Performance Test: 802.11b Takes a Lickin' and Keeps on Tickin'
Subject:   what about 2.4ghz phones
Date:   2001-04-04 11:11:15
From:   rflicken
Response to: what about 2.4ghz phones

You mention an 802.11 card-- which one?

There are two different technologies used in the old 802.11 (non-b) cards: Frequency Hopping, and Direct Sequence Spread Spectrum.

Most 2.4Ghz phones use Frequency Hopping to try to cope with noise in the band. The problem is that other frequency hopping devices in the same band may get very near into phase with each other, causing noise most of the time! I suspect that your 802.11 card is a freqency hopper.

The later 802.11 cards (and all 802.11b equipment, like the Lucent gear in this article) use DSSS, which uses one of eleven possible 'channels' and does tricky math to work around errors. This stuff tends to do better in the presence of FHSS, but worse in the presence of other DSSS equipment on the same (or an overlapping) channel.

Incidentally, I didn't throw a 2.4G phone into the test environment for this article because I don't own one (donations gratefully accepted! =) Although I do have friends who use them happily right along side their home 802.11b networks.


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  • what about 2.4ghz phones
    2001-04-07 21:43:07  corey [View]

    I thought it was supposed to be the other way around. I have heard that the 11Mb 802.11b DSSS handled the older 802.11 DSSS in the 2.4GHz space moderately well, but that FHSS at any speed would thrash DSSS and make it a very poor performer.

    Would you please share more information?


    • what about 2.4ghz phones
      2001-05-10 16:35:05  onkelbob [View]

      It's true an FHSS transmitter that is in the path of your DSS receiver will induce many problems. FHSS signals are much stronger (over 20 dB) and will desensitize a DSS receiver therefore inducing errors. The solution is to identify the source (transmitter) and change your receive path to avoid "hearing" the transmitter. If the receiver is using omni-directional antena, change to a directional antenna. Another possibility is to change polarization (antenna orientation) of the DSS system (both TX and RX) or get the FHSS to chnge their polarization.
      Home 2.4 Ghz cordless phones "should" work with home 802.11b systems because the phones will hear the interference from the AP and change over to another channel on the ISM band, i.e., you set the AP to operate on channel 1, the phone will usually hear that interference and move its center carrier over to channel 6 automatically.
  • what about 2.4ghz phones
    2003-12-30 21:06:27  anonymous2 [View]

    This is an interesting topic because I'm about ready to rip my phone out of the wall because I get so much static. I change the channel countless times and it's like a 1 in 10 chance of getting a clear channel... until I move. My wireless AP (Linksys BEFSR11) is an 802.11b on Channel 1, which is 2412 Mhz (2.412 GHz). My phone is a Panasonic 2.4 Ghz phone. What can I do to eliminate interference problems? I've looked at a spectrum of 802.11b channels and all of them are in the 2.4 GHz range, so I can't see a way of altering that at all!

    ANy ideas are appreciated - alex(at), if you will.