Development of a GPS system

A

Abdulhussain Songerwala

Joined
Sep 5, 2015
Messages
4
Reaction score
0
Hello,
I am a student pursuing BTech and want to implement a GPS system for my project. This is the first time I am going to use GPS. I have read literature about GPS systems and am planning to use MAX2769 as RF front end for my GPS receiver. It outputs I and Q bits. I am confused about what I am supposed to do further in order to get position data. Could someone please provide some guidance/relevant reading material for the same.

Thanks! :)
 
The MAX2769 is as you say an 'RF front end' sub-system component, it outputs I (In-phase) and Q (Quadraphase) baseband sampled data, the data contained in these I & Q outputs is not decoded into Latitude, Longitude, time etc. It is not a 'one-chip' solution, unless you can source a suitable device to input this baseband data, I don't think you are going to be able to use this device
 
Thanks for your reply Nuvi-Nebie. Yes even through my searches I came to the same conclusion. I was not sure how to proceed further. What processing of the signal will have to be carried out if I use MAX2769? Also, what other alternates do I have to develop a GPS system?
 
I have only seen the baseband outputs from this device connected to a micro controller, which would obviously need to be running a decoding routine, I have no knowledge of how this would be done. I would look for a device that outputs NMEA data sequences via RS232, some hand held GPS devices output NMEA sequencies, like the Garmin Etrex and Garmin GPSmap60Cx. Also some GPS modules output NMEA like this one :-
http://www.rfsolutions.co.uk/acatalog/info_GPS_622F.html

This is a UK company, data sheet here :-

http://www.rfsolutions.co.uk/acatalog/DS-GPS622F-3.pdf
 
I went through the datasheet. Thanks for the reference. Though I have to fit it into a bigger application and I am not sure if I can directly incorporate the module. Are there any other ways to process the baseband signal? Are there software techniques for the same?
 
You would have to find an existing chip set for getting readable data from the MAX2769, maybe one exists, I couldn't fine one on the net, as I say the only references I could find, shows the MAX2769 connected to a micro-controller, I have no knowledge of the software techniques needed to decode the MAX2769 outputs. Devices that output NMEA sequences are well documented, units often output several NMEA sentences e.g:-

GSA - Overall Satellite data
GLL - Lat/Lon data
RMC - recommended minimum data for GPS

These sentencies are documented here :- http://www.gpsinformation.org/dale/nmea.htm#nmea
they are in readable Comma Separated Values, here are the RMC sentence details :-

RMC - The Recommended Minimum for GPS

$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A

RMC Recommended Minimum sentence for GPS

123519 Fix taken at 12:35:19 UTC
A Status A=active or V=Void.
4807.038,N Latitude 48 deg 07.038' N
01131.000,E Longitude 11 deg 31.000' E
022.4 Speed over the ground in knots
084.4 Track angle in degrees True
230394 Date - 23rd of March 1994
003.1,W Magnetic Variation
*6A The checksum data, always begins with *
 
Yes I read about the format of these sentences and found the docs on 'Software Implementation of GPS Receiver'. Even I am not too clear on how to go about the processing of the baseband signal. I also had the following two doubts:

1. As you mentioned, several NMEA sentences are output so are they output periodically or how is it? In my application I continuously want latitude & longitude. Can I write some register in the GPS module/receiver to do this?
2. I plan to use this at altitude > 18 km. What permissions will I need to proceed?
 
The sentence or sentences are usually output every 1 second, they are output at 4800bits per second so all of the info. below would output in half a second or so, then there would be a half second pause before a new set of data is output :-

Garmin etrex summit outputs
$GPRMC,002454,A,3553.5295,N,13938.6570,E,0.0,43.1,180700,7.1,W,A*3F
$GPRMB,A,,,,,,,,,,,,A,A*0B
$GPGGA,002454,3553.5295,N,13938.6570,E,1,05,2.2,18.3,M,39.0,M,,*7F
$GPGSA,A,3,01,04,07,16,20,,,,,,,,3.6,2.2,2.7*35
$GPGSV,3,1,09,01,38,103,37,02,23,215,00,04,38,297,37,05,00,328,00*70
$GPGSV,3,2,09,07,77,299,47,11,07,087,00,16,74,041,47,20,38,044,43*73
$GPGSV,3,3,09,24,12,282,00*4D
$GPGLL,3553.5295,N,13938.6570,E,002454,A,A*4F
$GPBOD,,T,,M,,*47
$PGRME,8.6,M,9.6,M,12.9,M*15
$PGRMZ,51,f*30
$HCHDG,101.1,,,7.1,W*3C
$GPRTE,1,1,c,*37
$GPRMC,002456,A,3553.5295,N,13938.6570,E,0.0,43.1,180700,7.1,W,A*3D

A GPS receiver does not require any permission to operate it wherever it is as far as I am aware, however, flying something at 18km may need permission, I can't say
 

Members online

No members online now.
Total: 49 (members: 0, guests: 49)
Back
Top