| The flight navigation GPS unit | - GPS Units |
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GPS units provide:
Download a 138 page, 516 kByte, pdf document ICD-GPS-200C on the details of the GPS system implementation. |
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from http://www.qinetiq.com/home/commercial/gps_and_rfid/gps/GPS_Products/high_sensitivity_gps.html Until recently GPS positioning relied on direct satellite view, excluding many environments from the advent of GPS. Many GPS enabled devices in the market are simply unable to meet customer requirement due to these limitations. In response QinetiQ has developed a high sensitivity module which continues to provide position information where conventional GPS fails.
QinetiQ High Sensitivity GPS brings the advantages of satellite navigation to a whole range of new applications. Using a dedicated baseband processor with massive parallel correlation and frequency search capability, our Q20 receiver is much more sensitive and faster to fix than other GPS engines. In urban and indoor environments our technology provides greatly increased availability of position and timing solutions. In many cases even the GPS antenna can be eliminated saving cost and improving the form factor of customers products. We supply a range of Q20 GPS receiver products to support the developer from demonstration kits and integration boards to Q20 modules in high volume. Please also talk to us about your requirements for custom modules and 'zero' antenna solutions.
The Q20 HS is a complete GPS receiver module with very fast acquisition and very low signal strength tracking capability. Proprietary low level data demodulation capability allows the Q20 HS to provide sustained operation indoors without network assistance. The Q20 HS is available now in quantity for use in embedded applications.
The Q20 Integration Board has been designed to make prototyping and integration into customer solutions as easy as possible. It comprises a Q20 receiver module mounted onto a carrier board with all the peripheral components and connectors required to get you up and running.
The Q20 High Sensitivity GPS Demonstration Kit is for developers who want to explore the advantages that a highly sensitive GPS receiver can provide in their positioning applications. The kit contains a small battery powered demonstration unit based on the Q20 module and all the accessories and software required to start with high sensitivity GPS.
Above and below from http://www.sirf.com/products/GSC3LPProductInsert.pdf
from http://www.sirf.com/products/GSC3LPProductInsert.pdf
from http://www.u-blox.com/products/Product_Summaries/UBX-G5010_Prod_Summary (GPS.G5-X-06042).pdf UBX-G5010, UBX-G5000 u-blox 5 GPS Single Chip and Chipset for Mobile Terminal Applications Preliminary Data – Chipset scheduled for Q2 2007
Overview The u-blox 5 chip family is the latest GPS technology generation from u-blox that redefines the boundaries of GPS performance, integration and cost efficiency.
A dedicated acquisition engine with over 1 million effective correlators is
capable of massively parallel searches across the time/frequency space. This
enables satellite acquisition in under 1 second and acquisition sensitivity
reaching –160 dBm. Acquired satellites are passed on to a power-optimized
tracking engine. This setup simultaneously allows the t
Power needs lower than 50 mW ensure long battery times. The UBX-G5000 baseband
IC will be capable, via a simple software upgrade into external Flash EPROM, of
receiving and processing L1 Galileo signals once they become available. The
ability to perceive Galileo satellites will bring higher &nb
Highlights
Features
from
http://www.u-blox.com/products/lea_4t.html
The LEA-4T, supporting precision GPS timing and raw measurement data for
demanding positioning applications, provides high sensitivity, exceptionally low
power consumption and USB connectivity.
The LEA-4T features a Time Mode function whereby the GPS receiver assumes a
stationary 3D position, whether programmed manually or determined by an initial
self-survey. Stationary operation enables GPS timing with only one visible
satellite and eliminates timing errors which otherwise result from positioning
errors. The accuracy of the time pulse is as good as 50 ns, synchronized to GPS
or UTC time. An accuracy of 15 ns is achievable by using the quantization error
information to compensate the granularity of the time pulse. The built-in
2-channel time mark and counter unit provides precise time measurement of
external signals (EXTINT0 and 1).
The LEA-4T also supports raw measurement data (carrier phase with half-cycle
ambiguity resolved, code phase and Doppler measurements) which can be used in
external applications that offer precision positioning, real-time kinematics
(RTK) and attitude sensing.
Above: part of the u-blox LEA-4T evaluation kit we ordered in March 2007.
The National Marine Electronics Association (
NMEA
) has developed a specification that defines the interface between various
pieces of marine electronic equipment. See
http://www.nmea.org/
to purchase a copy of the NMEA 0183 Standard. We have derived the information
for the u-Blox NMEA codes from
http://www.gpsinformation.org/dale/nmea.htm#ZDA
and from the
http://home.mira.net/~gnb/gps/nmea.html#gprmc
web sites. The folowing is an example of a section of data that is output each
second to a logging text file created by the u-Blox evaluation module:
$GPRMC,143903.00,A,5112.31099,N,00158.66984,W,0.004,,151007,,,A*64
$GPVTG,,T,,M,0.004,N,0.007,K,A*20
$GPGGA,143903.00,5112.31099,N,00158.66984,W,1,07,1.21,136.0,M,48.2,M,,*41
$GPGSA,A,3,21,05,06,24,13,31,16,,,,,,1.90,1.21,1.47*0B
$GPGSV,3,1,09,21,46,150,41,05,10,118,37,06,61,070,49,07,,,47*45
$GPGSV,3,2,09,24,51,093,48,13,08,340,37,10,,,39,31,53,216,40*42
$GPGSV,3,3,09,16,42,293,47*4A
$GPGLL,5112.31099,N,00158.66984,W,143903.00,A,A*7B
$GPZDA,143903.00,15,10,2007,00,00*6A
The meaning of this information, as derived from the above mentioned web sites,
is as discussed next.
