RF & Wireless Communications
Design and Test
Ron Harrison
Product Marketing Manager
RF & Communications
Generic Communication System Block Diagram
Bits
Bits
Bits
I Q
Channel
Upconversion
I Q
Downconversion
Modulation
Bits
Demodulation
Channel Coding
Bits
Channel Decoding
Source Coding
Bits
Source Decoding
Communication System Block Diagram
National Instruments PXI RF Platform
• NI PXI-5660 RF Vector Signal Analyzer
• NI PXI-5671 RF Vector Signal Generator
• NI PXI-5690 RF Preamplifier
• NI PXI RF Switches to 26.5 GHz
• LabVIEW & LabWindows/CVI Modulation Toolkit
•LabVIEW & LabWindows/CVI Spectral Measurements Toolkit
Extending the PXI RF Platform
Tire Pressure Monitoring System
•Cable modem/CMTS design
verification system
•Broadcast Television
•ZigBee
Compliance
Software
•802.11
•Radio/Telematics Test
•GSM/EDGE
•Up/Downconverters
Bits
Bits
Bits
I Q
Channel
Upconversion
I Q
Downconversion
Modulation
Bits
Demodulation
Channel Coding
Bits
Channel Decoding
Source Coding
Bits
Source Decoding
Source Coding/Decoding
Source Coding/Decoding
• Source Coding
• Process of encoding information using fewer bits
• Re-represents original message by reducing redundancies
• Reduces the consumption of expensive resources, such as disk
space or connection bandwidth
• Example – converting image from .bmp to .jpg
Source Coding/Decoding
.BMP File 1.35 MB
.JPG File 350 KB
Vabbinfaru Island, Maldives
Source Coding Algorithm Examples
• Lossless Data Compression
– Dictionary Coders
• LZ77 & LZ78
• DEFLATE (used by ZIP and PNG files)
• LZW (used by GIF files)
• LZMA
– Entropy Encoding
• Huffman Coding
• Arithmetic Coding
• Range Encoding
– Linear Predictive Coding
• TTA (lossless audio compression)
• FLAC (lossless audio compression)
• Lossy Data Compression
– Fractal Compression
– Wavelet Compression
• JPEG 2000
– Discrete Cosine Transform
• JPEG (image compression
using a discrete cosine
transform, then quantization,
then Huffman coding )
• MPEG (audio and video
compression standards)
– MP3 (part of MPEG-1 for
sound and music
compression)
– MPEG-2 (used in DVDs)
Bits
Bits
Bits
I Q
Channel
Upconversion
I Q
Downconversion
Modulation
Bits
Demodulation
Channel Coding
Bits
Channel Decoding
Source Coding
Bits
Source Decoding
Channel Coding/Decoding
Channel Coding/Decoding
• Transformation that enables the original message to
better withstand the effects of channel impairments
such as noise, fading, etc.
• Adds bits to the original message – increases the
message size
1100
1111111111 00000 00000
Channel Coding
Message
Parity
Codeword
000
100
010
110
001
101
011
111
0
1
1
0
1
0
0
1
0000
1100
1010
0110
1001
0101
0011
1111
Channel Coding/Decoding Models
• BCH
• Golay
• Hamming
• Convolutional
• Reed-Solomon
Bits
Bits
Bits
I Q
Channel
Upconversion
I Q
Downconversion
Modulation
Bits
Demodulation
Channel Coding
Bits
Channel Decoding
Source Coding
Bits
Source Decoding
Modulation/Demodulation
Modulation
Changing a higher frequency (Carrier) signal proportional
to a message signal
Ac cos(2πf c t + φ )
Amplitude
Frequency
Phase
Angle
(Frequency = Rate of change of Angle)
Note: All Modulation schemes change one or both of amplitude and angle
Modulation/Demodulation - IQ Data
• Represents the state of the carrier as a vector
– Amplitude & Phase offset
• I and Q signals are control signals for changing an RF carrier signal
s (t ) = Ac cos(2πf c t + φ )
A
Q (t)
φ
I (t)
How can frequency be changed?
