Kid is traveling in Europe, -90dB, what's the sensitivity Nexus 5

Discussion in 'Wireless Internet' started by Paul B. Andersen, Jun 30, 2015.

  1. Paul B. Andersen, Jun 30, 2015
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  2. I don't have a Nexus 5. It might be helpful to note that poor wi-fi
    sensitivity seems to be a common problem with Lolipop (Android 5.0),
    but which is now allegedly fixed:
    Suggestions vary from rebooting the wi-fi by going in and out of
    airplane mode, to rolling the phone back to Kitkat. Some hints.

    How far away is the access point that's producing the -90dB signal on
    her phone? It might be too far away, or there may be too many
    obstructions in the way.
    Jeff Liebermann, Jun 30, 2015
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  3. It's about 60 feet away but through walls and I think it's just
    attenuated. That's why every decibel counts.

    If the sensitivity is, say, -98dBm, then she has 9 dB of headroom,
    which isn't much but it might be enough.

    I generally shoot for 10dB to 15dB of headroom on the SNR.
    But it would be helpful if I could find the spec for the
    Nexus 5 (all other radios provide the receiver sensitivity).
    Paul B. Andersen, Jun 30, 2015
  4. That's a fairly good reason for low signal levels, even if the Nexus 5
    didn't have a wi-fi sensitivity problem. By "walls", I assume that
    means 2 or more walls, which is usually enough at 60 feet to reduce
    the signal level to near zero. I just tried it with my office router,
    putting one wood wall (no foil backed insulation) and a concrete wall
    between my router and my Nexus 7 tablet at 60 ft. One bar and many
    disconnects. You might be expecting too much at 60ft.
    The sensitivity of the receiver doesn't tell the whole story. I could
    dig out the chipset used in the Nexus 5, try to find the
    specifications, which usually require an NDA to obtain, the produce a
    range of numbers depending on the connection speed and frequency (2.4
    or 5GHz). However, I would also need to know the gain, orientation,
    and location of the antenna in order to get the field strength
    sensitivity. In other words, this is going to get complicated very
    You're doing it the right way. Using SNR instead of signal strength
    includes local noise and interference levels. These are important and
    could also be a problem. If the Nexus 5 has a problem where "noise"
    from the circuitry lands on 2.4 or 5GHz and trashes the receiver, it
    might explain why the Nexus 5 seems to have a sensitivity problem. The
    sensitivity might be there, but if the signal is buried in the noise,
    the radio is not going to hear much.

    Anyway, I don't think she has much of a chance getting the phone to
    work at 60ft through 2 walls. Glass windows aren't much help these
    days because they're all covered with Low-Emissivity coatings, which
    block heat and RF, but pass light. Maybe finding a hot spot will
    help. I suggest she grab WiFi Analyzer:
    and use the meter display to search the strongest signal.
    The update rate (scan interval) can be tweaked down to about 2 seconds
    (under Settings) making it practical for sniffing around for the
    strongest signal.

    Good luck.
    Jeff Liebermann, Jul 1, 2015
  5. Yes. They are solid walls. She doesn't know what they are made out
    of (kids), but I told her to knock on them and she said they didn't
    Yes but. It's a basic measurement. All radios have them.
    They just don't seem to publish them for cell phones.
    I'm surprised, because it matters MORE the weaker the equipment
    is (so to speak).
    And I know none of that, and she couldn't possibly either.
    Yes. But. I'm guessing on the noise level of something like 95dBm or
    thereabouts (just based on noise levels here at home).
    I switched the T-Mobile plan this morning. Luckily they have a toll
    free International number +1-505-998-3793 where she can ask them
    for help.

    They got her going on cellular data (she had roaming turned off)
    and they showed her how to set up the "personal hot spot" so her
    friend on AT&T could glom off her cellular signal.

    It's only 3G but she was able to Skype with video today with me,
    so, it's good enough for the most basic stuff.

    T-Mobile said the new plan has unlimited data, but at 3G speeds
    only (at best). They said roaming is free. And texting is free
    and unlimited. The only thing that costs money is all phone calls
    (whether to the USA or within the country) are 20cents per minute.

    So, for now, since she can't get the WiFi going, she's OK; but
    her friend, who is on AT&T (different plan) has only 800MB of
    data before they start chargingher, and phone calls at 15 cents
    per minute, free unlimited texting, but no personal hotspotting
    (the friend is on an iPhone so it's dumber than the Android phone).

    They both said they tried to go to a place that offered free
    Internet but they said neither phone would connect. Since both
    phones are "modern", I suspect they didn't know about a web
    authentication or some other authentication process.
    I told her about it, but I had put on InSSIDer long ago, when it
    was still free (maybe two years ago when the Nexus 5 was new?)
    so that's how she knew the decibels.

