Uncategorized - 12 July 2012
Author: Jim Szymanski

WiFi

Last week I stumbled upon a trick that will keep WiFi running on your WP device long after the screen has gone to sleep. The bug, or feature, was met with mixed reactions from; “great news” to “oh, we better tell Microsoft about this so we all don’t inadvertently kill our batteries.” That was enough ammunition for me to run a test. I did some preliminary testing on my non-SIM HTC Surround, which turned out to be very promising, but wanted to be absolutely certain I got my facts right, so here we go.

To recap, my phone (Lumia 900) is setup with the following:

  • - Data (mostly LTE) and Wi-Fi ON – Bluetooth OFF
  • - 8 Active Background Tasks (3 Internal)
  • - Location Services ON
  • - 5 Email accounts syncing (3 push, 1 every 15 minutes, 1 every 2 hours)
  • - Phone set down and untouched for a 8 hour period

My previous baseline tests have resulted in an 16%, or 2% per hour, battery drain in an overnight 8 hour test. For clarification, my Background Tasks include; USA Today, Fox News, Weather Channel, Mehdoh, Urban Dictionary, Network Dashboard, Clever-To-Do and Battery Meter (a homebrew app set to update every 10 minutes).

Test 1 – To setup for this test, I started by fully charging my L900. After taking the phone off the charger, I opened the iHeartRadio app (Skype, Spotify will work the same) and started to play some music. After about 5 seconds I paused the music and put my phone to sleep. I waited about 2 minutes and turned my phone on, verifying that WiFi was active at wakeup (it was) and then used the Back button to close out of iHeartRadio and any other running apps. Put the phone to sleep again and waited 2-3 minutes before waking a second time to verify that WiFi was remaining on. I then put the phone to sleep again and let it sit untouched for my 8 hour test. FYI, when I woke the phone after 8 hours I did verify that WiFi was still running (persistent WiFi).

In the immortal words of Joe Pesci (My Cousin Vinny) , “So what did you find out”. The results: 100% at 12:33AM / 85% at 8:32AM – Difference of 15% or 1.875% per hour. Wow, 1% less than the baseline. Let’s try this again.

Test 2 – Same setup as above. The results: 100% at 1:07AM / 86% at 9:06AM – Difference of 14% or 1.75% per hour. Dang, that’s even better. Think I’ll have another.

 WiFi-7-7 WiFi-7-8

Test 3 – Same setup as above. The results: 100% at 12:25AM / 80% at 8:27AM – Difference of 20% or 2.5% per hour. Ok, I have seen enough anomalies running these test to not be all that surprised, but I should do one more test just to be certain.

Test 4 – Same setup as above. The results: 100% at 12:28AM / 84% at 8:28AM – Difference of 16% or 2% per hour. So what is going on here. if I average all four results I am at 16.25% in my 8 hour test, which is almost the same as my baseline. And if I take out the anomaly, I am at 15%. So does persistent WiFi actually “save” battery power. Before making that kind of claim I wanted to be sure that my baseline had not changed. So a couple more baseline tests are in order.

WiFi-7-9 WiFi-7-10

Test 5 – This was a baseline test, so my phone was setup as normal. In other words, no persistent WiFi. The results: 100% at 12:49AM / 82% at 8:50AM – Difference of 18% or 2.25% per hour. Whoops, a little baseline slip there. One more time to be sure.

Test 6 – Another baseline test. The results: 100% at 12:24AM / 84% at 8:31AM – Difference of 16% or 2% per hour. That’s more like it. As a side note, I generally use the lower of multiple numbers and here is why. There are a lot of things that might increase the overnight drain on my battery; a poorer than usual cellular signal, those gremlins working on the towers, some background tasks that Microsoft is performing (I do have all their update, feedback, marketplace services turned on), but the only way that the drain could be lower would be if something on my phone was turned off or disabled. And that just does not happen by itself.

WiFi-7-11  WiFi-7-12

In case you are beginning to doubt that WiFi is actually running persistently in the background, and that icon at the top of the screen is simply a placebo, my non-SIM Surround has had WiFi running persistently almost 24/7 for the past week while I run various tests. Because I have my Hotmail account set to "push” on the Surround and L900, every time a new message is received, day or night, I get stereo as both phones tingle at exactly the same time. So yes, WiFi is on and working constantly.

So what does this mean. How can LTE and  persistent WiFi both running on a phone use less power than LTE running alone. Well think about this. You cellular radio has multiple power levels. While your phone is sleeping, the radio is at its lowest power level, but when it needs to move some data, the power level jumps up to get you that background email as fast as possible. Now, we already know that when Data and WiFi are both on, WiFi is in control of your data exchange. So, when persistent WiFi is on, your cellular radio never needs to wake up. That means whatever power your persistent WiFi is consuming it is returning back to you with more efficient data transfer. Can I prove this. Well, maybe not, but here is a piece of anecdotal evidence. I have been running close to 300MB of data usage per month on my Unlimited AT&T Data Plan (I know, dumb me) . With several nights of WiFi testing behind me, I am currently at 133.5MB at 17 days into my monthly cycle. Extrapolated out to 30 days, that would be 235MB of data usage for the month. The lowest it has been in six or eight months. That’s good enough for me.

