Help with Boosting wireless router signal

Discussion in 'Home Networking' started by Roy Amin, Oct 7, 2005.

  1. On Mon, 10 Oct 2005 14:35:10 GMT, John Navas

    [att.wireless deleted as Newsguy claims its an invalid group]
    I beg to differ. A directional antenna improves the signal strength
    in both transmit and receive. An increase in transmit range also
    creates an increase in receive range. Although it does help
    substantially, there is no requirement that the client antenna also be
    directional in order to derive benifits from a directional antenna at
    the access point.

    Directional antennas also much of their gain by borrowing signal from
    what would otherwise be useless directions. For example, if the
    desired coverage pattern is all at the same elevation, there is no
    need to send signals into the sky or into the ground. This is the way
    a high gain omnidirectional antenna works. It borrows signal that
    would normally go up or down, and sends it out horizontally. The net
    improvement in range is at the expense of vertical radiation angle. No
    corresponding change in client antennas are required.
    Not perhaps, but required. When increasing transmit power at one end,
    there must be a corresponding increase in transmit power at the other
    end or the exercise is futile. Let's pretend that instead of the
    usual 80 milliwatts (+17dBm) of insipid power, one purchases a 1 watt
    amplifier for the access point. That's a 13dB increase in transmit
    gain which should correspond to a 4 times increase in range. Sounds
    great?

    Well, it doesn't work that way. The range in one direction will
    increase 4 times, but the client radio is still transmitting at only
    +17dB. The receiver at the access point hasn't been improved by this
    exercise. Therefore the access point receive range remains the same
    as before the power amplifier and no net improvement in range is
    achieved.

    The addition of a power amplifier also creates a situation resembling
    an "alligator" or an animal with a big mouth and small ears. It can
    talk much furthur than it can hear. The above 1 watt amplifier
    example can be heard in an area 16 times as large as the area in which
    it can effectively communicate. In my never humble opinion, that's a
    jammer. That's also why I detest Tropos Networks and other mesh
    network vendors deploying 1 watt poletop radios. If the clients also
    had 1 watt laptops, then the range in both directions would be equal
    and all would be well, but they don't.

    There is one situation where a tower top amplifier is workable. That's
    on a tower, with a long length of very lossy coaxial cable. The
    addition of a receive preamplifier to the power amplifier improves the
    overall receive sensitivity by eliminating the coax loss from the
    receive equations. However, the overall receive sensitivity will
    probably not be better than that of the original access point because
    they typical all digital receiver is already operating at the noise
    floor of the technology. (Exact details and equations on request).

    Another situation where an amplifier is workable is a point to point
    link. However, to insure equal range in both directions, there has to
    symmetry which requires that there be an amplifier at both ends of the
    link.
    Methinks repeaters suck. See previous article in this thread. MIMO
    is especially good for high reflection environments such as indoors.
    However it's currently impossible to add an external antenna to a MIMO
    system.
    My order and sequence would be (in order).
    1. Move the wireless router closer to the clients.
    2. Install a better antenna system on the wireless router end.
    3. Add a 2nd access point on a different channel.
    4. Replace everything including clients with MIMO technology.
    5. Add directional or better antennas on the client radios.
    6. Repeater or range extender. Watch out for compatibility issues.
    7. Power amplifier (don't bother).
     
    Jeff Liebermann, Oct 10, 2005
    #21
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  2. Roy Amin

    Roy Amin Guest

    Thanks for the advice. It seems that an antenna which expands the
    horizontal at the expense of vertical may be the answer for me.

    My router is positioned such that the devices are no more than 2 metres
    above or below it.

    What type of antena do I need? I am not familiar with the jargon. Dougnut
    Omni directional?

    Thanks
    Rohit

     
    Roy Amin, Oct 10, 2005
    #22
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  3. I can't really tell without have a look at the layout and premsis. My
    guess is almost anything with over about 6dBi of gain will work. That
    includes coffee can antennas, biguads, and panels. The reflectors in:
    http://www.FreeAntennas.com
    are an easy start and good way to test if the antenna will make a
    difference. Don't use a dish or yagi as they are too high in gain and
    will result in a very narrow pattern. A higher gain omni antenna
    might be possible, but I don't like the reflection problems they
    create. Therefore, I my bias is towards a patch or panel antenna with
    about 8-12dBi gain.