By changing phase continuously
• Effectively same as changing
frequency (Frequency = rate of
change of phase)
Modulation Formats in Modulation Toolkit
• 2, 4, 8, … ASK and PAM
• 4, 8, 16, 32, 64, 128, 256-QAM
• 2, 4, 8, 16-FSK
• MSK and GMSK
• 8, 16, 64-PSK
• BPKS, QPSK, OQPSK, DQPSK, π/4
DQPSK
• Also supported - Custom Modulation
Formats
Impairments
• Real world channels distort RF signal in time and
frequency domain
– Transmitter: Additive White Gaussian Noise (AWGN),
Phase Noise, IQ Gain Imbalance, Carrier Phase/Frequency
Offset
– Channel: Fading, AWGN
Impairments
• Allows for stress testing a communications system in
the presence of channel degradation
– Determine receiver sensitivity
– Determine coding efficiencies
– Validate total system performance
No Impairments
DC Offset (Q)
DC Offset (I)
IQ Gain Imbalance
Quadrature Skew
Frequency Offset
Bits
Bits
Bits
I Q
Channel
Upconversion
I Q
Downconversion
Modulation
Bits
Demodulation
Channel Coding
Bits
Channel Decoding
Source Coding
Bits
Source Decoding
Upconversion/Downconversion
Upconversion/Downconversion
• Mixer – a device that multiplies two voltages
Upconversion
RF
IF
Downconversion
IF
RF
LO
LO
RF = IF + LO
IF = RF - LO
Filtering
• Filter – removes unwanted parts from a signal (like
noise) and/or extract useful parts (within a certain
frequency range)
• Two types
– Analog (signal is a voltage or current)
• Made up of resistors, capacitors, and op amps
– Digital (signal is represented by a sequence of numbers)
• Uses a processor to perform numerical calculations on sampled
values of a signal
Digital Filtering
• Benefits:
–
–
–
–
–
Programmable
Easy to design, test, and implement on a computer
Do not suffer from drift
Stable over temperature
Easier to handle series of filters in series or cascade
What is the Digital Filter Design Toolkit?
• Software for interactive
and/or programmatic
design, analysis, and
implementation of
digital filters
• An add-on toolkit for
LabVIEW
Bits
Bits
Bits
I Q
Channel
Upconversion
I Q
Downconversion
Modulation
Bits
Demodulation
Channel Coding
Bits
Channel Decoding
Source Coding
Bits
Source Decoding
Digital Communication System – Design
PXI
Communications System Demo
RF & Communications
Marketing
Joseph Kovacs
Marketing Manager
RF & Communications
Marketing Strategy
RF Instruments Market (F&S 2005) $2B
Radio Test
Sets,
$400,000,000 ,
21%
Electronic
Counters,
$55,000,000 ,
3%
Power
Meters,
$75,000,000 ,
4%
Network
Analyzers,
$280,000,000 ,
14%
Signal
Generators,
$530,000,000 ,
27%
Signal
Analyzers,
$600,000,000 ,
31%
$400M Total
Addressible
Market
$180M
Addressible
Generator &
Analyzer
Market
Communications Test (F&S 2005)
6%
18%
45%
6%
25%
Communications
Industrial/Autos
Others
Aerospace Military
Electronics manufacturing
RF Sales Data
RF Sales by Category
$125,861.46
$164,419.95
$102,111.00
$332,512.18
$1,166,829.11
$622,398.61
$1,053,142.93
$1,048,289.40
Wireless Communications
Uncategorized
Cellular
Signal Security
Military
Misc
Academic
Research & Design
Competitive Landscape
Signal Generator Market
Competitive Landscape
Spectrum Analyzer Market
National Instruments as an Instrument Vendor
% of Total Respondents
100%
80%
60%
40%
20%
0%
Top of Mind
Unaided
Awareness
National Instruments
Tektronix
Short list
Agilent
Leading Provider
Fluke
Instruments Study: US, Germany, Japan, BI Database Code: NI.36.Q2.2005, Base: All respondents who use/used/plan to use instruments.; Total Number of Respondents: 760;
Questions: When you think of instrument suppliers, which vendors come to mind? (open ended), When evaluating vendors for your current/most recent system, which of the following vendors were included in your short-list?
