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1 © 2013 The MathWorks, Inc.
Wireless Communication and RF System Design
Using MATLAB and Simulink
Giorgia Zucchelli – Technical Marketing RF & Mixed-Signal
2
Outline of Today’s Presentation
Introduction to RF system-level simulation of wireless transceivers
MathWorks tools for RF top-down design
802.15.4 design example
Conclusions
Digital Baseband
Analog
Baseband
RF
3
Model and Simulate Wireless Systems
System-level simulation including RF
Digital
baseband
Digital to
Analog
Converter
RF Digital
baseband
Analog to
Digital
Converter RF
Transmitter (TX) Receiver (RX)
4
Model and Simulate Wireless Systems
System-level simulation including RF
RF = high frequency analog signals
RF causes imperfections that cannot be neglected
Digital
baseband
Digital to
Analog
Converter
RF Digital
baseband
Analog to
Digital
Converter RF
Transmitter (TX) Receiver (RX)
5
Why Do We Need RF System Simulators?
Deal with RF complexity with:
Models at high levels of abstraction
Solvers that use larger time-step
Radio Frequency
Signals
Small simulation time-
step Long Simulation Runs
~10psec
~5GHz
6
Simulink and SimRF
System-level simulation including RF
Architectural design of RF transceivers
Tradeoff simulation time and modeling fidelity
7
Trade Off Simulation Speed and Modeling Fidelity
Modeling fidelity
Sim
ula
tio
n s
pe
ed
True Pass-Band
Circuit Envelope
Equivalent Baseband
8
Trade Off Simulation Speed and Modeling Fidelity How do your signals look like?
Modeling fidelity
Sim
ula
tio
n s
pe
ed
True Pass-Band
Circuit Envelope
Equivalent Baseband
Carrier
Signal
bandwidth
freq
Sp
ectr
um
Carrier 1 freq
Sp
ectr
um
Carrier 2 DC
freq
Sp
ectr
um
9
SimRF Libraries:
Circuit Envelope Equivalent Baseband
10
Design of a Wireless Receiver
802.15.4 Air interface @2.4GHz
– 250 kbps
– 2 Mchps
– O-QPSK modulation
– ½ sine pulse shaping
Robustness to -20dBm UMTS interference
-100dBm sensitivity @0.00625%BER
Ultra low cost / power
Digital
baseband DAC RF
Digital
baseband ADC RF
Transmitter (TX) Receiver (RX)
11
Wireless Receivers Architectures
Desired Signal
Interference
Super Heterodyne High performance
Low power
Great sensitivity
High RF complexity / cost
Discrete filters for image
rejection and channel selection
Multiple LOs
12
Wireless Receivers Architectures
Desired Signal
Interference Low IF Moderate performance
Moderate power
Good sensitivity
Moderate RF complexity
Integrated filters for image
rejection
13
Wireless Receivers Architectures
Desired Signal
Interference
Direct Conversion Moderate performance
Moderate power
Good sensitivity
Moderate RF complexity
No image rejection
Noise mitigation
Quality of matching
14
Typical Direct Conversion Receiver Design
ADC
AnalogFilter
AnalogFilter
ADC
90°
0°
LNA
VGA
VGA
Analog PLLDigital
Baseband
DecimationFilter
DecimationFilter
Analog Baseband
Analog Baseband
broadband direct
conversion receiver
high speed SD data
converters
reconfigurable analog
filters
analog phase locked
loop
CIC filters and down-
samplers
baseband DSP
15
Top-Down Design of the RF Receiver
Model the overall communication chain
Refine the receiver model with a top-down approach
Verify the specifications at each step
Trade off model fidelity and simulation speed
16
Demo
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Demo: Design of a ZigBee Receiver
Executable specification of the system
Architecture exploration and refinement of the RF front-end
?
18
ZigBee Specifications
802.15.4 Air Interface for 2.4 GHz ISM Band
250 kbps
2 Mchps
O-QPSK modulation
½ sine pulse shaping
Robustness to -20 dBm UMTS interference in IMT-2000 band spanning
2500 MHz to 2690 MHz
-100 dBm sensitivity @ 0.00625% BER
Ultra low cost
19
Step 1: How Much Noise Can Be Tolerated?
