I’d like some technical info on vehicle tracking using GPS, GSM and CDMA.
I have found some excellent information on the 'net related to this topic, but I still have some questions.
To be more precise, I’m aware of how they [GPS, GSM and CDMA] work. What I need to know is how well each one works.
I’d really appreciate a comparison of GPS vs. GSM vs. CDMA for vehicle tracking, especially with regards to accuracy and reliability.
Thanks.
Consumer level? Or commercial/scientific/military?
I’m not up to date in this market (it changes pretty quickly), but I would think the better ones combine GPS and one of the others (SnapTrack). But a lot is determined by what the infrastructure supports in your deployment areas.
If it’s really critical and you’ve got a big budget you want it to be integrated with inertial.
A good industry search term for detailed information is “automated vehicle location”.
I can’t comment on GSM or CDMA as I’ve never used them for vehicle tracking, but I have used GPS for navigating. In fact, I’ve used it in India.
In my experience, a basic hand-held unit - which I’m assuming is not that different from the automotive versions - is able to pinpoint a location to within 8-9 meters outside of North America. (Forget about altitude if it’s available; it’s just not reliable.) Your accuracy will be affected by the number of satellites you’re picking up, so sometimes moving a bit away from buildings and whatnot will get you a better reading.
I was happy enough with my GPS in this regard, although admittedly the landmarks I had stored as waypoints were easy enough to find once I was in the approximate location.
The tracking with CDMA phones generally uses both GPS and information about the distance from the CDMA base stations. I have seen demonstrations that were accurate enough to determine what lane cars were in.
Commercial grade.
**The infrastructure supports all three types (and, by extension, combo devices).
That’s exactly what I was looking for. Although I got some great info, not too many sites go into technical details in depth.
Could you elaborate on this ? How does your CDMA phone get information from GPS ? Are you saying GPS information is available by default on a CDMA network ? Or does it require some additional hardware ?
I understand that CDMA uses time of arrival of signal from base station, strength of signal, and angle of arrival to calculate location. GSM uses one or more of the above. I’m not clear on which ones.
I understand that CDMA (by itself, without GPS) offers a tracking accuracy of upto 125 metres. I’m not clear on where GPS fits into a CDMA mobile phone network.
I’m not clear on the tracking accuracy that GSM offers, and how it compares with what CDMA offers.
I am assuming that GPS offers the highest accuracy, but not necessarily the greatest reliability in a dense urban environment.
I am assuming that GPS requires a minimum of 3 satellites to be able to calculate location. Is this correct ?
The phone listens to the GPS satellites. Some GPS information is available from the network. Specifically accurate GPS time, knowledge of what satellites are in the sky currently and a pretty good idea of where they are now.
They use delay from the base station. Signal strength is pretty much useless because if varies so much due to factors unrelated to distance from the base station. You cannot tell angle with a single antenna phone. I suppose the base station could get a vauge idea of angle because they usually have more than one antenna but I have not heard about it. CDMA can get the delay difference between two base stations pretty accurately because of the high bandwidth of the CDMA signal. Plus they really need to do this anyway for handoff between base stations. GSM phones will not have as good resultion into the difference in path lengths of base stations because the GSM signal has a much lower bandwidth.
All the GSM solutions that I know about use stand alone GPS receivers.
I am not sure about this. CDMA in the US has a higher chiprate than GPS so it should be able to give a more accurate result because of this. However, there may be problems getting good signal from 3 or 4 base stations.
Probably but you may need four because of the uncertainty of time.
Though the altitude accuracy is far less then the other 2, I have found it to be very reliable and not subject to air pressure changes that plague other altimeters. I am usually within 50 ft of a benchmarked altitude.
If you only have 3 ‘birds’ locked you will not get an altitude reading and the gps will assume an altitude. This will increase the error and put you into what is commonly called 2d navigation mode.
xash, I worked for a company two years ago that sold the gear. All of it was crap, IMHO. We had one unit that stored the information in the box, and then you downloaded it to your PC later on. It was incredibly inaccurate. It had me traveling at something like 120 MPH+ at various points in time (my car can’t manage to go that fast) or in locations I wasn’t, and that was when I could get the unit to work at all.
The other unit was more accurate, but was nearly usesless because of a lack of maps. No doubt there’s been improvements over the years, but I’d recommend doing a lengthy trial period before I agreed to buy any unit. (Sorry, I don’t remember the brand names of the units we sold, or I’d post them.)
A CDMA phone may have a GPS chip as part of the hardware; this can allow it to exploit this information and the CDMA signal to locate itself. But, more particularly, there’s nothing in the 3GPP UMTS standard that refers to GPS, so such information isn’t available by default.
Well, I commonly get altitude to within 12-15 meters, which is not that much worse than what you give for horizontal error.
When SA was turned on, altitude was generally much worse. But it’s been several years since that was killed.
After 10 years, I imagine that the OP has resolved his problem.
Several times:)