Viavi 87339, Руководство по эксплуатации

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Principals of Operation
6 -26
6.1.8.C L5
Civilian, safety of life signal planned to be available with first GPS IIF launch (2009). Two
PRN ranging codes are transmitted on L5: the in-phase code (denoted as the I5-code);
and the quadrature-phase code (denoted as the Q5-code). Both codes are 10,230 bits
long and transmitted at 10.23 MHz (1ms repetition). In addition, the I5 stream is
modulated with a 10-bit Neuman-Hofman code that is clocked at 1 kHz and the Q5-code is
modulated with a 20-bit Neuman-Hofman code that is also clocked at 1 kHz.
•
Improves signal structure for enhanced performance
•
Higher transmitted power than L1/L2 signal (-3 dB, or twice as powerful)
•
Wider bandwidth provides a 10× processing gain
• Longer spreading codes (10× longer than C/A)
• Uses the Aeronautical Radio-Navigation Services band
• The recently launched GPS IIR-M7 satellite transmits a demonstration of this
signal.
L5 Navigation message
The L5 CNAV data includes SV ephemerides, system time, SV clock behavior data, status
messages and time information, etc. The 50 bit/s data is coded in a rate 1/2 convolution
coder. The resulting 100 symbols per second (sps) symbol stream is modulo-2 added to
the I5-code only; the resultant bit-train is used to modulate the L5 in-phase (I5) carrier.
This combined signal will be called the L5 Data signal. The L5 quadrature-phase (Q5)
carrier has no data and will be called the L5 Pilot signal.
L5 Frequency information
Broadcast on the L5 frequency (1176.45 MHz, 10.23 MHz × 115), which is an
aeronautical navigation band. The frequency was chosen so that the aviation community
can manage interference to L5 more effectively than L2.
6.1.8.D L1C
Civilian use signal, broadcast on the L1 frequency (1575.42 MHz), which currently
contains the C/A signal used by all current GPS users. The L1C will be available with first
Block III launch, currently scheduled for 2013. The PRN codes are 10,230 bits long and
transmitted at 1.023 Mbps. It uses both Pilot and Data carriers like L2C.
The modulation technique used is BOC(1,1) for the data signal and TMBOC for the pilot.
The Time Multiplexed Binary Offset Carrier (TMBOC) is BOC(1,1) for all except 4 of
33 cycles, when it switches to BOC(6,1). Of the total L1C signal power, 25% is allocated
to the data and 75% to the pilot. Implementation provides C/A code to ensure:
•
Backward compatibility.
•
1.5 dB increase in minimum C/A code power to mitigate any noise floor increase.
•
Data-less signal component pilot carrier improves tracking.
•
Greater civil interoperability with Galileo L1.
CNAV-2 Navigation message
The L1C navigation message, called CNAV-2, is 1800 bits (including FEC) and is
transmitted at 100 bit/s. It contains 9-bit time information, 600-bit ephemeris, and 274-bit
packetized data payload