May 6, 2008 - WIRELESS USB: WIMEDIA® UWB-Deepak Chellamani

University of Kansas | School of Engineering

Department of Electrical Engineering and Computer Science

WIRELESS USB: WIMEDIA® UWB

Deepak Chellamani2308366

[email protected] 766 Technology Presentation

05/06/2008



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.

2Wireless USB: WiMedia® UWB



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




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)




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 @ 36cm • Power level adjusted to -70 dBm @ 22m • Ignore if distance > 22m




• A low energy level, short-range & large bandwidth technology in radio frequency spectrum

• Bandwidth usually > 500 MHz

• Shannon’s Law C ≈ Blog2(S/N)

• Definition of a UWB transmission – signal having fractional bandwidth η >0.25, 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

ULTRA WIDEBAND TECHNOLOGY

From: Australian National University “http://www.anu.edu.au/RSISE/teleng/teleng2004/research/uwb.php”

lh

lh

ff

ff

)(2

Figure 1. Comparison of various coexisting wireless transmission schemes




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/article2/0,1697,2129892,00.asp




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

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

Figure 3. Multi Band OFDM Transmitter




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)

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

Figure 4. Receiver for MB OFDM




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

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

Figure 5. DS UWB Transmitter




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

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

Figure 6. DS UWB Receiver




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, Δ-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




UWB PHYSICAL LAYER

• Simulations using MATLAB

• Assumptions:

• Quantization effects neglected

• Ideal Channel Estimation

• FER < 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

PERFORMANCE COMPARISON

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

Table 2. Comparison of Physical Layers

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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


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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 device’s 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




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 9. Merger of two BPs due to Mobility Figure 10. Potential Beacon collisions after a merger of BPs





• 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 @ 3 meters and 110 Mbps @ 10 meters range

HIGHER LAYERS


From: WiMedia UWB Technology, A Reality – Press Event Video (http://www.wimedia.org/en/resources/index.asp?id=res”)

Figure 11. WiMedia Architecture



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

Modified from: Wireless USB Specifications Accessed through “http://www.usb.org/developers/docs/”

Wireless USB

Device

Wireless USB

Device

Wireless USB

Device

Wireless USB

Device

Wireless USB

Device

Wireless USB

Device

Wireless USB

Device

Wirekess USB Host

Figure 12. Wireless USB Topology





• 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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• 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 1:1 match with logical topology familiar to USB architecture

Figure 14. Data flow Model for WUSBFigure 15. Physical topology of WUSB

Modified from: Wireless USB Specifications Accessed through “http://www.usb.org/developers/docs

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• 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 host’s 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 host’s Cluster ID

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WIRELESS USB – PROTOCOL STACK

Figure 19. WUSB Packet format





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





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, or 12.6 % using WUSB This year out of 2.5 billion USB devices

only 3 million, or 0.1 percent will be WUSB-enabled.

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




Figure 19. BELKIN Wireless USB Hub

From: http://catalog.belkin.com/IWCatProductPage.process?Product_Id=377793#

SCENARIO




CONCLUSION

Wireless USB is a fast growing PAN technology, it’s 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

1. Wireless USB Specifications Accessed through http://www.usb.org/developers/docs/

2. “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

3. “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

4. Ultra Wideband Radio Technology Kazimierz Siwiak and Debra McKeown John Wiley & Sons Ltd. Edition 2004

5. WiMedia UWB Technology, A Reality – Press Event Video Accessed through http://www.wimedia.org/en/resources/index.asp?id=res

6. Future of Wireless USB starts now Neal Leavitt proceedings of IEEE Computer magazine July 2007 accessed through http://www.leavcom.com/pdf/WirelessUSB.pdf




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/ultrawideband/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

10. http://catalog.belkin.com/IWCatProductPage.process?Product_Id=377793#

11. http://www.extremetech.com/article2/0,1697,2129892,00.asp

12. Wikipedia Article: “Ultra-wideband.” http://en.wikipedia.org/wiki/Ultra-wideband

13. http://www.extremetech.com/article2/0,1697,2129892,00.asp

14. http://www.anu.edu.au/RSISE/teleng/teleng2004/research/uwb.php


May 6, 2008 - WIRELESS USB: WIMEDIA® UWB-Deepak Chellamani

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