Digital Modulation Frederic BIS Webinar Signal Analysis ... · Signal Analysis Specialist Agilent Technologies. Agenda Brief refresh on analog modulation. Concepts of digital modulation

Digital Modulation Webinar

Frederic BISSignal Analysis SpecialistAgilent Technologies

Agenda

Brief refresh on analog modulation.

Concepts of digital modulation.

Modulation Formats.

I-Q Modulator and Demodulator.

Filtering.

Signal Generation Solution.

VSA Presentation and demonstrations.

Agenda.



Modulation Formats.


Filtering.



Modulation of a Carrier A sin2 ππππfct

Intentional modification of a carrier signal for transmission of information.

◆Types of Modulation:

)](2[)()( ttfSintAtV c Φ+= πAM PMFM

◆ Unintentional modification of a carrier degrades Intentional Modulation

◆Types of Modulation:

✦ Amplitude Modulation (AM) - Modifies A(t)✦ Frequency Modulation (FM) - Modifies fc ✦ Phase Modulation (PM) - Modifies Ф(t)✦ Digital Modulation - Modifies both A and Ф

◆Goal of Modulation:

✦ To transmit information with high fidelity✦ Adequate S/N, signal quality and minimize cost and power✦ Obtain maximum spectral efficiency

✦ (bits/sec/Hz - information density)

Agenda.



Modulation Formats.


Filtering.



x(t)= A(t)cos{2πfct+φ (t)}

Quadrature

Phase

0 deg

Phase Change φ (t)

Digital Modulation Review

QuadratureCarrier Amplitude Change

Frequency ChangeQAM changes both A(t) & φφφφ (t)

0 deg

∆φ (t)

0 deg

In-phase∆A(t)

Digital Modulation can change any one of the variables.

Polar Display-Magnitude andPhase represented together.

Phase

ampl

itude

Mag=Vpeak

t2

t10 deg

timeam

plitu

de

t1t3

t4

t1 t4t3t2

The polar display shows the time relationships of s inusoids.The polar display of an IQ demodulator can be assum ed tobe "normalized" to the carrier frequency of the IQ demodulator.

Project signalto I and Q axes

Q

{Q-Value

Polar vs « I-Q » Format

Instead of measuringphase, measure basebandDC voltages.

0 deg

I

{I-Value

Signal changes or modifications

Magnitude Change

Phase0 deg

Phase0 deg

Phase Change

Both Change0 deg Frequency Change

0 deg

States, Bit Rate & Symbol Rate

01 00

1011

Quadrature P hase Shift K eyingTwo bits per symbol

State DiagramBit Rate = 2 x Symbol Rate

Bit Rate: is the number of bits per second in the system.

Symbol Rate = Bit Rate / No. of bits per symbol, AKA Baud Rate.

Symbol Rate determines the minimum system bandwidth requirement

Agenda.



Modulation Formats.


Filtering.



Digital I/Q Modulation Formats

BPSK QPSK π/4 π/4 π/4 π/4 DQPSKBPSK QPSK π/4 π/4 π/4 π/4 DQPSK

16QAM MSK32QAM 8 PSK

Modulation Formats

BPSK encodes one binary bit per symbol by a 180o phase change of the Carrier

The Occupied spectrum bandwidth is proportional to the symbol frequency.

• Quadrature modulation formats increases the bit rate by 2X using the same symbol clock frequency and therefore same occupied bandwidth.

Binary Phase Shift Keying Quadrature Phase Shift Keying

1

00

1011

2 states

4 states

symbols

01

0

Two bits per symbolOne bits per symbol

Q

I

0

1

QPSK & “Offset” QPSK I-Q Mod. Variations

QPSK

Q

I

Eye ConstellationQ

I

Q

I-Q Trajectory ➨➨➨➨ 0 Carrier Power

Offset QPSK minimizes power variations between symbo ls by delaying the I to Q timing so the carrier tra jectory does not go through zero, the origin.

