WIRELESS USB: WIMEDIA

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WIRELESS USB WIMEDIA UWB

• Deepak Chellamani
• 2308366
• cdeepak_at_ku.edu
• EECS 766 Technology Presentation
• 05/06/2008

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ABSTRACT

• Wireless USB (WUSB) is a growing short range
  wireless mode of connectivity among devices in
  WPAN. WUSB is rapidly becoming the substitute for
  wired USB without cables. Certified WUSB promoter
  group WiMedia Alliance develop specifications to
  standardize the technology by providing Ultra
  Wideband radio platforms for WUSB
  implementations. This presentation provides a
  descriptive study of WUSB in context of its
  underlying physical and MAC layers, evolution,
  architecture, protocol stack and future prospects
  of the technology.

Wireless USB WiMedia UWB
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OUTLINE

• Introduction
• WiMedia Alliance
• Ultra wideband Technology
• UWB Physical Layer
• MAC Layer
• Higher Layers
• WUSB Architecture
• WUSB Protocol Stack
• Recent Developments and Future prospects
• Conclusion

Wireless USB WiMedia UWB
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INTRODUCTION

• PERSONAL AREA NETWORK
• Network range of few tens of feet
• Generally associated with peripheral and
  hand-held devices
• Operate in close proximity
• Standard - IEEE 802.15
• Bluetooth, ZigBee, USB and IrDA
• WAN devices used in close proximity are
  subjected to interference
• PAN devices used in broad networks become
  infrastructure prohibitive
• As we travel down from WAN to PAN
• The power requirement decreases (from few watts
  to 0.1W)
• The bandwidth requirement increases (from 16kb to
  400Mb)

Wireless USB WiMedia UWB
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WIMEDIA ALLIANCE

• An ISO-published radio platform standard for
  high-speed wireless transmission in UWB
• WiMedia Alliance develop and maintain
• PHY and MAC Layers
• Certifications test
• Design pan radios and protocol stacks by toolkit
  approach
• Sense and prevent collision with higher priority
  transmission is an important issue since these
  devices operate at extremely close proximities
• While sensing Radar signal which has higher
  priority WiMedia device will switch off i.e.
  power level adjusted to -70dBm
• While sensing WiMax devices in following ranges
• Power level adjusted to -80 dBm _at_ 36cm
• Power level adjusted to -70 dBm _at_ 22m
• Ignore if distance gt 22m

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ULTRA WIDEBAND TECHNOLOGY

• A low energy level, short-range large bandwidth
  technology in radio frequency spectrum
• Bandwidth usually gt 500 MHz
• Shannons Law C Blog2(S/N)
• Definition of a UWB transmission signal having
  fractional bandwidth ? gt0.25, where
• fh and fl are highest and lowest frequency
• Energy per frequency band is very small
• Goal of UWB system is to co exist with other
  narrow band wireless transmission systems

Figure 1. Comparison of various coexisting
wireless transmission schemes
From Australian National University
http//www.anu.edu.au/RSISE/teleng/teleng2004/res
earch/uwb.php
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ULTRA WIDEBAND TECHNOLOGY

• Attempt standard IEEE 802.15.3a
• Task group voted to withdraw
• Evolved into WiMedia Alliance
• Faces significant regulatory hurdles
• MultiBand OFDM was popular among the proposals
• FCC specify average power/MHz of spectrum space
• Between 3.1 GHz and 10.7 GHz
• Power level - 43.1 dBm/MHz
• High data rates and exploit vast amount of
  spectrum

Figure 2. Detect and Avoid frequency hop model
for MB OFDM From http//www.extremetech.com/art
icle2/0,1697,2129892,00.asp
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UWB PHYSICAL LAYER

• MB-OFDM technology viewed as combination of
  frequency hopping (FH) and OFDM technologies
• Transmitter
• Series of tones or sine waves at regularly spaced
  frequencies
• Each group has two or three sub-bands each
  having bandwidth of 528MHz (128 4.125 MHz)
• FH preamble patterns are used to differentiate
  simultaneously operating piconets (SOPs)
• Sub carriers used for coherent detection, pilots,
  guard carriers and nulls
• Multi-band OFDM is 165 samples long transmitted
  through a sub-band separated by FH patterns
• Ecma-368 standard specifies a MB-OFDM scheme to
  transmit information
• Frequency, time domain spreading FECs used to
  vary data rates