(Choose all that apply), Which of the following do you consider to be the leading provider of instruments? (Choose one)
Top of Mind = % of resp. who typed in vendor as 1st vendor for the question “When you think of instruments suppliers, which vendors come to mind”
Wireless Expands From Vertical To Horizontal
Telecommunications
Industry
Wireless Technology
Semiconductors
Automotive
Food
Processing
Petrochemical
Communications
Consumer Electronics
cdma2000
Evolving Wireless Standards
UMTS
802.22
802.11
WiMAX – 802.16e
802.11a
ZigBee
IS95
802.11b
802.11h
HSDPA
802.11j
AMPS
802.15.1
IS136
802.20
WiMAX – 802.162004
GPRS
TD-SCDMA
802.11i
802.11n
802.11g
IS54
GSM
UWB
EDGE
802.11d
802.11f
802.11k
802.11e
802.11u
802.11j
RFID
1990
1995
2000
2005
2010
•WPAN – Wireless Personal Area Network
Wireless Networks
•WLAN – Wireless Local Area Network
•WMAN – Wireless Metropolitan Area Network
•WRAN – Wireless Regional Area Network
WPAN
0
WLAN
10m
WMAN
100m
WRAN
40km
•WPAN – Wireless Personal Area Network
Wireless Networks
•WLAN – Wireless Local Area Network
•WMAN – Wireless Metropolitan Area Network
•WRAN – Wireless Regional Area Network
RFID ZigBee
UWB
Bluetooth
0
802.11
(Wi-Fi)
10m
802.16-2004
& 802.16e
(WiMAX)
100m
802.22
40km
Multiple Technologies on a Single Device
• Standards for interoperability of multiple technologies
– For Example: UWB and Bluetooth
•Phone
•Email
•SMS
•browser
•Bluetooth
•Quad-band
850/900/1800/1900
MHz GSM/GPRS
•Bluetooth
•HSCSD
•GPRS
•EGSM/GSM
•4096-color screen
•XHTML Browser
•Wireless phone-to-phone
or phone-to-computer
connectivity
One Platform – Multiple Standards
Sell the platform
(RF platform for
emerging wireless
technologies)
Flexibility
Price vs.
Functionality
Speed/Throu
ghput
Small
size/transportab
ility
RF standards
802.11 (a/b/g/n)
AM/FM/RDS
ASTC (8-VSB)
Bluetooth
CDMA
DAB IBOC
DVB
EDGE
GNSS (Galileo)
GPS
GSM
ITU-J.83B
RFID
Sirius Satellite
UMTS
W-CDMA with
WiMax
XM Satellite
Zigbee
50%
27%
8%
35%
21%
5%
7%
13%
6%
36%
37% currently use 1 RF application
30% currently use 2-3 RF applications
33% currently use 4+ RF applications
18%
3%
30%
7%
11%
16%
16%
7%
21%
0%
% Currently Use
50%
100%
% Have not used but plan to use
Instruments Study: US, Germany, Japan, BI Database Code: NI.36.Q2.2005,
Base: Respondents who indicated RF measurements in question “What types of measurements do you take with your current/most recent system?”
Question: Please indicate your usage of each of the following RF applications below. (Please select only one response per RF application). Total Respondents: 228-229 Margin of Error: +/- 5.5%
Multiple Standards – One Platform
802.11 (a/b/g/n)
BLUETOOTH
RFID
WIMAX
ZIGBEE
802.11 (a/b/g/n)
100%
57%
67%
71%
75%
AM/FM/RDS
36%
35%
43%
14%
25%
ASTC (8-VSB)
4%
9%
10%
29%
0%
BLUETOOTH
31%
100%
47%
57%
25%
CDMA
29%
28%
23%
43%
25%
DAB IBOC
1%
7%
7%
14%
0%
DVB
2%
2%
3%
14%
25%
EDGE
12%
13%
17%
43%
50%
GNSS (GALILEO)
1%
4%
3%
0%
0%
GPS
43%
48%
57%
71%
50%
GSM
19%
35%
23%
29%
25%
ITU-J.83B
0%
4%
7%
29%
0%
RFID
24%
30%
100%
57%
50%
SIRIUS SATELLITE
1%
7%
10%
29%
0%
UMTS
6%
15%
10%
29%
0%
W-CDMA WITH
HSPDA
11%
13%
17%
43%
25%
WIMAX
6%
9%
13%
100%
25%
XM SATELLITE
1%
7%
10%
29%
25%
ZIGBEE
4%
2%
7%
14%
100%
Total Respondents
83
46
30
7
4
18. Please indicate your usage of each of the following RF applications below. (Please select only one response per RF
application).
