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Your Computer and Cell Phone Are Lying To You 479

Posted by timothy
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 ..."
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Your Computer and Cell Phone Are Lying To You

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  • Pshaw (Score:5, Funny)

    by MistaE (776169) on Tuesday July 29, 2008 @09:03AM (#24384363) Homepage
    And I bet you're going to tell us next that DRM isn't for our own good and is just a way for conglomerates to steal more of our money with little effort done on their part. Hah!
    • Re:Pshaw (Score:5, Insightful)

      by cushdan (949520) on Tuesday July 29, 2008 @09:09AM (#24384483)

      And I bet you're going to tell us next that DRM isn't for our own good and is just a way for conglomerates to steal more of our money with little effort done on their part. Hah!

      skillful integration of two /. themes "I already knew that" "DRM is bad"

      • Re:Pshaw (Score:5, Funny)

        by hahiss (696716) on Tuesday July 29, 2008 @09:18AM (#24384689) Homepage

        I was impressed too, though really I was hoping for a car analogy as well. But I'm a guild the lily sort of guy.

        • Re: (Score:3, Informative)

          by hahiss (696716)

          D'oh. That's gild the lily. . . .

        • Re:Pshaw (Score:4, Funny)

          by Chris Mattern (191822) on Tuesday July 29, 2008 @09:43AM (#24385153)

          But I'm a guild the lily sort of guy.

          Ohhh, we represent the lily pad guild, the lily pad guild, the lily pad guild...

        • Re:Pshaw (Score:5, Funny)

          by Godji (957148) on Tuesday July 29, 2008 @09:48AM (#24385219) Homepage
          And I bet you're going to tell us next that DRM isn't for our own good and is just a way for conglomerates to steal more of our money with little effort done on their part, just like car manufacturers are telling you that driving an SUV is good for your safety while they make them with cheap truck chassis that are less maneuverable and do not reduce the impact of a collision nearly as much as a car chassis. Hah!
          • Re: (Score:3, Interesting)

            by internewt (640704)

            just like car manufacturers are telling you that driving an SUV is good for your safety while they make them with cheap truck chassis that are less maneuverable and do not reduce the impact of a collision nearly as much as a car chassis.

            Based on some of the replies in this thread, the manufacturers propaganda is working well. Suckers seem to be lining up to defend their death trap SUVs.

            But your post has been modded funny, no doubt as an attempt by someone who has a bad case of buyers-remorse that they can't admit to, to attempt to undermine your insight by getting your post labelled funny.

            I bet the crack-addled moderator likes the laughter track on "comedy" like Friends because it tells him when he should be laughing. So he projects this l

        • Re:Pshaw (Score:4, Funny)

          by lysse (516445) on Tuesday July 29, 2008 @11:22AM (#24387157)

          I'm a guild the lily sort of guy.

          Yes, because unionised flora is the only way to ensure fairness for plants at the hands of the oppressive petit-fauna elite.

  • [Citation-Needed] (Score:5, Insightful)

    by FredFredrickson (1177871) * on Tuesday July 29, 2008 @09:04AM (#24384399) Homepage Journal
    The article was indeed interesting, and believable. But it has a bad case of [Citation-Needed].
    • by zappepcs (820751) on Tuesday July 29, 2008 @09:23AM (#24384781) Journal

      There is no citation needed. I can personally attest to the fact that unless you pay tens of thousands for the equipment it's metering capabilities are ONLY an indicator, more or less like your gas gauge, and not some sensitive sensing system. period. ever.

      Most of the work done on electronics in the world is done without exacting measuring equipment. Yes, there will be those that argue, but *MOST* work is done with less than optimal equipment. Think that mechanic working on your car is using micrometers to do everything, or $2500 torque wrenches? For most of the world, good enough is ... well, good enough. Battery monitoring systems can only count down from full charge based on use and time. At best it is a simple calculation that cannot do much to account for aging of the battery or temperature compensation.

      No citation needed. That is simply how life is, and why this is a huge 'duh' article, even if joe bloggs doesn't realize it. It's the reason that your vehicle gauges are not calibrated. This applies to just about everything we use.

      • by fabs64 (657132) <beaufabry+slashdot,org&gmail,com> on Tuesday July 29, 2008 @09:32AM (#24384927)
        I know it's de rigeur, but that was quite a lot of writing for someone who didn't RTFA.

