Wireless Communication and Rf System Design Using Matlab and Simulink

Wireless Communication and RF System Design Using MATLAB and Simulink

Giorgia Zucchelli – Technical Marketing RF & Mixed-Signal

© 2013 The MathWorks, Inc. 1

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 RF Analog Baseband

Digital Baseband

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Model and Simulate Wireless Systems 

System-level simulation including RF

Digital baseband

Digital to Analog Converter

Transmitter (TX)

RF

RF

Analog to Digital Converter

Digital baseband

Receiver (RX) 3

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

Transmitter (TX)

RF

RF

Analog to Digital Converter

Digital baseband

Receiver (RX) 4

Why Do We Need RF System Simulators? Radio Frequency Signals

Small simulation timestep

Long Simulation Runs

~10psec

~5GHz

Deal with RF complexity with:  Models at high levels of abstraction  Solvers that use larger time-step 5

Simulink and SimRF   

System-level simulation including RF Architectural design of RF transceivers Tradeoff simulation time and modeling fidelity

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Simulation speed

Trade Off Simulation Speed and Modeling Fidelity Equivalent Baseband

Circuit Envelope

True Pass-Band

Modeling fidelity 7

Trade Off Simulation Speed and Modeling Fidelity Equivalent Baseband

Spectrum

Signal bandwidth

Carrier

Circuit Envelope

freq

Spectrum DC

Carrier 1

Carrier 2

freq

True Pass-Band Spectrum

Simulation speed

How do your signals look like?

freq

Modeling fidelity 8

SimRF Libraries: Circuit Envelope

Equivalent Baseband

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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

Transmitter (TX)

RF

RF

ADC

Receiver (RX)

Digital baseband

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Wireless Receivers Architectures Super Heterodyne  

High performance  Low power  Great sensitivity High RF complexity / cost  Discrete filters for image rejection and channel selection  Multiple LOs

Interference

Desired Signal

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Wireless Receivers Architectures

Interference

Low IF  

Desired Signal

Moderate performance  Moderate power  Good sensitivity Moderate RF complexity  Integrated filters for image rejection

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Wireless Receivers Architectures

Interference

Desired Signal

Direct Conversion  

Moderate performance  Moderate power  Good sensitivity Moderate RF complexity  No image rejection  Noise mitigation  Quality of matching 13

Typical Direct Conversion Receiver Design high speed SD data converters

broadband direct conversion receiver

CIC filters and downsamplers

Analog Baseband

ADC Analog Filter

VGA

0°

Decimation Filter

Digital Baseband

Analog PLL

90°

LNA

Decimation Filter

ADC Analog Filter

VGA

Analog Baseband

reconfigurable analog filters

analog phase locked loop

baseband DSP

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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

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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

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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

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Step 1: How Much Noise Can Be Tolerated?  

Direct sequence spread spectrum (DSSS) Determine minimum allowable SNR to meet specifications

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Step 2: Overall RF Receiver Performance  

Determine Receiver Gain / Noise Figure ADC dynamic range

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Step 3: RF Receiver Noise and Power Budget 

Refine the model of the RF Receiver and determine the link budget

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Step 4: Design the RF Architecture 

Specify the architecture of the Receiver: Direct Conversion

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Step 5: Add RF Impairments 

Explore the causes and effects of DC offset

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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

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More Technical Details

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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

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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

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From Pass-Band to Equivalent Baseband

Pass-band transfer function

fc

… MHz …GHz … 0

Bandwidth = 1/Ts

0

Baseband-complex equivalent transfer function

frequency -0.5/Ts

+0.5/Ts

Complex Equivalent Baseband Baseband equivalent time-domain impulse response

Number of sub bands (freq. resolution) equals length of impulse response 0

time 28

Circuit Envelope RF Models Multi-carrier Simulation of Arbitrary RF Networks  

Interferers and spurs analysis at system-level Arbitrary networks

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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

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Multi-Carrier Envelope Simulation carriers

Complex envelope of modulated input signals

fc1

… MHz …GHz …

fc2 frequency

0

Circuit-envelope simulation … MHz …GHz …

fc1

fc2-fc1

fc2+fc1

fc2

frequency

0

Circuit Envelope Complex envelope response around the selected carrier … MHz …GHz … 0

fc2+fc1

harmonic tones signal envelope frequency 31

Circuit Envelope 1/2  

Based on multiple Harmonic Balance analysis The coefficients of the harmonic tones are time-varying

Vin  Re{V (t )e

jcarrier t

} N

Vout  Re{ Vk (t )e

j carrier k t

t1

}

fcarrier1

fcarrier2

k 0

t2 fcarrier1

fcarrier2 t3

fcarrier1

fcarrier2 32

Circuit Envelope 2/2 

Transient simulation to calculate the time-varying envelopes of the signal around the harmonic tones f1

t1

t1

fcarrier

t3

fcarrier

f3

Time simulation

HB

fcarrier

t2

f2

t2

t3

f1 f2 f3

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SimRF and Simscape

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Modeling of the IF Chain for Image Rejection 

Model the RF chain with SimRF and IF chain the electrical domain

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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

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Behavioral Modeling of Analog Electronics  

Simscape: Acausal, implicit, differential algebraic equations Very similar to VerilogA VerilogA module Amplifier(in_port, out_port);

Simscape component Amplifier

analog begin inout in_port, out_port; … I(in_int) <+ cin*1e-9 *ddt(V(in_int)); electrical in_port, out_port; I(in_int) <+ V(in_port)/rin*(1-s11)/(1+s11); I(in_int) <+ -a2*s12/(sqrt(rin)*(1+s11)); end

equations nodes in … in_port = foundation.electrical.electrical; % Iin == cin * Vin.der + ... in:left Vin/rin*(1-s11)/(1+s11) + ... out_port = foundation.electrical.electrical; % -a2*s12/(sqrt(rin)*(1+s11)); out:right end 37

Conclusions

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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

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Next Steps 

For more information please contact me: [email protected]



For an evaluation or trial please contact your account manager



Thank you for your interest

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