Wireless Communication and RF System Design Using MATLAB and Simulink Giorgia Zucchelli Technical Marketing RF & Mixed-Signal

Transcription

1 Wireless Communication and RF System Design Using MATLAB and Simulink Giorgia Zucchelli Technical Marketing RF & Mixed-Signal 2013 The MathWorks, Inc. 1

2 Outline of Today s Presentation Introduction to RF system-level simulation of wireless transceivers MathWorks tools for RF top-down design design example Conclusions RF Analog Baseband Digital Baseband 2

3 Model and Simulate Wireless Systems System-level simulation including RF Digital baseband Digital to Analog Converter RF RF Analog to Digital Converter Digital baseband Transmitter (TX) Receiver (RX) 3

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 RF Analog to Digital Converter Digital baseband Transmitter (TX) Receiver (RX) 4

5 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

6 Simulink and SimRF System-level simulation including RF Architectural design of RF transceivers Tradeoff simulation time and modeling fidelity 6

7 Simulation speed Trade Off Simulation Speed and Modeling Fidelity Equivalent Baseband Circuit Envelope True Pass-Band Modeling fidelity 7

8 Spectrum Simulation speed Spectrum Spectrum Trade Off Simulation Speed and Modeling Fidelity How do your signals look like? Equivalent Baseband Signal bandwidth Carrier freq Circuit Envelope DC Carrier 1 Carrier 2 freq True Pass-Band Modeling fidelity freq 8

9 SimRF Libraries: Circuit Envelope Equivalent Baseband 9

10 Design of a Wireless Receiver Air 250 kbps 2 Mchps O-QPSK modulation ½ sine pulse shaping Robustness to -20dBm UMTS interference -100dBm Ultra low cost / power Digital baseband DAC RF RF ADC Digital baseband Transmitter (TX) Receiver (RX) 10

11 Wireless Receivers Architectures Interference Super Heterodyne High performance Low power Great sensitivity High RF complexity / cost Discrete filters for image rejection and channel selection Multiple LOs Desired Signal 11

12 Wireless Receivers Architectures Interference Desired Signal Low IF Moderate performance Moderate power Good sensitivity Moderate RF complexity Integrated filters for image rejection 12

13 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

14 Typical Direct Conversion Receiver Design broadband direct conversion receiver high speed SD data converters CIC filters and downsamplers Analog Baseband ADC Analog Filter VGA Decimation Filter 90 0 Analog PLL Digital Baseband LNA Decimation Filter ADC Analog Filter Analog Baseband VGA reconfigurable analog filters analog phase locked loop baseband DSP 14

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 15

16 Demo 16

17 Demo: Design of a ZigBee Receiver? Executable specification of the system Architecture exploration and refinement of the RF front-end 17

18 ZigBee Specifications 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 % BER Ultra low cost 18

19 Step 1: How Much Noise Can Be Tolerated? Direct sequence spread spectrum (DSSS) Determine minimum allowable SNR to meet specifications 19

20 Step 2: Overall RF Receiver Performance Determine Receiver Gain / Noise Figure ADC dynamic range 20

21 Step 3: RF Receiver Noise and Power Budget Refine the model of the RF Receiver and determine the link budget 21

22 Step 4: Design the RF Architecture Specify the architecture of the Receiver: Direct Conversion 22

23 Step 5: Add RF Impairments Explore the causes and effects of DC offset 23

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 24

25 More Technical Details 25

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 26

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 27

28 From Pass-Band to Equivalent Baseband Pass-band transfer function MHz GHz f c 0 Bandwidth = 1/T s Baseband-complex equivalent transfer function Baseband equivalent time-domain impulse response -0.5/Ts 0 0 Complex Equivalent Baseband +0.5/Ts time frequency Number of sub bands (freq. resolution) equals length of impulse response 28

29 Circuit Envelope RF Models Multi-carrier Simulation of Arbitrary RF Networks Interferers and spurs analysis at system-level Arbitrary networks 29

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 30

31 Multi-Carrier Envelope Simulation carriers Complex envelope of modulated input signals MHz GHz f c1 f c2 Circuit-envelope simulation MHz GHz f c2 -f c1 0 f c1 f c2 f c2 +f c1 frequency Complex envelope response around the selected carrier 0 MHz GHz Circuit Envelope f c2 +f c1 frequency harmonic tones signal envelope 0 frequency 31

32 Circuit Envelope 1/2 Based on multiple Harmonic Balance analysis The coefficients of the harmonic tones are time-varying V in Re{ V ( t) e j carrier t } V out Re{ N k 0 V k ( t) e j carrier k t } f carrier1 f carrier2 t1 t2 f carrier1 f carrier2 t3 f carrier1 f carrier2 32

33 Circuit Envelope 2/2 Transient simulation to calculate the time-varying envelopes of the signal around the harmonic tones f 1 f 2 f 3 t1 f carrier HB t1 Time simulation t2 f carrier t2 t3 f carrier t3 f 1 f 2 f 3 33

34 SimRF and Simscape 34

35 Modeling of the IF Chain for Image Rejection Model the RF chain with SimRF and IF chain the electrical domain 35

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 36

37 Behavioral Modeling of Analog Electronics Simscape: Acausal, implicit, differential algebraic equations Very similar to VerilogA VerilogA Simscape component Amplifier equations in nodes in_port = foundation.electrical.electrical; % Iin in:left == cin * Vin.der +... out_port Vin/rin*(1-s11)/(1+s11) = foundation.electrical.electrical; +... % out:right -a2*s12/(sqrt(rin)*(1+s11)); end module Amplifier(in_port, out_port); analog begin inout in_port, out_port; I(in_int) electrical <+ cin*1e-9 in_port, *ddt(v(in_int)); out_port; I(in_int) <+ V(in_port)/rin*(1-s11)/(1+s11); I(in_int) <+ -a2*s12/(sqrt(rin)*(1+s11)); end 37

38 Conclusions 38

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 39

40 Next Steps For more information please contact me: For an evaluation or trial please contact your account manager Thank you for your interest 40