Instruments Combination
(%) = % of total respondents using that instrument
100%
Instrument
>80%
DMM
100%
Instrument
>80%
Oscilloscope
100%
Instrument
>60%
Power Supply
77%
Power Meter
72%
RF source w/ Digital
Modulation
16%
of
resp.
use
a(n)
RF source w/o Digital
Modulation
Of
those
70%
also
use
a(n)
Spectrum Analyzer w/
Digital Modulation
11%
RF source with Digital
Modulation
73%
Serial Bus Analyzers
14%
Spectrum Analyzer w/
Digital Modulation
74%
Power Meters
70%
Serial Bus Analyzers
12%
Vector Network Analyzers
73%
Serial Bus Analyzer
5%
Lock-in Amp
75%
Frequency Counter
5%
Lock-in Amp
75%
Function Generator
Instruments Study: US, Germany, Japan, BI Database Code: NI.36.Q2.2005, Base: All respondents who use/used/plan to use instruments.; Total Number of Respondents: 943-946, Margin of Error: +/- 2.68%);
Question: Please indicate your usage of each of the following instruments below. (Please select only one response per instrument).
Wireless Design & Development
September 2005 Issue – Special Section
NI RF Application Strengths
• RFID (Radio Frequency Identification)
– Need: speed in manufacturing, flexibility
– Demo: ASK/FSK
• Wireless Telemetry/Wireless Sensors
– Need: flexibility, price
– Demo: FSK
– Example: TPMS (Wineman Technologies)
• Spectral monitoring
– Need: fast sweeping (speed), wide RTB,
Frequency Accuracy
– Demo: Spur sweep, Power-in-Band
– Example: Summitek Instruments
• Research & Design
– Need: flexibility, integration with other
measurements
– Demo: Complex modulation – 64 QAM, 3D eye
• Testing of simple communications systems
(physical layer, parametric testing)
– Need: flexibility, speed in manufacturing,
platform offering full functionality
– Demo: EVM, ACPR
• Transportable applications
– Need: small size, integration with other
measurements, price
– Demo: Spur sweep, Power-in-Band
• Signal Generation (Jamming/Base station)
– Need: flexibility, easy signal creation
capability
– Demo: Wide complex modulated signal
– 128 QAM @ 10 Ms/S, Multi-carrier,
Multi-tone
Applications Requiring Partner Involvement
Application
TV & Video
Broadcast
Radio Data
System (RDS)
NI Contact Alliance
Person
Member
Sean
Thompson
Rick Ary,
Chris
Bowman
Wireless
Heath
Communications Noxon
GSM, EDGE
Richard
Keene
Demo
DAQTron
64 QAM
AmFax
QPSK
SeaSolve
16 QAM
AmFax
GMSK
Low-Probability RF Applications
• Base Station Testing
– One-button test, performance, dynamic range
• Cell Phone Testing
– One-button test, call processing
• Head-to-head replacement of these single function boxes
– Vector Network Analyzer (sophisticated, complex hardware and software)
• Cost, performance, do not have a common LO between receivers, software
– Power Meter (very demanding in accuracy and stability)
• Accuracy & cost
– Frequency Counter (very demanding in accuracy and stability)
• Cost
– BUT…if they need these in a MULTI-FUNCTION test system, then
NI’s platform is great!
Marketing Strategy
• RF Partner Program
• Alliance Member Press Releases
Summitek Instruments, Inc. offers an “Off-the-Shelf” Spectrum Monitoring
Solution for the National Instruments PXI-5660 Vector Signal Analyzer
OASIS spectrum monitoring software now provides users of the NI PXI-5660 an option
for advanced spectrum monitoring capabilities without the need for software
development.
