ivarsson, Torbjorn (T) wrote:

> I am not an expert in WiFi-technology, but I am a working professional in the field of RF (Radio Frequencies). Your statement does not surprise me. 

Thanks: but which one!  I'm left a bit confused by your comments...

> It is also a function of the technology you use - 802.11a, b, or g. Comparing a with b and g should give lower coverage for a. 802.11a operates in the 5.3GHz frequency spectrum, whereas 802.11b/g operates in 2.4GHz. Because of physics, the higher the frequency, the smaller the coverage. Though not accurate, a rough rule of thumb would estimate that twice the frequency yields half the coverage.

OK: but remember I'm not using 802.11a at all here: I'm comparing
coverage of an 802.11b card (the Cisco) with an 802.11b-compatible
card (the IBM/Atheros) that happens to be doing it via 802.11g - the
same wavelength, as you say.  The IBM also supports 802.11a, but I've
never tried it and don't have an 802.11a access point.

> Therefore, you *should* get the best coverage with 802.11g (efficient modulation, 2.4GHz). Assuming identical hardware of course... Again, the hardware may not be as good as your other cards.

OK so... why don't I? :)  It's the new 802.11g card that's got a much
lower range than my old b card when run at what amounts to still only
upper-end 802.11b speeds.  If someone were to tell me that the Atheros
chip in the IBM card is just a much less efficient transmitter than
the Cisco one, then I guess I'd sigh and be satisfied that at least
I hadn't broken my antenna*.

> Ahh, the beauty of marketing. First of all, the datarates, or more accurately throughput, you get from WiFi depends on the amount of interference in the frequecy spectrum. 

Yep, understood: I quickly realised that with 802.11b a year or so
ago, when I found that 5Mb/s was about the practical maximum for
802.11b: so that means I expect about 20Mb/s maximum from 802.11g.
It's the disparity between this figure and the 7Mb/s I actually got,
and what iwconfig tells me, that confused me.

> Having two antennas (in the lid) is usually only beneficial when receiving from the AP (access ponint). Transmission (in wireless technologies) is most often done using just one antenna. Therefore, expect higher throughput from AP to laptop than from laptop to AP.

Thanks, didn't know that: useful!  Although, hard to test as TCP/IP
is a two way protocol?  I may get lost here, but if the ACK's don't
arrive back in time from the receiver then transmission is throttled
- at least in TCP?  I'd better stop here before I embarrass myself.

On further testing I realised that a cleaner test was to use the
ttcp command to do proper performance testing: I am sometimes now
getting what ttcp tells me is up to 20Mb/s with TCP, but it varies
widely with time sometimes down to 4Mb/s and less (in the same
physical location) so I guess that may be interference.  At least
I'm happier that it's outperforming 802.11b sometimes: and I guess
the madwifi drivers will improve soon.  Which just leaves my primary
worry, the vast difference in range between the IBM and Cisco cards.
If anyone has swapped these cards and can confirm or deny this big
difference I'd be very grateful.

> BTW: Antennaes are for bugs, antennas are for humans... but who cares?

So, we use the latin plural for creepy crawlies and the anglicized one
for TV sets?  rec.radio.amateur.antenna seems to agree with you, but
sci.bio.entomology.lepidoptera differs.  Let's settle on "aerials" :)