Two Letters Re: Cell Phone E-911 Tracking

Sunday, Apr 23, 2006

I'm an engineer working on E911 systems and I'd like to correct this whole post. I've included some references so all your readers can peer review.
> #1 The chip does not function unless you either... Incorrect. The requirements typically state for Public Safety and in support of local laws, the mobile station (cell phone) has to handle all network requests for location.
> #2 Its not real GPS. There are two separate systems that can be hybridized together.
First is the network based system described above that works great in urban areas with lots of compatible cell towers. It is fast, but it can not get down to 3 ft., maybe 100 m.
The second system is Mobile Station based (Cell phone) and it typically uses GPS just like a Garmin. It works great in rural areas. It is not so great in large cities as all the concrete, steel and coated glass both block and reflect the GPS signals. A differential GPS system in time can achieve accuracies in cm. However just like your Garmin, it can take a long while to search for satellites and download the data from them.
The hybridized systems, where the network and the mobile work together, can achieve the best of both accuracy/speed and urban/rural performance. The network can tell the GPS on the mobile station approximate time, approximate position (with xx km of the cellular tower), where the satellites are in the sky and lots of other information that it would take your Garmin 20 minutes to get from the satellites.Reference. Section 10.10 GPS Assistance Data for more information. This document applies to GSM and 3G/UMTS phones, but it is not atypical.
Also the new hybridized systems can combine the cell tower ranging with the GPS satellite ranging to get a system that works where neither system alone will.
#3 While it is possible...
Ah, no. The solution is Periodic measurements. in other words generating a location every 5 minutes would not affect battery life much. It is used to track commercial delivery personnel all the time.
#4 Yes there really is....
Again no. This is internet Fear, Uncertainty, and Doubt (FUD). The FCC requirement is that x% of mobile stations can be located to certain accuracy. GPS is not a requirement.
#5 There is also the secondary issue.
The analog is not illegal, yet. It is just not cost effective for the bandwidth reasons. Second for some networks that depend on GPS in the mobile station (typically CDMA), the old phones stand in the way of meeting the FCC requirement.
#6 Analog shutoff.
I do not have any information on this.
#7 Cell phones use lots of electrical power...
Motorola Razor talk time 200-430 minutes. Standby 180-290 hours. Reference [JWR Adds: I believe that the writer was referring to cell phone cell tower facilities rather than hand-held cell phones themselves.]

As to charging more during blackouts, any company that did this would invite a class action lawsuit for breach of contract and endangering the public.

OBTW, one other bit of FUD that I'd like to comment on:
Yes, off does not mean off in regards to modern electronic devices including cellular phones. While "off" they may need to support an alarm clock, calendar alerts, monitor battery charging, alert for low battery and do a lot of other things. However, removing all the power sources kills anything! If your phone continues to run without a charger or batteries, I think you could name your price to sell it to any of the big cell phone companies. - Raven



I have personally been present, when a 'Federal investigator' ordered a cell phone security manager (what the heck that is I don't know) to 'turn on' a particular Electronic Serial Number (ESN).

It was my understanding that the phone had to be 'on' in the first place. It was explained to me that there was a dual mode capability. One was the retransmission of GPS positioning data and the second triangulation.

We found the 'bad guy' we were looking for for a covert surveillance regarding a narcotics investigation.

He wasn't in a call - it was a pretty weird moment for me to see this happen, and it was about four years ago. I can only imagine the capabilities built into the system mandated by post-9/11 are more enhanced than then.

I trust the data given to me by the writer about GPS positioning as he understood it. I saw different. The federal investigator was pretty closed mouth about it, and the black box he used that (I suppose) received the data was no larger than a lunchbox. Steered us right in.

I've long ago given up on trying to maintain much privacy in my electronic life. I really don't have much to hide, but if I did - electronics wouldn't have any place in my home. - Jimsee

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