        Dan is claiming that (at least in cell phones) there is a deliberately misleading fudge factor.
      • by FredFredrickson (1177871) * on Tuesday July 29, 2008 @09:32AM (#24384937) Homepage Journal
        But that's just it- the article is very suggestive of conspiracy. Maybe the gauges are aproximations- I don't think that was ever up for debate. But your personal experience doesn't change the need for citations in this article- which I suggest you read.
        • Re:[Citation-Needed] (Score:5, Informative)

          by amram9999 (829761) on Tuesday July 29, 2008 @09:55AM (#24385401)
          I used to work for Motorola, and I can attest that the standard 3 bar battery gauge showed:

          50% of the battery life at 3 bars
          30% at 2 bars
          15% at 1 bar
          5% at 0 bars

          And yes, this was customizable by the carrier to make it better or worse. Of course, this is hard to prove to the sceptics unless the software is open source.

          There are numerous other technical reasons why the gauges might not be accurate, but this is a big factor.
          • by electrictroy (912290) on Tuesday July 29, 2008 @12:12PM (#24388151)

            Every car I've ever owned has worked the same way. The bar will remain on "F" until 60% is reached, and then it gradually starts dropping. When the gauge claims I have "1/4" I really only have 15% of my fuel tank left.

            I've heard stories of car companies trying to make more accurate gauges, but the customers complained that the car was "half empty" after "only" 150 miles. They prefered the old gauges that still showed almost-full, even though those gauges were lying.

            So I suspect the real conspiracy is just "the ignorance of the average citizen" that led to deceptive gasoline and battery meters.

               

      • Re: (Score:3, Insightful)

        by Derosian (943622)
        I know it isn't the point of your post but you seriously only need at most a $100 dollar torque wrench for accurate results.
    • Wikipedia disease (Score:2, Interesting)

      by Medievalist (16032)

      The article was indeed interesting, and believable. But it has a bad case of [Citation-Needed].

      Cites are not required for independently verifiable claims.

      This is the difference between faith and science. If you give someone information that they can independently verify, and they base their belief on the results of their independent results, that's science (even if they are wrong, it's still application of the scientific method). If you ask someone to believe something based on the idea that a person who says it is trustworthy, that's faith (although not necessarily religious faith). Insistence on

  • pedantry (Score:5, Insightful)

    by caffeinemessiah (918089) on Tuesday July 29, 2008 @09:04AM (#24384403) Journal

    Neither display is actually telling you what you think it's telling you.

    Who cares? When it's full, my laptop or cellphone works great. When it's empty, the thing stops working. When there's only a few bars left, I either plug it in / move to a different location. IMO, it perfectly performs its intended duty. Anything beyond that is geek pedantry and nitpicking.

  • by sudog (101964) on Tuesday July 29, 2008 @09:05AM (#24384413) Homepage

    And I even have a little meter for it mixed in with my signal strength.

    I find it pretty useful.. I'm pretty sure everyone's wireless chipset can tell them how much noise or at least how many mangled packets arrive. It's just the little dummy strength meter doesn't convey any of that. I liken most of those sorts of things to the CEL light in cars anyway. Good to know when something's not *perfect* but not so good for understanding why (nor whether it's just a gas tank cap seal broken, or a head gasket blown.)

  • Wifi meters (Score:5, Interesting)

    by lisaparratt (752068) on Tuesday July 29, 2008 @09:06AM (#24384443)

    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.

    • by wattrlz (1162603)

      It does seem a little dishonest though, don't you think? In the past when I had five bars I thought that meant that I'd a decent margin of error between a conversation and *NO CARRIER*. It just sort of made sense.

    • Re:Wifi meters (Score:5, Insightful)

      by russotto (537200) on Tuesday July 29, 2008 @10:21AM (#24385947) Journal

      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.

      Not in the least because many common wifi chipsets don't make raw signal strength available to the rest of the system. Cellular modules do, but if you ask a phone maker how the number of bars corresponds to the error rate and signal strength, they won't tell you. Although a bit of experimentation reveals that as long as the error rate is low and the signal is above the noise floor, you get full bars. That's probably marketing.

