The Fix

"The Fix"
i.e. acquiring or reacquiring a position with your GPS

Intro

Since you're going to be on the bleeding edge and use a GPS receiver with your PocketPC, you probably don't want to be waiting for ever for the GPS to acquire or reacquire its position, right? There are countless complaints on message boards about endless waiting time for the GPS to acquire a position. While some people blame this on the navigation software, I can't see any reason why that would be, because once they're powered up, GPS receivers "do their own thing" and start looking for a position.

Test methodology

Let me first state that his test has no scientific pretensions and is only here to hopefully give you an idea of "real life" usage:

To obtain comparable results, I used Leadtek's excellent little utility called CE Monitor that is linked on this page. It runs on a PPC and therefore allows for the best possible mobility. It also lets you initialize your GPS to have it start from its Factory Settings/Cold/Warm/Hot.

Summary Table of GPS "states"

State

Impact

Real Life Equivalent

Factory

GPS has no idea where it is, reset to original protocol/bitrate

You've just unpacked your GPS ;-)

Cold

GPS has no idea where it is

You haven't used your GPS for ages and the internal battery has run out.

Warm

GPS knows where it last was and which satellites were around but needs to get data from the satellites again (elevation, azimuth)

You turned off your GPS or your PocketPC

Hot

GPS knows where it last was and will reuse the satellite data

You've driven under a bridge/tunnel and lost reception

I put the GPS receivers in three environments, obstructed (in my office amidst of sea of electronics, screens and otherwise general clutter), normal (in my car, a BMW 325ic) and clear (in my backyard). So the readings in seconds will be in this order obstructed/normal/clear.

Timings were done 3 times and averaged.

To account for the fact that it may sometimes be harder to get a GPS position based on the satellite configuration, I always used my benchmark Bluetooth GPS to make sure the timings were consistent. If not I repeated them.

Note: As expected, it quickly became obvious that even staying in the same spot didn't guarantee consistent results. While I'm not certain what makes a satellite configuration difficult, I'll venture that having fewer visible satellites, especially if they're close in azimuth to each other will make getting a "fix" more difficult. The C** factor is an attempt at factoring this in.

The Fix - Obstructed/Normal/Clear

Model

Form factor

Portability

TTF *
Factory/Cold

TTF *
Warm

TTF *
Hot

C**
Factor

Comments

***

ob/nl/cl

Magellan M330

Standalone

n/a

500"/ - /40"

100"/ - /20"

Wasn't really possible to do a cold/warm reset here so both are the same

PocketMap CF GPS

CF/L

85"/ - /75"

n/a

10"/10"/10"

n/a

	A bit difficult to test because the Cold/Warm/Hot commands of CE Monitor are ineffective. It always does a Hot Reset unless it's been off for several hours
	Like for other CF receivers, it should benefit from the use of an antenna to speed up acquisition time for difficult satellite configurations in Cold/Warm starts

Emtac Bluetooth GPS

Bluetooth

48"/-/49"

37"/ - /42"

4"/ - /4"

Very consistent results even in difficult satellite configurations.

Billionton CF GPS

CF /T

B+

51"/-/50"

42"/40"/42"

10"/-/10"

4.5

Pretty variable results - see here for detailed comments
In some cases, external active antenna was required to get a fix.
You can get a lower C** Factor by using the antenna.

Transplant CF GPS

CF/L

80"/ - /75"

40"/40" /42"

10"/10"/10"

Consistent results, will benefit from the use of an antenna to speed up acquisition time for difficult satellite configurations in Cold/Warm starts

Pharos i180 GPS

Mouse

n/a

60"

n/a

<10s

	Testing was a bit difficult because this is the first GPSr I come across that doesn't respond to CE Monitor commands.
	As there is no internal battery in the receiver, cold resets were obtained by subtly unplugging the device...

Navman iGPS

Sleeve

-/140"/-

-/50"/-

-/10"/-

Good performance although a bit slow when starting from a cold state. Happily nowhere near the 30 minutes that some have complained about though !

DigiTraveler GPS

Mouse

75"

n/a

<10s

	Testing was a bit difficult because this GPSr likely does not use a SiRF chipset and doesn't respond to CE Monitor commands.
	As there is no internal battery in the receiver, cold resets were obtained by subtly unplugging the device...
	Uses a position near Tokyo as its original position. Not very useful in other parts of the world...

Holux CF GPS

CF/TL

47"/50"/-

41"/ 40"/-

4"/4" /-

	Excellent performance thanks to the SiRF IIe/LP chipset
	First CF GPS to offer this type of performance

Notes:
*         TTF - Time to Fix
x         no fix
-          not yet tested
**        This "C factor" is my attempt at a "Consistency" factor. It really should be the standard deviation but since the data collected isn't sufficient enough, what I did was take
            the Max TTF add it to the Min TTF and divide the result by the average TTF. Patient people will not mind a high C factor, others will prefer a lower number !
***     Portability is my subjective evaluation along these lines (from a reply to a question I got): "Well the wireless BT GPS would be an A since it's transparent to the PPC, then
          the CF GPS receivers that require a sleeve, stick out and weigh on the PPC would be a B with the "thin and light" CF GPS receivers a B+ for the reduced bulk and weight.
          Mouse GPS receiver are not portable unless you somehow power them from a home made battery pack but there would still be a whole mess of wires !