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 TTFF Comparisons

04th May 2003

 

We get a lot of requests in the forums, via email and also people we talk to asking us What is the best GPS Receiver around ?.  The best way to measure this is in the TTFF (Time To First Fix) and re-acquisition times. 

 

When the satellites try to acquire a lock they need to rely on both Almanac and Ephemeris data.  Almanac data is course orbital parameters for all satellites in the GPS constellation which isn't very accurate information but is usually current for up to several months.  Then there's Ephemeris data which is very precise orbital and clock correction for each satellite and is required for precise positioning, eg 3D fix.  Each satellite broadcasts only it's Ephemeris data which has a life span of approx 5 hours per satellite.  Each satellite will broadcast the Ephemeris data for a 30 second period, and then re-transmit, so if the GPS receiver loses track of the data part way through the 30 second cycle, you will have to start again at the next 30 second cycle.

 

There are 4 TTFF start types depending on the amount of Almanac and Ephemeris data that is present in the GPS Receiver and where it thinks it is and the satellites are which can help aid the GPS acquire a lock quicker.  These are designated as Factory, Cold, Warm and Hot. 


Factory is where the receiver has no knowledge whatsoever of Almanac data in turn to locate the satellites and retrieve Ephemeris data, and for a full Almanac to be downloaded can take approx 12.5 mins, hence most companies suggest a factory start of 15 minutes. 

 

Cold start is usually the slowest TTFF you'll witness on a regular basis which has some knowledge of Almanac data but no Ephemeris data.  Almanac data is not precise, but current for several months.  When a cold start is required, the receiver has to download a full set of Ephemeris data which as already mentioned above is broadcast over a 30 second cycle and re-transmitted every 30 seconds. 

 

When starting the receiver in a Warm or Hot mode usually you'll find that the receiver has some Ephemeris data in the case of a Warm start, and in the case of a Hot start it has nearly a full set of Ephemeris data, which aids in making quicker TTFF's.

 

One thing to bear in mind is that although Manufacturers quote their average Cold, Warm and Hot TTFF's, these will vary.  Depending on where you are can dramatically change the quickness of acquiring a satellite lock.  To load the Ephemeris data form the satellites, the GPS Receiver requires a full 30 seconds of data reception.  If this is interrupted from a tall building, or a branch from a tree, or if the signal you are receiving is being reflected off of a building then all of this can cause a problem in the data reception.  If the data isn't received in full, the Ephemeris data collection has to start again at the next cycle.

 

When you see longer times in our table tests below, this is where the GPS receiver hasn't been able to receive the full amount of data in the quickest time possible.  The only other equation is how good the GPS Receiver antenna is, or in the terms of Compact Flash GPS Receivers and iPAQ sleeves, is whether there is any interference caused from the Pocket PC Processor.

 

Each acquisition made below in the table was from a 3D fix, which is a satellite lock that not only allows you to tell where you are longitude and latitude on the blue marble (planet earth), but also the altitude.  A 2D fix typically will not have any altitude information so theoretically cannot exactly position you in a 3D environment.

 

The quicker the TTFF, the better, because it means you can commence your journey quicker.  If you have a slow TTFF, then you could be waiting anything from 5 minutes+.  If you commence driving before receiving all the Almanac and Ephemeris data then you will severely increase your problems in acquiring fixes.  You can then sometimes find this increasing your TTFF time to anything up to 50 minutes due to the movement of the GPS receiver and being blocked or having signals reflected. 

 

The Pocket GPS team have received well over 50 TTFF's at around 15-20 minute mark in the last 3 months, and over a dozen at around 30-50 minutes both using the Navman sleeve.

 

As people put so much faith in TTFF's to choose which GPS Receiver to purchase, we felt it only right to produce a list of TTFF's recorded and to also show the quickest and slowest times we've achieved in each test which hopefully allow you to make a better selection on which GPS Receiver to purchase next.

 

The tests we performed were mainly to check the GPS receiver in a cold state, but have included an average warm and hot test and have compared all of these with the manufacturer quoted time (which again is only an approximate that they have experienced in their tests).  As time goes on and the Pocket GPS Team test more GPS receivers, more TTFF's will be added to this table.

