In another topic -- can't find it at the moment -- I saw mention of the sensitivity of a GPS receiver, which would appear to be a useful criterion in the selection of such receiver. This got me to wondering about the sensitivity of the GPS receiver in my HTC Dream mobile phone (T-mobile G1) but the 222 page user manual has no information on it. Googling, I found various specification terms for a GPS receiver (www.tootoo.com/d-rp18208563-GPS_receiver_with_state_of_art_SiRF_STAR_III_high_sensitivity_technology/) such as:

1)General

Core Module: firmware by SiRF starIII,chipset by SiRF starIII Solution

Satellite channel number: all-in-view 20 parallel satellites; GPS frequency: 1575.42 MHz

Receiver: L1, C/A code.

Antenna type: built-in ceramic patch antenna

External connector: standard MMCX

2)Acquisition Time

Refresh: 0.1 sec

Cold start: <42 secs(average, normally occurred in first use of GPS receiver life) Warm start <38 secs(average)

Hot start: <1 secs(average)

Position information update period: 1 sec

Tracking sensitivity: -159dBm

3)Precision/ Accuracy

Position accuracy: <10m(2D RMS) or <5m(WAAS enable) Speed: 0.1m/sec, typical

Time: 1 msec(satellite time)

I understand nothing of this technical talk but guess that the tracking sensitivity, measured in dBm – apparently not part of the International System of Units but explained here in Wikipedia: http://en.wikipedia.org/wiki/DBm – is important and there is a formula to convert dBm to Watt (W). However, I am not quite sure how to read this. Is -158 dBm (1.58^-19 W) better than -111 dBm (7.97 ^-15 W), which is said to be "thermal noise floor for commercial GPS single channel signal bandwidth (2 MHz)"?

I have two Bluetooth GPS receivers lying around and if they have a better tracking sensitivity than the receiver built into my phone I will try to use one of these receivers. So this is my question: what is the tracking sensitivity of the GPS receiver built into the HTC Dream phone?

For the Bluetooth receivers, Google gives me the following information regarding tracking sensitivity:

-- QSTARZ BT-Q818: -158 dBm

-- QSTARZ BT-Q1000: -158 dBm

hi, well thats a technical Q for TV. let me try to answer it.

Firstly the log power ratio formula is:-

decibels = 10 * log (powerout/powerin)

where powerin(can be) = .001 watts

I checked your figures and make the second thermal noise 7.943 * (10^-15) watts but thats predantic!

I always think that with any system you need the total noise in the system whereas here it appears you only have the thermal noise.

Standard ways of calculating (summing) total noise while keeping in decibels is something like:

Total noise = thermal noise(cold nights wanted!) + noise from antenna( better aerials/signal give lower noise) + noise from gain circuits (stronger signals need less gain so less noise)

+reflected signal noise (from mountains etc)+power supply noise

This is not comprehensive as there could be other noise introduced or even errors introduced at the digital stage.

But to answer your question -158 DBm is a much better thermal noise floor compared to -111DBm but there are other (outwaying orders of magnitude) factors in the equation and as been shown an aerial with slightly better gain would probably change the signal to noise ratio considerably.

Just because the thermal noise floor of a system is lower certainly doesnt mean its better !!

Incidently I have a GPS phone(N95) it needs to be outside no obstacles to get any signal whereas my car tomtom GPS is a much stronger receiver (works thru glass etc) I suspect it's aerial is much better...

Exotic Matter