Each sentence begins with a '$' and ends with a carriage return/line feed
sequence and can be no longer than 80 characters of visible text (plus the line
terminators). The data is contained within this single line with data items
separated by commas. The data itself is just ASCII text and may extend over
multiple sentences in certain specialized instances but is normally fully
contained in one variable length sentence. The data may vary in the amount of
precision contained in the message. For example time might be indicated to
decimal parts of a second or location may be show with 3 or even 4 digits after
the decimal point.
Programs that read the data should only use the commas to determine the field
boundaries and not depend on column positions. There is a provision for a
checksum at the end of each sentence which may or may not be checked by the unit
that reads the data. The checksum field consists of a '*' and two hex digits
representing an 8 bit exclusive OR of all characters between, but not including,
the '$' and '*'. A checksum is required on some sentences.
- from
http://www.gpsinformation.org/dale/nmea.htm#ZDA
The satellite PRN number per
ICD-GPS-200
. This is a required data item as it is the GPS user's primary means of
identifying GPS satellites. It is equivalent to the space vehicle identification
(SVID) number of the satellite. The PRN number lies in the range from 01 to 32.
- from
http://celestrak.com/GPS/almanac/SEM/definition.asp
RMC
RMC
NMEA has its own version of essential GPS PVT (position, velocity, time) data.
It is called RMC, The Recommended Minimum.
example:
$GPRMC,143903.00,A,5112.31099,N,00158.66984,W,0.004,,151007,,,A*64
hhmmss.ss
UTC time of fix
143903.00
A
Data status:
A = valid position
V = navigation receiver warning
A
llll.ll
Latitude of fix
5112.31099
a
N or S of longitude
N
yyyyy.yy
Longitude of fix
00158.66984
a
E or W of longitude
W
x.x
Speed over ground in knots
0.004
x.x
Track made good in degrees True
Track angle in degrees true
null
ddmmyy
UTC date of fix
151007
x.x
Magnetic variation degrees
Easterly variation subtracts from true course
N/A
a
E or W of magnetic variation
null
Mode indicator for NMEA 0183 Version 3.00 active
A = Autonomous
D = Differential
E = Estimated
N = Data not valid
not used
m*hh
Checksum
A*64
VTG
VTG
VTG
= Velocity Made Good. The GPS receiver may use the LC prefix instead of GP if it
is emulating Loran output.
example:
$GPVTG,,T,,M,0.004,N,0.007,K,A*20
x.x
True course made good over ground, degrees
null
a
T
x.x
Magnetic course made good over ground, degrees
null
a
M
x.x
Ground speed
0.004
a
N = knots
N
x.x
Ground speed
0.007
a
K = Kilometers per hour
K
Mode indicator for NMEA 0183 Version 3.00 active
A = Autonomous
D = Differential
E = Estimated
N = Data not valid
not used
m*hh
checksum
A*20
GGA
GGA
Essential fix data which provides 3D location and accuracy data.
example:
$GPGGA,143903.00,5112.31099,N,00158.66984,W,1,07,1.21,136.0,M,48.2,M,,*41
hhmmss.ss
UTC of position
143903.00
ddmm.mmm
latitude of position
5112.31099
a
N or S, latitutde hemisphere
N
dddmm.mmm
longitude of position
00158.66984
a
E or W, longitude hemisphere
W
a
GPS Quality indicator
0 = No fix
1 = Non-differential GPS fix
2 = Differential GPS fix
3 = PPS fix
4 = Real Time Kinematic
5 = Float RTK
6 = estimated (dead reckoning) (2.3 feature)
7 = Manual input mode
8 = Simulation mode
1
nn
number of satellites in use
07
x.x
horizontal dilution of precision
1.21
x.x
Antenna altitude above mean-sea-level
136.0
a
M = units of antenna altitude, meters
M
x.x
Geoidal height
48.2
a
M = units of geoidal height, meters
M
x.x
Age of Differential GPS data
seconds since last valid RTCM transmission
null
*xx
checksum, always starts with " *"
*41
GSA
GSA
GPS DOP and active satellites. This sentence provides details on the nature of
the fix. It includes the numbers of the satellites being used in the current
solution and the DOP. DOP (dilution of precision) is an indication of the effect
of satellite geometry on the accuracy of the fix. It is a unitless number where
smaller is better. For 3D fixes using 4 satellites a 1.0 would be considered to
be a perfect number, however for over-determined solutions it is possible to see
numbers below 1.0.