OffsetQPSK

Q

I

Q

I

I-Q Trajectory avoids 0 carrier Power

Binary Phase Shift Keying and 8 Level Phase Shift Keying

TRACE A: Ch1 IQ Ref Time

A

1

I-Q

200

m

/div

TRACE A: Ch1 IQ Ref Time

A

1

I-Q

200

m

/div

-1.308 1.308

-1

-1.3071895838 1.30718958378

-1

BPSKOne Bit per Symbol

Symbol Rate = Bit Rate

8PSK3 Bits per Symbol

Symbol Rate = 1/3 of Bit Rate

Quadrature Amplitude Modulation

I

Q

32 QAM

16 QAM

4 Bits per SymbolSymbol Rate = 1/4 of Bit Rate

5 bits per SymbolSymbol Rate = 1/5 of Bit Rate

Major Modulation Goal: Spectral Efficiency

Theoretical Bandwidth Efficiency Limits:• BPSK 1 bit/second/Hz• QPSK 2 bits/second/Hz• 8PSK 3 bits/second/Hz• 16QAM 4 bits/second/Hz• 32 QAM 5 bits/second/Hz

Note: The figures are theoretical limits and CAN NOT be achieved in practical radios

• 32 QAM 5 bits/second/Hz• 64 QAM 6 bits/second/Hz• 256 QAM 8 bits/second/Hz• 512 QAM 9 bits/second/Hz• 1024 QAM 10 bits/second/Hz• 2048 QAM 11 bits/second/Hz• 4096 QAM 12 bits/second/Hz • 8192 QAM 13 bits/second/Hz

Agenda.



Modulation Formats.


Filtering.



I and Q Modulator

Composite

Output

Signal

90o

Phase Shift

Q(t)

Σ

Sine 2π fc

Quadrature (90o) mixing, I and Q are "Orthogonal” to each other and do not

interact.

Local Osc.(Carrier Freq.)

I(t)

Cosine 2π fc

I - Q Modulation

1 .5V ^2

0 .3/d iv

F1 +(K 4 * F2 ) 2 :1

1.5V

0.3/d iv

D1+(K4*D3) 1

1.5V

-1.5

Real

ms124.9390 s

Time 1

-90o

Q(t)

1.5

V

IFFT(D8) 1

D3*D4 2:1

1.5V

-1.5

Real

ms124.9390 s

Time 1

Q(t) sin 2π fc(t)

sin 2 ππππ fc(t)

+1

-1

-1 .5

Imag in ary

V ^22 .1 9 6 3 5 3 -2 .1 9 6 3 5 3 V ^2 Real

-1.5

Imaginary

V2.284768 -2.284768 V Real

1.5V

-1.5

R ea l

ms124.9390 s

Time 1

-90

I(t)

Local Osc.

D1*D2 2:1

1.5V

-1.5

R eal

ms124.9390 s

Time 1

-1.5

R eal

ms124.9390 s

I(t) cos 2πfc(t)

+1

-1

Σ

CompositeInput Signal

90o

Phase Shift

Quadrature Component

M (t) cos [ωct +φ(t)]

2 sin ωLOt

Power

splitter

Demodulating I and Q in a Receiver

x M (t) cos [ωct +φ(t)] = ?

Let ωc = ωLO

Local Osc.

(Carrier Freq.)

In-Phase Component

I(t) = In-Phase, Q(t) = Quadrature

Can be extracted from the carrier with simple circuits

M (t) cos [ωct +φ(t)]

2 cos ωLOt x M (t) cos [ωct +φ(t)] = ?

Quadrature

MQAM(t) cos ωωωωct + φφφφ(t)

90o

Phase Shift

x2(t)

Local Osc.

Down converted composite input signal MQAM(t)

Detecting I(t) and Q(t)

f

Power

splitter

x1(t) = [M QAM(t) cos ωωωωct + φφφφ(t)] 2 cos ωωωωLOt = [I(t) cos ωωωωct + Q(t) sin ωωωωct] 2 cos ωωωωLOt

x1(t) = I(t)cos 2ππππ(fc- fLO) + I(t) cos 2ππππ(fc +fLO) t + Q(t) sin 2ππππ(fc +fLO) t + Q(t) sin 2ππππ(fc - fLO) t

In-PhaseIncident

x1(t)

x2(t) = [MQAM(t) cos ωωωωct + φφφφ(t)] 2 sin ωωωωLOt = [I(t) cos ωωωωct + Q(t) sin ωωωωct] 2 sin ωωωωLOt

x2(t) = I(t) sin 2 ππππ(fc- fLO) - I(t) sin 2 ππππ(fc +fLO) t + Q(t) cos 2 ππππ(fc - fLO) t - Q(t) cos 2 ππππ(fc +fLO) t

The Trigonometric identities cos φφφφ x cos θθθθ & cos φφφφ x sin θθθθ applied to QAM demodulation of carrier ωωωωc = ωωωωLO.

f

x1(t) = I(t) + I(t) cos 2 ωωωωct + Q(t) sin 2 ωωωωct Low pass filter selects I(t) & rejects the 2 ωωωωc

Agenda.



