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Wireless Sensor System Design

Wireless Sensor System Design. A Joint Course of the University of South Florida and Tennessee Technological University Spring 2002 Lecture 11 – Multipath / Course Wrap-up. Tennessee Tech UNIVERSITY. Weekly Lecture Topics. Course Introduction

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Wireless Sensor System Design

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  1. Wireless Sensor System Design A Joint Course of the University of South Florida and Tennessee Technological University Spring 2002 Lecture 11 – Multipath / Course Wrap-up Tennessee Tech UNIVERSITY

  2. Weekly Lecture Topics • Course Introduction • Analog and Digital Modulation Methods (1/11) • Fundamentals of Antennas and Propagation (1/18) • Signal Processing Techniques (1/25) • Microwave Systems: Communications Hardware, Noise, Linearity (2/1) • System Test, Evaluation and Documentation / Effective Presentation Styles (2/8) • Preliminary Design Review (student presentations*) (2/15) • Microwave Sensor Technology (2/22) @ TTU • Modern Wireless Communication Systems (3/1) • Microwave Proximity Sensors (3/8) • Microelectromechanical Systems for Communications (RF - MEMS) (3/22) • Internal CDR (4/5) • Wireless Sensor System Research (Paul Flikkema from NAU) (4/12) • Multipath / Course Wrap-up (4/19) * On-site internal reviews/preparation will precede inter-university presentations.

  3. Motivation for Today’s Talk Free space propagation is not reality! Note: Path loss is directionally dependent Source: University of Kansas' Information & Telecommunications Technology Center and Kansas Applied Remote Sensing Program

  4. Motivation for Today’s Lecture • Free space propagation is not (virtual) reality! • Dr. Sarabandi’s WAMI Forum presentation

  5. Propagation Loss – Two Categories • Large scale path loss – predicts mean signal strength from transmitter to receiver (T-R) • Distance, Reflection, Diffraction and Scattering • Small scale path loss – rapid changes in signal strength over a small travel distance or time interval • Multipath • Doppler

  6. Multipath • The environment produces “echoes” • The signal received gets spread out in time • From Fourier analysis: • Spreading in time  Reduction in Frequency • Filtering of baseband signal (information)! • The environment changes due to • Moving transmitter or receiver • Dynamic environment

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  13. $1M Animation Large scale effects Small scale effects

  14. So what happens? Fading • Flat or Frequency-Selective • Fast or Slow Speed: 75 mph Wavelength: 0.33 m p. 211 of Rappaport

  15. Why is this bad? • Signals corrupted by multipath are more susceptible to channel noise • Degradation in • BER (digital) • SNR (analog) • Bottom Line – Information quality is compromised

  16. Multipath Effects on Time Domain Data I Q W/O multipath W/ multipath

  17. So what can be done? • Equalization • Diversity • Channel Coding

  18. Equalization • Equalization “undoes” the multipath filtering effect • Filtering will induce intersymbol interference (ISI) • Equalization makes pulses look “rectangular” again • Two classes of algorithms • Those requiring training sequence • Those that don’t: Blind techniques channel Equalizer freq time time time

  19. Equalization with a Training Sequence • A known sequence will be sent at regular intervals • The equalizer will adapt to minimize the error between the known signal and recovered signal (LMSE optimization) • Advantage: minimizes computation • Disadvantage: utilizes bandwidth resources

  20. Equalization of Training Data I I Q Q Known Desired Received New coefficients Equalizer Equalized output equals known Adaptive Algorithm LSME

  21. Blind Equalizations Q • Equalizer continuously adjusts based on the statistics of the received signal • Advantage: no training sequence • Disadvantage: more computationally intensive I e.g., 16-QAM

  22. Blind Equalization Process Q I Q Equalizer Statistics of received data I Adaptive Algorithm Statistics of for 16-QAM

  23. What is needed? Digital FIR Filter Input 0 Z-1 1 Flat Fading Frequency Selective Z-1  2 AGC Slow Fading Z-1 3 Z-1 High-Speed Adaptive Equalizer 4 Fast Fading Output Coefficients

  24. Antenna Diversity • Idea: if multipath is a small scale random effect that is spatially dependent, then the fading experienced by two antennas spaced a short distance from each other will be uncorrelated • Methods • Selection diversity – use the antenna with the strongest signal • Maximal ratio combining – use the antennas as an array to achieve max power out

  25. Maximal Ratio Combining 1 Adjustable Weighted Summer 2 Output Detector 3 m Adaptive Control

  26. Frequency Diversity • Idea: if multipath is a small scale random effect that is wavelength dependent, then the fading experienced at two frequencies spaced a short distance from each other will be uncorrelated • Buzz words • 1:N protection switching • Frequency Hopping Spread Spectrum (use: WLAN) • Direct Sequence Spread Spectrum (use: CDMA) • OFDM (divide bits to modulate many different carriers)

  27. Time Diversity • Idea: if multipath is a small scale random effect that is time dependent, then the fading experienced by the signal at two different points in time will will be uncorrelated • Buzz words • RAKE receiver

  28. RAKE Receiver Adjustable Weighted Summer Correlator 1 Correlator 2 Output Integrator/ Detector Correlator 3 Correlator m Adaptive Control

  29. Channel Coding (Error Correction Codes) • Add redundancy (extra bits) in data so that information has better chance of being recovered (think parity on steroids) • Costs • Complexity • Bandwidth • Buzz word • Turbo coding (aka Parallel Concatenated Convolution Codes)

