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Sub-GHz UWB Overview

This submission provides an overview of sub-GHz UWB technology for 802.15.4a alt-PHY, including baseband pulse sequences, advantages and disadvantages, and various applications.

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Sub-GHz UWB Overview

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) • Submission Title:Sub-GHz_Overview • Date Submitted: July 18th, 2005 • Source:Mark Jamtgaard (1) • Companies: • (1) Æther Wire & Location, Inc., 520 E. Weddell Drive, Suite 5, Sunnyvale, CA 94089, USA • Voice: (1) 408 400 0785 • E-Mail: (1) mark@aetherwire.com • Abstract: An overview of sub-GHz UWB technology for 802.15.4a alt-PHY • Purpose: To present an overview of sub-GHz UWB • Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. • Release: The contributors acknowledge and accept that this contribution becomes the property of IEEE and may be made publicly available by P802.15

  2. Sub-GHz UWB • Baseband Pulse Sequences • Doublets • Pairs of pulses with opposite polarity • Spectrum has lobes and notches with a Gaussian envelope

  3. Advantages • Ranging Relies On First Arrival Detection • The estimation performance is degraded considerably when the energy of the first arriving component is not dominant among multipath components of a received signal • Material Propagation Is Important • Low Frequencies Have Better Propagation Characteristics Than High Frequencies • Low Frequencies Experience Less Shadowing • Results In High Accuracy First Arrival Detection

  4. 1.2cm Wallboard Attenuation • Attenuation at 620 MHz = 0.4 dB • Attenuation at 4.12GHz = 0.45 dB R. Buehrer, W. Davis, A. Safaai-Jazi, and D. Sweeney, “Ultra wideband propagation measurements and modeling - Final report to Darpa NETEX program,” tech. rep., Virginia Tech, 2004.

  5. 4.5cm Door Attenuation • Attenuation at 1.01GHz = 0.51 dB • Attenuation at 3.81GHz = 1.56 dB

  6. 5.9cm Cloth Office Partition Attenuation • Attenuation at 520 MHz = 0 dB • Attenuation at 4.02 GHz = 1.91 dB

  7. 5.8cm Brick Attenuation • Attenuation at 1.01 GHz = 2.06 dB • Attenuation at 4.01 GHz = 5.27 dB

  8. Suburban Home Propagation • Sub-GHz band propagation advantage over 3-5 GHz band

  9. Office Building Propagation • Link through 5 partitions. • Sub-GHz band has a 10dB propagation advantage over 3-5 GHz band

  10. Disadvantages • More Interference In The Sub-GHz Band • Non-coherent detection not possible • Longer code lengths • Larger dynamic range

  11. Applications • Numerous applications require 3D position tracking in buildings. • These applications require 5 links per node to compute 3D position. • To robustly maintain 5 links in real applications requires: • Penetration through multiple walls / objects • 30 meter range

  12. Track Firefighter Status • A network of locators determine their location relative to each other and transmit their location to a command center • Can penetrate Buildings, Metal containers, Fire and smoke

  13. Military Operations in Urban Terrain Penetrates Interior Walls MOUT 1-meter accuracy 50-200m range UWB Localizer Wearable Computer Low power LPI/LPD Lightweight GPS Receiver

  14. Regulator Status • FCC: “In the frequency band below 960 MHz these devices are permitted to emit at or below the 15.209 limits” [First order and report, 2002] • 15.209 • Measured With Quasi-Peak Detector (CISPR 16-1) with 120-kHz resolution filter • Charge time is 1ms • Discharge time is 550ms

  15. FCC Mask

  16. System Block Diagram Time-Integrating Correlator Time- Integrating Correlator RF Amplifier A/D Converter Large Current Radiator Crystal Oscillator Real Time Clock Code Sequence Generator Transmitter Antenna Driver Processor and Memory

  17. Large Current Radiator Baseband impulses (<1GHz) can be effectively radiated from small (<4cm) Large Current Radiator (LCR) antenna (FDTD simulation)

  18. Antennas • Large Current Radiator • Preserves impulse shape • Frequency response varies <6dB from <100MHz to >2.5GHz • Requires low (1W) source impedance • Direct drive from CMOS • No transmission line • 6cm Electric Dipole (for comparison, 4cm LCR fits within 6cm sphere) • Differentiates impulse shape • Gain varies 40dB from 100MHz to 2.2GHz • Other UWB antennas with comparable low-frequency response (e.g. TEM horn) are physically large (> 1 meter)

  19. Reception • Coherent Reception via Correlation • Time Integrating Correlator is a Matched Filter • Analog input signal is multiplied by Reference code & integrated • Each of 32 correlator phases represents a different time alignment of input signal & reference code • Each correlator is offset ¼ chip • Tolerant of clock jitter and drift • 30dB Process Gain with families of orthogonal 1023-chip codes • Each reception starts with zero integrated noise

  20. Sub-GHz UWB Correlator Snapshots

  21. 320 ns Scan Window Rapid Acquisition Received correlator output of Beacon signal plus noise. Peaks exist every tm =310 nanoseconds. Receptions are spaced tc = 1.024 ms plus offset shown on Timeline. 20 ms 10ms 10ms 10ms First Detection Window Scan Window (Scan 320 ns, then jump 10 ms) 20 ns overlap Five Receptions Per Scan Correlator window Size tw = 80 ns First Detection 80 ns

  22. Link Budget

  23. Conclusion • The Sub-GHz band propagation characteristics make it attractive for applications requiring 3D location in industrial environments.

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