Modulation Formats.


Filtering.



Filters-Modulation Shaping

Filtering Benefits

• Reduces transmitted bandwidth

• Improved Bandwidth efficiency

• Reduced noise interference

• Reduced Inter Symbol Interference

• Improved receiver sensitivity

Filtering Costs

• Complexity

• Possible inter-symbol interference

• Increased power amplifier Linearity

• Higher Peak Power

Filter Types

• Nyquist, square-root Nyquist

• Gaussian

• IS-95 (CDMA Filter)

• User-defined

I-Q Modulation Occupied Band Width

No Filtering of the Modulating Signal

I(t) Modulating Signal I(f ) Spectrum

Nyquist or Raised-Cosine FilterZero Inter-Symbol Interference

0.6

0.8

1.0

Frequency Response

Raised Cosine

Impulse Response

Raised Cosine

Symbol Clock0.2

0.4

00 0.2 0.4 0.6 0.8 1.0

Normalized Frequency ➙ Impulse Response crosses 0 for all adjacent symbol clock transitions.

Raised Cosine Digital Filter

Log Mag RAISED COSINE FREQUENCY RESPONSE

IMPULSE RESPONSE

Time Response I(t)

RAISED COSINE FILTER

Filter Bandwidth Parameter " αααα"

Alpha describes the "sharpness" of the filter.

Occupied bandwidth is approximately: Symbol rate x (1 + α).

0.8

1.0

α = 1.0Frequency

0

0.2

0.4

0.6

0 0.2 0.4 0.6 0.8 1.0

α = 0.3

α = 0.5

α = 0

α = 1.0

fsSymbol Rate

Normalized Frequency ➙

Frequency

Response

Cosαααα

f/ fs

Raised Root Cosine αααα = 1/2

LogMag

Root Raised Cos/ SinX/X

Raised Cosine Filter Band Width

α = 1

I(t) No Filtering

α = 1/2

Raised Cosine

α = 1

α = 0.5

Effect of Different Filter Bandwidths

QPSK Vector Diagrams

No Filtering α = 0.75 α = 0.375

More OvershootNo Overshoot

Symbol Rate, Filter Shape and Occupied Bandwidth

0

1

010.2 0.4 0.6 0.8

αααα = 0.5

TRA

Ch1 IQ R

B

12dB/div

Occupied Bandwidth

OCCBW (Hz)= Symbol Rate x (1+ α)= 10kHz x 1.5 = 15 kHz

Symbol Rate = Bit Rate / 2 = 10 kHz

0.8fs : Symbol Rate

Filter ShapeBit Stream= 20 kHz

Vector Diagram

ACE

B:

Ref Spec

Span: 78.125 kHz

DATA?

-120

Frequency Spectrum

The Error Vector vs Time Measurements

I-Q Magnitude ErrorQ Error Vector Time

MeasuredVector

=( Error Vector / Reference Vector) * 100%

)](Q)(Q[)](I)([IEVT

2mearef

2mearef tttt −+−

=

)(Q)(I

)(Q)(I)(Q)(I

ref22

ref

2ref

2ref

2mea

2mea

tt

tttt

+

+−+

φφφφ

)(θ)(θ)θ( refmeas ttt −=I-Q Phase Error =

I-Q Mag Error =

I

Reference Vector

I-Q Phase Error

θθθθ

ReferenceDecision Point

)(Q)(I

)](Q)(Q[)](I)([IEVT

ref22

ref

mearefmearef

tt

tttt

+

−+−=

φφφφ(t))II(

)Q(Q

refmeas

refmeas1

−−= −Tan

14444244443

Reference to Decision Point

ModulatorQ

I

Phase Imbalance

I

Q

Gain Imbalance

I

Q

I-Q Offsets

Modulation Impairments

Impairments & Measurements

Interference Added NoisePhase Noise

Modulation Impairments

Digital Communication System Characterization

Transmitter

Processing/Compression/Error Correction Encode

SymbolsA/D

ModI I

Q Q

Q

VoiceInput

Receiver

AGC Demod

Q

I I

Q

DecodeBits

Adaption/Process/Decompress D/A

IF

RF

IF RF

VoiceOutput

Agenda.