      The battery conspiracy thing is a bit silly. Rechargable battery chemistry follows an S-curve. There's a very short period at the beginning with the battery over the nominal voltage, a long and almost linear middle section, and a short period at the end where the voltage drops quickly. So a naive voltage measurement gives exactly as described in the article -- almost full most of the time with a quick drop at the end. A less naive measurement is very tricky because the voltage in the linear section depends not only on state of charge, but current draw, recent current draw, temperature, the age of the battery being used, etc. The best way to do it accurately is to track a particular battery through its charge cycle and monitor current in and current out. Smart batteries like those in laptops do. I don't think cell phone batteries are smart batteries.

    • Re:Wifi meters (Score:4, Interesting)

      by usul294 (1163169) on Tuesday July 29, 2008 @10:43AM (#24386431)
      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.
  • by Renegade Lisp (315687) * on Tuesday July 29, 2008 @09:07AM (#24384453)

    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.

  • by millwall (622730) * on Tuesday July 29, 2008 @09:09AM (#24384495)

    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.

    • by Steve J 83 (1267120) on Tuesday July 29, 2008 @09:20AM (#24384723)
      No, that's because the base station that you're getting your signal from has no bandwidth left. You could be standing next to the antenna, and have 'full' signal, but if 'all circuits are busy' you're SOL regardless of the signal strength.
      • by millwall (622730) *

        This is also a plausible reason seeing that every radio base station can handle X number of connections simultaneously.

        How do you know for sure that this is what is happening and that it is not the noise ratio that is too high?

        A phone will not give you any indication as to what is going on behind the scenes.

  • If I'm being lied to, will my tinfoil hat help in this case?
  • The balance (Score:4, Insightful)

    by Midnight Thunder (17205) on Tuesday July 29, 2008 @09:10AM (#24384513) Homepage Journal

    The engineers dilemma, at least for battery levels:
      - how the real value taking into account all variances including current usage and thus constantly move up and down the value
      - average out the results to something close, but not exact, since this is what satisfies most people

  • by Aliencow (653119) on Tuesday July 29, 2008 @09:11AM (#24384519) Homepage Journal
    Is it just my luck or are all cars like that? You go 200km on the first 25% of the gauge, but can barely get to 550km before it's empty?
    • Re: (Score:3, Informative)

      by Wiarumas (919682)
      Don't quote me on this because I'm not entirely sure on it. My fiance's father is an automechanic and he once told me this - the last quarter tank is the smallest. In other words, the guage does indeed lie to you... the second half of the tank will dwindle faster because its smaller.
      • by X0563511 (793323)

        The best part about my car is the huge dent in the bottom of the tank... previous owner had jacked up the car with the fuel tank.

        Mine goes from 1/4 to empty REAL fast.

      • Re: (Score:3, Interesting)

        by shiftless (410350)

        There are a lot of factors involved that cause fuel tank gauges to not read linearly. For one, there is a "float" in the tank attached to a pivot arm that moves an arm across a rheostat to change resistance depending on tank level. Since the arm swings in an arc, the resistance change is not linear. Second, the tank is oddly shaped which throws off the reading. Third, there is usually a "reserve" capacity built in where the gauge may read empty, but there is still fuel in the tank below the level of the flo

    • by rob1980 (941751)
      The one in my car is always wrong - it's broken, and reads as empty all the time. ;) But I have noticed that in some other cars I've driven, though.
      • by smoker2 (750216)
        Why not replace it ?
        It's usually only fuel inside the float so that it sinks to the empty position. If you can find the hole you could easily fix it with a self tapping screw.
    • by houghi (78078)

      Yep, same with mine and every other I have seen. And then even empty does not mean empty all the time.

    • by wattrlz (1162603)

      There was a time, I believe, where the fuel gauge was connected to a float in the tank that would hit the top at around three quarters full and thus be pinned there, semi-submerged, from full to a little over half a tank. From half down it would be relatively accurate though. Perhaps this time hasn't quite ended?

  • Batteries (Score:5, Interesting)

    by fitten (521191) on Tuesday July 29, 2008 @09:15AM (#24384599)

    Dan doesn't seem to know much about batteries. Check out batter power discharge curves and such...
      http://www.mpoweruk.com/performance.htm [mpoweruk.com] 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.

    • Re:Batteries (Score:4, Insightful)

      by maxume (22995) on Tuesday July 29, 2008 @09:33AM (#24384945)

      You statement implies that you think it is more useful for the battery meter to display the charge level of the battery rather than the approximate amount of run time left.

