Digital Radio Modulator

1
Digital Radio Modulator

• Members
• Ben Chen
• Jamie Lim
• Saron Nhong
• Long Tran

• Contacts
• Matthew Bredel
• Frank Winter

2
Agenda

• Project Objectives
• Modulation schemes
• QPSK, OQPSK, GMSK, 16-QAM
• Systemview Simulations
• ISL-5217 Evalulation Kit
• Experimental Results
• Accomplishments
• Future Goals

3
Objective

• Project Goal Evaluate and program a digital
  radio modulator with various modulation schemes
  operating at a frequency of 16 MHz
• Simulate the system with different filter
  coefficients using Elanix Systemview
• Program the board with the coefficients and
  compare the performance of the various modulation
  schemes

4
Overall Implementation of Project
5
QPSK Modulation

• The transmitted equation is given as
• 4 Symbols, 2 bits/symbol
• Signal shifts between the phase states are
  separated by 90 degrees
• Since the two carriers, cos(wct) and sin(wct) are
  orthogonal they do not interfere with each other
• Any symbol can transition to any other symbol

6
OQPSK Modulation
Transitions for a QPSK modulated signal
Transitions for a OQPSK modulated signal

• Variation of QPSK
• Q channel is delayed by a ½ bit interval from I
  channel
• I and Q channel signals transition at different
  times
• Range of phase transitions is from 0-90 degrees
• This eliminates the 180 degree phase shift so an
  OQPSK signal never goes through a zero
• In non-linear amplification, a zero causes
  regeneration of sidelobes and spectral spreading
  in the signal
• Thus, OQPSK signals yield a more efficient
  amplification process

7
GMSK Modulation

• GMSK can be viewed as OQPSK with a special pulse
  shaping filter
• GMSK uses constant envelope (no amplitude
  variation)
• Avoid spectral regrowth
• Improve power transmitter
• Constant envelope occupies larger bandwidth than
  modulations that are linear

8
16-QAM Modulation

• Combination of ASK and PSK
• 4 I values, 4 Q values
• 16 possible states, 24 16, so 4 bits/symbol can
  be sent
• Compared to QPSK, 16-QAM has the same bandwidth,
  but increased data rate
• More spectrally efficient transmission
• Susceptible to noise and requires linear
  amplification
• QAM is bandwidth efficient but not power efficient

9
Systemview Simulation
10
Power Spectrum Density (Systemview)
QPSK, OQPSK, 16-QAM
GMSK
11
Systemview I/Q Data
QPSK
OQPSK
GMSK
16-QAM
12
ISL5217 Evaluation Kit
Agilent E4440A Spectrum Analyzer
13
Error Vector Magnitude (EVM)

• EVM compares ideal symbol value with measured
  symbol value
• Combination of phase error and magnitude error
• Value is normalized to amplitude of the outermost
  symbol

14
Experimental Results
QPSK
OQPSK
GMSK
16-QAM
15
Accomplishments

• Successful simulation of modulation schemes
  through Systemview
• Implementation of filter coefficients into the
  ISL-5217EVAL1 Board
• By adjusting the number of filter coefficients,
  EVM was lowered
• ISL-5217EVAL1 Board is ready to be interfaced
  with Digital Radio Exciter

16
Future Goals

• Implementation of different filters with
  different filter coefficients
• Lower the EVM
• Interface with RF Exciter and Predistortion filter