• Increase visibility with editors
• Increase PR
– For 2006, 1 full page RF ad in 3 RF publications:
• Wireless Design & Development
• Microwaves and RF
• Electronic Design
• Increase tradeshow presence
• Push for more demo equipment in field
Extending the PXI RF Platform
Tire Pressure Monitoring System
•Cable modem/CMTS design
verification system
•Broadcast Television
•ZigBee
Compliance
Software
•802.11
•Radio/Telematics Test
•GSM/EDGE
•Up/Downconverters
Tire Pressure Monitoring System (TPMS)
Tire Pressure Sensor
Radio / Telematics Test
Broadcast Television
Audio
Video
Modulation Toolkit
NI PXI-5671 VSG
SeaSolve Software - Compliance Testing an IEEE
802.15.4 (ZigBee) Device
Marketing Strategy
• RF Partner Program
• Alliance Member Press Releases
Summitek Instruments, Inc. offers an “Off-the-Shelf” Spectrum Monitoring
Solution for the National Instruments PXI-5660 Vector Signal Analyzer
OASIS spectrum monitoring software now provides users of the NI PXI-5660 an option
for advanced spectrum monitoring capabilities without the need for software
development.
• Increase visibility with editors
• Increase PR
– For 2006, 1 full page RF ad in 3 RF publications:
• Wireless Design & Development
• Microwaves and RF
• Electronic Design
• Push for more demo equipment in field
• Increase tradeshow presence
US Tradeshows
Show Name
CTIA
IEEE MTT-S
ARFTG (this show
is in conjunction
with IEEE MTT-S)
Date
4/5/2006 - 4/7/2006
Location
Focus
Las Vegas, NV
Cellular
6/11/2006 - 6/16/2006
San Francisco, CA
T&M
6/16/2006
San Francisco, CA
T&M
RFID World
2/27/2006 - 3/1/2006
Dallas, TX
RFID
Sensors
6/6/2006 - 6/8/2006
Rosemont, IL
Wireless
Austin, TX
Wireless
Anaheim, CA
Military
Sep-06
Atlanta, GA
RFID
6/4/2006 - 6/8/2006
Chicago, IL
Communications
WNCG Symposium
AutoTestCon
EPC Global
GlobalComm
Oct-06
9/18/2006 - 9/21/2006
International Tradeshows
Show Name
Date
Wireless Connectivity
World
May-06
ExCel, London
Wireless
IBC
Sep-06
Amsterdam
DVB
Barcelona, Spain
Cellular
Paris, France
T&M
Nov-06
Munich, Germany
Wireless
5/10/2006 - 5/11/2006
Birmingham, UK
T&M
3GSM World
Congress
European Microwave
Exhibition
Productronica
Nepcon
2/13/2006 - 2/16/2006
10/1/2006
Location
Focus
Thank You
RF Fundamentals
120 Minutes
Agenda
• Overview of RF systems
• Measurement terminology
• Spectral measurements
• Modulation
• Common RF measurement instruments
What & Why
• RF and microwave
– Radio Frequency
– Generally high frequency signals
– Typically associated with wireless/modulation
– No strict definition
• RF
• Microwave
~ few kHz to 1GHz
~ 1GHz to 100 GHz
• Efficient propagation of signals over longer distances
• Smaller antennae
C = f •λ
RF Systems
• Wireless
–
–
–
–
–
–
Industrial communications (ISM bands, Zigbee, ..)
RFID
Communications (Cell, point to point links,…)
Broadcast (FM, AM, TV, Satellite )
WLAN (802.11a/b/g.., )
Telemetry.
• Wireline
– Cable TV, Modems
– DSL
• Other
– Radar, Spectral Monitoring, instrumentation (non electronic), uWave Oven
RF Frequency Bands
• Industrial, Scientific, Medical (ISM)
– License Free
– 400 MHz, ~900MHz, 2.4 GHz, 5GHz – 6 GHz
• Cell phones
– 900MHz, 1800MHz-1900 MHz
• GPS
– ~1.6 GHz
• Cable TV
– Broadcast Satellite Set top box
~50MHz to 850MHz
~1000MHz to 2000MHz
What is IF?
• Intermediate frequency
– Intermediate frequency that is useful in one type of
up/downconversion scheme
– Popular IF’s: 10.7MHz, 21.4 MHz, 44MHz, 70MHz,…..
