Saturday, April 17, 2010

Phone wallpaper color can affect battery life

It seemed like some kind of a joke when I first read about it: with the recent phone displays made of OLED (Organic LED), the battery power consumed by the display varies based on the color being displayed. This was however not true with normal LCD displays found in most current and older generation phones or laptops.

In regular LCD displays, the screen is illuminated by a separate back-lit and the pixels themselves do not emit any light. In the case of OLED displays, the pixels themselves are illuminated and there is no need for a back-lit. Therefore, the power consumed by the display is basically dependent on how many of these pixels are illuminated and to what level. According to an article, a color profile with black background and white text consumes nearly 1/3rd of the power consumed by one with white background and black text.  In this case, the pixels that display the black color are not illuminated at all thereby saving battery life. HTC Nexus One has an OLED display, whereas all versions of the iPhone until now has regular LCD displays with back-lit.

OLED displays have other advantages aside from battery savings: their refresh rate is much higher, and they also render pretty sharp colors.  However, they do not fare well under sunlight as the maximum brightness of OLED pixels is still lower than what separate back-lits can provide.

So to save battery life on the Nexus one, set a dark background!

Friday, April 16, 2010

Holy Basil

I wanted to give away this Holy Basil plant of mine as I was moving, and was concerned if there'd be anyone interested in taking it. I posted a note in the local Desi club here in Mountain View for what it is worth, and was surprised to see more than 20 people respond within 5 minutes of sending it, many of them seemed frantically interested.

I just don't get the reason for that kind of enthusiasm.  I do understand the sentimental aspect which was why I was having it in the first place.  But clearly this is not so rare an item - anyone could get basil seeds from Walmart or any other store and grow their own plant in less than a month.

Monday, April 12, 2010

Is Assisted GPS better than Standalone?

Personally, I think GPS is one of the great marvels of science. The ability to precisely pinpoint your location with an accuracy of a few feet is incredible and is exceptionally useful. While GPS technology has been around for a long while, it's becoming more pervasive in the recent years after it found it's way into cell phones. Most medium to high-end cell phones today have inbuilt GPS hardware. In the context of cell phone GPS, I am sure everyone would have heard the term "A-GPS" which stands for "Assisted GPS". There's been poor understanding about the difference between the GPS hardware present in conventional navigation systems and these A-GPS hardware present in recent cell phones. So far, I've been under the impression that A-GPS  is something that cannot function without data about the initial co-ordinates (orbit/ephemeris) from a cell tower, until I talked about this to one of my friends (an MIT graduate) who is an expert in this field. There's been conflicting information about this on the web, and it also appears that some of the Wikipedia articles on this topic have incorrect information.

So apparently conventional navigation systems have a stand-alone version of GPS which obtains a location fix from scratch on their own, including the initial orbit/ephemeris data. This initial setup is pretty computation-intensive and takes a long time to obtain, thereby consuming significant battery power. Once the ephemeris information is obtained, the precise location fix is pretty fast. Stand-alone GPS systems can sometimes take even tens of minutes to obtain a fix because of this initial computation. They can also sometimes never get a fix when they are not in clear view of the sky.

A-GPS however, has an add on to the standalone GPS chip which is capable of obtaining precomputed orbit/ephemeris data from the cell tower instead of computing it on it's own from scratch, and hence is many times faster and energy efficient compared to standalone GPS. A-GPS chips' functionality is however a strict super-set of the functionality of a standalone GPS, as even if the cell tower fails to deliver the data, the A-GPS can fall back to normal standalone mode. According to my friend, there is no such GPS chip that cannot fall back to the standalone mode in the event of not being able to get the assistance of the cell tower, and if at all such a limitation exists, say, in a cell phone, it is artificially imposed by software. So according to my friend, if you have a cell phone whose GPS does not work without a cell signal, you should blame the phone software for it.

So yes, Assisted GPS is better than standalone, in all respects.

Note: Of course, obtaining approximate location using cell phones by cell tower "triangulation" is totally different from the above, and it can be done in pretty much any cell phone, as it does not require any GPS hardware.

Sunday, April 4, 2010

Zeno's paradox

I've always been intrigued by paradoxes in Physics, my favorite being the Zeno's paradox.  While there are various paradoxes in different fields, most I've come across are too mathematical in nature and do not directly relate to real world examples.  Zeno's on the other hand is a pretty interesting one and I've never had to try too hard to explain it to someone.   I was recently having a conversation about the Zeno's paradox with one of my colleagues and he had an interesting explanation and reasoning about the paradox.

The Zeno's paradox involves a segmented view of space or time. The tortoise and the rabbit (or Achilles) paradox says that in a race between a tortoise and a rabbit where the rabbit begins the race after a non-zero time delta from the time the tortoise began the race, it is impossible for the rabbit to ever win the race. This is because, say the starting position of the race is A, and while the rabbit began the race, the tortoise had moved to a position A+in the time interval d mentioned above.  Now, by the time the rabbit reaches the position A+x, the tortoise would have reached a different position A+x+y. This can be generalized to any position of the rabbit during the race, where, when it reaches a previous position T of the tortoise, the tortoise would have reached a different position T+farther from the rabbit, as the tortoise is in continuous motion.  Therefore, the rabbit always stays behind the tortoise and can never win the race, irrespective of how much faster the rabbit moves compared to the tortoise. It's also pretty easy to write a proof for this using mathematical induction.

Here is the reasoning that convinced me: the paradox is caused due to a distorted understanding of finiteinfinite, and infinitesimal distances. The laws associated with finite distances cannot hold true when the space is divided into infinitesimally short segments, as in the above case of the tortoise and the rabbit.  My colleague had a clearer explanation for this: basically the distance between any two points A and B in space can be divided into an infinite number of segments. Mathematically, the sum of an infinite number of distance segments is infinity.  However, when the individual distances themselves are infinitesimally short, their sum need not necessarily be infinity, and can be finite.  Therefore in the race between the tortoise and the rabbit, although there were infinite number of points, their sum is still finite (as the race is for a finite distance), and the above induction logic wouldn't hold true. 

Another of Zeno's paradoxes, the "Arrow of Flight" paradox is interesting too, and the above explanation seems to apply to that as well.