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MB UWB Overview

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    AN OVERVIEW OF MB-UWB OFDM

    S Ali Ghorashi, Ben Allen, Mohammad Ghavami, A. Hamid Aghvami

    Centre for Telecommunications Research, King's College London

    [email protected] k

    INTRODUCTION

    In Fehrualy 2002, the-FCC allowed.3.1GHz to 10.6GHz for use by Ultra Wide Band (UW B) devices. Thisruling has generated lots of interest in developingUWB communication systems. UWB technology ishighly anticipated because it provides the WirelessPersonal Area Network (WPAN) connectivity ofBluetooth, but at speeds of up to 500 times fasterorpossibly even more. With this technologythe energy isspread across an extremely large bandwidth to insurethat the presence of the transmitted signal is virtuallyundetectable by traditional frequency-selective radioreceivers. Other applications include: radar, sensornetworks, hio-medical imaging. This paper focuses onWPAN applications.

    UWB systems can be divided into two groups: singlehand and multi-band. Candidate single hand systemsare: time-hopping spread spectrum impulse radio(TH-UWB) and direct sequence spread-spectrum impulseradio (DS-UWB). In TH-UWB, the time when pulsesare transmitted is determined based on a pseudorandomsequence, while in DS-UWB, a pseudorandomsequence is used to spread the information bits whichare continuously transmitted. In multi-band UWB, the

    spectrum is divided into several sub bands. One strongUWB candidate employs orthogonal frequencydivision multiplexing (OFD M) together w ith frequencyhopping between each suh-hand. Signals aretransmitted in each band with sufficient time intervaltominimise the inter symbol interference. This is termedmulti-band OFDM (MB-OFDM).

    Two main proposals are being introduced to theIEEE 802.15.3a standardisation committee forWPANs, which is charged with finalisinga standardfor short range, high data rate applications. The twoproposals include the Multi-Band-OFDM Alliance(MBOA) [I], ed by Intel Corp., andthe double-bandscheme proposed by XtremeSpectrum group, led byMotorola Inc.. The multi-band approach would dividethe 7.5 GHz of spectrum into several smaller sub-hands, that would he added or dropped depending uponthe interference from or to) other systems [2,3]. Thesecond approach is based upon the D S-CDMA systemwhich splits the hand intotwo sub-hands (low band:3.1 to 5.15 GHz and high hand: 5.825 to 10.6GHz).This activity is lead by Motorola. Till May2004 MB-OFDM proposal has not yet achieved the necessaly75% votes to he approved. This paper presents anoverview of the UWB-OFD M proposal.

    MULTI-BAND OFDM M B OFDM)

    In MB-OFD M the spectrum between 3.1to 10.6 GHzis divided into 14 bands that are 528 MHz (Fig.1). Thethree lower hands are used for standard operation(mandatory) and the rest of the bands are allocated foroptional use or future expansions since propagationloss severely limits signals at higher frequencies [4].Information is transmitted using Orthogonal FrequencyDivision multiplexing (OFDM) modulation on eachband and different Time-Frequency Codes (frequencyhopping patterns) are utilised for channelisation.

    One OFDM symbol hasa duration of 312.5 ns and abandwidth of 528 MHz. The proposed UWB systemuses a total of 122 sub-carriers that are modulatedusing quadrature phase shift keying (QPSK). In thetransmitter a 128-point IFFT is used.100 sub-carriersare allocated to data, 12 sub-carriesare allocated topilot for channel estimation and 10 sub-carriers areallocated to guard interval which provides sufficienttime for switching between bands. The rest ofthe sub-carriers, 62 to 66 and the0 (DC) input, are setto zeroA 60.6111s cyclic prefix du ration pro vide s robustn essagainst multi-path. The proposed physical layer UW Bsupports data ratesof 80 110, 160,200 , 320, and 480

    Mhps where the support for transmitting and receivingat data rates of 5 5 110, and 200 Mbps is mandatoly.Forward error correction coding (convolutionalcoding) is used with a coding rate of 11/32,112, 5/8and 3/4.

    Multiple access is achieved by utilising differentpreambles and Time-Frequency Codes (TFC) fordifferent UWB users. As an example, when a UWBpiconet uses theTFC of [I 3 2 1 3 21, it means that forthat user the first OFDM symboli s sent on both bands1 and 3, the second OFDM symbol is repeated onbands 2 and 1 and the informationin the third OFDMsymhol is sent on hands 3 and 2. This time domainspreading operates for data rates of 55,80 I IO 160and 200 Mhps. Four TFCs per hand group ( l- 4) andtwo TFCs per hand group( 5) allows fora total of 18(4x4+2) piconets to simultaneously operate (Table1).The transmitter structure is shownin Fig. 2.

