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					          WCA102
    Fundamentals of Digital
         Modulation


        Digital Modulation – Introduction
      Digital Modulation in Wireless Communications




1
Agenda

 Introductions
 Who Cares?
 What is Modulation
 IQ Modulation Types
 Filters and How Things Go Wrong
 Measurements
Advantages of Digital Modulation

 Spectral efficiency – use of a narrow bandwidth to
  send a large amount of data
   Effective use of limited frequency resources
 Good privacy and security features
   Digital encryption techniques may be employed
 Lower power consumption
 Repeatable, more easily produced
 Reduced device size
Modulation for Wireless

 Media
   Carrier
              V(t) = A cos(2πfc t + Φ)

 The 3 essential parameters
   Amplitude value    A(t)   ― Amplitude Modulation
   Frequency value    f(t)   ― Frequency Modulation
   Phase value       φ(t)    ― Phase Modulation
Analog Modulation

 Amplitude Modulation
   AM radio
 Frequency Modulation
   FM radio, TV audio signal
 Phase Modulation
   TV color image signal (including Amplitude Modulation)
Transmission of a Digital Message

 Basically, it’s the same as Analog Modulation
  Methods

   ASK:     Amplitude shift keying
             V(t) = A(t) cos(2πfc t + Φ)
   FSK:     Frequency shift keying
             V(t) = A(t) cos(2πf(t) t + Φ)
   PSK:     Phase shift keying
             V(t) = A(t) cos(2πf(t) t + Φ(t))
 Digital modulation: Amplitude, frequency and/or
  Phase are used to represent a digital state
ASK

 Amplitude shift keying
   1’s or 0’s represented by different amplitudes
   Could be accomplished with an AM system


                              +


                              =
ASK in IQ domain

 ASK(OOK)
    I: In phase component
    Q: Quadrature component
                                I
                Q
                                0
                         I
              (0)     (1)
                                Q


Amplitude variation on I axis   0
FSK

 Frequency shift keying
   Select frequency based on each bit, 0 or 1
   Could be done with simple FM system

                         +
                                                 =
FSK in IQ
 Frequency change causes
  constant-rate phase change versus
  the reference carrier
 Amplitude remains constant on the
  IQ circle
                                      Phase
      1 Symbol only turns π(ex)

               Q
                                      π



                                                                                     Time
                                  I         1Sp        2Sp     3Sp    4Sp     5Sp


 If the phase change is 90 degrees
                                    -π
  in one symbol period, the
  modulation type is called Minimum
                                          Pos offset    Neg. Offset    Pos. Offset
  Shift Keying (remember this one)
PSK

 Phase shift keying
   At the bit transitions invert the phase by 180°




                             =
             +
Representation of PSK in IQ

 PSK
    Specifically, BPSK(Binary Phase Shift Keying)
                         I

            Q
                         0
   (1)            I
                      (0)

                       Q


                         0
Change Phase to 180°
 Relative to reference
       Digital Modulation in
     Modern Wireless Systems




13
Digital Modulation Block Diagram

Raw Data       Compression,       011010100101                                 01 10 10 10 01 01
                                                                 Convert to
              Error Correction,                                   Symbols
110101           Encryption



                01       00
                                  I - Signal
                                               Low Pass Filter
                                                                              To IQ
                                  Q - Signal                                  Modulator
               10        11                    Low Pass Filter


          Modulation Mapping


         I - Signal
                                                             RF
                        Modulation,
     Q - Signal                                              Amplifier
                        Upconversion
Raw Data Conversion

 Raw Data    Compression,
                                011010100101   Convert to
            Error Correction,
             Interleaving,                      Symbols
 110101        Encryption



 Raw data comes from the user
   Digitized voice, keystrokes, jpegs…
 Compression is employed for efficiency
 Error correction is applied for transmission quality
 Interleaving creates signal-dropout resistance
 Encryption is applied for security
Data Bits, to Symbols

 Raw Data    Compression,       011010100101                01 10 10 10 01 01
                                               Convert to
            Error Correction,                   Symbols
 110101        Encryption




 Symbols are represented by the possible states of
  digital modulation
 Higher order modulation allows more bits per
  symbol
 What in the world does that mean?
    Mapping symbols to I and Q
IQ Mapping

 What is Mapping:              Example
    Translate a Symbol to a
      point in the IQ space                Q

                                   (01)        (11)
           01     00




          10      11                                  I
       Modulation Mapping

                                   (00)        (10)
Differential Modulation

 QPSK(Quadrature PSK)             DQPSK(Differential QPSK)
    Assign the value to points       The value is based on the
     in IQ Space                        transitions between 2 points

