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PowerPoint Presentation - U.S. Coast Guard Navigation Center

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					L2CS Technical Description
                   Tom Stansell
                Technical Agenda

• Signal Development Framework
    – Objectives and Constraints
•   The L2 Civil Signal (L2CS) Description
•   Signal Performance Characteristics
•   Design Decisions and Tradeoffs
•   Eventual Civil Signal Options
Signal Development Framework

     Objectives and Constraints
             Technical Framework (1 of 3)

• Civil L2 signal power ~2.3 dB less than L1 C/A
• Code chip rate must remain at 1.023 MHz
   – To separate the M Code and Civil Code spectra
• Only one bi-phase signal component available
   – L5-type quad-phase not possible
   – L2CS shares L2 with military signals
• Definition needed by the first of March
   –   Technical meetings began in mid-January
   –   Definition complete by mid-February
   –   Coordinated with Lockheed-Martin and Boeing
   –   First draft of ICD-GPS-200 PIRN completed
                  Code Spectra: BOC (10,5) M & C/A




                                    C/A code
                                    spectrum




Effect on GPS noise floor of
   a strong M code signal
    One Civil Component on L1


                           0,1 = 109.5 deg




     Civil = 1                                P/Y = 0




                                                         0,0 = 0 deg

1,1 = 180 deg




                 P/Y = 1                                Civil = 0

                                                    L1 Phase Relationships
                            1,0 = -70.5 deg
                                                        Civil is 3 dB stronger than P/Y
     One Civil Component on L2

                                   0,1 = 84.7 deg




                 Civil = 1                              P/Y = 0




                                                                  0,0 = 0 deg

1,1 = 180 deg




                P/Y = 1                             Civil = 0


                                                      L2 Phase Relationships
                                                           Civil is 0.4 dB weaker than P/Y
                             1,0 = -95.3 deg
               Technical Framework (2 of 3)

• Serve the current large and valuable dual frequency
  survey, science, and machine control applications
   – Approximately 50,000 in service
   – Primary need is for robust carrier phase measurements
   – Typically use semi-codeless L2 access, but many also are
     equipped with an L2 C/A capability
• Improve cross-correlation for single frequency applications
  (e.g., wooded areas or indoor navigation)
   – A strong C/A code signal can interfere with weak signals
• Receiver technology has advanced enormously compared
  with the 1970s when C/A was developed
   – The outdated C/A should be replaced with a better code
Technology Has Changed

    1984                          2001



                              Consumer 12
                             channel digital
                             with color map




                             Consumer 12
                            channel digital
           5 Channel Analog
                            for under $100
          Technical Framework (3 of 3)

• New signals on IIR-M and IIF satellites
• When will full coverage with the new signals
  become available?
  – See estimated launch schedule chart
• Will the IIR-M be able to transmit an L5-type
  message on the L2CS?
  – Lockheed-Martin implementation study underway
  – Backup modes will be provided
            Signals on IIR, IIR-M, & IIF

Signal\SV         IIR         IIR-M        IIF

 L1 C/A

 L1 P/Y

  L1 M

 L2 Civil

 L2 P/Y

  L2 M

 L5 Civil
                Number of Satellites with New Signals




                0
                    5
                         10
                              15
                                        20
                                             25
                                                       30
                                                            35
       Feb-03


       Feb-04
                                              L5

       Feb-05
                                              L2CS




       Feb-06


       Feb-07




Year
       Feb-08


       Feb-09
                                                                 Civil Signal Availability




       Feb-10


       Feb-11
                                   18
                                         21
                                         24
                                                  28
L2 Civil Signal (L2CS) Description
                   Definitions

• L2CS – the L2 Civil Signal
• CM – the L2CS moderate length code
  – 10,230 chips, 20 milliseconds
• CL – the L2CS long code
  – 767,250 chips, 1.5 second
• NAV – the legacy navigation message
  provided by the L1 C/A signal
• CNAV – a navigation message structure like
  that adopted for the L5 civil signal
                       IIF Signal Generation