RF Up Conversion
Message
(Baseband)
IF
Frequency
RF
Measurement Terminology
Power Level Dynamic Range
• High power transmitters
–
kWatts
(+60 dBm)
(Broadcast)
• Medium power transmitter
–
2 Watts
(+33 dBm)
• Low power transmitters
–
100 mWatts (+20 dBm)
• Receiver sensitivities
–
~100 femtoWatts (-100 dBm)
(Cell phone)
Frequency Domain (FFT) Review
Sampling Interval
Tacquistion
FFT Bin Size
Frequency Resolution
(RBW)
Frequency Span = 1/ (2 X Sample Interval)
FFT Bin Size (Resolution) = 1/ Tacqusition
Frequency
Span
Spectrum Analyzer Display / Controls
Full Scale Range
Reference Level (dBm)
Attenuation (dB)
Amplitude (dB)
Frequency
Frequency Resolution
(FFT Bin Size )
Resolution Bandwidth or RBW (Hz)
Frequency Span
Reference Level/Attenuation
Mixer Level = Reference Level - Attenuation
Constant
Reference Level
RF Input
Attenuator
Mixer Level
Attenuation
Tuning Frequency
Spectrum Analyzer Front End
Both control the input Full Scale power
Typically both change the attenuation the same way – linked controls
Reference Level/Attenuation
Decreasing Ref Level (Range)
Increased distortion potential
Decreased noise floor potential
Optimum compromise between distortion and noise floor will maximize
Instrument performance (dynamic range)
Note: Decreasing Attenuation by 10 dB decreases noise floor by 10
dB (and vice versa)
OBJECTIVE
Instructor Demo 1
To understand the impact of the reference level on RF
measurements
Resolution Bandwidth
Horizontal (X Axis) effects of lowering resolution bandwidth
•Increases frequency resolution (# of spectral lines)
•Increases acquisition time
RBW = 100 kHz
RBW = 10 kHz
RBW = 100 Hz
Resolution Bandwidth (Cont.)
Vertical (Y Axis) effects of lowering resolution bandwidth
•Lowers noise floor
•Increases dynamic range (narrowband signals only)
RBW = 100 kHz
RBW = 10 kHz
RBW = 100 Hz
Review: Dynamic Range and Distortion
Fundamental Frequency (f)
Harmonic Distortion (2f, 3f, 4f, etc)
Noise Floor
Total Harmonic Distortion (THD)=
Ratio of Fundamental to Distortion
Signal to Noise Ratio (SNR) =
Ratio of Fundamental to Noise
Signal to Noise and Distortion (SINAD) =
Ratio of Fundamental to Noise + Distortion
Dynamic Range - Wideband Signals
Average Power
Apparent
Dynamic
Range
• Multi-tone or modulated signals
– Large peak to average power ratios
Freq
• Crest factor
– Reduction in apparent dynamic range
by crest factor (dB)
Peak Power
Average Power
Time
Instrument full scale range (reference
level) must be set to handle peak power
Crest Factor = Peak Pwr/Avg Pwr
10 * log (Peak/Avg) dB
A(dBm)
Power Spectral Density (PSD)
• Normalized spectrum
• PSD plot normalizes
the displayed power
(Effective RBW = 1Hz)
RBW=100Hz
RBW=10Hz
PSD (RBW*=1Hz)
Frequency
Total Power = Power per bin X Number of bins
Constant
(Smaller RBW )
Power spectral density scales the Y-axis to display the effective power in 1Hz
Does NOT actually improve the frequency resolution
Phase Noise
Time Domain
Jitter
Freq Domain
Phase Noise
• Measure of short term stability of
timebase
• Units dBc/Hz at offset X kHz
(X=1,10,100,…)
• Phase noise function of offset from carrier
Modulation
Modulation Basics
Changing a higher frequency (Carrier) signal
proportional to a message signal
Ac cos(2πf c t + φ )
Amplitude
Frequency
Phase
Angle
(Frequency = Rate of change of Phase)
All Modulation schemes change one or both of amplitude and angle
Receiver detects these changes and thus detects the message signal
Modulation Basics (Cont...)
