What is the difference between cheap and expensive GPS receivers?

Question

The cheapest class of GPS receivers is what we all have inside our smartphones etc.

Then we have devices like this U-blox.

In the end there are professional GPS like this SPAN combined with INS (IMU).

The latter one is basically 1 box including support for GPS+Antenna+INS.

It's understood why the INS component is expensive (MEMS gyro etc.), how the INS correcting the GPS and same with the Antenna.

This raising the question what is the difference solely in the GPS component inside the professional expensive device versus the cheaper one? Because if it's essentially the same, one can take $50 GPS receiver and by adding Antenna get same result like buying the expensive professional GPS...

Thanks,

IMO you are comparing apples to oranges. Even if you weren't, "cheap vs expensive" is an unending debate in any field. — Wesley Lee, Mar 21 '17 at 13:18
@WesleyLee Why apples to oranges? Inside the professional device you do have pure GPS component. — michael, Mar 21 '17 at 13:29
@FakeMoustache Inside the professional box you have {pure GPS, INS, Antenna}, in "pure GPS component" I simply refer to all the electronics related to the functionally of the GPS, and not the INS and the Antenna. — michael, Mar 21 '17 at 13:40
@FakeMoustache Smartphone can cost $100 and the GPS is not the most important & expensive component there. ublox is $50. The professional staff can be even $30,000. Yes, price is a function of marketing & demand. However difference between $50 to $30,000 is more that that. — michael, Mar 21 '17 at 13:43
However difference between $50 to $30,000 is more that that. Again, you're making assumptions. Of a professional device, less units will be sold so development cost per unit is higher. Professionals require support for longer, supporting a device costs money. Who are you to say that this does not explain the price difference. — Bimpelrekkie, Mar 21 '17 at 13:47
Apples to oranges because U-blox is a module for PCB mount, while the SPAN is a solution in which the machined enclosure alone is going to cost more than the whole U-blox itself, not to mention connectors, etc. — Wesley Lee, Mar 21 '17 at 14:09
Consider the price difference between military and COTS components. The military rated ones are not more expensive because they are "better", but often simply cause they're "ruggedized" + the point that FakeMoustache made about development costs divided per units sold. Your question sounds a lot like "Why does a luxury watch cost orders of magnitude more than a cheap digital watch? The components inside them do not justify this difference". — Wesley Lee, Mar 21 '17 at 14:13

Andrew · Answer 1 · 2017-03-21T14:58:41.270

The differences between a cheap GPS and a high end commercial GPS:

Narrow band RF front end Vs wide band front end.
A cheap GPS will only track L1 C/A which is a fairly narrow signal, a good GPS will also track the P(Y) code which is wider bandwidth.

1 bit Vs 2 bits sampling.
A low end GPS will use a 1 bit front end, a better one will normally be 2 bits.

16 MHz Vs 25/50 MHz sample rate.
Lower end systems tend to use a lower sampling rate, that's all you need for C/A code.

Single frequency / signal Vs multi-band, multi signal.
A basic GPS only tracks L1 C/A, in addition to the already mentioned L1 P(Y) code a high end one will also track signals on the L2 (L2C and P(Y)) and L5 (L5C) bands.

Dual antenna support
Some high end GPS systems will support two antennas and run an RTK like correction between the two allowing you to get good accuracy heading information even when stationary. Low end GPS you can get direction of travel accurately when moving but that doesn't tell you which way you are facing and only works well above a certain speed.

RF shielding.
GPS signals are really weak. If you mount a GPS antenna close to the receiver or other electronics then you risk noise getting into your GPS system. In the past I've spent weeks stopping the 37th harmonic of a clock signal from leaking into a GPS antenna in order to gain an extra 0.5 dB of SNR. For a cheap system no one would care about that, it only matters when you are trying to get the last little bit of performance.

Running completely stand alone and only tracking L1 a good GPS will (with a lot of assumptions, hand waving and approximations) give an RMS error that is around half that of a cheap consumer unit.

And this is before we get into the extra CPU power and investment in terms of software engineer time required to allow things like RTK corrections to improve accuracy down to 1 cm with just GPS alone, no IMU needed.

And then you have all of the extra stuff needed for GLONASS, Beidou, Galileo and all of the other GNSS things that are outside GPS that a good receiver will do.

Those NEO-7P modules from ublox are very good position accuracy for the price but are very similar in terms of hardware to the $15 base model NEO modules. The extra cost isn't for parts, its for the development effort behind the software they are running. They are still a long way off from a high end of GPS, list price for a high end GPS with all the features enabled can be over $10,000. Those $10,000 systems aren't just a Ublox with a GPS antenna put together in the same box.

Fully agree. Add semi-codeless P(Y), narrow correlators (needs high sample rate), delta-delta-DLL, coherent discriminators (all of these pushing baseband complexity), vector tracking and RINEX-output (controller processing load). — Andreas, Mar 21 '17 at 19:19

score 5 · Answer 2 · edited Apr 13 '17 at 12:32

5

See How many GPS channels make sense?

That long answer details how adding more channels to a reciever (at additional cost) can:

Speeds up satellite acquisition
Reduces power consumption
Reduces likelihood of losing a 3D fix even in urban canyons
Provide better sensitivity, allowing fixes in dense forests, and even in some tunnels
Provides better positioning accuracy

Edit: channels are one factor. A big factor seems to be the fiber-optic gyros in those other units; those are something I can't even find pricing for on the internet. But really I suspect a lot of the costs for the professional kit are non-recurring expense (NRE) of various sorts. More complex software, especially for sensor fusion. Proprietary position-enhancement techniques. Certification and compliance (I see "export compliance" on one of those feature lists, maybe there's a legal cost associated with that?)

High NRE divided across small number of units sold = very high unit cost for seemingly modest performance improvements. Not unusual when dealing with lab or test equipment.

edited Apr 13 '17 at 12:32

Community

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answered Mar 21 '17 at 13:35

pjc50

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This is it? Just the channels thing? – michael Mar 21 '17 at 13:41
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I've added some other possible factors. – pjc50 Mar 21 '17 at 13:57
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Be careful on channel count, it depends on what you count as a channel. e.g. Say you have a high end dual band system (L1 and L2) then when tracking a satellite you will typically be running 6 correlators in two sets of 3, early, punctual, and late, for each frequency. Within the group of 3 they are tightly locked together and only a limited variation is allowed between the two sets. So is that 1 channel, 2 channels or 6 channels? The answer is that it depends who's marketing department wrote the datasheet. – Andrew Mar 21 '17 at 15:56

score 2 · Answer 3 · answered Mar 21 '17 at 14:10

These have an accuracy down to a cm. Does your phone do that?

\Between these two models there is a huge difference.

Compare to this one with 555 channel, all-constellation, multi-frequency positioning solution, Built-in Wi-Fi support, and 16 GB of internal storage

What is the difference between cheap and expensive GPS receivers?

3 Answers3