Figure 3. Multi Band OFDM Transmitter
From "Performance evaluation of MB-OFDM and
DS-UWB systems for wireless personal area
networks" Oh-Soon Shin Ghassemzadeh, S.S.
Greenstein, L.J. Tarokh, V. Div. of Eng. Appl.
Sci., Harvard Univ., MA, USA Proceedings of IEEE
International Conference 2005
Wireless USB WiMedia UWB
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UWB PHYSICAL LAYER

• Receiver takes 128 samples of effective data by
  detaching prefix from the signal
• Null suffix used instead of cyclic suffix to
  prevent ripples in spectrum
• Inter-carrier Interference can be removed by
  cyclic addition
• FFT and QPSK demodulation with channel
  estimation.
• Least square channel estimation assumed in
  absence of ideal channel estimation
• Repetitions are combined using Maximal Ratio
  Combining (MRC)

Figure 4. Receiver for MB OFDM
From "Performance evaluation of MB-OFDM and
DS-UWB systems for wireless personal area
networks" Oh-Soon Shin Ghassemzadeh, S.S.
Greenstein, L.J. Tarokh, V. Div. of Eng. Appl.
Sci., Harvard Univ., MA, USA Proceedings of IEEE
International Conference 2005
Wireless USB WiMedia UWB
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UWB PHYSICAL LAYER

• Direct Sequence UWB
• Two separate bands to prevent interference with
  IEEE 802.11a
• Lower Band (3.1 GHz 4.85 GHz) Higher Band
  ( 6.2 9.7 GHZ)
• U NII Bands ( 5.15- 5.35 GHz and 5.725 5.825
  GHz)
• Each data symbol spread by specific spreading
  code to form a transmit sequence as well as
  offsets in chip rates
• Frame structure similar to MB-OFDM system
• Preamble divided into acquisition sequence, start
  frame delimiter and training sequence
• Transmits data by pulses of energy generated at
  very high data rates

Figure 5. DS UWB Transmitter
From "Performance evaluation of MB-OFDM and
DS-UWB systems for wireless personal area
networks" Oh-Soon Shin Ghassemzadeh,
S.S.Greenstein, L.J.Tarokh, V.Div. of Eng.
Appl. Sci., Harvard Univ., MA, USA Proceedings of
IEEE International Conference 2005
Wireless USB WiMedia UWB
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UWB PHYSICAL LAYER

• Rake Receivers and Chip Matched Filter (CMF)
• Hard decision based Decision Feedback Equalizer
  (DFE) to suppress ISI (tap coefficients depend on
  MMSE)
• Matched Filter Bound
• Soft decision Viterbi Decoding

Figure 6. DS UWB Receiver
From "Performance evaluation of MB-OFDM and
DS-UWB systems for wireless personal area
networks" Oh-Soon Shin Ghassemzadeh,
S.S.Greenstein, L.J.Tarokh, V.Div. of Eng.
Appl. Sci., Harvard Univ., MA, USA Proceedings of
IEEE International Conference 2005
Wireless USB WiMedia UWB
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UWB PHYSICAL LAYER

• A reliable channel model, which captures the
  important characteristics of the channel, is a
  vital prerequisite for system design
• Channel Models
• Rayleigh fading model, Saleh-Valenzuela model,
  ?-K model
• S-V model prevailed
• Multi-path arrivals in clusters rather than in
  continuum
• Four models - based on LOS(0-4m), NLOS (0-4m),
  NLOS (4-10m) and to fit 25ns RMS delay spread
• All models are based on 167 picoseconds sampling
  time
• IEEE 802.15 model is not a stochastic.

