1 11/24/2008

Ultra-WideBand (UWB)

2 11/24/2008

Not to be confused with Ultra Mobile Broadband

(UMB) from Qualcomm!!!

Word of caution

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Recap

• Short range transmissiono High directivityo Low powero Large bandwidth

• Wireless Personal Area Networkso Range l imited to ~ 10 mo Ad-hoc networks - infrastructurelesso Wheel-and-Spoke piconet topologyo Master-Slave and “anchored” P2P communication

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Recap

• Mult iple “open” standards for different app scenarioso Wireless USBo IEEE802.15.3ao Ecma368

• Mult iple stakeholderso WiMedia/MBO All ianceo ECMAo UWB – IEEE802.15.3x WG and WUSB Forumo WiHD Forumo Wireless HDMI Forumo Sony Corporation (TransferJet)

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Recap

• RF bandwidth allocationso Licensed vs. unlicensed spectrum

• Applicationso HDTVo HD Audioo IPTV

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Recap

• Operational l imitso Unlicensed usage

• FCC mandates “Do no evil, tolerate all evil”• Devices using unlicensed spectrum

o Must be able to “coexist” in an “uncontrol led” environment

o Must not “interfere” with the operation of devices operating on l icensed spectrum

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UWB - Basics

• First bandwidth allocation by the FCC in 2002• 10 dB bandwidth > 500 MHz = “Ultra-Wide

Band”• Typical bandwidth of >= 7.5 GHz

o FCC mandates 3.1 – 10.6 GHz band• Severe power restrict ions

o FCC mandates <= -41 dBm/Hz EIRPo “Narrow Band” wireless consumer devices do not

“accumulate” enough interference within their operational bandwidth l imits

o Short range (SR) and Close Proximity (CP) communications

8 11/24/2008

UWB - Basics

• Competing proposals (current)o Multiband OFDM-UWB from the Multiband OFDM

All iance (MBOA) Supported by WiMedia All iance

o Direct Sequence-UWB from the UWB Forum Almost defunct

• Advantages of MB-OFDMo More robust to multipatho Easier spectrum sculptingo Less prone to interference

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Approaches to UWB

• Tradeoff between total power and bandwidtho Either have very high power and operate on narrow

bandso Or, have very low power and operate over very large

bandwidths

2 5 10 f (GHz)

PSD (Watts/Hz)Noise Floor

WLAN IEEE 802.11a

UMTS 3GPP UWB

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Common Platform

IEEE 802.15.3x Architecture

IEEE 802.15.3a UWB PHY

IEEE 802.15.3 UWB MAC

Convergence Layer

Wireless USB

Bluetooth 3.0

Non IP P2P (Wireless Firewire)IP (UPnP)

MB-OFDM All iance

WiMedia All iance

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Power Management

• Power depends on several factorso Digital modulation used (QPSK)o ADC/DAC resolutiono Internal resolution of the FFT

All values are for 90 nm fab process

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Tradit ional UWB

• Time Modulated UWB (TM-UWB)• Gaussian Monocycle is the basis function

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Tradit ional UWB

• Frequency domain representation – “ the Ultra Wide Band” spectrum

3.2 GHz

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Tradit ional UWB

• Data is modulated onto a Gaussian monocycle pulse traino Pulse Position Modulation (PPM)o Pulse Time Modulation (PTM)

• Zero-IF modulation requires no intermediate up/down conversion to RFo Homodyne receiver architecture makes design

simpler

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Modern Approaches to UWB

• Mult i-carrier OFDM (tradit ional OFDM)o IEEE802.15.3a

• Single carrier Direct Sequence-UWB (DS-UWB) based on 16-f inger RAKE receivero IEEE802.15.3a

• Mult i-Band OFDMo 528 MHz sub-channelso Supported by the WiMedia/MBO All iance

• Single carrier Direct Sequence-UWB (DS-UWB) based on M-ary bi-orthogonal keying (MBOK)

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DS-UWB

• DS-UWBo Single Carriero 1368 MHz chip rateo 16-finger RAKE receiver

• Indoor environments are highly dispersiveo RMS delay spread ranges from 14 ns to 25 ns

• To boost the received signal, receivers collect signal energy from as many delayed “copies” of the signal as possibleo Larger number of RAKE fingers required

• Larger Inter-Symbol Interference (ISI)

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MB-OFDM

• Mult i Band-Orthogonal Frequency Division Mult iplexing

• MBOA stipulates 5 channelso 5 channels for a 7.5 GHz UWBo Channels 1-4 have 3 sub-bands each; Channel 5 has

2 sub-bandso Each sub-band = 528 MHzo One OFDM symbol (with 128 sub-carriers)

transmitted in one t ime slot per channel

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MB-OFDM

One OFDM symbol

128 sub-carriersOne channel = 528 MHz

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MB-OFDM

• Time-Frequency Codingo 1-3-2 shown earlier

• Guard Interval (GI) to switch between channelso 9.5 ns

• Cyclic Prefixing to reduce the complexity of the Rx circuitryo 60.6 nso Simple multipl ication operations instead of Shift-

Mult iply-Add in frequency domain

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MB-OFDM

• Larger GI and CP values contribute to system latency and redundancy

• Shorter GI complicates channel switching hardware circuitry

• Larger CP increases overhead but also increases the “accumulated” mult ipath signal strengtho CP duration should be in direct proportion to delay

spread• Mult ipath signals not “accumulated” manifests

as Inter-Channel Interference (ICI)• Zero Prefixing (ZP) may also be used

o Larger latency but less spectral leakage

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MB-OFDM

• WiMedia/MBO All iance has effectively won the contest (as of 2007!!)

• Advantages of using Mult i Band approach over DS-UWBo Higher spectral eff iciency inherent in OFDMo Resil ience to RF interferenceo Robustness to multipath effectso Proven technology in indoor

environments(IEEE802.11a/g)

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UWB PHY

Scrambler Convolutional Encoder

Puncturer

Interleaver

Constel lation Mapper

IFFT

Insert Pi lot Carriers

Insert CP and GIDAC

Time Frequency Kernel

fc

100 data points

12 points

10 points + 6 nulls

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UWB MAC

• Data is requested using Information Elements (IE)

• Actual data is sent in the form of bursts of MAC Protocol Data Units (MPDU)

• Priorit ized Channel Access (PCA)o Based on Enhanced Distributed Channel Access

(EDCA) used by IEEE802.11xo Util izes Carrier Sense Multiple Access/Coll ision

Avoidance (CSMA/CA)• Distributed Reservation Protocol (DRP)

o “Coll ision Free” channel access

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UWB MAC

• PCA

AIFS

Slot Time

MIFS

SIFS

Burst Ack

Data burst

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UWB MAC PCA

• Short InterFrame Space (SIFS)o At the end of a MPDU

• Minimum InterFrame Space (MIFS)o In between 2 consecutive burst frames

• Soft Reservation policyo Inferior QoS

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UWB MAC DRP

• 1 Super Frame = 256 Medium Access Slots (MAS)o 1 MAS = 256 µs

• Each SF begins with a Beacon Period (BP)o 1 BP = n MAS (n < 256)

• At the end of BP, Data Transfer Period (DTP) is sento DTP contains actual data payloado 1 DTP = (256-n) MAS

• Beacons are used for synchronization, device discovery, sleep mode operation and reservation request

• Hard Reservation policyo Higher QoS applications

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THANK YOU