       L5-Like CNAV
         Message                 Rate 1/2 FEC
        25 bits/sec


                                  Legacy NAV
                                    Message
                                   50 bits/sec


       10,230 Chip                    Chip by Chip
      Code Generator     CM            Multiplexer
                        Code
 511.5 kHz Clock

       767,250 Chip
      Code Generator     CL         B2                   A1   Transmitted
                        Code        B1                           Signal
1/2                                                      A2
         C/A Code
         Generator

                                             1.023 MHz
                                                Clock
            IIF L2CS Signal Options

• The ability to transmit any one of the following
  three signal structures upon command from the
  Ground Control Segment:
  – The C/A code with no data message (A2, B1)
  – The C/A code with the NAV message (A2, B2)
  – The chip by chip time multiplexed (TDM) combination
    of the CM and CL codes with the CNAV message at
    25 bits/sec plus FEC
    bi-phase modulated on the CM code (A1)
                     IIR-M Signal Generation

       L5-Like CNAV                                       B1 is a potential software
         Message              D1                          option to be uploaded by
                                   Rate 1/2 FEC
        25 bits/sec                                         the Control Segment
                              D2
                                                      C1
                                                      C2
        Legacy NAV                 Legacy NAV
          Message                    Message
         25 Bits/sec                50 bits/sec


       10,230 Chip                     Chip by Chip
      Code Generator    CM              Multiplexer
                       Code
 511.5 kHz Clock

       767,250 Chip
      Code Generator    CL           B2                      A1     Transmitted
                       Code          B1                                Signal
1/2                                                          A2
         C/A Code
         Generator

                                              1.023 MHz
                                                 Clock
          IIR-M L2CS Preferred Mode


• The Preferred mode is the ability to transmit
  the following signal structure upon command
  from the Ground Control Segment:
  – The chip by chip time multiplexed (TDM)
    combination of the CM and CL codes with
    the CNAV message at 25 bits/sec plus FEC bi-
    phase modulated on the CM code
    (A1, C1, D1)
            IIR-M L2CS Backup Mode


• One backup mode is the ability to transmit the
  following signal structure upon command from
  the Ground Control Segment:
  – The chip by chip time multiplexed (TDM) combination
    of the CM and CL codes with
    the NAV message at 25 bits/sec plus FEC
    bi-phase modulated on the CM code
    (A1, C1, D2)
           IIR-M L2CS Optional Modes

• The ability to transmit any one of the following
  three signal structures upon command from the
  Control Segment:
  – The C/A code with no data message (A2, B1)
  – The C/A code with the NAV message (A2, B2)
  – The chip by chip time multiplexed (TDM) combination
    of the CM and CL codes with the NAV message at 50
    bits/sec bi-phase modulated on the CM code (A1, C2)
• Control Segment implementation is under
  evaluation for these & the previous options
            L2CS Code Characteristics

• Codes are disjoint segments of a long-period
  maximal code
   – 27-stage linear shift register generator (LSRG) with multiple
     taps is short-cycled to get desired period
   – Selected to have perfect balance
• A separate LSRG for each of the two codes
• Code selection by initializing the LSRG to a fixed
  state specified for the SV ID and resetting (short-
  cycling) after a specified count for the code period or
  at a specified final state
• 1 cycle of CL & 75 cycles of CM every 1.5 sec
                              L2CS Code Generator

     DELAY
     NUMBERS




3     3            2           3             3           2            2         3   1   1   1   3

                                                                                                    OUTPUT




     INITIAL CONDITIONS ARE A FUNCTION OF PRN AND CODE PERIOD (MODERATE/LONG)



