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Your Computer and Cell Phone Are Lying To You

Posted by timothy on from the they're-in-it-with-the-aliens dept.

Ant writes with a story from Dan's Data, which says that the battery meter and connection-strength displays in your portable electronics are lying to you, "and not just when they whisper to you in the night." Quoting: "Mobile phones, and most modern laptops, have signal strength and battery life displays. One or both of these displays has probably been the focus of all of your attention at one time or another. Neither display is actually telling you what you think it's telling you. The signal strength bars on a mobile phone or laptop do, at least, say something about how strong the local signal is. But they don't tell you the ratio between that signal and the inevitable, and often very considerable, noise that accompanies it ..."

10 of 479 comments (clear)

  1. Wifi meters by lisaparratt · · Score: 5, Interesting

    Exsqueeze me?

    I've written a wifi signal strength meter for an embedded product. During my research, I found it was pretty much standard to base the bumber of bars on the signal to noise ratio, not the raw signal strength.

    1. Re:Wifi meters by tlhIngan · · Score: 5, Interesting

      I've written a wifi signal strength meter for an embedded product. During my research, I found it was pretty much standard to base the bumber of bars on the signal to noise ratio, not the raw signal strength.

      ... which is then overruled by the marketing department because brand 'B' only uses the signal strength, so that makes your product look bad when compared side-by-side, since theirs has more signal bars.

      In the case of cellphones, it's the carrier that determines how the bars map to signal strength (or quality, if it's possible to estimate). Some carriers demand that you show 5 bars down to a really pathetic signal strength value (I've seen close to -100dbi - just as a quick comparison, most wifi chipsets lose all connectivity between -80 to -90dbi, and the best tend to disconnect around -96dbi). The headroom between that and when the baseband loses the signal completely isn't that much.

      Which is why I laugh when I hear "More bars in more places". It's easy to get a "stronger" signal if you mandate that a phone must show more bars all the time.

      Now, this was for a non-GSM phone, so it was mandatory to get carrier qualified. But GSM carriers are equally bad, except they don't have as much control since you can bring in any compatible phone onto the network. The only thing the carrier can claim is their phones get a "better" signal (see? more bars than your phone!).

      I wonder if Apple had to jump through these hoops with the iPhone or just said to the carriers to screw it - they're designing the software their way and that includes battery and signal strength meters that make sense. Given what I see of cellphones, there's often a special baseband/firmware build for each carrier to cope with the differences... but the iPhone software seems to be either unified, or just a single build around the world. (Carriers oblige because the customers want the phone).

    2. Re:Wifi meters by usul294 · · Score: 3, Interesting

      SNR (signal to noise ratio) is how many dB of signal you have above your noise. (funny log math says log(A/B) = log(A)-log(B)), its a much much better measure of signal strength than just the signal power that you receive. The bars for your wi-fi reception meter correspond to bits encoded per cycle; wi-fi transmits up to 16 different shapes, each corresponding to a different 4 bit word, more noise leads to smaller words. The word length is determined by the bit error rate, which is basically a function of SNR.

  2. Laptop Battery Dying Too Soon by Renegade+Lisp · · Score: 4, Interesting

    This article gives me a hunch why my no-name laptop battery dies so quickly even when Ubuntu still thinks it has 10% charge and several minutes left. Didn't happen with the manufacturer's battery...

    Ubuntu usually does an excellent job analysing how good your battery really is (not sure if it's the kernel ACPI or HAL or GNOME that's actually doing it). But when the battery lies so blatantly, it seems even Ubuntu can't keep my laptop from sudden death without a proper warning or shutdown.

  3. No connection on a full signal by millwall · · Score: 3, Interesting

    Both my Blackberry and my Sony Ericsson sometimes decide not to connect a call when I have close to full signal. Judging from TFA this could then be because of high noise ratio.

    At the same time, I have always wondered why my phones do not give me any indication why the calls were not connected at the time. They both just return to the main screen after a long period of connection attempts.

  4. Batteries by fitten · · Score: 5, Interesting

    Dan doesn't seem to know much about batteries. Check out batter power discharge curves and such...
      http://www.mpoweruk.com/performance.htm Remaining power is estimated based on the charge of the battery. If you notice on those graphs, when you get out to the end of the stored charge, it drops off very quickly, which is why the gauge goes from half to empty quickly.

  5. Grey-ware needs input. by Therefore+I+am · · Score: 5, Interesting

    It really does not matter what these meters say as long as they are consistent. From long experience, my grey-ware then interprets the bars to give me a realistic expectation of battery life or signal strength. Move along now please. Nothing of interest here.

  6. Re:[Citation-Needed] by dotancohen · · Score: 4, Interesting

    Car manufacturers so the same thing with the gas gauge. the top half is more than the bottom half. If the gauge on my car is sitting at half, I'm down to 24 Litres out of a 60 Litre tank. Also, there's a gallon or two left when the needle is at E.

    Cadillac invented this in 1984 when they rolled out the electronic gauges which were linear. Customers complained about bad mileage despite the car being thriftier than it's predecessor. Some research showed that they were going by *how*often* they were filling up, not by *how*much*. So they made the gauge logarithmic and allowed another unaccounted for gallon at the end for safety.

    --
    It is dangerous to be right when the government is wrong.
  7. Re:gauges by compro01 · · Score: 4, Interesting

    They REALLY should bring that back, Hell, all manufacturers should put that kind of thing in their cars. I can't think of a better way to make going for high mileage widely "cool". Like trying for the high score on an arcade game.

    "Hey, guess what? I got 48MPG on my way to work!"
    "Oh yeah? Well I got 52MPG! Beat that!"

    Just simply harnessing people's competitive drive (not to mention the desire to save money) could do more than all the hybrids in the world, though that would likely lead to people buying hybrids in a quest for ever higher mileage.

    --
    upon the advice of my lawyer, i have no sig at this time
  8. Bullshit by vojtech · · Score: 3, Interesting

    1) Cell phones.

    Cell phones use a so called RSSI value for the number of the bars. RSSI is a Relative Signal Strength Indication, which is a best guess of the device how well the data transmission will go. Most use SNR directly, some use a product of signal strength and bit error rate (BER).

    The reason why it doesn't always match reality is that it's really a best guess by the phone, and reality is much more complicated than just that.

    2) Laptop batteries.

    Laptop batteries are using charge counters. Those are resistors with very small resistance ( 0.1 Ohm) tied to a precise voltmeter in a controller chip. By integration the controller knows rather well how much charge (how many electrons) have passed through it. With Li-Ion and Li-Pol batteries in use today, however, the situation got harder because the voltage of the battery varies a lot during discharge. Nowadays, modern batteries count energy, that is the product of charge and voltage as it moves in an out, giving a very precise output of remaining energy.

    The reason some batteries die very quickly once they stop showing full is because as Li-Ion batteries age, their internal resistance increases. More energy is lost within the battery during the discharge process and the amount of energy lost (and voltage decrease) is directly proportional to the current taken from the battery. At the same time, modern devices have switching regulators which take more current when voltage decreases to provide the same flow of energy to the device. Combined, this means that once the battery voltage of an aged battery starts dropping, it drops very fast.

    For cell phones, this is even harder, since they don't have charge counters - the batteries have to be cheap. There the remaining energy is guessed purely based on voltage. And old Li-Ion batteries will have almost full voltage when under light load, and fail when the load is applied, causing a phone to switch off.