CM1
CM2
CM3
CM4
Table 1. Model characteristics for UWB standard
model
From Foerster Channel Models for UWB Personal
Area Networks J.R.Foerster, M.Pendergrass,
A.F.Molisch proceedings of IEEE conference Dec
2003
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UWB PHYSICAL LAYER
PERFORMANCE COMPARISON

• Simulations using MATLAB
• Assumptions
• Quantization effects neglected
• Ideal Channel Estimation
• FER lt 0.08 with 90 probability
• Results show MB-OFDM performs better than DS UWB
• But in case of MFB the trend gets reversed
• At the higher bit rates, MB-OFDM uses less
  coding hence less able to exploit the inherent
  diversity of channel frequency selectivity.
• Due to finite number of taps DS-UWB performance
  is affected by ISI

Table 2. Comparison of Physical Layers
From "Performance evaluation of MB-OFDM and
DS-UWB systems for wireless personal area
networks" Oh-Soon Shin Ghassemzadeh,
S.S.Greenstein, L.J.Tarokh, V.Div. of Eng.
Appl. Sci., Harvard Univ., MA, USA Proceedings of
IEEE International Conference
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MAC LAYER

• The IEEE 802.15.3 network called a piconet
  consists of Piconet Controller (PNC) and devices
  associated with it
• Communications can only be carried out when
  enabled by PNC similar to IEEE 802.11
  infrastructure of centralized control
• Disadvantages
• When PNC disappears it may require several
  seconds before the rest of the devices reorganize
  and re-elect a new PNC
• QoS cannot be sustained
• Centralized TDMA efficiency degrades with
  overlapping piconets
• Lack of coordination
• WiMedia MAC distributed architecture
• Better support in mobility and QoS

Figure 7. IEEE 802.25.3 piconets and potential
interference
From Mobility Support Enhancements for the
WiMedia UWB MAC Protocol Chun-Ting Chou, Javier
del Prado Pavon, and Sai Shankar N proceedings
of IEEE International conference, Oct 2005
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MAC LAYER

• WiMedia MAC protocol all devices perform
  identical functionality using local information
• Time divided into super frames each of duration
  65.536 ms and further divided 256 slots each of
  256 µs
• Superframe contains
• Beacon Period (BP) divided into 85 µs slots and
  extend over one or more MASs
• Data Transfer Period (DTP) Priority Channel
  Access (PCA) or Distributed Reservation Protocol
  (DRP) to access the slots
• Each device transmits a beacon frame during BP
• Provides fast device discovery and
  synchronization
• Provides information for power management
  reservation
• Provides a neighborhood information to remove
  hidden node problem
• Permit spatial re-use of medium

Figure 8. Superframe structure in WiMedia MAC
protocol
From Mobility Support Enhancements for the
WiMedia UWB MAC Protocol Chun-Ting Chou, Javier
del Prado Pavon, and Sai Shankar N proceedings
of IEEE International conference, Oct 2005
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MAC LAYER

• A device may create its own BP with own Beacon
  Period Starting Time (BPST)
• Devices scan for one superframe to prevent
  overlapping between devices in proximity
• If a beacon is received device sends its beacon
  in available slot
• Otherwise creates its own BP
• Information included in BPs are called
  Information Elements (IE)
• Beacon Period Occupancy IE (BPOIE) contains list
  of devices in devices beacon group (BG)
• On reception device records the Device Address of
  transmitter and beacon slot number
• Neighborhood information used to detect
  collisions
• If own address is not found then conclude that
  collision occurred previous superframe
• On repetition the colliding device will change
  its beacon slot
• To minimize the collisions initial scan
  determines the beacon slots for its transmission
• Devices transmit only in that slots till
  collision occurs
• Devices with two hops may use different beacon
  slots to avoid collisions
• In case of more than two hops same beacon slots
  is used thus enabling spatial re-use of beacon
  slots

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MAC LAYER

• Overlapping of superframes due to clock drifting
  or mobility
• Solution Merging two BPs into one BP
• On reception of beacon from device outside BG
  (called alien devices) multiple times, the device
  adjusts its own BPST to relocate its beacon slot
  in new BP
• To ensure unanimous merging the device must
  initiate merger in BPMergerWaitTime 128
  superframes
• By merging WiMedia MAC protocol provides
  mobility support in distributed manner
• Limitations
• Lack of Coordination when device is beyond the
  radio range of alien beacons may result in loss
  of communication
• Enhancements Coordinated Merger and Merger
  weights

Figure 10. Potential Beacon collisions after a
merger of BPs
Figure 9. Merger of two BPs due to Mobility
From Mobility Support Enhancements for the
WiMedia UWB MAC Protocol Chun-Ting Chou, Javier
del Prado Pavon, and Sai Shankar N proceedings
of IEEE International conference, Oct 2005
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HIGHER LAYERS