    MB - OFDM ADVANTAGES

    The multi-band design of MB-OFDM allows thetechnology to cope with local regulations bydynamically turning off some hands to comply withlocal rules of operation on allocated spectrum. In

    2004 The Institution of Electrical EngineersPrin ted and publ ished by theIEE, Michael F a r a d a y House, Six Hills Wa y, S t e v e n a g e , Herts SG1 2AY, UK

    Authorized licensed use limited to: University of Waterloo. Downloaded on March 14, 2009 at 17:51 from IEEE Xplore. Restrictions apply.

    mailto:[email protected]:[email protected]
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    addition, the proposal also allows good coexistencewith narrowband systems (Fig. 3). For example there isthe flexibility to avoid group band 2 when and ifUnlicensed-National Information Infrastructureinterference, such as from IEEE 802.11a WLANs, is

    present. The low in-band and out-of-band emissionlimits ruled by FCC (or European organizations suchas ETSI ERM TG31A which is working towardsthestandardization of the UWB technology) ensure thatUWB devices do not cause harmful interference tolicensed services and other radio operators such ascellular, PCS, GPS, 802.11a, satellite radio andterrestrial radio.

    OFDM, which allows for each UWB suh-band to bedivided into a set of orthogonal narrowband channels(with much larger symbol period duration),successfully reduces the effects o ISI. This robustmultipath tolerance comes at the price of increased

    transceiver complexity (compared to impulse radioarchitecture), the need to combat inter-carrierinterference (ICI), and tighter linear constraint onamplifying circuit elements. The key signal-processingblock in OFDM (the FFTOFFT) has been showntorequire around50K gates, which contribute only a verysmall area to the total silicon real estate[ 5 ] Otheradvantages of the proposed MB-OFDM include lowcost, high data rate, good quality of service, low powerconsumption, capability to be mesh networked, copewith ad-hoc decentralized environment, adaptationtodifferent regulatory environments and future scalabilityand backward compatibility. It should he noted that802.15.3.a is supposed touses the same media accesscontrol (MAC) layeras IEEE 802.15.3 [6]. However,the MBOA has proclaimed that it will add somefbnctions to the MAC layer. These functions are formobile devices and meshes, where groups of UWBdevices create their own networks on an ad-hoc basisP I .

    COMPARISON WITH OTHERTECHNOLOGIES

    MB-OFDM and impulse radio DS-CDMA proposalsare different in many aspects. An impulse radio systemmitigates the effect of narrow hand interferencethrough the processing gain inherent in a DS-SSsystem with a Rake receiver. In MB-O FDM system the

    band under attack can be dropped, thus, MB-OFDMhas greater flexibility in coexisting with otherinternational wireless systems and future governmentregulators. CDMA impulse radio needs a Rakeequalizer to exploit multipath, while MB-OFDM doesnot require an equalizer in its receiver structure.Impulse radio has more resolvable multipathcomponents becauseof its wider bandwidth; thereforeit needs a more complex receiver with high number ofRake fingers.

    MB-OFDM also has major differences with WiFisystems. MB-OFDM has a much shorter range: upto10 meters versus 3 0.to 60 meters for Wi-Fi. While W i-Fi can supply a higher date rate than Bluetoothtechnology, it still does not deliver sufficient

    performance to effectively allow streaming of multiplesimultaneous high-quality video streams. The wirelessnetworking technologies developed for wirelesslyconnecting PCs, such as Wi-Fi* and Bluetooth*technology, are not optimized for multiple high-bandwidth usage models of the digital home.

    APPLICATIONS

    MB-OFDM UWB technology can.enable high-speedwireless universal serial bus (WU SB) connectivity forPCs and PC peripherals. The USB, with one billionunits in the installed base, is the most. successfulinterface in PC history. Projections are for 3.5 billion

    interfaces shipped by 2006. Wireless USB will buildon the success of wired USB, bringing USBtechnology into the wireless future. Examples includeprinters, scanners, digital projectors, PDAs, DVDs, andexternal storage devices (Fig. 4).It can also replaceIEEE1394 cables between portable multimedia CEdevices, such as camcorders, digital cameras, andportable MP3 players, with wireless connectivity[SICables in next-generation devices, such as 3G cellphones, as w ell as IP/UPnP-based connectivity for thenext generation of IP-based PC/CE/ m obile devices canalso be replaced. These all can be used in wirelesshome connectivity solutions such as video streaming,digital TV, DVDs, Set Top Boxes, PVRs, stereos,camcorders, digital cameras, and other CE devices, aswell as fast downloads of rich content, camera to PC,home gateway to portable device. The aim would bethe replacement of every in-room wire, except thepower cord, by a wireless connection.