GPS Hardware TTFF (Time To First Fix)

 

Cold

Test 1

Cold

Test 2

Cold

Test 3

Cold

Test 4

Cold

Test 5

Cold

Test

Average

Warm

Test

Hot

Test

CoPilot CF 1m 22s 1m 8s 56s 1m 17s 54s 1m 07s 52s 16s
Emtac Sleeve/CoPilot 40s 37s 42s 37s 46s 40.4s 10s 9s
Emtac/Socket BT GPS 47s 53s 42s 36s 38s 43.2s 10s 17s
Garmin eTrex 39s 44s 40s 41s 43s 41.4s 8s N/A
Garmin eTrex Summit 38s 41s 45s 39s 42s 41.0s 8s N/A
Garmin eTrex Vista 37s 57s 32s 35s 38s 39.8s 17s N/A
Garmin GPSMap76 42s 34s 23s 56s 32s 37.4s 12s N/A
Garmin GPSMap76S 32s 53s 32s 39s 36s 38.4s 11s N/A
Garmin Geko 101 1m 37s 45s 38s 44s 41s 53s 15s 13
Garmin Geko 201 34s 45s 38s 43s 40s 40s 19s 10
HaiCom 302 CF 50s 33s 1m 25s 36s 1m 25s 57.8s 23s 10s
HaiCom 303 MMF 42s 1m 05 s 41s 1m 02 s 1m 18s 57.6s 36s 3s
Holux GM-210 42s 38s 35s 37s 42s 38.8s 30s 4s
Holux GM-270 54s 1m 07 s 1m 03s 50s 1m 12s 61.2s 39s 4s
Holux GM-270U 46s 49s 42s 1m 01 s 49s 49.4s 35s 3s
Holux GR-230 1m 02s 55s 50s 49s 52s 53.6s 39s 5s
LeadTek 9531 / 9532 29s 37s 39s 41s 43s 37.8s 9s 5s
Magellan Meridian Range of GPS 38s 53s 43s 33s 35s 40.4s 18s 15s
Magellan SporTrak Range of GPS 37s 47s 46s 41s 41s 42.4s 19s 16s
Navman 3000 (ROM 2.0.0) 49s 52s 1m 33s 3m 23s 8m 5s 2m 56s 20s 11s
Navman 3400/3420 (ROM 2.1.2) 1m 33s 2m 30s 1m 32s 52s 1m 17s 1m 32.8s 20s 12s
Navman 3450 (ROM 2.1.2) 57s 50s 1m 09s 48s 1m 0s 56.8s 20s 11s
Navman 4400 53s 1m 03s 1m 19s 54s 53s 1m 00.4s 0s 0s
Pretec Compact CF 1m 28s 2m 47s 57s 45s 1m 2s 1m 23s 1m 16s 12s
Pretec Compact LP CF 3m 48s 5m 32s 4m 59s 1m 53s 4m 02s 4m 04s 52s 33s
Rikaline X5 41s 41s 34s 41s 42s 39.5s 39s 0s
Rikaline X6 34s 60s 44s 48s 57s 48.6s 38s 0s
RoyalTek Onyx 1m 28s 1m 39s 2m 23s 1m 38s 1m 35s 1m 46s 1m 24s 17s
RoyalTek Sapphire RGM 1m 02s 1m 0s 56s 41s 55s 54.8s 37s 10s
RoyalTek RBT-3000 57s 46s 43s 41s 55s 48.4s 30s 9s
RoyalTek RGM-2000 48s 52s 40s 45s 39s 44.8s 33s 7s
SysOnChip BT GPS 48s 77s 66s 67s 51s 61.8s 37s 4s
SysOnChip CF Plus (SIRFXTrac) 40s 30s 33s 38s 39s 36s 30s 0s
TFAC MG30 Mouse 1m17s 1m 26s 1m 38s 1m 36s 2m 11s 1m 37s 34s 4s
TomTom Bluetooth GPS 48s 52s 46s 59s 51s 51.2s 37s 3s

 