  30. Summary • Multipath effects band limit systems • Will definitely be a driving factor in higher data rate 3G systems • These effects can be counteracted through processing • Requirements for DSP in 3G systems will thus be more demanding

  31. Wireless Sensor Systems Design Course Review A Joint Course of the University of South Florida and Tennessee Technological University Spring 2002

  32. Course Objectives • As advertised: • USF/TTU - This course satisfies the Senior Design Project Requirement (3 Credit Hours) • Objectives • Hands-on design experience • Coverage of emerging wireless and sensor system technologies • Interdisciplinary, collaborative project development (USF and TTU) • Putting the E into Experimental

  33. What we hoped you learned • Problems/advantages of a distributed design process • Ability to take an idea and make it happen • Design • Analysis • Implementation • Scheduling • Ability to be objective in assessing performance • Yours and others • How system level performance can be dependent on subsystem characteristics • Working on a team in an interdisciplinary environment in a relevant area

  34. Hands-On (BBD group) Future USF grad student? Sensor Conditioner

  35. Hands On (TX and Power Group) FM transmitter Sensmitter Power System

  36. Hands On – Literally! (RX group) PLL Bit detector

  37. Learned Something About Mixers

  38. Data Visualization (DSP Group)

  39. 2.45 GHz Antennas – Rob Harris 55 X 55 mm 280 X 135 mm Circularly Polarized Antenna (Transmitter) 4 X 2 Linearly Polarized Antenna Array (Receiver) S11 (reflection coefficient) on VNA S11 (reflection coefficient) on VNA • Corporate-fed rectangular array. • .65λ spacing • -7.56 dB @ 2.45 GHz • ƒc~ 1% design frequency • T-junction with 90º phase shift • λ / 4 transformers • -16.67 dB @ 2.45 GHz • ƒc~ 2 % design frequency USF EEL 4935/TTU ECE 499 SPECIAL TOPICS: WIRELESS SENSOR SYSTEMS

  40. Frequency Shift Key (FSK) Bit Detector by Leonard Guerra Simulated vs.Actual

  41. Sensor/Microwave Topics • Course Introduction • Analog and Digital Modulation Methods (1/11) • Fundamentals of Antennas and Propagation (1/18) • Signal Processing Techniques (1/25) • Microwave Systems: Communications Hardware, Noise, Linearity (2/1) • System Test, Evaluation and Documentation / Effective Presentation Styles (2/8) • Preliminary Design Review (student presentations*) (2/15) • Microwave Sensor Technology (2/22) @ TTU • Modern Wireless Communication Systems (3/1) • Microwave Proximity Sensors (3/8) • Microelectromechanical Systems for Communications (RF - MEMS) (3/22) • Internal CDR (4/5) • Wireless Sensor System Research (Paul Flikkema from NAU) (4/12) • Multipath / Course Wrap-up (4/19) * On-site internal reviews/preparation will precede inter-university presentations.

  42. Communication Systems/Signal Processing Topics • Course Introduction • Analog and Digital Modulation Methods (1/11) • Fundamentals of Antennas and Propagation (1/18) • Signal Processing Techniques (1/25) • Microwave Systems: Communications Hardware, Noise, Linearity (2/1) • System Test, Evaluation and Documentation / Effective Presentation Styles (2/8) • Preliminary Design Review (student presentations*) (2/15) • Microwave Sensor Technology (2/22) @ TTU • Modern Wireless Communication Systems (3/1) • Microwave Proximity Sensors (3/8) • Microelectromechanical Systems for Communications (RF - MEMS) (3/22) • Internal CDR (4/5) • Wireless Sensor System Research (Paul Flikkema from NAU) (4/12) • Multipath / Course Wrap-up (4/19) * On-site internal reviews/preparation will precede inter-university presentations.

  43. Other Topics • Course Introduction • Analog and Digital Modulation Methods (1/11) • Fundamentals of Antennas and Propagation (1/18) • Signal Processing Techniques (1/25) • Microwave Systems: Communications Hardware, Noise, Linearity (2/1) • System Test, Evaluation and Documentation / Effective Presentation Styles (2/8) • Preliminary Design Review (student presentations*) (2/15) • Microwave Sensor Technology (2/22) @ TTU • Modern Wireless Communication Systems (3/1) • Microwave Proximity Sensors (3/8) • Microelectromechanical Systems for Communications (RF - MEMS) (3/22) • Internal CDR (4/5) • Wireless Sensor System Research (Paul Flikkema from NAU) (4/12) • Multipath / Course Wrap-up (4/19) * On-site internal reviews/preparation will precede inter-university presentations.

  44. Results: Our Impression • Unique educational experience – rewards depend on effort • Projects doable but require more time for successful integration • Collaboration • Good with-in groups and within schools. • Limited between schools. • Should get students together early • Tutorials have a good range of topics • Distance learning technology not perfect, but effective

  45. Results: Your Impression • Please fill out the course survey form and return them by Monday (TTU). • Your feedback will be compiled and disseminated

  46. Final Words Wireless remote monitor is becoming ever more popular for industrial, environmental & military applications Drones for military activities (monitoring/targeting/comm) Global Hawk relays data @ 500 Mbit/sec Military arena predicted to require 20 Gbit/sec wireless data links (!) Program to use drones to drop low-data rate ground sensors for in situ monitoring vs. using high-rate video Requires systems level knowledge in comm/devices/processing/networks http://www.msnbc.com/news/661255.asp#BODY

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