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Thread: separating MIMO antennas

  1. #1
    TomaszK
    Guest

    separating MIMO antennas

    I have a PC that acts as a wired router/gateway, and I want to add
    this wireless PCI card http://www.modecom.eu/product.php?id=428

    My only worry is my router is in the basement, and I'm not so sure if
    the signal is going to make it through two ceilings...

    I was wandering what would happen if I placed each antenna on
    different floor? Will a MIMO card still work?

  2. #2
    seaweedsl
    Guest

    Re: separating MIMO antennas

    On Sep 4, 10:00*am, TomaszK <tomasz...@gmail.com> wrote:

    > I was wandering what would happen if I placed each antenna on
    > different floor? Will a MIMO card still work?


    No, don't do that. There is a report on a study by Cisco that Jeff
    can link for you, but basically, it confuses the system if the
    antennas are different, directional or too far apart and can make
    things whacky. These antennas are meant to be in the same place both
    transmitting/recieving to the same clients - only seperated a bit.

    Apart from that, it's not too clear what your setup is. Is it your pc
    acting as router or do you have another router in the basement?

    Instead of running an antenna cable upstairs, run an ethernet cable
    from your existing router to upstairs and use an additional access
    point or router (operating as access point) where ever coverage is
    too weak.

    In fact, if you don't need wifi in the basement, just operate the AP/
    Router upstairs and it may cover the upper two floors.

    There may be some advantage to using a pc as router, and a wireless
    pci card for an AP, but in most cases, I think it's limiting, more
    trouble and complicates things without saving any money. Generally
    best to get an inexpensive wireless router.

    Also, consider if you really need the speed of N because you are
    planning to stream video around your house ? If not, then G is
    less expensive and very good choice.

    Cheers,
    Steve


  3. #3
    Jeff Liebermann
    Guest

    Re: separating MIMO antennas

    On Fri, 5 Sep 2008 07:06:22 -0700 (PDT), seaweedsl
    <seaweedsteve@gmail.com> wrote:

    >There is a report on a study by Cisco that Jeff
    >can link for you, but basically, it confuses the system if the
    >antennas are different, directional or too far apart and can make
    >things whacky.


    Holdit. You're mixing up MIMO and diversity reception. The article I
    was referring to:
    <http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml>
    is only about diversity reception, not MIMO.

    If you remove all but one of the typically 3 antennas from a MIMO
    router, you get essentially 802.11g speeds. If the error rate is
    insufficient to maintaint MIMO speeds, the router will revert to
    802.11g. I presume (not sure) that the multiple antennas revert back
    to a diversity receive mechanism when not running MIMO speeds.
    Therefore, diversity reception issues might still apply and become a
    problem. I'm admittedly a bit muddled about exactly how the MIMO
    chips operate under non-ideal conditions and will need to do some
    testing and reading before offering any more bad guesses.

    Also note that MIMO comes in two flavors. Spatial Diversity and Beam
    Forming. The routers with visible antennas are spatial diversity. The
    ones with internal PCB antennas are beam forming. The characterists
    of these technologies are very different and should never have been
    conglomerated into one acronym and one (preliminary) standard.

    --
    Jeff Liebermann jeffl@cruzio.com
    150 Felker St #D http://www.LearnByDestroying.com
    Santa Cruz CA 95060 http://802.11junk.com
    Skype: JeffLiebermann AE6KS 831-336-2558

  4. #4
    seaweedsl
    Guest

    Re: separating MIMO antennas

    On Sep 5, 11:57*am, Jeff Liebermann <je...@cruzio.com> wrote:

    >
    > Holdit. *You're mixing up MIMO and diversity reception. *The article I
    > was referring to:
    > <http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note091...>
    > is only about diversity reception, not MIMO. *
    >
    > If you remove all but one of the typically 3 antennas from a MIMO
    > router, you get essentially 802.11g speeds. *If the error rate is
    > insufficient to maintaint MIMO speeds, the router will revert to
    > 802.11g. *I presume (not sure) that the multiple antennas revert back
    > to a diversity receive mechanism when not running MIMO speeds.
    > Therefore, diversity reception issues might still apply and become a
    > problem.



    OK. My bad. Thinking I understood! So, it's not the same at all as
    diversity, though it might be ultimately have similar problems when
    the antennas are seperated from each other?

    How's this ?

    " You can't seperate the multiple antennas in a multiple antenna radio
    (be it diversity or MIMO) and expect it to work like two or more
    radios in different places, sending and receiving appropriately to
    each client connecting seperately to each antenna. Instead, it will
    likely confuse the radio causing it to drop back to G (if N) and
    possible attempts to transmit on one antenna in response to reception
    on another - generally screwing the link up when multiple users
    connect to different antennas with different coverage."

    Please correct me Jeff (no doubt you will!) I'm just trying to
    extract some direct advice out of the confusion.

    Related question? If I understand correctly, the only way to run
    multiple antennas with different coverage (on the same radio) is to
    use an RF splitter (expensive, with some losses) on a single antenna
    jack, so as to transmit and receive on all antennas simultaneously?

    Steve


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