                                                              SHIFT DIRECTION




    Linear shift register generator with 27 stages and 12 taps
                   37 of the 100 Selected Codes
            PERIOD=10230               PERIOD=767250
      SHORT CODE STATES (OCTAL)   LONG CODE STATES (OCTAL)
PRN      START           END        START            END
  1
  2
       742417664
       756014035
                      552566002
                      034445034
                                  624145772
                                  506610362
                                                 267724236
                                                 167516066
                                                             • Medium code = CM
  3    002747144      723443711   220360016      771756405
  4
  5
       066265724
       601403471
                      511222013
                      463055213
                                  710406104
                                  001143345
                                                 047202624
                                                 052770433      – 10,230 chips
  6    703232733      667044524   053023326      761743665
  7
  8
  9
       124510070
       617316361
       047541621
                      652322653
                      505703344
                      520302775
                                  652521276
                                  206124777
                                  015563374
                                                 133015726
                                                 610611511
                                                 352150323
                                                                – 20 msec
 10    733031046      244205506   561522076      051266046
 11
 12
       713512145
       024437606
                      236174002
                      654305531
                                  023163525
                                  117776450
                                                 305611373
                                                 504676773
                                                             • Long code = CL
 13    021264003      435070571   606516355      272572634
 14
 15
       230655351
       001314400
                      630431251
                      234043417
                                  003037343
                                  046515565
                                                 731320771
                                                 631326563      – 767,250 chips
 16    222021506      535540745   671511621      231516360
 17
 18
 19
       540264026
       205521705
       064022144
                      043056734
                      731304103
                      412120105
                                  605402220
                                  002576207
                                  525163451
                                                 030367366
                                                 713543613
                                                 232674654
                                                                – 1.5 second
                                                             • Begin and end states
 20    120161274      365636111   266527765      641733155
 21    044023533      143324657   006760703      730125345
 22    724744327      110766462   501474556      000316074
 23    045743577      602405203   743747443      171313614
 24
 25
       741201660
       700274134
                      177735650
                      630177560
                                  615534726
                                  763621420
                                                 001523662
                                                 023457250   • Perfectly balanced
 26    010247261      653467107   720727474      330733254
 27
 28
 29
       713433445
       737324162
       311627434
                      406576630
                      221777100
                      773266673
                                  700521043
                                  222567263
                                  132765304
                                                 625055726
                                                 476524061
                                                 602066031
                                                             • 37 codes listed in the
 30
 31
       710452007
       722462133
                      100010710
                      431037132
                                  746332245
                                  102300466
                                                 012412526
                                                 705144501     ICD-GPS-200 PIRN
 32    050172213      624127475   255231716      615373171
 33
 34
 35
       500653703
       755077436
       136717361
                      154624012
                      275636742
                      644341556
                                  437661701
                                  717047302
                                  222614207
                                                 041637664
                                                 100107264
                                                 634251723
                                                             • 100 codes defined
 36    756675453      514260662   561123307      257012032
 37    435506112      133501670   240713073      703702423
                   Code Tracking

• Early minus late (E-L) code tracking loops try to
  center windows, e.g., narrow correlator
  windows, on code transitions
• For each of the two L2CS codes, there is a
  transition at every chip
  – Because the other code is perfectly balanced, the
    alternate chips average to zero
  – Twice the transitions, half the amplitude, and double
    the average noise power (time on) yields –3 dB S/N
    in a one-code loop
  – Both codes can be tracked, but CL-only is OK
Narrow Correlator Tracking
Narrow Correlator on L2CS
              The CNAV Message

• The CNAV message data rate is 25 bps
• A rate-1/2 forward error correction (FEC),
  without interleaving, (same as L5) is applied,
  resulting in 50 symbols per sec
• The data message is synchronized to X1
  epochs, meaning that the first symbol
  containing information about the first bit of a
  message is synchronized to every 8th X1
  epoch
           CNAV Message Content


• The CNAV message content is the same as
  defined for the L5 signal with the following
  differences and notes:
  – Because of the reduced bit rate, the sub-frame
    period will be 12 seconds rather than 6 seconds
  – The time parameter inserted into each data sub-
    frame will properly represent the 12-second epoch
    defined by each sub-frame
  – The terms provided by the Control Segment
    representing time bias between the P code and
    the civil codes for L1, L2, and L5 will be included
          Message Sequence Options

