Sue... said:
On Feb 3, 12:26 pm, Koobee Wublee
[...]
Even if you do not correct any of the frequencies involved:
** Almanac signal (50bits/sec), the payload
** Chipping rates: 10.23MHz and 1.023MHz
** Carriers: 1-2GHz, RF
http://electronicdesign.com/Articles/Index.cfm?ArticleID=15475
http://www.csr.utexas.edu/texas_pwv/midterm/gabor/gps.html#anchor1735013
<< It is time for Sam to actually learn how GPS works. <shrug> >>
GPS has basically two functions
o Navigation signals
o Nuclear detection
L1 1575.4200 Civil/Military Frequency
L2 1227.6000 Civil/Military Frequency
L3 1381.0500 Nuclear Burst Detection
L4 1841.4000 Ionospheric correction (proposed)
L5 1176.4500 Civil/Military Frequency
There are currently three frequencies used and a fourth (L5)
beginning in 2009.
L5 L2 L3 L1 L4
------------+-------+-----------|---------------------------+--------------+----
1176.45 1227.60 1381.05 1575.42 MHz 1841.40
115 x 120 x 135 x 154 x 10.23 MHz 180 x
| | | |
| | | |
Current | | | C/A
Signals | P(Y) NUDET P(Y)
| | |
| | |
| | |
Proposed P-like C/A(Possibly P-like code) C/A
New Signal code P(Y) P(Y)
Structure M-Codes M-Codes
Note that the military and other authorized users have access to
the Y-code at the chip rate of 10.23 Mbps. Course Acquisition (C/A)
is at a chip rate of 1.023 Mbps. However, since the unknown Y-code
is identical on both L1 and L2, several techniques can be used to
extract the 10.23 MHz carrier information, which is used in high
accuracy differential receivers (surveying).
Technique SNR loss**
---------------------------------------------------------
Squaring -30 dB
Cross correlation -27 dB
Code correlation plus squaring -17 dB
Z-Tracking (reported by Ashjaee and Lorenze 1992) -14 dB
**Loss compared to direct code correlation as used on
military dual frequency receivers.
L1 and L2 Navigation satellite Signal Power Budget
Parameter L1 P-Code L1 C/A-Code L2 P-Code
-----------------------------------------------------------------------
User minimum received power -163.0 dBw -160.0 dBw -166.0 dBw
Users linear antenna gain 3.0 dB 3.0 dB 3.0 dB
Free-space propagation loss 184.4 dB 184.4 dB 182.3 dB
Total atmospheric loss 2.0 dB 2.0 dB 2.0 dB
Polarization mismatch loss 3.4 dB 3.4 dB 4.4 dB
Required satellite EIRP +23.8 dBw +26.8 dBw +19.7 dBw
Satellite Antenna gain at 14.3? 13.5 dB 13.4 dB 11.5 dB
worst case Block II off-axis angle
Required minimum satellite antenna +10.3 dBw +13.4 dBw +8.2 dBw
input power 10.72W 21.88W 6.61W
Of course all the new signals are being implemented at this time and the
signal structures for GPS and Galileo are complex. My old links to the
articles have broken... which implies to me that the information is now
incorrect... when I re-run across a current spectral chart, I'll do a
follow up posting.
____________________________________________
CNAV Messages on GPS L2 to Begin in Fall 2009
http://mg.gpsworld.com/gpsmg/content/printContentPopup.jsp?id=562790
Nov 3, 2008
GPS World
In the fall of 2009 GPS operators at the U.S. Air Force's 50th Space Wing and the 2nd
Space Operations Squadron will upload software to the IIR-M satellites enabling the first
broadcast of a transitional civil navigation (CNAV) message on the already transmitted
second civil signal (L2C).
With the upcoming launches of the remaining two IIR-Ms, there will be a total of eight
modernized GPS satellites broadcasting on the L2C frequency (1227.60 MHz) with the new
CNAV message. GPS IIF satellites will also be launched with the built-in capability to
broadcast the new message.
The modernized L2C signal was designed with several significant advantages over the
existing L1 signal, according to the Air Force. It will provide a lower tracking threshold
and better cross-correlation protection. Furthermore, the data portion of the L2C signal
is also different; instead of the current structure with subframes of data repeating in a
fixed pattern as on L1, the CNAV structure which will be used on L2C has individual
messages which can be broadcast in a flexible order with variable repeat cycles.
The CNAV structure, as defined in Interface Specification (IS)-GPS-200D, allows up to 63
different message types, of which 15 types have already been defined, the Air Force said.
The 15 CNAV message types will be incrementally phased in over time, with the first CNAV
message to broadcast being the default message, also known as Message Type 0. Message Type
0 consists of a 12-second, 300-bit long message including the preamble, satellite
pseudorandom noise (PRN) number, message type ID (=0), GPS time of week, a sequence of
alternating 1s and 0s, and a cyclic redundancy check (CRC) parity block. The GPS time of
week will change every 12 seconds, as will the CRC bits.
Eventually a third civil signal will be added centered at the L5 frequency (1176.45 MHz),
as well as M-Code signals on L1 and L2, will be added as part of the GPS modernization
program. L5 will also carry CNAV messages and will broadcast from IIF and the GPS III
satellites.
)