Direct sequence spread spectrum (DSSS)
Determine minimum allowable SNR to meet specifications
20
Step 2: Overall RF Receiver Performance
Determine Receiver Gain / Noise Figure
ADC dynamic range
21
Step 3: RF Receiver Noise and Power Budget
Refine the model of the RF Receiver and determine the link budget
22
Step 4: Design the RF Architecture
Specify the architecture of the Receiver: Direct Conversion
23
Step 5: Add RF Impairments
Explore the causes and effects of DC offset
24
Modeling RF Front Ends with SimRF
Model the entire system including RF
– Leverage MATLAB and Simulink
Two libraries supporting two simulation approaches
– Equivalent Baseband for all digital simulations of 2-port single carrier cascaded
systems
– Circuit Envelope for multi-carrier simulation of arbitrary topologies
Trade off simulation speed and modeling fidelity
25
More Technical Details
26
Equivalent Baseband RF Models Rapid Single-Carrier Simulation of RF Cascades
Link budget analysis for super heterodyne transceivers
In-band odd-order spectral regrowth and mismatches
27
Equivalent Baseband Library Discrete-Time Frame-Based RF Simulation
Frequency defined (linear) elements
– S-parameters, Lumped components, Transmission lines
– Equivalent baseband (FIR) descriptions taking into account input / output mismatches
Nonlinear elements
– Amplifiers, Mixers
– Static odd-order characteristics
28
Complex
Equivalent
Baseband
From Pass-Band to Equivalent Baseband
… MHz …GHz … fc
Bandwidth = 1/Ts
0
-0.5/Ts +0.5/Ts
Baseband-complex equivalent transfer
function
Number of sub bands (freq. resolution)
equals length of impulse response
0
frequency
Baseband equivalent
time-domain
impulse response time
0
Pass-band
transfer function
29
Circuit Envelope RF Models Multi-carrier Simulation of Arbitrary RF Networks
Interferers and spurs analysis at system-level
Arbitrary networks
30
Circuit Envelope Library A Transient Simulation Superimposed to Harmonic Balance
Frequency defined (linear) elements
– Lumped components, Transmission lines
– S-parameters: frequency domain models for “flat” characteristics
– S-parameters: rational fitting for broadband components
Nonlinear elements
– Amplifiers, Mixers
– Static even and odd order characteristics
Author your own model using Simscape
31
Circuit
Envelope
Multi-Carrier Envelope Simulation
… MHz …GHz … fc1
Circuit-envelope
simulation
0
Complex envelope of
modulated input signals
Complex envelope response
around the selected carrier
fc2
… MHz …GHz …
0 frequency
fc1 fc2 fc2-fc1
fc2+fc1
… MHz …GHz …
frequency
fc2+fc1
0
frequency
carriers
harmonic tones
signal envelope
32
Circuit Envelope 1/2
Based on multiple Harmonic Balance analysis
The coefficients of the harmonic tones are time-varying
t1 fcarrier1
t2 fcarrier1
t3 fcarrier1
})(Re{0
N
k
tj
koutkcarrieretVV
fcarrier2
fcarrier2
fcarrier2
})(Re{tj
in
carrieretVV
33
Time
simulation HB
Circuit Envelope 2/2
Transient simulation to calculate the time-varying envelopes of the signal
around the harmonic tones
t1 fcarrier
t2 fcarrier
t3 fcarrier
t1
t2
t3 f1 f2 f3
f1 f2 f3
34
SimRF and Simscape
35
Modeling of the IF Chain for Image Rejection
Model the RF chain with SimRF and IF chain the electrical domain
36
Using Simscape Together with SimRF
Early exploration of the receiver architecture
Intuitive analog model of the IF chain
Refine complex architectures:
– Differential
– Biasing networks
Build your own models using the Simscape language
– Models compatible with SimRF Circuit Envelope
37
Behavioral Modeling of Analog Electronics
Simscape: Acausal, implicit, differential algebraic equations
Very similar to VerilogA
module Amplifier(in_port, out_port);
inout in_port, out_port;
electrical in_port, out_port;
VerilogA
component Amplifier
nodes
in_port = foundation.electrical.electrical; %
in:left
out_port = foundation.electrical.electrical; %
out:right
end
Simscape
equations
in
…
Iin == cin * Vin.der + ...
Vin/rin*(1-s11)/(1+s11) + ...
-a2*s12/(sqrt(rin)*(1+s11));
analog begin
…
I(in_int) <+ cin*1e-9 *ddt(V(in_int));
I(in_int) <+ V(in_port)/rin*(1-s11)/(1+s11);
I(in_int) <+ -a2*s12/(sqrt(rin)*(1+s11));
end
38
Conclusions
39
Modeling RF Systems with MathWorks
Combine digital baseband, analog and RF
► Integrate your design and find errors early
Progressively refine your design with a top-down methodology
► The verification effort will be limited
Trade off accuracy and execution speed by choosing the desired abstraction
level
► You don’t have to become a modeling guru
40
Next Steps
For more information please contact me: giorgia.zucchelli@mathworks.com
For an evaluation or trial please contact your account manager
Thank you for your interest
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