    You don't sound like you're going to build anything so I suggest:
    http://www.fab-corp.com
    and a source and supplier. Keep the coax cable lengths short.
     
    Jeff Liebermann, Oct 10, 2005
    #23
  4. I've only seen three types of repeaters.

    One is extremely dumb and will store and forward literally anything
    that it can decode. No filtering by any criteria. Fortunately, these
    are long gone. Unfortunately, some repeaters (DWL-900AP+) can
    simulate this abomination by using ANY or a blank for the SSID.

    The 2nd type is one that filters by SSID. It will regurgitate
    anything that it can decode for a specific SSID. That also includes
    broadcasts, ARP requests, multicast, beacons, management frames, flow
    control frames, and such. The SSID filtering is crude and not very
    effective at limiting useless traffic. It would be really nice if
    there were additional filters available, such as by MAC address or IP
    address, but I haven't seen that. Neither have I seen one that only
    rebroadcasts traffic that is connected through the repeater.

    If the repeater were a true wireless bridge, which only passes traffic
    to devices that appear in a bridging table, that would work the way
    you describe. However, that's difficult bordering on impossible
    because the repeater only has one bridge port. There's no way to tell
    if a MAC address is appearing at an input or output to the bridge as
    the input and output are one and the same in a repeater. If the
    wireless bridge worked on two different channels, one for input and
    one for output, then it would work as you describe. However, none of
    the commercial repeaters or range extenders work like this. I have
    built what I guess could be construed as a wireless repeater out of
    two WAP11 wireless bridges back to back on different channels. That's
    what it takes to only pass unicast traffic to the connected endpoint.
    Nobody sells those (yet).

    The 3rd type is a WDS bridge. These are limited to compatible
    chipsets but work very well. All unicast traffic is directed and the
    bridge only repeats traffic destined to the other WDS device. That's
    because the MAC addresses of all connected WDS repeaters are
    pre-programmed into each WDS device. This is the least obnoxious
    repeater and operates the way you describe.
    The common range extender store and forward repeater does not work
    like that. It will repeat any traffic it can decode for a specified
    SSID even if that traffic is not destined to a device that goes
    through the repeater.
    That will work with two radios and two channels. There's also no
    reduction in wireless thruput as the system is full duplex. Nobody
    makes such a product and few (except me) bother to implement it due to
    the cost of two boxes. There are several mesh network vendors that
    also make multichannel, full duplex, poletop radios. For example:
    http://www.belairnetworks.com
    They have 3 radios in the box.
    No they're not. There's no input or output port distinction on a
    wireless repeater. It can't tell whether to forward a packet based on
    its MAC address as in a real bridge. Instead, the repeater has to use
    some other criteria to decide whether to regurgitate a packet. Except
    for WDS repeaters, they just retransmit anything they decode for a
    given SSID. Are you perhaps thinking of a WDS repeater?
    Ah yes. Convenience is a good thing. Incidentally, I've tinkered
    with the Dlink DWL-G710 range extender. It has horrible thruput
    problems when in the 802.11b compatibility mode. It's bad enough that
    the access point has to switch between 802.11g and 802.11b in the
    802.11b compatibility mode. Getting the DWL-G710 to switch at the
    exact same time seems to be a problem. When I tested the thruput with
    a DI-624 the packet loss with an 802.11b client (Orinoco Silver) was
    terrible. Turning off the compatibility mode prevented connections to
    802.11b clients, but at least sorta worked with 802.11g clients.

    Are you sure you still want to recommend using repeaters?
    Adding a 2nd access point does have it's limitations but nothing as
    bad as the excess traffic, chipset compatiblity, and 802.11b
    compatibility mode problems that I've itemized. If the 2nd access
    point is on the same channel as the main wireless router, then there
    is a possibility of mutual interference. However, if they are
    isolated by an aluminium foil back insulation RF barrier, methinks
    they could survive on the same channel. I installed a 2nd access
    point in a long thin house, with one radio at each end of the house.
    The two access points can barely hear each other and do not interfere
    much. Works fine. Of course, using different channels is the right
    way to do this and totally eliminates the interference problem. The
    only downside is that one must run a CAT5 cable between the boxes, or
    as you suggested, use power line networking to extend the system.
     