Fastest

TTFF

Cold

Tests

Slowest

TTFF

Cold

Tests

Manufacturer

Stated

Times

Warm

TTFF

Tests

Manufacturer

Stated

Times

Hot

TTFF

Tests

Manufacturer

Stated

Times

CoPilot CF 54s 1m 22s Not Stated 52s N/A 16s N/A
Emtac Sleeve/CoPilot 37s 46s Not Stated 10s N/A 9s N/A
Emtac/Socket BlueTooth GPS 36s 53s 1m 20s 10s 45s 6s 10s
Garmin eTrex 39s 44s 45s 8s 15s N/A N/A
Garmin eTrex Summit 38s 45s 45s 8s 15s N/A N/A
Garmin eTrex Vista 32s 57s 45s 12s 15s N/A N/A
Garmin GPSMap76 32s 56s 45s 12s 15s N/A N/A
Garmin GPSMap76S 32s 53s 45s 12s 15s N/A N/A
Garmin Geko 101 38s 1m 37s 45s 15s 15s 13s N/A
Garmin Geko 201 34s 45s 45s 19s 15s 10s N/A
HaiCom 302 CF 33s 1m 25s 48s 23s 38s 10s 8s
HaiCom 303 MMF 41s 1m 18s 48s 36s 38s 3s 8s
Holux GM-210 35s 42s 45s 30s 38s 4s 8s
Holux GM-270 50\s 1m 12s 45s 39s 38s 4s 8s
Holux GM-270U 42s 1m 01s 45s 35s 38s 3s 8s
Holux GR-230 39s 1m 02s 45s 39s 38s 5s 8s
LeadTek 9531 / 9532 29s 43s 48s 9s 38s 5s 8s
Magellan Meridian Range of GPS 33s 53s <2m 18s <1m 15s <15s
Magellan SporTrak Range of GPS 37s 47s <5m 19s <1m 16s <15s
Navman 3000 49s 8m 05s 2m 0s 20s 48s 11s 18s
Navman 3400/3420 (ROM 2.1.2) 52s 2m 30s 2m 0s 20s 48s 12s 18s
Navman 3450 (ROM 2.1.2) 48s 1m 09s 2m 0s 20s 48s 11s 18s
Navman 4400 53s 1m 19s n/a 0s n/a 0s n/a
Pretec Compact CF 45s 2m 47s 1m 0s 1m 16s 45s 12s 8s
Pretec Compact LP CF 1m 53s 5m 32s 2m 10s 52s 45s 33s 20s
Rikaline X5 34s 42s 45s 39s 38s 0s 8s
Rikaline X6 34s 1m 00 s 45s 38s 38s 0s 8s
RoyalTek Onyx 1m 28s 2m 23s 45s 3m 0s 45s 17s 20s
RoyalTek Sapphire 41s 1m 02s 45s 37s 38s 10s 45s
RoyalTek RBT-3000 41s 57s 45s 30s 38s 9s 8
RoyalTek RGM-2000 39s 52s 45s 33s 38s 17s 45s
SysOnChip BT GPS 37s 77s 45s 37s  38s 4s 8s
SysOnChip CF Plus (SIRFXTrac) 30s 40s 45s 30s  38s 0s 8s
TFAC MG30 1m 17s 2m 11s 45s 34s  8s 4s 0.1s
TomTom Bluetooth GPS 48s 59s 45s 37s 38s 3s 8s

 

How we obtained these fix statistics

 

 

All tests were completed using the TomTom Navigator GPS Support Program with no other mapping software loaded which would increase processor cycles and a 3D Lock was requested to achieve these timings.

 

  Cold tests
   

were performed when both Pocket PC and GPS receiver were powered off (if GPS receiver has a separate power source, the GPS receiver was unplugged) for a period of between 8 to 12 hours requiring a cold start. 

  Warm tests
   

Warm tests were performed when both Pocket PC and GPS receiver were powered off (if GPS receiver has a separate power source, the GPS receiver was unplugged) for a period of 30 minutes

 

  Hot tests
   

Hot tests were performed when both Pocket PC and GPS receiver were powered off (if GPS receiver has a separate power source, the GPS receiver was unplugged) for a period of 15 minutes

 

     

 

As you can see there is a great varying degree of TTFF's in the table above.  The Leadtek 9531 which is also supplied with TomTom Navigator and PowerLOC Destinator has come out the clear winner from a Pocket PC GPS Receiver with an average Cold TTFF of around 40 seconds, and a Hot TTFF of around 5 seconds.

Navman 3000 Sleeve unfortunately came in last with extended TTFF's, making the average TTFF at just under 3 mins which does compare to what a lot of Pocket GPS Readers say about having to wait for extended TTFF's for the Navman GPS 3000 sleeve to acquire fixes compared to other GPS receivers.

We have been in contact with Navman, and asked why the TTFF's are considerably slower in comparison with other devices.  Navman said that the largest cause of poor reception / time to fix with the Navman receiver, is electromagnetic interference from the processor on the PDA.   Navman discovered that by increasing the baud rate at which the GPS receiver communicates with the PDA, they could transfer the NMEA data, process it on the PDA and then put the PDA into idle (and electromagnetically quiet state) allowing the GPS receiver to increase it's performance.  This is what Navman have done with the new SmartST Pro software, and TTFF's have been enhanced slightly if you use SmartST Pro with the GPS Receiver, but we have still seen some extended TTFF's with the Navman GPS 3000 Sleeve.

 

For more information on acquisition times and Almanac/Ephemeris information, please check out Joe Mahaffey's website.

 

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