July 2005

Sub-GHz_Overview

doc.: IEEE 802.15-05-0390-01-004a

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: Sub-GHz_OverviewDate Submitted: July 18th, 2005Source: Mark Jamtgaard (1) Companies:

(1) Æther Wire & Location, Inc., 520 E. Weddell Drive, Suite 5, Sunnyvale, CA 94089, USA

Voice: (1) 408 400 0785E-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

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Sub-GHz UWB• Baseband Pulse

Sequences• Doublets

– Pairs of pulses with opposite polarity

– Spectrum has lobes and notches with a Gaussian envelope

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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

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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.

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4.5cm Door Attenuation

– Attenuation at 1.01GHz = 0.51 dB– Attenuation at 3.81GHz = 1.56 dB

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5.9cm Cloth Office Partition Attenuation– Attenuation at 520 MHz

= 0 dB– Attenuation at 4.02 GHz

= 1.91 dB

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• 5.8cm Brick Attenuation– Attenuation at 1.01

GHz = 2.06 dB– Attenuation at 4.01

GHz = 5.27 dB

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Suburban Home Propagation

• Sub-GHz band propagation advantage over 3-5 GHz band

text

text

Node A

Node B

4 x Drywall @ 0.05dB 0.2dB

1 x Door @ 2dB 2dB

1 x Brick @ 3dB 3dB

5.2dB

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Slide 9

Office Building Propagation

• Link through 5 partitions.

• Sub-GHz band has a 10dB propagation

advantage over 3-5 GHz band

text

text

Node B

Node A

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Disadvantages

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

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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

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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

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Lightweight

1-meteraccuracy

LPI/LPD

50-200mrange

MOUT

WearableComputer

UWBLocalizer

GPSReceiver

Penetrates Interior Walls

Lowpower

Military Operations in Urban Terrain

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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

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FCC Mask

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System Block Diagram

TransmitterAntennaDriver

TransmitterAntennaDriver

CodeSequenceGenerator

CodeSequenceGenerator

Time-IntegratingCorrelator

A/DConverter

A/DConverter

Time-IntegratingCorrelator

Time-IntegratingCorrelator

Real TimeClock

Real TimeClock

Processorand Memory

Processorand Memory

CrystalOscillator

CrystalOscillator

LargeCurrentRadiator

RF Amplifier

RF Amplifier

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Large Current RadiatorBaseband impulses (<1GHz) can be effectively radiated from small

(<4 cm) Large Current Radiator (LCR) antenna (FDTD simulation)

4cm LCR Source Waveform

-1

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7 8 9 10

ns

Vo

lts

4cm LCR Far-Zone Electric Field

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0 1 2 3 4 5 6 7 8 9 10

ns

Vo

lts/

met

er

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Antennas• Large Current Radiator

– Preserves impulse shape

– Frequency response varies <6 dB from <100 MHz to >2.5 GHz

– Requires low (1) source impedance• Direct drive from CMOS• No transmission line

• 6 cm Electric Dipole (for comparison, 4 cm LCR fits within 6cm sphere)

– Differentiates impulse shape

– Gain varies 40 dB from 100 MHz to 2.2 GHz

• Other UWB antennas with comparable low-frequency response (e.g. TEM horn) are physically large (> 1 meter)

Far-Zone Electric Field from 5 v / 1 Gaussian Edge Stimulus

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0 1 2 3 4 5ns

Vo

lts

/me

ter

4cm Large Current Radiator 6cm Electric Dipole

Relative Antenna Gain with Gaussian Edge Stimulus

-60

-50

-40

-30

-20

-10

0

10

20

0.0 0.5 1.0 1.5 2.0 2.5GHz

dB

Ga

in

4cm Large Current Radiator 6cm Electric Dipole

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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

– 30 dB Process Gain with families of orthogonal 1023-chip codes

– Each reception starts with zero integrated noise

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Sub-GHz UWB Correlator Snapshots

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Rapid Acquisition

20 s

Scan Window(Scan 320 ns, then jump 10 s)

10 s 10 s 10 s

First Detection Window

80 ns

20 ns overlap

Five ReceptionsPer Scan

320 ns Scan Window

First Detection

Received correlator output of Beacon signal plus noise.

Peaks exist every tm = 310 nanoseconds.

-1500

-1000

-500

0

500

1000

1500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

-1500

-1000

-500

0

500

1000

1500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Correlator windowSize tw = 80 ns

Receptions are spaced tc = 1.024 ms plus offset shown on Timeline.

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Link BudgetSub-band Center Frequency ( fc ) 0.4 GHz FCC Allowed Energy Density -61 dBm/MHz Occupied Transmit Bandwidth 700 MHz Target Range 30 m Path Loss At Target Range L1 + L2 = 20log(4πfc/c) + 20log(d) -43.03 dB Wavelength At Center Frequency 0.75 m Best Case Antenna Capture Cross-section 0.5625 m2 Realistic Antenna Length 0.1 m Capture Cross-section of the Realistic Antenna 0.01 m2 Extra Loss For Not Using A Full Wavelength Antenna ( GR = 0.5626 / 0.01 )

-17.5 dB

Path Loss Including The Small Antenna L = L1 + L2 + GR -60.53 dB Long Term Average Transmit Power -61 + 20log(700E6) -32.55 dBm Pulses Per Doublet 2 Doublets Per Symbol 1023 Pulses Per Symbol 2046 Total Symbols Per Second 10000 Total Pulses Per Second 20460000 Pulse On Time 1 ns Total Duty Cycle Off Time To On Time Every Second 47.88 Duty Cycle Gain For The Pulses (over the continuous average) 16.8 dB Transmit Power During The Pulse Active Time ( PT=Pavg_long_term+Gduty_cycle )

-15.75 dBm

Tx Power Backoff To Account For Non-flat Spectrum ( GNonFlat ) 1.5 dB Received Power (during a pulse) ( PR = PT + L – GNonFlat ) -77.78 Processing Gain of a Symbol Over A Single Pulse ( GProcess= 10log(2048) )

33.11 dB

Received Power in a Symbol ( Psymbol = PRX + GProcess ) -44.67 dBm Thermal Noise Floor ( N ) -174 dBm/Hz Rx Front-end Noise Figure ( NF ) 7 dB 3dB Bandwidth Of The Rx Baseband Filter 805 MHz Noise Power In Band ( PN = N + NF + 20log(805) ) -77.94 dBm SNR On A Per Symbol Basis ( SNR = Psymbol - PN ) 33.27 dBm Required S/N For Reliable Acquisition (S) 12 dB Implementation Loss ( I ) 3 dB Extra Environmental Noise Over The Thermal AWGN ( IInt ) 14 dB Link Margin ( M = SNR – S – I – IInt ) 4.3 dB

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Conclusion

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