    Jeff Liebermann, Oct 10, 2005
    #24
  5. Roy Amin

    Jeff Gaines Guest


    If I remember the bad old days of CB radio burners were quite popular,
    wonder if anybody has come up with one for wireless networks yet?
     
    Jeff Gaines, Oct 10, 2005
    #25
  6. Roy Amin

    John Navas Guest

    [POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]

    In <> on Mon, 10 Oct 2005 10:31:52
    Yes. As I wrote in my follow-up, I've gotten good results without the
    downside of using a different channel. To be fair, both cases were 802.11g
    networks running in 802.11g mode only.
    As noted in my earlier replies, I select hardware carefully. ;)
    My experience: In the real world they often (usually?) won't be, and on
    different channels (as you recommended in your earlier post), they will
    pollute an additional primary channel, which I personally think is the greater
    sin.
    Indeed, in that special case. Where they overlap, as they often do,
    interference can be a big issue.
     
    John Navas, Oct 11, 2005
    #26
  7. Roy Amin

    John Navas Guest

    [POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]

    In <> on Mon, 10 Oct 2005 08:35:13
    <http://www.ce-mag.com/archive/02/Spring/cutler2.html>:

    In indoor applications, directional antennas can provide better
    performance than omnidirectional antennas. This is not due to the
    gain increase typically associated with directional antennas, but
    rather to backside and off-axis rejection that can reduce multipath
    cancellation. Not all directional antennas (e.g., Yagi antennas) have
    much backside rejection.

    Antenna gain results from focusing transmitted energy into a smaller
    cross-sectional area. Ideal radiators, called isotropic radiators,
    radiate energy in all directions from a point source at equal
    intensity. Limiting the radiated energy to a portion of this ideal
    sphere increases signal intensity in the focal area.
    Not necessarily -- depends on which device is operating closer to its noise
    floor. If that's the client, then an increase in access point transmit power
    can help, and vice versa.
    Fair enough -- we disagree.
    Except for our different feelings about repeaters, I don't think we all that
    far apart, except that I'm perhaps a bit more pragmatic and sensitive to
    creating problems for neighbors. My order and sequence would be (in order).
    1. Move the wireless router closer to the clients.
    Ideal, but often not possible/practical.
    2. Better access point antenna orientation.
    Easy fix. Lock down access point with tough Velcro.
    Glue antenna in place.
    3. Better hardware.
    Way too much junk out there.
    4. Repeater or range extender. Watch out for compatibility issues.
    Agreed.
    5. Install a better antenna system on the wireless router end.
    Tradeoffs (loss of coverage in another area) may make that impractical.
    6. Add a 2nd access point on a different channel.
    Piss off the neighbors.
    7. Replace everything including clients with MIMO technology.
    High cost.
    8. Add directional or better antennas on the client radios.
    Impractical on mobile computers.
    9. Power amplifier (don't bother).
    Agreed.
     
    John Navas, Oct 11, 2005
    #27
  8. Of course there are power amps, linears, boosters, and all manner of
    illegal devices:
    http://www.hyperlinktech.com/web/24ghz_hp_amplifiers.php
    Is 25 watts for $4,000 enough? Of course you have to military,
    government, amateur radio operator, exporter, or wealthy to buy one.

    Some more made for ham radio:
    http://www.ssbusa.com/kunamp1.html
    Ooooh... 100 watts output. That should cook the coax, antenna,
    neighbors, and your dinner.

    Just one problem. You might have the strongest signal in the
    neighborhood (or country) but you still can hear any better than with
    a conventional wireless access point. Unless the other end of a point
    to point link is using a similar amplifier, all you're doing is
    jamming and creating un-necessary interference. Please note that
    Wi-Fi is one of the few technologies developed in the last 20 years
    that does not have automagic transmitter power control to minimize
    interference.
     