 Type 1
 Type 2          36 sec frame
Other Type
                                  Message Types
                                  1 = Ephemeris A
                                  2 = Ephemeris B
                                  3 = Iono, Bias, Health
                                  4 = Almanac
 Type 1                           5 = Text

 Type 2                         Type 4 message gives one
                 48 sec frame     satellite almanac per
 Other A
                                        sub-frame
 Other B
        CNAV Message Sequencing

• Message sequences will be determined by
  the Control Segment. One possible
  sequence is three sub-frames grouped into
  repeating frames of 36 seconds, each
  containing Ephemeris 1 and Ephemeris 2
  messages plus another sub-frame
• The third sub-frame of each 36 second frame
  contains one almanac message or another
  message when and as needed
            Another CNAV Sequence

• Another possible sequence is four
  sub-frames grouped into repeating frames of 48
  seconds, each containing Ephemeris 1 and
  Ephemeris 2 messages plus two other
  sub-frames
• It also will be possible for different satellites to
  transmit different almanac messages at the
  same time, as defined or scheduled by the
  Ground Control Segment
             Compact Almanac


• A new compact almanac message type is
  being developed to minimize the time
  required to collect a complete almanac
• Up to 7 satellite almanacs per sub-frame
• The new message type will be described in a
  following presentation
Signal Performance Characteristics
          Relative Channel Power

  Comparing L2CS with C/A on L2
                  Relative       Relative
                Data Channel     Data-Less
                   Power       Channel Power

L2 C/A code        0.0 dB      None (Costas)



  L2 CS           -3.0 dB          -3.0 dB
       Data & Tracking Thresholds

   Comparing L2CS with C/A on L2
              Relative Data     Relative Carrier
                Recovery           Tracking
               Threshold          Threshold

L2 C/A code       0.0 dB            0.0 dB



  L2 CS           +5.0 dB           +3.0 dB
                (FEC = 5 dB)     (Phase locked
              (25 bps = 3 dB)   tracking = 6 db)
                Signal Acquisition

                           Relative Acquisition
                                  Power
          L2 C/A code            0.0 dB

              L2 CS          -3.0 dB (-1.0 dB
                            using both codes)

C/A code acquisition may    Modern, multiple correlator
 be impossible for very      technology overcomes the
   weak signals in the        L2CS power deficit and
  presence of a strong      permits rapid acquisition of
      C/A signal                 very weak signals
      Power from IIR-M & IIF

Comparing Three Civil Signals
               Received     Relative
                 Power     Total Power
L1 C/A code   -157.7 dBW     0.0 dB

  L2 CS       -160.0 dBW     -2.3 dB

 L5 signal    -154.0 dBW    +3.7 dB
             Relative Channel Power

     Comparing Three Civil Signals
                    Relative        Relative
                  Data Channel     Data-Less
                     Power       Channel Power
L1 C/A code          0.0 dB      None (Costas)

  L2 CS              -5.3 dB          -5.3 dB

 L5 signal           +0.7 dB          +0.7 dB
          Data & Tracking Thresholds

      Comparing Three Civil Signals
                 Relative Data     Relative Carrier
                  Recovery       Tracking Threshold
                  Threshold
L1 C/A code         0.0 dB            0.0 dB

  L2 CS             +2.7 dB           +0.7 dB

 L5 signal          +5.7 dB           +6.7 dB
               Signal Acquisition


                                       C/A code acquisition
              Relative Acquisition
                                      may be impossible for
                     Power           very weak signals in the
L1 C/A code          0.0 dB          presence of a strong C/A
                                             signal

L2 C/A code         -2.3 dB            Modern, multiple
                                     correlator technology
  L2 CS        -5.3 dB (-3.3 dB      overcomes the L2CS
                                       power deficit and
              using both codes)
                                         permits rapid
 L5 signal    +0.7 dB (+2.7 dB        acquisition of very
              using both codes)          weak signals
            Tracking/Data Performance