Eighth Truth – Persistent WiFi does not only use virtually zero power while running in the background. Combined with a data connection, especially power guzzling LTE, it can actually save you battery power. Let me state that again, more slowly this time. “Persistent……WiFi………..saves…….you……..battery……..power”.

I sense a serious rant coming on, so if you are sensitive to these kind of things, or are still only able to view PG programming, best to not visit the site this weekend. I gave you fair warning.

 

 









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(11) Readers Comments

  1. I presume that if one is out and about town with one’s phone, it would still pay to turn off wi-fi so that it’s not burning power by constantly (and fruitlessly) seeking out wi-fi connections. Does my thinking seem to be correct?

  2. True Phillip. Most of my time is spent between home and office, so the little time I spend out and about, I don’t bother to turn off WiFi. If I know I will be away froma signal for an entire day, I probably would turn it off though.

    The trick used above will automatically turn off WiFi as soon as you leave the range of the currently connected access point. If I were to build a feature for Windows Phone, I would keep WiFi running in the background, as it works today, but I would maintain a connection with an access point until it was out of range. Once out of range, WiFi would go back to sleep until you woke the phone again and it was able to connect to a new access point, and remain connected until you were out of range again. This would be an efficient method for implementing persistent WiFi.

  3. Hey Jim.

    Thanks for the results. I was expecting them since I was running my own tests too.

    Please note that I do not have a data plan so before this trick, my phone one would remain disconnected at night. My Nokia Lumia 900 averaged 0.828%/h without wifi.

    After trying the wifi trick, my drain average overnight is 1.046%/h. That is with hotmail set to fetch as items arrive, and whatsapp running.

    This is very acceptable and convenient for those without a data plan and your findings are even more surprising. Microsoft needs to look into this!

  4. Interesting results Xsever. I am still trying to figure out what uses the juice on my non-SIM HTC Surround, but your numbers are not that far off from mine. On the Surround, I forced WiFi on and let the phone sit for nearly 3 days, 71 hours total. I dropped a total of 86%, or 1.21%/hr over that time period, but remember the Surround only has a 1230mAh battery. Converting the percentage to the L900s 1930mAh battery, and the number equates to a total drop of 53%, or 0.75% per/hr.

    I only had Hotmail push and 2 internal background tasks (Network Dashboard and Battery Meter) enabled. I received multiple emails that I opened daily. And on the second morning I had 26 app updates waiting for me to install (it’s been a long time since the phone had a connction for 24+ hours) , which I did do, forgetting the phone was under test. Actually, I had updates waiting every morning. So of that 0.75% per/hr average in L900 battery life, WiFi was probably not responsible for more than about 0.2 to 0.3% per hour. Easy to understand how a persistent WiFi connection could actually save you energy.

    Glad you can now make better use of your phone.

  5. I also forgot to mention that next to the Hotmail email account, I have my university’s email account set to fetch every 15 minutes. This makes my numbers even more impressive.

    I have also been using my HP Touchpad charger to charge the 900. Where the original Nokia charger manages 650 ma, the Touchpad’s charger pushes 850 ma until the battery reaches the 90% range where the rate drops to trickle charge. This allowed me to fast charge the phone and I do not notice any excess of heat of anything.

    Back to the WIFI trick, it is really amazing and I am very glad that I can stay connected now. I like your idea at the end of the article about the WIFI policy. I thought of that too since on campus, you get handed from an AP to another and that requires applying the trick again.

    We need to get in touch with MS and show them our results. After Stephen Elop (NOKIA’s CEO) replying to my email today concerning something else, I believe we are a great feedback source for both Nokia and MS!

  6. Pingback: The Truth About Windows Phone Persistent WiFi « Windows Phone News

  7. Its called connected standby in windows phone 8 and windows 8

    what is described here is a bastardised version of that.

  8. Interesting Joker, and good news assuming the info is accurate. Hope Microsoft gets it right the first (well, second) time.

  9. basically wp8 connected standby is based on system on chip wifi.

    but if someone can edit the wp7 registry to poll and connect with phone screen off periodically or after disconnect when moving to a different place with a different wifi AP …that will be great..

  10. Pingback: Why did Microsoft cripple WiFi? | Mobility DigestMobility Digest

  11. I’ve found a solution to this. Keeping the search app open in the background will keep the WiFi connection live.