• The higher layer could be any of following
  Wireless USB, Bluetooth or 1394 (fire wire)
• Focus here on WUSB
• WUSB is a protocol promulgated by the USB-IF that
  uses WiMedia's UWB radio platform
• A logical bus that connects host and devices
  simultaneously
• Motivation
• Ease-of-use
• Port-expansion
• Goals
• Intelligent hosts and behaviorally simple devices
  
• Security as in wired system
• Investment preservation
• Provide effective power management
• Capacity of 480 Mbps _at_ 3 meters and 110 Mbps _at_ 10
  meters range

Figure 11. WiMedia Architecture
From WiMedia UWB Technology, A Reality Press
Event Video (http//www.wimedia.org/en/resources/i
ndex.asp?idres)
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WIRELESS USB - ARCHITECTURE

• USB systems consist of a host and some number of
  devices
• Three definitional areas Host, Interconnect and
  Devices
• Topology connection mode between USB devices and
  host
• USB schedule shared interconnect and scheduled
  to support isochronous data transfers and
  eliminate arbitration overhead

• Hub and spoke model
• Each spoke is a point-to-point connection between
  the host and device
• WUSB hosts can support up to 127 devices
• Due to absence of physical ports port expansion
  is easy
• Host
• USB interface of host computer system Host
  Controller
• Wire Adapters
• Devices can be printers, camera, speakers mass
  storage etc
• Required to carry self information for self ID
  and generic configuration

Figure 12. Wireless USB Topology
Modified from Wireless USB Specifications
Accessed through http//www.usb.org/developers/do
cs/
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WIRELESS USB - ARCHITECTURE

• WUSB logically a polled, TDMA based protocol like
  wired USB
• Packets contain token, data and handshake
• Multiple token information are combined into
  single packet to eliminate costly transactions
• Host indicates the specific time when the
  appropriate devices should either listen (IN) or
  transmit (OUT)
• Data transfer between end points referred to as
  pipe
• WUSB defines new packet sizes for some endpoint
  types to enhance channel efficiency
• AES-128/CCM encryption providing integrity as
  well as encryption

Figure 13. Comparison of Wired USB and WUSB
protocol
From Wireless USB Specifications Accessed
through http//www.usb.org/developers/docs/
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WIRELESS USB - ARCHITECTURE

• Communication topology of WUSB is identical to
  USB 2.0
• Function layer has little or no change only
  difference being isochronous transfer model has
  enhancements to react unreliability of bus layer
• Device Layer has small changes in framework
  extensions for security and management commands
• Bus Layer includes significant changes to provide
  an efficient communication service over wireless
  media
• Host and devices in the range form WUSB cluster
• Physical topology of Wireless USB is a 11 match
  with logical topology familiar to USB
  architecture

Figure 15. Physical topology of WUSB
Figure 14. Data flow Model for WUSB
Modified from Wireless USB Specifications
Accessed through http//www.usb.org/developers/do
cs
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WIRELESS USB - ARCHITECTURE

• WUSB preserves the device endpoint as the
  terminus of communication flow between host and
  device
• All devices must implement at least the Default
  Control Pipe (Endpoint zero) which is a pipe used
  for device initialization and logical device
  management
• WUSB information Exchange methods three
  functional buckets host transmitted,
  asynchronous device transmitted and WUSB
  transaction protocol
• WUSB device notification Time Slots
• Broadcast control information
• WUSB Transactions
• Self Beaconing devices implements full MAC
  layer protocol and manages synchronization
• Device identifies hosts or a cluster member DRP
  IEs based on following keys
• Reservation type field is Private
• Stream index field derived from MAC Header
  Delivery ID field
• DevAddr field set to channel broadcast or hosts
  Cluster ID

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WIRELESS USB PROTOCOL STACK
Figure 19. WUSB Packet format
From Wireless USB Specifications Accessed
through http//www.usb.org/developers/docs/
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WIRELESS USB

• Three basic parts of addressing
• All packet transmissions use same stream index
  field of MAC Layer Header
• Unique device address is assigned in WUSB
  relative to cluster
• Packets which originate or terminate on function
  endpoint must include Application Header