      For 99.99999999% of the people on Earth (that's everyone other than you), I'm pretty sure that a linear run time indicator is wildly more useful than an actual charge indicator.

      • Re:Batteries (Score:5, Informative)

        by imsabbel (611519) on Tuesday July 29, 2008 @09:54AM (#24385379)

        No, like the article, you dont get it:

        They use this curves to make a voltage->charge conversion.
        But take a look at them, and guess what will happen if there is only small calibration error/battery defect/heat influence, that shifts the voltage a few 10mV: Suddenly, you might already be on the curve sloping down while the device still thinks its in the middle of the platau.

        Smart electronics try to learn from past discharge behaviours, but for many gadgets, its just not possible: The ipod you left in your car in the summer will behave diffrent for the next charging cycle than the one that was near freezing in the winter.

        The cellphone that was just running for a week in standby will behave different after the next charge compared to the one that was drained dry in 3 hours by watching divx videos on it.

        And dont even mention partial chargings, which add a hysteresis on top of this things.

        Its a very difficult problem, and devices really try their best to solve it.
        But there is a reason why the controller board of a bigger laptop battery (that has 1% accurate meassurements) is bigger than you whole cell phone...

  • It's just like the fuel tank in my gas-hungry 300M... I can go 300km before I hit the half empty mark, but only 125km before it's empty.

    On another (more geeky) note, it's also like the progress bar of any install program. It take 2 minutes to get to 98% done, and another 5 minutes before the install is actually completed.

    Progress bars, meters and measurement instruments are there only to give you an approximate indication of where you are compared to where you were. Some are more precise (ruler, multi
  • by Therefore I am (1284262) on Tuesday July 29, 2008 @09:16AM (#24384637)
    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.
  • yes, yes they do (Score:3, Insightful)

    by 192939495969798999 (58312) <<info> <at> <devinmoore.com>> on Tuesday July 29, 2008 @09:16AM (#24384647) Homepage Journal

    That's funny, because when I have no bars, I can't call out, and when I have all the bars, my calls are great. Likewise, when the battery indicator is full, i can talk for a long time, but when it says it's low, it usually dies soon after that. That's all I need them to tell me. I could care less if it's counting signal strength or magic pixie dust, as long as less pixie dust means the phone is going to die that's fine with me.

    • Re: (Score:3, Insightful)

      by TubeSteak (669689)

      Likewise, when the battery indicator is full, i can talk for a long time, but when it says it's low, it usually dies soon after that. That's all I need them to tell me.

      I think the point is that it'd be nice if these things worked in a linear and predictable fashion.

      Showing 'full' from 100% to 51% is neither linear nor predictable.

  • GASP (Score:5, Funny)

    by oodaloop (1229816) on Tuesday July 29, 2008 @09:16AM (#24384653)
    Are you trying to tell me that the constantly changing field of electro-magnetic radiation pouring through my laptop does not always match up precisely to the five bars in the display? Frankly, I find that hard to believe.
  • very discouraging
  • by captaindomon (870655) on Tuesday July 29, 2008 @09:22AM (#24384753)
    Signal strength and battery time remaining can get pretty complicated, the more you look into it. There are a ton of different measurements, historical information, performance expectations, etc. that are constantly changing based on how the device is being used, who is using it, etc. At some point, you need to condense all of that information into some pretty little bars that a *normal* user (i.e. someone who has never heard of Slashdot) can comprehend. Is there going to be some precision lost? Of course. Is the graphical representation going to convey all the data gathered and interpreted by the device? Of course not. But the idea is to make it as useful as possible.
  • by glindsey (73730) on Tuesday July 29, 2008 @09:26AM (#24384837)

    Cingular loves to tout "More bars in more places".

    "Higher signal-to-noise ratio across a broader range of the United States" just isn't quite as catchy a slogan.

    • Re: (Score:3, Insightful)

      by maxume (22995)

      Taking the article to heart, maybe the reason they have more bars in more places is because they start at 3 bars for no signal and go all the way up to 4 bars for full signal.