    Jeff Liebermann, Oct 11, 2005
    #28
  9. Please not that I did not recommend using an omni antenna. I only
    offered it as an option.
    That's correct. However, I can't tell from the description where the
    access point is located relative to ALL the users. A 10dBi panel
    antenna will have a beamwidth of about 60 degrees which is more than
    enough to cover the entire house. However, if the garage user is
    located behind the antenna, there will be problems. I've done indoor
    directional antennas, but only when the radios are at the ends of
    house and the antenna is pointed inward. Working from the back of a
    panel antenna does not work very well.
    True. I'll dig out my notes and run some calculations on the
    theoretical maximum sensitivity at 10^6 BER for various modulation
    schemes and data rates. What you'll find is that most of the chipsets
    advertise RX sensitivities that are very close to the noise floor.
    Unless someone comes out with a cryogenically cooled front end, the
    current crop of GaAsFET front ends are about as sensitive as can be.
    Incidentally, when I was doing bench tests for sensitivity and other
    specs, I found that the digital noise sprayed all over the circuit
    board by the non-RF parts of the circuit had a substantial effect on
    the receive sensivity. On the better boards, with little digital
    noise to ruin my tests, the variation in measured sensitivities over a
    production lot was as bad as 6dB. These were basically rejects as the
    bulk of the test boards were within a 2dB spread.

    So, lets see if the numbers make sense. The worst case sensitivity
    deterioration that I saw was 6dB (in dBm not dBv). Yet the suggested
    power amplifier will go from +17dBm to +30dB or an increase in 13dB TX
    gain. However, the receiver sensitivity only varies 6dB so we have
    anywhere between 7 and 13dB of overkill in one direction. I don't
    think that cranking up the tx power to compensate for a crappy
    receiver is going to do much good.
    I like your list better except for the repeater and range extender
    issue. Incidentally, if you had specified a WDS repeater, I might be
    a bit less venement about my hatred of repeaters.
    A variation of this is to seperate the access point (radio) from the
    router/modem section. The problem is that the conglomerated
    modem/router/access-point devices want to live where all the wires
    tend to come together. That's usually in the basement, in a closet,
    under a desk, or other places where hiding the wires is practical.

    However, the radio does not work very well buried in these locations.
    Therefore, by seperating the radio section (access point) from the
    rest of the boxes, there's quite a bit more versatility in locating
    the box and antenna. Up high, on a bookshelf is a good place. There
    are only two cables (power and ethernet) required so wiring isn't as
    bad as to a modem/router which has many more cables involved. It also
    has the advantage of allowing easy replacement of the radio section
    when the next generation of acronyms appear on the market.
    Linksys makes SM01 mounting plate for their plastic boxes. Costs
    about $2/ea.
    | http://www1.linksys.com/products/product.asp?grid=36&scid=47&prid=504
    As you noted with the WG511, it's somewhat difficult to differentiate
    between the good stuff and the junk. I'm in the biz and I get fooled
    a bit too often.
    I would repeaters and range extenders in the desperation category.
    That's what I would do first or 2nd. Not because it's the best
    solution but because it's one of the easiest to try and probably the
    cheapest.
    A repeater will also piss them off if they're within range by doubling
    the amount of traffic floating in the air. However, at least the
    repeater only trashes one channel. However, the 2nd access point
    could easily be on the same channel as the main wireless router if
    (and only if) they are sufficiently seperated and isolated from each
    other so as not to interfere with each other.
    Yep. Also impossible to add external antennas.
    Well, they are a pain but not bad it you're willing to tolerate some
    directionality. Most users will NOT tolerate directionality on
    devices like cell phones, where a change in user position can easily
    result in a dropped call. If the directionality is really obvious,
    like a panel antenna plastered on the back of a laptop lid, methinks
    most users can figure out where to aim it. If the laptop or PDA is
    too small for a decent directional gain antenna, then I agree, it's
    impractical.

    (I have some antenna design ideas and few prototypes that methinks may
    be practical, but nothing that will work for every possible client
    radio or attached computer/PDA).
    Thanks. At least we agree on one out of nine items.
     