    MARKET CONSIDERATIONS

    For MB-OFDM UWB technology to become awidely adopted radio solution, some key issues need tobe resolved such as data rate performance, powerconsumption, co-existence with other w ireless devices,immunity to interference, interoperability, ease ofproduct integration and certification, and globa lspectrum allocation. In May 2004, a MB-OFDM

    transceiver chip UB501 was built with SiGe-BiCMOS technology. It supports a range of data ratesup to 480Mbps in a frequency spectrum between 3.1and 7,4GHz. It has 56-pin package and requires severalpassive components, an off-the-shelf crystal and noexternal power amplifier. It also has fast-switchinggenerator needed to enable rapid switching among theeight MBOA bands the chip supports switch withinseveral nanosecondsto any band of the eight allowedfrom 3.1 to 7.4 GHz [9 ]

    Authorized licensed use limited to: University of Waterloo. Downloaded on March 14, 2009 at 17:51 from IEEE Xplore. Restrictions apply.

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    All actors in UWB expect early versionsof workinghardware and software to become available late thisyear or early 2005, with consumer products appearinglater in that year. The market is expected to grow fromzero to nearly six million UWB nodes embedded in

    various devices by2007, accordin g to tech consultancyIn-StamDR [lo].

    SUMMARY

    This paper has proposed an overview of the MB-OFDM UWB wireless solution. It has been comparedwith other proposals, especially in termsof spectrumco-existence.

    REFERENCES

    http://www.multibandofdm.org

    IEEE P802.15-031268r3, Multi-hand OFDMPhysical Layer Proposal for IEEE 802.15 TaskGroup 3a, March.2004.IEEE 802.15-04/0220rl, Multi-Band OFDMPhysical Layer Proposal Update, Presentation,May. 2004.A Armogida, B Allen, M Ghavami, M Porretta,GManara, H Agbvami, Path Loss Modelling inShort-Range UWB Transmissions, InternationalWorkshop on Ultra Wideband Systems, Oulu,Finland, June 2003.

    5 R. Kolic, Ultra Wideband, the Next-GenerationWireless Connection,htt~:lldevicefor~e.com/articleslAT87 1287040.htmlK. Mandke, H. Nam, L. Yerramneni, TheEvolution of Ultra Wide Band Radiofor WirelessPersonal A rea Networks,h n u : l l w w w. h i ~ h h F r e q u e n c v e l e c t r o n i c s . c o m / A03lHFE0903 TechReuolt.Ddf

    deepens,httu:llnews.zdnet.co.ukicomrnu~1icationslwirelesslO.39O20348.39149350.00.htrn

    high-speed wireless personal area networks, Intelwhite paper,ht to : l lwww. in te l . co~technoloev/u l t rawideban~downloadsNltra-Wideband.udf

    httu:llwww.unstruns.com/docurnent.asu?doc d=50742

    htto:/lnetscaoe.businessweek.comltechnoloev1contentifeb2004ltc20040218 3031 tcl40.htm

    6

    I7. R. Goodwins, Ultrawideband standards split

    8. Ultra-Widehand (UW B) Technology Enabling

    9. Wisair Intros MB-OFDM Chip,

    10. Then T heres UW B, WiM%

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    110

    Emit tedSignalPower

    4 . 2 5 d B m0.056 mW)

    1.6 1.9 2.4 3.1 5 10.6Frequency GHz)

    Figure 3. UW B spectrum and other radio operators

    i Prin teri -PDA-RW/CD-RW-Mass Storaoe . .__Devices-Dig i ta l P ro jecto r

    Access - ------- - _ _a t a lA u d io S can n e r

    Long RangeNetworking/ConnectivityWireless LAM)

    -PCVideo Conference_I

    , Gaming:-P laysta t ion iCamera-Play Station- M P ~layer-Digital camera

    I Flash Card Reader. . . . . . . .

    Wireless LAN

    - - - - Wireless USBFieure 4. Wireless USB scenarios

    Authorized licensed use limited to: University of Waterloo Downloaded on March 14 2009 at 17:51 from IEEE Xplore Restrictions apply