• Several possible states visible to the host or
  internal to devices
• Unconnected not established connection with any
  established communication
• default state on power up, reconnection attempt
  fails, 4-way handshake does not complete
  successfully
• Unauthenticated substate of connected state
  only security messages allowed
• Authenticated normal operating state
• Default
• Address
• Configuration
• Reconnecting on timeouts

Figure 16. States of WUSB
From Wireless USB Specifications Accessed
through http//www.usb.org/developers/docs/
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RECENT DEVELOPMENTS AND FUTURE PROSPECTS

• Main players Agere Systems, HP, Intel, Microsoft
  Corporation, NEC, Philips, Semiconductors and
  Samsung Electronics
• Computer manufactures Lenovo and Fujistu will
• offer CWUSB as an option in their laptops later
• this year
• Barriers to Success
• Keeping cost down and performance up
• Competitions such as from Bluetooth
• Predictions
• In 18 months most laptops will have
• the technology
• In couple of years data rates from
• 2 to 3 Gbps possible
• Lower power consumption for better
• support for mobile devices
• 4 billion USB-enabled devices
• worldwide by 2011 with 503 million,

Figure 18. Stat predictions for WUSB in future
years
From Future of Wireless USB starts now Neal
Leavitt proceedings of IEEE Computer magazine
July 2007
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SCENARIO
Figure 19. BELKIN Wireless USB Hub
From http//catalog.belkin.com/IWCatProductPage.p
rocess?Product_Id377793
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CONCLUSION

• Wireless USB is a fast growing PAN technology,
  its the latest iteration of USB technology, will
  offer the same functionality as standard wired
  USB devices but without the cabling. In this
  presentation its underlying UWB technology along
  with its architecture were visited. As the new
  Wireless USB Promoter Group prepares to develop
  the specifications that will help standardize the
  technology, the industry is planning products
  that can take advantage of the convenience and
  mobility that this new device interconnect will
  offer.

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REFERENCES

• Wireless USB Specifications Accessed through
  http//www.usb.org/developers/docs/
• Performance evaluation of MB-OFDM and DS-UWB
  systems for wireless personal area networks"
  Oh-Soon Shin Ghassemzadeh,S.S. Greenstein, L.J.
  Tarokh, V. Proceedings of IEEE International
  Conference Sep 2005
• Mobility Support Enhancements for the WiMedia
  UWB MAC Protocol Chun-Ting Chou, Javier del
  Prado Pavon, and Sai Shankar N proceedings of
  IEEE International conference, Oct 2005
• Ultra Wideband Radio Technology Kazimierz Siwiak
  and Debra McKeown John Wiley Sons Ltd. Edition
  2004
• WiMedia UWB Technology, A Reality Press Event
  Video Accessed through http//www.wimedia.org/en/r
  esources/index.asp?idres
• Future of Wireless USB starts now Neal Leavitt
  proceedings of IEEE Computer magazine July 2007
  accessed through http//www.leavcom.com/pdf/Wirel
  essUSB.pdf

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REFERENCES

• 7. Channel Models for UWB Personal Area Networks
  J.R.Foerster, M.Pendergrass, A.F.Molisch
  proceedings of IEEE conference Dec 2003
• 8. Intel Corporation Wireless USB The First
  High Speed Personal Wireless Interconnect
• White Paper Intel Developer Forum March
  14, 2004
• http//www.intel.com/technology/ultrawideba
  nd/downloads/wirelessUSB.pdf
• 9. MAC Protocols for Ultra-Wide-Band (UWB)
  Wireless Networks Impact of Channel Acquisition
  Time Jin Ding, Li Zhao, Sirisha R. Medidi and
  Krishna M. Sivalingam
• http//catalog.belkin.com/IWCatProductPage.process
  ?Product_Id377793
• http//www.extremetech.com/article2/0,1697,2129892
  ,00.asp
• Wikipedia Article Ultra-wideband.
  http//en.wikipedia.org/wiki/Ultra-wideband
• http//www.extremetech.com/article2/0,1697,2129892
  ,00.asp
• http//www.anu.edu.au/RSISE/teleng/teleng2004/rese
  arch/uwb.php

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