AM Modulated Carrier
Message
Carrier
(RF)
Ac cos(2πf ct + φ )
What the #$!@ are I/Q Signals ?
I and Q signals are control signals for changing an RF carrier signal
What properties can be changed?
Amplitude
Phase
How can frequency be changed?
By changing phase continuously – Effectively same as changing frequency
Generalized Modulator
Message
Signal
Amplitude Control
Modulated RF
Modulator
Phase Control
In Phase
Osc Control
Message
Signal
I
Modulator
Quadrature
Osc Control
Modulated RF
+
Q
I/Q Signals Demystified
Carrier Frequency Sine Wave
(Reference Signal)
Φ
Modulated RF Signal
1
Φ
Q (Quadrature)
I (In phase)
Amplitude 1 (same amplitude as reference signal)
Phase
Φ with respect to Reference Carrier
Vector Representation
(with respect to carrier)
I/Q Signals
AM
PM
Q
I
Describe amplitude and phase changes by changes in only amplitudes
of I and Q
Easier to change amplitudes of 2 quadrature RF carrier signals and sum them
than to change phase of 1 RF carrier
I/Q Modulation Example: Phase Modulation
1/8 Full Scale
X
• Message
0
X
Amplitude = 1, Φ = 0º
Amplitude = 1 Φ = 45º
Q=0
I=1
Φ
I=0.7
Q=0.7
Phase Modulation Example (Cont’d)
Fc
I =0,0.7
Message
Signal
(0, 1/8)
Phase Modulated RF
Modulation
(Phase)
+
Q =0,0.7
Fc90
Quadrature Mixer
Note the RF portion (Quadrature mixer) independent of modulation type
Big advantage
OBJECTIVE
Instructor Demo 2
To understand I/Q measurements
I/Q Plots
• Digital modulation quality visualization
Q
PM
Strips carrier frequency information
from a modulated signal
What’s left
Baseband (Message signal only)
Dot Represents
Sine wave at Carrier frequency
Magnitude r
Phase Ф
AM
I
Symbols
• Symbols
– Symbol = Discrete I/Q State representing Combination of Bits
• Binary
• Quarternary
• M-Ary
Two Symbols
4 Symbols
M Symbols
0, 1
00, 01, 10, 11
….
1 bit/sec/Hz
2 bits/sec/Hz
M bits/sec/Hz
1.66
1.25
1.00
750m
– Example: Quad Phase Shift Keying (QPSK)
• 4 symbols (4 possible amp/phase states)
• 4 symbols -> 2 bits/Symbol
500m
250m
0.00
-250m
-500m
-750m
-1.00
– Symbol Rate = 1 Mega Symbols/sec -> 8 Mbits/sec
-1.25
-1.66
-1.66
Symbol rate sampled I/Q Plot is a Constellation Plot
-1.00 -500m 0.00
I
4 Symbols
500m 1.00
1.66
Constellation Plots
Similar to eye diagram for binary digital comm
QAM 4 : 4 symbols
QAM 16: 16 symbols
2(bits/sec)/Hz
4 (bits/sec)/Hz
1.66
1.66
1.25
1.25
1.00
1.00
750m
750m
500m
500m
250m
250m
0.00
0.00
-250m
-250m
-500m
-500m
-750m
-750m
-1.00
-1.00
-1.25
-1.25
-1.66
-1.66
-1.00 -500m 0.00
I
QAM 4
500m 1.00
1.66
-1.66
-1.66
-1.00 -500m 0.00
I
500m
QAM 16
1.00
1.66
I/Q to RF Conversion
• Direct Conversion
Fc
I
Q
Digital
D/A
D/A
Modulated RF
I
+
+
Q
Analog
Fc90
Fc
Vector summation is
analog at RF frequency
I/Q to RF Conversion
• IF architecture
– Vector summation is digital at Intermediate Frequency
IF
I
Modulated IF
+
+
Q
D/A
RF (Modulated)
IF
Fc
IF90
Digital
IF Generator
Analog
UpConverter
Digital Modulation
• Message signal is digital
– Modulation type : Many BUT variations on basic 3 (A,P,F)
• Naming decoder ring
Q
Binary (M=2)
Q-Quartenary (M=4)
M-Ary
(M)
P
A- Amplitude
P –Phase
F – Frequency
S
Shift
K
Keying
– ASK (Binary ASK aka OOK - ON OFF Keying)
– QAM (M=4,8,16,32,64,128,256…) Quadrature Amplitude
Modulation
OBJECTIVE
Instructor Demo 3
To show the effect of impairment (noisy channel) on the constellation
plot for QAM demodulation
Digital Modulation
• Why so many modulation schemes?