    • Re: (Score:3, Insightful)

      by torkus (1133985)

      Hey now - they said NOTHING about signal strength or SNR. Just "more bars". If (bars > 0) then bars++

  • ...they always tell me size doesn't matter
  • Ugh (Score:5, Informative)

    by Se7enLC (714730) on Tuesday July 29, 2008 @09:28AM (#24384871) Homepage Journal

    #1, even with a voltmeter you can't reliably predict battery life. With an alkaline AA battery, you could watch the voltage drop from 1.5V down to 1.1 and know that it was now dead - but with newer rechargeable batteries, the voltage doesn't drop until it's completely dead, so you can't easily guess how long it will take. The only way to do it would be to have the device keep a history of how long it is able to work before the battery dies completely and statistically predict future performance. As if they are going to waste time doing that!

    #2 Yes, noise should be considered, but an exact signal to noise ratio isn't going to predict bandwidth or call quality, either. I'm pretty sure that the "signal" they measure is actually signal-to-noise anyway. But even just signal strength is still useful, since you can assume that noise isn't changing that much.

    Gas gauges? How many people see that their car stays "full" for a long time and then drops sharply? Or says that it is empty when there's still a few gallons left? Mine will tell me "0 miles to empty" and drive for another 50 miles without coming close to empty. Speedometers? They can be off by 5 or 10% right from the factory. Really every gauge is inaccurate by some amount.

    My guess is that companies make the gauges vague on purpose, so that people DON'T try to get too much (false/misleading) information out of them. If your cell phone can make a phone call with "2 bars" of signal, that is all the information you should be taking away from that measure. And if your battery says full for 2 days and drops sharply on day 3, you know that when it starts to drop it's time to charge it. That's all the information you need. Does anybody really think that consumers will be happy with a voltage display? I don't even know what voltage my phone operates at, let alone what the low-end of operating voltage will be.

    • Re: (Score:3, Informative)

      by DougWebb (178910)

      My guess is that companies make the gauges vague on purpose, so that people DON'T try to get too much (false/misleading) information out of them.

      That's a guiding principal for conveying quantitative information. There's accuracy, and there's precision. The accuracy of a measurement tells you how correct the measurement is relative to the actual value you're trying to measure. The precision tells you how specific the measurement is, or to put it another way, now narrow the range of actual values the measurem

    • Re:Ugh (Score:4, Informative)

      by torkus (1133985) on Tuesday July 29, 2008 @10:31AM (#24386173)

      1) Li-Ion and Li-Po batteries have internal chips that can tell exactly how much charge is in a battery (you've never over-charged a Li-based battery). The curves are much more flat but under load it's not especially difficult to know the charge state quite accurately. Heck, IBM even will tell you the charge/discharge current to two decimal places with some of their utilities.

      2) You're guessing. In addition, noise is often more dynamic than signal levels. SNR is a MUCH more accurate determination of quality of bandwidth.

      Gas guages, yes they're inaccurate - likely because manufactureres assume people are stupid. I just watch the pump and see how much gas i put in, subtract from the full-tank size and it's not so hard to determine how accurate the guage is. Speedo's are allowed to be a certain % off of actual but you have to take into account that the diameter of the tires on a car change as they wear. So yes, consipracy theory this and that but a speedo is not going to be perfectly accurate by measuring the drive shaft rotation.

      Did you even glance at TFA? You're simple repeating much of what was said. The rest - assuming people are incapable of reading a simple guage frightens me. I mean, if you have to coddle the general population because they're all THAT stupid we've got bigger issues than the last 3 minutes of talk time on your cell.

  • For most phones the signal bars are NOT how well you can receive the tower, but the tower sending back to the the phone the RSSI (received signal strength indication) value. This is the tower telling the phone how well it can "hear" it. For sure, your tiny little phone is going to receive a signal from that tower better than it will receive one from your little 600mw handheld phone. Want a better signal? Use a 3-watt car phone.

    This is tied to the battery life. A hand held phone will only transmit at the

  • by oahazmatt (868057) on Tuesday July 29, 2008 @09:34AM (#24384971) Journal

    Your Computer and Cell Phone Are Lying To You

    Oh, thank God! I was worried I was the only one who could hear them!

  • It seems to me the phone's not the one that's lying. It's the marketing and promotion (I'm looking at you, AT&T) that implies that more bars = stronger signal. As the Chief Engineer succinctly puts it, "A computer doesn't lie." If we had some actual truth in advertising it would clear up many misconceptions about technology and how it really works. (Wow, my sig is actually pseudo-relevant in this thread!)
  • My first computer told me, Windows 95 was stable and secure...
  • As a developer (Score:4, Insightful)

    by timias1 (1063832) on Tuesday July 29, 2008 @09:39AM (#24385069)
    I have written code specifically around converting RSSI (Received Signal Strength Indication) into those signal bars, and a couple of things.

