L1 Band Software GPS Receiver by pdl20154

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									 Development of L1-Band C/A Code
   Software-based GPS Receiver
     Dinesh Manandhar, Ryosuke Shibasaki
          Centre for Spatial Information Science
         Shibasaki Lab, The University of Tokyo
              dinesh@skl.iis.u-tokyo.ac.jp




                  Background
• New Satellite based Navigation Systems in
  near future
  – QZSS (Japan)
  – Galileo (EU)

• Most of GPS Research Focus on Application
  Side

• GPS Receiver still used as a “Black Box”




                                                   1
                What is Software GPS ?
 Antenna




                                                                                           Hardware
                    RF to IF Conversion                          ADC




                                                    Acquisition & Tracking




                                                                                           Software
  Position                  Navigation             Software based Processing
 Velocity etc               Algorithm
                                                  (Change from Hardware based processing
                                                       to Software based Processing)




      Processing Speed vs. Flexibility


        Fastest                   Processing Speed                            Slowest
                                    FPGA
                    ASIC
  Analog                            (Field         Microprocessor      Microprocessor
                (Application
Components                      Programmable    (Assembly Language) (High Level Language)
                 Specific IC)
                                 Gate Array)


      Lowest                             Flexibility                           Highest

                                                         Source : Akos, D., Stanford University




                                                                                                      2
       Software GPS Advantage
• Simulation
  – Simulation of New Systems
     • QZSS
     • Galileo
     • GPS, L5 signal
• Education / Research
  – Develop our own receiver
  – In depth demonstration of system
• Future Trend
  – Software Defined Radio (SDR)
     • Multiple System in Single Device




       Software GPS Advantage
 • Innovation
    – New codes
       • Code for new GNSS e.g. QZSS, Galileo etc
       • Code for Pseudo Satellites
    – New algorithms
       • Acquisition of low power GPS signals
           – Indoor GPS Navigation
       • Multipath mitigation
    – New modulation schemes            GPS Signal                 GPS Signal
                                         (RHCP)                     (LHCP)
       • BPSK or QPSK ?
    – Detection / Imaging
       • GPS signal acts like passive microwave
         (1.5GHz)                                      water
           – Detect Soil Moisture
           – Delineate water boundary
                                                     Land / Soil




                                                                                3
                                         Software GPS Advantage
• Quick Development / Implementation
                            – No hardware component
                            – Quick upgrade, modification
• Flexibility
                            – On-the-fly change of parameters
                            – Variable thresholds            LH and RH Polarized Antenna
                                    • e.g. Analyze Signal Property from LHCP
                                      antenna for Multipath Analysis, Soil Moisture etc
• Integration / Aided Navigation
                            – Minimize data latency problem




                                         Software GPS Design Approach
             Antenna
                                              Code Acquisition                   Code Tracking
                                         Why Acquisition ?                   Tracking For :
                                         Estimate the Code Phase             Fine Tune Code Phase by DLL
RF/IF and ADC conversion




                           Filter
                                         Estimate Doppler Frequency          Fine Tune Carrier Phase by
                                                                                                          Navigation Algorithm




                                         And hence Identify Visible Satellites PLL
                           Gain
                                                                             And hence Extract the
                                         Acquisition Algorithms                  Navigation Data
                                         1. Time Domain Correlation
                                             1. Linear Search                Tracking Algorithms
                                             2. Data in a Block              Implementation of Code and
                                    L0   2. Frequency Domain Correlation Carrier Tracking Algorithms
                           Filter            1. Complete FFT Processing
                                             2. Half FFT Processing          • DLL for Code Tracking
                                         3. … … … … … ..                     • PLL for Carrier Tracking
                            Gain
                                         4. … … … … … … .                    • FLL / PLL Approach   Position
                                                                                                  X, Y, Z
                           Hardware                    Software Implementation




                                                                                                                                 4
                         GPS Raw Data




           Serial Search Acquisition
   Slowest yet most commonly used in commercial GPS receivers

                         ?      I
                                     ?tt1
                                        2
                                            ? ?2
  IF
       ?                                                     ?     Decision
                               Q
                   ?                 ?tt1
                                        2
                                            ? ?2


                  Local Oscillator                 Control Logic


            Code Generator

Schematic Representation of Linear Serial Search Acquisition Method




                                                                              5
     FFT based (Parallel) Acquisition

                  ?         LPF

IF
                                         FFT        ?              IFFT

         ?                  LPF

                                                  Conjugate
         I      Q                                                  ? ?2
         Local Oscillator     Code Generator        FFT


                                  Control Logic   Decision Logic


     Schematic Representation of FFT based Acquisition Method




                            Acquisition




                                                                          6
                                           Acquisition




                   Code and Carrier Tracking
                       IE
                       ?         IP                   ?     ? ?2
                                 ?                    ?
         I
                                            IL                          ?
                   ?                        ?         ?     ? ?2
IF                                                                     E-L
                                                                   Discriminator
                            QE
             ?              ?          QP             ?     ? ?2               atan(Q/I)
                                                                             Descriminator
     Q
                                       ?              ?
                                                                        ?
                                                 QL

                 PLL
                                                 ?    ?     ? ?2
                                     DLL

     Carrier NCO            Code Generator

                                                          Carrier Loop Filter




                                                                                             7
 Tracking




PLL Outputs




              8
                 Navigation Data Bits




    Matlab Demonstration of SGR
• GPS Signal        • Acquisition          • Tracking
  – RAW GPS             – Serial Search      – Delay Lock
    Signal              – FFT Based            Loop (DLL)
  – Signal              – Synthetic Data     – Phase Lock
    Properties                                 Loop (PLL)
    • Bandwidth
    • Power
      Spectrum
    • Signal Strength




                                                            9
                      Conclusion
• In-depth understanding of GPS signal structure and
  processing is necessary to develop own software receiver

• We have developed part of software GPS receiver that
  includes Acquisition and Tracking

• The Navigation Data Extraction and Position Computation
  will be completed soon

• The software GPS receiver will help us analyze various
  signal properties that are not possible in a conventional
  commercial GPS receiver




                                                              10

								
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