• With 50% power split, 25 bps, and rate-½ FEC
• Under moderate dynamic conditions (aviation)
   – Max acceleration = 29.8 Hz/sec
   – Maximum jerk = 9.6 Hz/sec2
   – BL = 8 Hz
• Balanced performance
   – 300 bit word error rate (WER) is 0.015
     with total C/No = 22 dB-Hz
   – Phase slip probability within 60 seconds is 0.001
     with total C/No = 23 dB-Hz
         Tracking/Data Performance

• With 50% power split, 25 bps, and rate-½
  FEC
• Under high dynamic conditions
  – Max acceleration = 300 Hz/sec
  – Maximum jerk = 100 Hz/sec2
  – BL = 15 Hz
• Performance
  – 300 bit word error rate (WER) of 0.015 with total
    C/No = 24.5 dB-Hz
  – Phase slip probability in 60 seconds of 0.001 with
    total C/No = 25.5 dB-Hz
Design Decisions and Tradeoffs
       Why two codes?
          Why TDM?
      Why Chip by Chip?
     Why L5 type message?
          Why FEC?
An Old Idea Revived

             • Transit, the world’s first satellite
               navigation system, provided a
               coherent carrier
             • But GPS used bi-phase data
               modulation, leaving no carrier
             • Bi-phase modulation favors data
               over continuous lock and
               measurement accuracy
                  – But data is redundant, slowly
                    changing, thus less important
 Transit     • A carrier component makes
Modulation     signal tracking & navigation
               measurements more robust
                 Why Two Codes?

• Carrier component first accepted for L5
  – Two equal power signal components in phase
    quadrature, each with a separate code
  – One component with bi-phase data
  – The other component with carrier & no data
  – Forward error correction (FEC) raised bit error
    probability to the level achieved with all the power in
    one bi-phase signal component
  – The carrier component improves tracking threshold
    by 3 dB
  – Win-win: better tracking, no data degradation
               Two L2 Codes

• Quad phase was not available for L2
• Two codes provided by time multiplexing one
  bi-phase signal component
• Data with forward error correction on
  moderate length code, CM
• No data on the long CL code, provides a
  carrier component and a 3 dB better tracking
  threshold
• Longer CL code improves crosscorrelation
                Multi-Code Options

• Considered 3 ways to provide two codes:
  – Majority vote of 3 codes
     • 000=0, 001=0, 010=0, 100=0,
       011=1, 101=1, 110=1, 111=1
     • One with data, two without data
     • Tracking only one code loses 6 dB
     • Knowledge of all three regains 3 dB
  – Time multiplexed, msec by msec
  – Time multiplexed, chip by chip
          Chip by Chip TDM Chosen

• Majority vote eliminated because:
  – Requires 3 rather than 2 code generators
  – Requires synch to all 3 codes for best results
  – No other advantage found
• Msec by msec TDM eliminated because:
  – Requires care to avoid 500 Hz sidetone
  – No other advantage found
• Selected chip by chip TDM
  – Simple to implement with no disadvantages
          Code Length Considerations

• The peak cross-correlation between existing C/A
  codes is -23.9 dB
  – The Gold bound for period 1023 chips
  – C/A codes are inadequate for indoor navigation
• Correlation sidelobe examples for TDM
  candidates
  – 20 msec period: 29 dB below full correlation
  – 200 msec period: 36 dB below full correlation
  – 1.5 sec period: 47 dB below full correlation
            Code Correlation Studies

• Fig 1 – Three individual code lengths
• Fig 2 – TDM 409,200
• Fig 3 – TDM 1,534,500 (10,230 & 767,250)
  – This is the selected code pair
  – CM for faster acquisition
  – CL for better crosscorrelation
     • Minimum crosscorrelation protection of 45 dB
• Fig 4 – TDM 613,800 (10,230 & 306,900)
• Fig 5 – TDM 1,534,500 (1 msec segments)
                                                                 Three Individual Codes

                                                              FIG 1. DISTRIBUTION OF CORRELATION FUNCTION OF TDMA CODE

                                               1


                                              0.9
PROB THAT CORRELATION PEAK EXCEEDS ABSCISSA




                                              0.8
                                                                                  PERIOD OF TDMA CODE=
                                                                                       20460 CHIPS
                                              0.7