            Q                                    Q
                                          (01)
    (01)              (11)                                (00)


                             I                                   I

                                             (11)         (10)
    (00)              (10)
                                                     00= 0 01= +90
                                                     10= -90 11= +180
Higher Order Modulation

 8PSK(8-PSK)                         p/4 DQPSK
    Assign the value to points          The value is based on the
     in IQ Space                          transitions between 2 points
    3 points per symbol                 Eliminates Zero Crossings
             Q                                    Q
                  (110)                               (11)
    (001)                 (011)

                                           (01)               (00)
 (111)
                                 I                                   I
                            (100)
                                                       (10)
  (000)
                          (010)
          (101)                                         00= -45 01= +135
                                                        10= -135 11= +45
More Higher Order Modulation
   16QAM(16-Quadrature Amplitude                                       Q
    Modulation)
      Each IQ symbol location is
         represented by 4 data bits      (000100) (001100) (011100) (010100)   (110100) (111100)(101100) (100100)
   64QAM (64-Quadrature Amplitude
    Modulation)
                                         (000101) (001101) (011101) (010101)   (110101) (111101)(101101) (100101)
      Each symbol is now worth 5 bits

              Q                          (000111) (001111) (011111) (010111)   (110111) (111111)(101111) (100111)



                                         (000110) (001110) (011110) (010110)   (110110) (111110)(101110) (100110)    I
    (0010) (0110) (1110) (1010)

                                         (000010) (001010) (011010) (010010)   (110010) (111010)(101010) (100010)
    (0011) (0111) (1111) (1011)
                                     I
                                         (000011) (001011) (011011) (010011)   (110011) (111011)(101011) (100011)
    (0001) (0101) (1101) (1001)
                                         (000001) (001001) (011001) (010001)   (110001) (111001)(101001) (100001)

    (0000) (0100) (1100) (1000)
                                         (000000) (001000) (011000) (010000)   (110000) (111000) (101000) (100000)
Why Not Just Keep Going?
    Errors in IQ modulation create symbol errors in
     transmission                                                     Q
    Vector Errors are created (what’s that?)
    Noise in the transmission channel create symbol
     errors
    Inaccuracies in the receiver creates errors
    Signal-to-noise requirements increase with higher   (0010)   (0110)   (1110)   (1010)
     order modulations

                Q
                                                         (0011)   (0111)   (1111)   (1011)
                                                                                             I
    (01)                        (11)
                                                         (0001)   (0101)   (1101)   (1001)

                                          I
                                                         (0000)   (0100)   (1100)   (1000)

    (00)                        (10)
The World’s Most Popular Modulation

 Gaussian Minimum Shift Keying
 Gaussian Filtered Form of FSK
 Sum of I and Q results in a constant amplitude circle
Symbol Rate and Bit Rate
 Modulation type determines number of bits per symbol
    BPSK              1 bit/symbol
    DBPSK             1 bit/symbol
    QPSK              2 bit/symbol
    p/4 DQPSK         2 bit/symbol
    DQPSK             2 bit/symbol
    8PSK              3 bit/symbol
    16QAM             4 bit/symbol
    64QAM             5 bit/symbol
    256QAM            6 bit/symbol
 For a fixed symbol rate, having more bits will provide a faster
  transfer rate
 Setting up a WCA requires you to know the modulation type
  and symbol rate, not the bit rate
Others (for evening reading….)

 32QAM                    HPSK
    ADSL etc                 Hybrid Phase Shift Keying
 256QAM                      Also known as
    Microwave                 Orthogonal Complex
     Communication             Quadrature Phase Shift
    Some Cable Modem          Keying (OCQPSK)
 1024QAM
                              Used in CDMA2000
                               (1xRTT) reverse link
    Still experimental
                           VSB
 OQPSK
                              Vestigial Side Band
    Offset QPSK
                              8VSB, 16VSB
    Used to avoid zero
     crossings                US Digital Broadcast TV
 DQPSK
Filters, For Spectrum Control
        01      00
                          I - Signal
                                       Low Pass Filter
                                                         To IQ
                          Q - Signal                     Modulator
        10      11                     Low Pass Filter


     Modulation Mapping
Sources of Error

Raw Data       Compression,       011010100101                                 01 10 10 10 01 01
                                                                 Convert to
              Error Correction,                                   Symbols
110101           Encryption