There are differences in the way the PRN's are presented which can effect the
ability of some programs to display this data. For example, in the example shown
below there are 5 satellites in the solution and the null fields are scattered
indicating that the almanac would show satellites in the null positions that are
not being used as part of this solution. Other receivers might output all of the
satellites used at the beginning of the sentence with the null field all stacked
up at the end. This difference accounts for some satellite display programs not
always being able to display the satellites being tracked. Some units may show
all satellites that have ephemeris data without regard to their use as part of
the solution but this is non-standard.
example:
$GPGSA,A,3,21,05,06,24,13,31,16,,,,,,1.90,1.21,1.47*0B
a
Autoselection of 2D or 3D fix
A = auto
M = manual
A
a
Mode:
1 = Fix not available
2 = 2D
3 = 3D
3
nn
PRN of Satellite Vechicle (" SV" ) 1 used in position fix (null for unused
fields)
21
nn
PRN of Satellite Vechicle (" SV" ) 2 used in position fix (null for unused
fields)
05
nn
PRN of Satellite Vechicle (" SV" ) 3 used in position fix (null for unused
fields)
06
nn
PRN of Satellite Vechicle (" SV" ) 4 used in position fix (null for unused
fields)
24
nn
PRN of Satellite Vechicle (" SV" ) 5 used in position fix (null for unused
fields)
13
nn
PRN of Satellite Vechicle (" SV" ) 6 used in position fix (null for unused
fields)
31
nn
PRN of Satellite Vechicle (" SV" ) 7 used in position fix (null for unused
fields)
16
nn
null
nn
null
nn
null
nn
null
nn
null
x.x
Position Dilution of Precision (PDOP)
1.90
x.x
Horizontal Dilution of Precision (HDOP)
1.21
x.x*nn
Vertical Dilution of Precision (VDOP)
followed by " *" followed by checksum
1.47*0B
GSV
GSV
Satellites in View shows data about the satellites that the unit might be able
to find based on its viewing mask and almanac data. It also shows current
ability to track this data. Note that one GSV sentence only can provide data for
up to 4 satellites and thus there may need to be 3 sentences for the full
information. It is reasonable for the GSV sentence to contain more satellites
than GGA might indicate since GSV may include satellites that are not used as
part of the solution. It is not a requirment that the GSV sentences all appear
in sequence. To avoid overloading the data bandwidth some receivers may place
the various sentences in totally different samples since each sentence
identifies which one it is.
The field called SNR (Signal-to-Noise Ratio) in the NMEA standard is often
referred to as signal strength. SNR is an indirect but more useful value that
raw signal strength. It can range from 0 to 99 and has units of dB according to
the NMEA standard, but the various manufacturers send different ranges of
numbers with different starting numbers so the values themselves cannot
necessarily be used to evaluate different units. The range of working values in
a given GPS unit will usually show a difference of about 25 to 35 between the
lowest and highest values, however 0 is a special case and may be shown on
satellites that are in view but not being tracked.
example:
$GPGSV,3,1,09,21,46,150,41,05,10,118,37,06,61,070,49,07,,,47*45
$GPGSV,3,2,09, 24,51,093,48,13,08,340,37,10,,,39, 31,53,216,40*42
$GPGSV,3,3,09,16,42,293,47*4A
m
number of sentences for full data
3
n
sentence number (n of m)
1
nn
number of satellites in view
09
nn
satellite PRN number
21
nn
elevation in degrees
46
nnn
azimuth in degrees
150
nn
signal-to-noise ratio in dB
41
nn
satellite PRN number
05
nn
elevation in degrees
10
nnn
azimuth in degrees
118
nn
signal-to-noise ratio in dB
37
nn
satellite PRN number
06
nn
elevation in degrees
61
nnn
azimuth in degrees
070
nn
signal-to-noise ratio in dB
49
nn
satellite PRN number
07
nn
elevation in degrees
null
nnn
azimuth in degrees
null
nn*nn
signal-to-noise ratio in dB
followed by the checksum data, always begins with " *"
47*45
GLL
GLL
Geographic Latitude and Longitude is a holdover from Loran data and some old
units may not send the time and data active information if they are emulating
Loran data. If a GPS is emulating Loran data they may use the LC Loran prefix
instead of GP.
example
$GPGLL,5112.31099,N,00158.66984,W,143903.00,A,A*7B
x.x
current latitude of position
5112.31099
a
N for North
S for South
N
x.x
current longitude of position
00158.66984
a
E for East
W for West
W
hhmmss.ss
UTC of position
143903.00
a
status: A = valid data
A
a*nn
A*checksum
A*7B
ZDA
ZDA
UTC Date / Time and Local Time Zone Offset
example
$GPZDA,143903.00,15,10,2007,00,00*6A
hhmmss.ss
UTC time
143903.00
xx
UTC day, 01 to 31
15
xx
UTC month, 01 to 12
10
xxxx
UTC year
2007
xx
Offset to local time zone in hours
00
xx*nn
Offset to local time zone in minutes
followed by " *" followed by checksum
00*6A
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