Modulation Formats.


Filtering.

Signal Generation Solution


Complex signal generation

made easy


First-to-market track record• Standards-based & custom

signal creation• Recognized benchmark

reference signal Broadest application coverage

ESG

PSG

MXG

PXB

New!

• Fully & partially coded signals• MIMO applications Easy-to-use • Flexible signal creation • Ready for automationValidated and performance-optimized

Agilent Signal Studio & Embedded Software

Multitone Distortion (ARB)

(Enhanced Multitone & NPR)

Multitone (ARB)

Jitter Injection (ARB)

Calibrated AWGN (ARB & RT)

Phase Noise Impairments (RT)

Toolkit (ARB)

General General

RF/MWRF/MW

Fixed WiMAX (ARB)

802.16d

Mobile WiMAX (ARB)

802.16e +MIMO

Wireless Wireless

ConnectivityConnectivity

Digital Video (ARB):

DVB-T/H/C/S/S2

J.83 Annex A/B/C

ISDB-T

DTMB

ATSC

CMMB/STiMi

Digital Video (RT)

Audio/VideoAudio/Video

BroadcastingBroadcasting

HSPA (RT)

TD-LTE (ARB)

W-CDMA/HSPA (ARB)

HSPA+ (ARB)

LTE FDD (ARB) + MIMO

Mobile Mobile

CommunicationsCommunications

W-CDMA/HSPA (ARB)

W-CDMA (RT)

Pulse Building (ARB)

GPS (RT)

1 to 8 satellites

Detection, Positioning,Detection, Positioning,

Tracking & NavigationTracking & Navigation

GPS (RT)

multi-satelliteWLAN (ARB)

802.11 a/b/g/p/j

802.11n + MIMOPhase Noise Impairments (RT)Bluetooth (ARB)

V1.1

V2.1+EDR

Ultra Low Energy (Wibree)

MB-OFDM UWB (ARB)

802.15

S-DMB (ARB)

T-DMB (ARB)

Digital Video (RT)

Broadcast Radio (ARB):

FM Stereo/RDS/RDBS

mono & stereo

DAB/DAB+

TDMA (RT):

GSM/EDGE/GPRS/EGPRS

NADC/PDC/PHS

DECT/TETRA

IS-95-A & CDMA2000 (ARB)

IS-95-A & CDMA2000 (RT)

IS-95-A & CDMA2000 (ARB)

1xEV-DO (ARB)

TD-SCDMA (ARB)

TDMA (ARB):

GSM/EDGE

NADC/PDC/PHS

DECT/TETRA

APCO/PWT/CDPD

TD-LTE (ARB)

GSM/EDGE (ARB)

EGPRS2 (ARB)

802.11n + MIMO

Custom Modulation (ARB & RT)

www.agilent.com/find/signalstudio

Agenda.



Modulation Formats.


Filtering.



VSA Software – 89601A.

Synthesis of the Reference I-Q Signal "Measurement and Reference Filters"

Transmitter

I-Q Data1001 0001 0110

Root Raised Cosine Filter

DAC

Root Raised Cosine Filter

Measurement Filter

Modulatorcos

PA

+Σ

Demod-ulator

Reference Filter

I-Q Error Waveform

(Receiver89600A)

Reference Waveform

Raised Cosine Filter

Ideal/Reference Signal Generated

Measured Waveform

Filter

Reference Signal Generation

coscos ×

Detected Bits

1001 0001 0110

cos

VSA Software – Hardware support.

High End Spectrum Analysers Dig RF v3 / v4 solutions

Middle-range Signal Analyzers

Logic Analysers Middle-range Scopes High End Scopes

Data Acquisition cards

Formats supported by VSA Software.

89601A Vector Signal Analysis Software• Advanced signal analysis capabilities

• Runs INSIDE the MXA or EXA

• All optional formats available

50+ Demodulation Types:AM/FM/ΦM, WiMAX 802.16 OFDM/OFDMA, WLAN IEEE 802.11a/b/g/j/p, Digital Video, WLAN IEEE 802.11a/b/g/j/p, Digital Video, Private Mobile Radio, CDMA (base), CDMA (mobile), CDPD, GSM, EDGE, NADC, PDC, PHP (PHS), W-CDMA, TD-SCDMA, HSDPA, 1xEV-DO, 1xEV-DV, Bluetooth™, ZigBee™,

APCO 25, DECT, TETRA 1, TETRA 2 (TEDS), VDL mode 3, FSK: 2, 4, 8, 16 level (including

GFSK), MSK (including GMSK), BPSK, QPSK, OQPSK, DQPSK, D8PSK, π/4-DQPSK, 8PSK, 3π/8-8PSK, 16/32/64/128/256/ 512/1024 QAM,

16APSK, 32APSK, 8VSB, 16VSB, RFID

Let’s take example of a Device.