                                              0.6


                                              0.5

                                                                                            40920 CHIPS
                                              0.4
                                                                                                             409200 CHIPS

                                              0.3


                                              0.2


                                              0.1


                                               0
                                                    25   30        35        40           45          50      55            60   65   70
                                                                         CORRELATION LEVEL, DB BELOW FULL CORRELATION
                                                              TDM of 409,200 Chips

                                                         FIG 2. DISTRIBUTION OF CORRELATION FUNCTION OF TDMA CODE

                                               1


                                              0.9
PROB THAT CORRELATION PEAK EXCEEDS ABSCISSA




                                              0.8


                                              0.7                                 PERIOD OF TDMA CODE=
                                                                                       409200 CHIPS

                                              0.6


                                              0.5


                                              0.4                                              CROSS


                                              0.3

                                                                AUTO
                                              0.2


                                              0.1


                                               0
                                                    40   45             50               55              60         65   70
                                                                    CORRELATION LEVEL, DB BELOW FULL CORRELATION
                                                                        TDM of 1,534,500 Chips

                                                         FIG 3. DISTRIBUTION OF CORRELATION FUNCTION OF TDMA CODE OF UNEQUAL PERIODS

                                               1
                                                         SHORT CODE PERIOD = 10230 CHIPS
                                              0.9        LONG CODE PERIOD = 767250 CHIPS
PROB THAT CORRELATION PEAK EXCEEDS ABSCISSA




                                                         PERIOD OF TDMA CODE = 1534500 CHIPS

                                              0.8


                                              0.7


                                              0.6                                              CROSS


                                              0.5


                                              0.4


                                              0.3                                                    AUTO


                                              0.2


                                              0.1


                                               0
                                                    45             50             55            60            65            70   75    80
                                                                                  CORRELATION LEVEL, DB BELOW FULL CORRELATION
                                                                          TDM of 613,800 Chips

                                                         FIG 4. DISTRIBUTION OF CORRELATION FUNCTION OF TDMA CODE OF UNEQUAL PERIODS

                                               1
                                                         SHORT CODE PERIOD = 10230 CHIPS
                                              0.9        LONG CODE PERIOD = 306900 CHIPS
PROB THAT CORRELATION PEAK EXCEEDS ABSCISSA




                                                         PERIOD OF TDMA CODE = 613800 CHIPS

                                              0.8


                                              0.7

                                                                                                                     CROSS
                                              0.6


                                              0.5


                                              0.4
                                                                                AUTO
                                              0.3


                                              0.2


                                              0.1


                                               0
                                                    40           45           50              55        60          65            70   75   80
                                                                                   CORRELATION LEVEL, DB BELOW FULL CORRELATION
                                                                   TDM with 1 msec Segments

                                                         FIG 5. DISTRIBUTION OF CORRELATION FUNCTION OF TDMA CODE OF UNEQUAL PERIODS

                                               1
                                                         SHORT CODE PERIOD = 10230 CHIPS
                                              0.9        LONG CODE PERIOD = 767250 CHIPS
PROB THAT CORRELATION PEAK EXCEEDS ABSCISSA




                                                         PERIOD OF TDMA CODE = 1534500 CHIPS
                                                         INTERLEAVE 1 MSEC SEGMENTS
                                              0.8


                                              0.7


                                              0.6                                              CROSS


                                              0.5


                                              0.4


                                              0.3                                                    AUTO


                                              0.2


                                              0.1


                                               0
                                                    45             50             55            60            65            70   75    80
                                                                                  CORRELATION LEVEL, DB BELOW FULL CORRELATION
               Data and FEC Rates

• Normally a signal can be tracked to a lower S/N
  than data can be demodulated reliably
• A team member suggested lowering the bit rate
  to 25 bps
• Using FEC with this change allows tracking and
  demodulation thresholds be be equivalent
  – Advantage in forest navigation
• The more compact and flexible L5-type message
  also makes this practical
• A bit rate of 25 BPS with a rate ½ FEC was
  chosen
                 Choosing Data & FEC Rates