– Different efficiency tradeoffs
• Spectral, power, cost, size, reliability
– Different constraints
• Handset (mobile terminal) vs basestation
– Backward compatibility
• Each new standard adds a new modulation scheme
BUT ALL built from the same building blocks
Amplitude, Frequency, Phase Modulation
Overview of Full RF Communication System
Base band
I/Q
Bits
RF
Communications Measurements
Channel
Adjacent
Channel
• Spectral Compliance
Power in band, spurious power outside band
No need to demodulate signal
Freq
• Modulation Quality
Time Domain measurements
Require Demodulation
Quantify deviation of signal from ideal
Error Vector Magnitude EVM (%)
Modulation Error Ratio MER (dB)
A
S
V
ly
n
O
RF Instruments
Instrument Types
• Frequency counter
• Power meter
Receive signals
• Spectrum Analyzer
• Vector Signal Analyzer
• CW or sine source
Generate signals
• Frequency synthesizer
• Vector Signal Generator
• Network analyzer
Both
• Radio test sets
Spectrum vs. Vector Signal Analyzer Architectures
• Classic swept tuned SA
– Magnitude Only
– Narrowband
• Possibly higher dynamic range
– $
• Modern FFT based VSA
– Magnitude and Phase
– Wideband
• Challenged on higher dynamic range
– Modulation Analysis
– $$
Measurement Instrument Comparison
Instrument
Accuracy
Power
Meter
Best
(None)
Better
(None)
(None)
Frequency Best
Counter
(None)
Better
(None)
(None)
Spectrum
Analyzer
Vector
Signal
Analyzer
Good
Selectivity
Better
Dynamic
Range
Best
Measurement Modulation
Quality
Coverage
Better
Spectral
(No demod)
Better
Best
Better
Best
Best
RF Generation Instruments
• Frequency Synthesizer
–
–
–
–
Creates (synthesizes) Sine waves from a Reference frequency
Frequency control
No Amplitude control typical (fixed low level output)
Common application
• Tunable Local Oscillator (LO) for up/downconverters
• Signal Generators
–
–
–
–
Frequency synthesizer with amplitude control
AKA as CW (Continuous Wave) sources
Modulation : AM, FM, PM typical built in or external inputs
Most Commonly used
• Vector Signal Generator
RF Vector Signal Generation Instruments
Analog LO
RF
I
+
Q
Digital
I
+
Traditional
IQ Based
Baseband
RF
Q
LORF90º
I/Q Generator
Analog
Digital
Baseband
LOIF
I
+
IF Based
Quadrature Modulator
I
Q
+
Q
LOIF90º
RF
IF
IF to RF
UpConverter
Comparison of I/Q Modulator vs IF Generator
• Direct Conversion (Analog Quadrature Modulator)
– Simpler, lower cost
– Upgrade option to a CW generator
• Add I/Q generator, I/Q Modulator
– Issues: LO leakage and image suppression
• Imbalances in the analog I and Q paths
• IF based VSG
– Multi-stage filtering -> superior LO leakage and image suppression
– Issues: dynamic range challenge
• Many stages of up or dowconversion, filtering impact signal to noise ratio
Network Analyzers
• Characterize RF impedances (S Parameters – S11, S12, S21, S22)
–
–
–
–
Provide stimulus
Measure response
Separate incident (forward) power from reflected power with directional couplers
Calibrate all cabling/fixturing to “de-embed” it from measurement
• Scalar or Vector
– Scalar network analyzers measure magnitude responses only
– Vector network analyzers measure magnitude and phase responses
• VNA is not the same as VSA
– Network analyzers have stimulus/response/ and directional couplers
VNA = VSA + VSG + Directional Couplers + Calibration