    I just installed WiFi Analalyzer on my Android phone and it
    is actually similar to InSSIDer, only it has ads. It has one
    page for the graphs, another page for a signal strength
    meter and beeper, and it shows the BSSID which is important
    when you have multiple access points with the same SSID.

    Overall, it seems like a nice 1:1 replacement for the otherwise
    venerable InSSIDer which used to be freeware but which seems
    to now be $10.

    Thanks for the help! It's hot today where you are!
    Paul B. Andersen, Jul 1, 2015
  6. I did this graph in 2007 for various wi-fi routers based on the
    manufacturers published wireless router sensitivity claims:
    < sensitivity.htm>
    The jump in sensitivity is the overlapping 802.11b to 802.11g
    transition. The problem is that you can't really supply a single
    number and claim that it's the "sensitivity". As near as I can tell,
    these wireless router manufacturers simply used the numbers from the
    chipset makers data sheets.

    I've measured wi-fi sensitivity in the past. It's not easy and
    requires some rather expensive test equipment, which I had to borrow
    or rent. For measuring base line noise levels, disconnecting the
    antenna in order to make a measurement is counterproductive as much of
    the "noise" is coming from the handset via the antenna.

    So, I invented my own crude test, which is good for comparisons, but
    does not yield the numbers you seek. I fix the speed of the wireless
    router to 802.11g 54 Mbits/sec. I start streaming video with UDP and
    the smallest buffer size I can configure on the player. I then walk
    away from the router until the streaming video starts to fall apart.
    The transition point is very abrupt and quite obvious. The measured
    range is a direct indication of the overall quality of the receiver
    and antenna system. Unfortunately, there are a dozen other factors
    involved, which prevent this method from becoming anything but a way
    to compare the overall performance of two or more phones or devices.
    Before I accuse a handset of having "poor wi-fi sensitivity" I compare
    it with other handsets to see if it's really the handset or something
    The base line noise level depends on the local RF environment. Much
    of the noise comes from the handset itself. The typical 802.11g
    signal is about 25 MHz wide, or 5 wi-fi channels. If there are uses
    on these adjacent channels, it will appear as noise to the receiver.
    There are plenty of external sources of interference, that will add to
    the noise level. However, the worst noise comes from the handset
    itself. Digital circuitry generates noise, and the close proximity of
    the digital noise source to the handsets wi-fi receiver insure that
    the noise level is going to be rather high.
    Can her friend with the iphone connect to the wi-fi router that's 60ft
    away? If both phones have problems, it's a fairly good indication
    that there's nothing wrong with her phone. Testing additional phones
    in the same manner might also be useful.
    Yeah, that happens. However, buggy wireless routers are also
    amazingly common. The local coffee shop uses whatever is inside their
    Comcast "gateway". Several of my devices will not connect while
    others work normally. There are also ancient routers that have
    problems dealing with hundreds of new connections each day. Some
    hotspot owners turn down the tx power to prevent non-customers in the
    parking lot from connecting. That works, but makes things difficult
    for the customers inside the coffee shop.
    Yes, but I'm near the ocean and spent the day in air-conditioned
    comfort. When the sun went down, the fog rolled in, and it became
    rather cold.

    Incidentally, I've had to deal with a few Android phones where the
    owner claims that the wi-fi "drops out" too often. Upon
    interrogation, I usually find that it coincides with the phone going
    into standby, where it switches back to cellular data. Leave the
    wi-fi on full time and that problem will go away.
    Jeff Liebermann, Jul 1, 2015
  7. Interesting how the Ubiquiti lightstation was far better than all
    the D-Link equipment, and that the sensitivity went down appreciably
    by as much as 25 decibels over the speed range for the devices.

    24 decibels would be 256 times less sensitivity at the higher
    speeds! That's a lot!
    That's interesting. So that's why the curves all dip at that one
    point at around 10Mbps?
    Yes, but that's a problem with *all* specifications.
    We have to start with some kind of 'standard' sensitivity rating.
    I guess the other option is to measure NOISE.
    That wouldn't require fancy test equipment if the software can handle
    it. I know WISP radios have the NOISE software built in, for example.
    A physical drop is always a good thing to measure, and very clever.
    This is a relatively large city, so, it's gonna be noisy.
    Hmmmmmmm.... is that right? That's interesting. You'd think they have
    that stuff filtered out.
    The fact these kids are always together and one is on the crappy
    iPhone virtually guarantees high noise then.
    Nope. What they are doing now, since they don't have WiFi, is that
    the iPhone user is on airplane mode and is glomming off my daughter
    who was walked through how to set up a personal hotspot.

    So, the T-Mobile Android personal hotspot is serving all the
    WiFi for the two kids' needs using her cellular data connection
    from T-Mobile (who says it's roaming with four companies).
    Interesting tidbit to look out for. Thanks!
    Paul B. Andersen, Jul 1, 2015
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