DSP

Digital (SSI) IF/RF BB (I-Q)

DUT

Multiple Signal InterfacesCommon Signal

Analysis Platform

Logic Analyzer Oscilloscope Signal Analyzer • common measurements• common interface• single learning curve

MXA BBIQ

Vector DiagramNADC, ππππ/4 DQPSK, 157 symbols, 10 points/symbol

Q

I

157 symbols1 point/symbol

Constellation Diagramππππ/4 DQPSK signal shown with added white Gausian noise contamination

Q

I

The EVM display shows the Magnitude of the error between the measured and ideal I(t) - Q(t) trajectories referenced to the Symbol State.

Error Vector Magnitude (EVM)

The green bars show the error at the symbol times. Errors can be seen at the symbol points and in between.

X axis scale expanded

The points per Symbol sets the number of points between symbols up to 20.

I/Q Eye Diagram Under Data Format Key

NADC Signal

Gain Imb:

What is the gain Match between

I & Q?

NADC ππππ/4 DQPSK Signal

Symbol Table and Error Summary

I - Q Modulator Quality:

Quad Skew Err:

How close to

90o

are I & Q?

See Product Note 89400-8 for definition of each ter m.

I - Q Offset

DC Offset

Digital Demodulation Default Quad Display Four Main Analysis Tools

Coupled Markers

Gain Compression?

Trace A: Constellation Display

Trace B: Spectrum

Trace C: Error Vector Magnitude

Trace D: Symbol Table & Error Summary

Hardware used for demonstrations

MXA Signal AnalyserN9020A

MXG Vector Signal GeneratorN5182

www.agilent.com/find/MXAwww.agilent.com/find/MXG

Demo 1

Demodulation of simple QPSK Signal with VSA software.

Filtering effects.

Demodulation of OQPSK Signal

Demo 2

Demodulation of perturbated signal.

Agenda.



Modulation Formats.


Filtering.



89600A VSA’s Adaptive Equalization

Compensates for Linear Gain/Phase • Multi-path Reception• Group Delay Error• Frequency Response

• Ripple/Tilt

Gcomp(f)Gcomp(f)

Does NOT Remove• Noise• Nonlinear Distortion

• Spectral Regrowth or IMD• Harmonic Distortion• Spurious Responses

Why Use Adaptive Equalization?

Most Receivers have internal Adaptive Equalizers

• Important to measure a signal the way a real receiver would.

Adaptive Equalizer may be required for Symbol Lock.

• Some signals cannot be measured without equalization.

Valuable Design and Troubleshooting Insights:Valuable Design and Troubleshooting Insights:

• Distinguish between linear gain/phase errors and non-linear distortion.

• Measure real systems while in service.

• Quantify amount of stress put on receiver's equalizer.

• Provides feedback to hardware and software designers.

Using the VSA’s Equalizer

1. VIEW CONSTELLATION, SYMBOL TABLE, EVM

2. TURN THE EQUALIZER ON

MeasSetup, Demod Properties

Check [ ✓✓✓✓ ] Equalization Filter

3. WATCH FOR:3. WATCH FOR:

EVM TO DROP

CONSTELLATION CLOUDS TO CONVERGE

4. IF CLOUDS DIVERGE OR LOSS OF LOCK

REDUCE [CONVERGENCE] (Small changes only!)

RESET EQUALIZER [EQ RESET]

Equalizer Measurement Results

Equalization FilterFREQ. RESP. Gain

Channel Frequency Response

A Math function

EQ’S IMPULSERESPONSE

Equalization FilterFREQ. RESP. Phase

A Math function Computed the FFT of the EQ. filters Impulse Response.

Demo 3

Demonstration of Equalization benefits.

Demo 4

Demodulation of a Wireless standard.

Summary

Documents

Digital Modulation Frederic BIS Webinar Signal Analysis ... · Signal Analysis Specialist Agilent Technologies. Agenda Brief refresh on analog modulation. Concepts of digital modulation