Carriers may have different modulations BPSK QPSK 64QAM I waveform Q waveform A

Carriers may have different modulations bpsk qpsk

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Carriers may have different modulations – BPSK, QPSK… 64QAM. I waveform Q waveform
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 15 The OFDM Radio Digital Section (ASIC/ FPGA) Digital I and Q Bus D/A D/A Filter Filter 90 o Sum PA Mixer Local Oscillator (LO) IF Modulator Digital Section (ASIC/ FPGA) A/D A/D Filter Filter 90 o PA Mixer Local Oscillator (LO) IF Demodulator IFFT FFT TX RF/uW RX RF/uW
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 16 Key Measurements: Constellation and EVM Pilot Symbols
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 17 Vector Signal Analyzer Measurements Modulation Quality Analysis Input Signal Analyzer Display Measurement Analysis I Q I Q Q I QPSK 8PSK 16QAM etc… Error Vector Magnitude Ratio of Measured Amplitude to Intended Amplitude (% or dB) Magnitude Error = “IQ Error Magnitude” Measured Signal Intended Signal Phase Error = “IQ Error Phase” Q I φ Unit Circle RCE (dB) = 20 log(EVM in %/100)
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 18 EVM Metrics P = RMS Power Source: Wikipedia
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 19 Introduction to Constellation Diagrams A constellation diagram is a representation of a digital modulation scheme in the complex plane. The real and imaginary axes are often called the in phase, or I-axis and the quadrature, or Q-axis. Example: four-symbol Quadrature Phase Shift Keying (QPSK) modulator 01 = φ 2 = 3 π /4 00 = φ 1 = π /4 10 = φ 4 = – π /4 11 = φ 3 = –3 π /4 00 11 10 01 π Quadrature Phase Shift Keying (QPSK) Data Æ 01 00 11 00 01 10 Φ (t) Q I
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 20 Recovering the Data QPSK and 16QAM Signals 1 I +1V 00 11 10 01 -1V -1V Q +1V Constant Magnitude circle Assign Voltages 1100 1101 1110 1111 1000 1001 1010 1011 0100 0101 0110 0111 0000 0001 0010 0011 Magnitude Changes -1V Q +1V I +1V -1V Noise QPSK 0.707 S I (t) -0.707 -1 0.707 1 S Q (t) -0.707 -1 01 00 11 00 01 10 0.5 -0.5 -1 1 0.5 -1 1 0100 1100 0110 16QAM S I (t) S Q (t) -0.5
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 21 Digital Modulation Overview I and Q Components of a Signal φ A I Q Q I Q 90 o I Sum Simple Pythagoras Amplitude (Length of A) = SQRT (I 2 + Q 2 ) Phase (Angle φ ) = tan -1 (Q/I)
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 22 Representation of Signal in Complex Plane I – axis ( Real ) Q-axis (Imaginary) φ A frequency signal f c = Asin φ Acos φ Independent Signal 1 Independent Signal 2 S(t) = A cos(2 π f c t + φ )
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A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc.
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  • Spring '16
  • WiMAX, Keithley Instruments

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