        Data rate              For WER = 0.015,         For 50% power split,
           &                    C/No in the data          C/No in the total
        FEC rate                 component =                  signal =
    50 bps, uncoded                25.8 dB-Hz                 28.8 dB-Hz

     50 bps, rate-1/2              20.6 dB-Hz                 23.6 dB-Hz

   33.33 bps, rate-1/2             18.8 dB-Hz                 21.8 dB-Hz

     25 bps, rate-1/2             17.6 dB-Hz                  20.6 dB-Hz

     50 bps, rate-1/3              19.9 dB-Hz                 22.9 dB-Hz

   33.33 bps, rate-1/3             18.1 dB-Hz                 21.1 dB-Hz

     25 bps, rate-1/3              16.9 dB-Hz                 19.9 dB-Hz

Theoretical requirements for data demodulation with perfect carrier phase tracking
              Balance Tracking & Demod.

 Data rate        Carrier power        WER = 0.015        Phase slip =
   (bps) &          percent           with total C/No    0.001 with total
  FEC rate                                   =               C/No =
 50 & None            Costas             26 dB-Hz          25.5 dB-Hz
 50 & None               50              29 dB-Hz           23 dB-Hz
 25 & None               50             26.5 dB-Hz          23 dB-Hz
   50 & ½                50              24 dB-Hz           23 dB-Hz
  33.3 & ½               50             22.5 dB-Hz          23 dB-Hz
   25 & ½                50              22 dB-Hz           23 dB-Hz
   25 & ½                25              24 dB-Hz           26 dB-Hz
   25 & ½                75              24 dB-Hz           21 dB-Hz
 33.3 & 1/3              50              22 dB-Hz           23 dB-Hz

For max acceleration = 29.8 Hz/sec, maximum jerk = 9.6 Hz/sec2, BL = 8 Hz
             Higher G Tracking & Demod.

 Data &      Carrier   Optimum      WER = 0.015      Phase slip =
FEC rates    Power        BL       with total C/No    0.001 with
             percent                      =          total C/No =
50 & none    Costas      15 Hz        27 dB-Hz         29 dB-Hz
  50 & ½      50%        15 Hz       25 dB-Hz        25.5 dB-Hz
  25 & ½      50%        15 Hz      24.5 dB-Hz       25.5 dB-Hz
 25 & ½      66.7%       15 Hz       24 dB-Hz        24.5 dB-Hz
 25 & ½       75%        13 Hz       24 dB-Hz         24 dB-Hz
33.3 & 1/3    50%        13 Hz      24.5 dB-Hz       25.5 dB-Hz
33.3 & 1/3   66.7%       15 Hz       24 dB-Hz        24.5 dB-Hz
33.3 & 1/3    75%        13 Hz       25 dB-Hz         24 dB-Hz


Maximum acceleration = 300 Hz/sec and maximum jerk = 100 Hz/sec2
Eventual Civil Signal Options


       For each application,
  companies will choose the most
     appropriate signal to use
            Civil Signal Characteristics

  Carrier     Code      Code
Frequency    Length    Clock                        Correlation
  (MHz)      (Chips)   (MHz)   Phases   Available   Protection
1,575.42      1,023    1.023    Bi-       Now        > 21 dB
                               Phase
1,227.60      10,230   1.023    Bi-      ~ 2011      > 45 dB
             767,250           Phase
1,176.45     10,230    10.23   Quad      ~ 2015      > 30 dB
             10,230            Phase
                    L2CS Features

• Best crosscorrelation protection
  – Aids navigation indoors and in forest areas
  – Provides headroom for increased SV power
• Lower chip rate:
  – Saves power and minimizes thermal rise
  – Allows use of narrowband RF/IF filters
     • Lower cost
     • Protection against nearby interfering signals
• Available years sooner than L5

				
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posted:8/5/2012
language:English
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