                01       00
                                  I - Signal
                                               Low Pass Filter
                                                                              To IQ
                                  Q - Signal                                  Modulator
               10        11                    Low Pass Filter


          Modulation Mapping


         I - Signal
                                                             RF
                        Modulation,
     Q - Signal                                              Amplifier
                        Upconversion
Sources of Error

 IQ Quadrature modulation

                      cos(2πfct)
         I     LPF


                              fc
                                   BPF

                          90 90°
                          90



        Q      LPF

                      sin(2πfct)
Errors Receiving the Signal

 IQ Quadrature demodulation
                      cos(2πfct)
                                      LPF       I

                               fc
          BPF
                           90 90°
                           90


                                      LPF        Q
                       sin(2πfct)
 This could be your customers receiver, or it could be a
  WCA vector spectrum analyzer
     Common Measurements




29
What data was sent?

                       Data Display
                       Time vs.
                        Amplitude
                       Error Summary
Error Summary

                 Error Vector
                  Magnitude
                 Magnitude
                  and Phase
                  Error
                 Freq. Error
                 IQ offset
Modulation Errors vs. Time

                          Amplitude errors
                           correlated to EVM
                          WCA is especially
                           good at this
What can a WCA do?
                                          Tektronix
 Modulation types                        Wireless
                                          Communication
                                          Analyzer
                                          WCA230A /

 Symbol rates        Modulation types
                                          WCA280A
                                          BPSK, QPSK, Pai/4
                                          Shift DQPSK,
                                          8PSK, 16QAM,
                                          64QAM, 256QAM,
 Filter types                            GMSK, GFSK
                      Symbol rates        to 12.8 Msps
                      Filter types        Measurement Filter:

 One button setups
                                          Root Cosine
                                          Reference Filter:
                                          Cosine, Gauss
                                          Filter Parameter:
                                          α/BT: 0.0001 to 1,

 Standards                               0.0001 step

                      One button setups   PDC, PHS, NADC,
                                          TETRA, GSM,
                                          CDPD, Bluetooth

                      Standards           W-CDMA
                                          Downlink(opt.22),
                                          W-CDMA
                                          Uplink(opt.23),
                                          GSM/EDGE(opt.24)
Summary

 Digital modulation is cheaper, faster, more accurate,
  more efficient, more secure
 Higher order modulation is used for greater
  transmission rates in the same spectrum occupancy
 Higher order modulation is more susceptible to
  noise
 Baseband filters are used to control spectrum
 Wireless Communications Analyzers are used to
  evaluate modulation quality
   WCA is particularly good at connecting effects in
     multiple domains
Product Line Contact Information

 Dedicated Regional Contacts        Worldwide Factory Contacts

    Kurt Krukenberg                   Dave McDonald
      phone: +1 503-627-5039             phone: +1 503-627-1279
      Regional Product Manager           TSC Primary Contact
      Americas                           WCA200A and WCA300

    Dean Miles                        Tommy Sakurada
      phone: +44 1344-392249             phone: +81 3-3448-3272
      Regional Product Manager           Product Manager
      EMEA                               WCA200A & Wireless Apps

    Charles Wu                        Jerry Harris
      phone: +852 258-56774              phone: +1 503-627-4827
      Product Line Representative        Product Manager
      Asia/PacRim                        WCA300 & Non-Wireless Apps
     Slide Archive (extras)




36
Filters Alter The Signal

         01      00
                           I - Signal
                                        Low Pass Filter
                                                          To IQ
                           Q - Signal                     Modulator
         10      11                     Low Pass Filter


      Modulation Mapping
Common Filter Types

 Gaussian



 Raised Cosine



 Root Raised Cosine



 Setting up the WCA requires
  knowledge of what filter is
  used
Effect of Roll-off
 Usually α is between 0.2 - 0.5   α=0.0   α=1.0
 α determines the bandwidth
    BW = (1+α) *Symbol rate
Put IQ on the Carrier Wave

 IQ Quadrature modulation

                      cos(2πfct)
         I     LPF


                              fc
                                   BPF

                          90 90°
                          90



        Q      LPF

                      sin(2πfct)
Structure of Tx/Rx

                                        Encode

 Data                  Error correction
         Scrambling                          Interleaving 1st   Interleaving 2nd
stream                    encoding




                           IQ mapping               IQ modulation




                  IQ demodulation              IQ de-mapping




         De-interleaving   De-interleaving     Error correction                     Data
                                                                    Scrambling
               2nd               1st              decoding                         stream