    Jeff Liebermann, Oct 11, 2005
    #29
  10. Roy Amin

    John Navas Guest

    [POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]

    In <> on Mon, 10 Oct 2005 19:37:59
    I don't see how that follows. The amount of traffic on a given channel
    shouldn't be a significant factor in the amount of interference.
    No way would I put up with plastering a directional antenna onto my ThinkPad.
    :)
     
    John Navas, Oct 11, 2005
    #30
  11. Traffic amount most certainly does have an effect on interference.
    Double the traffic by repeating everything twice and you have twice
    the chance of a collision and 1/2 the available airtime during which
    to transmit. The speed adjustment mechanism actually makes things
    worse. When the access point detects errors and corrupted frames, it
    intentionally slows down the connection speed in order to improve the
    signal to noise ratio. As the speed goes slower and slower toward the
    1Mbit/sec lower limit, the amount of air time necessary to send a
    single packet increased proportionally. The longer the air time, the
    less time another station has to send their traffic. I've had some
    fun with an old Teletronics 802.11 (1-2Mbits/sec only) PCMCIA card.
    When I start to move traffic, everything else just about stops because
    there's very little available air time left.

    For intereference testing, I use streaming UDP audio from some station
    on Shoutcast. The traffic rate is well controlled and there are few
    ACKS/NACKS floating around. As I switch to higher and higher UDP
    bandwidth sources, the interference level (as measured by the
    sustained thruput) of a nearby access points drops rapidly. As I
    said, increased traffic means increased interference.

    Incidentally, you can defeat the speed reduction system by fixing the
    speed of the access point. For high interference environments, I
    usually pick 6, 9, or 12Mbit/sec OFDM as well as turn on CTS/RTS flow
    control. The resultant thruput is nothing spectacular, but is far
    less susceptible to interference induced problems. Lowering the
    fragmentation threshold, in order to send smaller packets doesn't seem
    to help much so I just leave it alone.
    I was going to ask you what you thought of my idea. Violent
    opposition usually implies that it's a fabulous idea. Perhaps I'll
    work on it some more.

    I have a semi-working prototype. It's about 6" x 6" x 0.35" thick.
    It's a patch antenna made from foam board, aluminium foil elements,
    and a vacuum formed cover. In order to keep the thickness down, I
    have to live with about 8dBi gain instead of the 10dBi that a thicker
    antenna would produce. For additional gain, I was thinking of
    replacing the patch with 4ea phased folded dipoles in an array, but
    that will require an expensive circuit board.

    There's a flange around the edge which allows mounting with Velcro,
    scotch tape, chewing gum, and threaded fasteners. I'm working on a
    spring loaded clip on mount that's designed for temporary attachment
    to the laptop lid. Surely the added gain and directionality will
    compensate for any aesthetic considerations.

    I also have an inflatable version that works amazingly well.
     
    Jeff Liebermann, Oct 11, 2005
    #31
  12. Roy Amin

    John Navas Guest

    [POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]

    In <> on Tue, 11 Oct 2005 09:55:25
    With all due respect, that's just relative amount of sucking, which I don't
    think is in the same ballpark as consuming another primary channel -- in my
    experience, a repeater on the same primary channel is usually much less of an
    overall interference problem than hogging two of only three primary channels
    with two access points would be.

    A caveat is that many consumers and access points are dumb enough to use only
    channel 6, which in my not so humble opinion is a big (if not the biggest)
    reason for WiFi dissatisfaction. (There's really no excuse for an access
    point not being smart enough to sniff signals and pick the clearest available
    primary channel by default, with of course the ability to override auto
    selection.) In this case adding a repeater will tend to make things worse
    than putting a separate access point on a different primary channel, although
    again that's relative amounts of sucking -- it would be better still to put
    both an access point and a repeater on the same different primary channel,
    thus eliminating all interference on channel 6, and minimizing consumption of
    the band.
    I suspect there are cases where that might be an acceptable tradeoff, but not
    in most cases I can think of, in part because of the need to orient the
    computer in a particular direction. If and when I really need a better
    antenna, I'd rather have something as compact as possible that just plugs into
    my PC Card so that I can position it independently of my computer. But then
    I'd also have to get a good PC Card with an antenna connector that also works
    well without an external antenna. I just can't get excited about all that.

    As an additional data point, I've done some careful testing of the Netgear
    WG511 against a Toshiba notebook with integrated 802.11g WiFi and an
    (omnidirectional) antenna in the lid, and haven't found significant
    differences.
     
    John Navas, Oct 11, 2005
    #32
  13. Roy Amin

    C Denver Guest

    Just centralise the router.

    Put it in the centre of the house.
     
    C Denver, Oct 24, 2006
    #33
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