    There isn't standard regarding what reported dBm value should be associated with 1-5 bars. It is purely up to the discretion of the programmer. I have heard RSSI referred to as Relative Signal Strength Indication as well, because the value is at the mercy of internal A/D tolerances. I have seen several copies of the same radios in a lab, (Faraday Cage) report drastically different RSSI values (AKA Bars). Nearby RF sources can influence the signal levels as well.

    So that part of the article is true. I dare say anyone who actually knows anything about RF won't claim, bars guarantee connectivity. To say that it is lying to you because you don't understand how it works, makes the submitter look silly. Definition of "Lie" from Wikipedia: "A lie (also called prevarication) is a type of deception in the form of an untruthful statement with the intention to deceive"

    We aren't trying to deceive you, we give you the indication because it is better than nothing, and most of the time it is good enough.

  • I could easily believe that the wireless strength meter is "lying" by not reporting S2N ration but the battery meter is a different kettle of fish.

    I, too, have seen how mobile phone batteries are full according to the meter then drop rapidly but I have always assumed this is because of the chemistry used. It's been a while since I studied chemistry but IIRC the way the "fullness" of a battery is measured is by it's potential. One of the really great things about Li based batteriees is that they have almost

  • by Petersko (564140) on Tuesday July 29, 2008 @10:25AM (#24386027)
    You mean that something with as many variables as strength and quality of a wireless connection can't be reduced to a value of "bars" between one and five without loss of information? Say it isn't so.

    Slow news day, apparently.
  • by Anonymous Coward on Tuesday July 29, 2008 @11:17AM (#24387079)

    It is quite common for laptop batteries to overestimate the remaining time, it even gets worse the older the batteries are: As they expose a sudden and sharp voltage drop at the lower end of their capacity, it really is hard to determine, how much time really is left.

    So even though the manufacturers tend to program too optimistic parameters into the drivers, they are bound to be inaccurate as time is passing and the batteries get old.

    You can use tools like IBAM from http://ibam.sourceforge.net/ to profile your batteries more accurately and gain more trustworthy readings for your time left running on batteries.

  • by CottonThePirate (769463) on Tuesday July 29, 2008 @01:30PM (#24389395) Homepage
    I have AT&T and I think they got more bars in more places by using this simple formula. I now NEED 3 bars to reliably make a call. I used to be able to have some hope at 1 or 2, but not in the last year or so. I realize the point of this article is that bars don't mean anything anyway, but I feel they have been adjusted a lot recently.
  • Bullshit (Score:4, Interesting)

    by vojtech (565680) <vojtech@suse.cz> on Tuesday July 29, 2008 @02:56PM (#24390773)

    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.

  • It doesn't matter. (Score:3, Insightful)

    by blair1q (305137) on Tuesday July 29, 2008 @07:24PM (#24394247) Journal

    Your phone isn't telling you either the strength of your signal or the SNR.

    It's telling you which level of transmit power it is using.

    If your phone can show n bars, it has n+1 transmit power levels. Subtract the number of bars it shows from n+1 and you will know the integer value that is in its transmit-power variable. If you see 0 bars, your transmit power is cranked up to 4, for example.

    Why does it vary the transmit power? Sometimes it's because the tower is measuring the power that it sees from your phone, and sends back an increase-power or decrease-power code in one of the messages they are exchanging. Your phone can't measure these things (waste of space and power). The tower doesn't want you blasting other phones off their links, either. If your phone can't see a signal it will simply go to full power and broadcasts connection requests (this is why your phone dies quickly when you go roaming).

    If the tower can't see you any more, it just doesn't say anything. If you can't see the tower, you start transmitting at full power. "Can't see you" includes rejecting packets that are corrupted by noise. So if there is a enough noise to make the signal unrecoverable, regardless of the real signal strength, your phone will be trying to get through by going to full power.

    The fact that some phones continue to send balky noises to your earpiece is a feature. It is giving you what it has rather than resetting the connection.

    And the noise that causes those balky noises in your earpiece may not be radio noise in your area. They could be radio noise at the other end, or errors in any part of the transmission chain between your tower and the other end. There will never be a way to measure the end-to-end bit-error-rate in a cell phone. No point telling you in a number what you can already hear.

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