ULTRA WIDEBAND Soo-Young Chang

TABLE OF CONTENTS Introduction Mathematical backgrounds Channel characteristics Optimal baseband waveforms Modulation schemes Multiple access techniques Detection Synchronization Antenna Transmitter structure Receiver structure MAC layer UWB networking Performance evaluation Future research issues

INTRODUCTON

DEFINITION Bandwidth more than 20% of carrier frequency or more than 0.5 GHz (defined by FCC) Very short duration pulses less than a few nsec transmitted – typically less than 1 nsec

UWB RADIO Impulse Time domain Non-sinusoidal Baseband Video pulse Carrierless Carrier-free Super wideband Ultrahigh resolution

HISTORY Radar history

ULTIMATE GOAL OF WIRELESS COMM. Goal of Generic wireless Amount of information: a lot of data Range: very far Data rate: very fast No. of users: for many users Real time: all at once Trend: short range wireless: favor for freq reuse UWB Amount of information: a lot of data Range: very small Data rate: very fast No. of users: for many users Real time: all at once + wired infrastructure: growth of high- speed wired

UWB BASIC CHARACTERISTICS Ultra wide Bandwidth Energy bandwidth (B E ) Percent bandwidth: contains 99% power Proportional bandwidth Time-bandwidth product (TB): for practical example, IS-95 has around 0.5, and for CDMA2000 and WCDMA numbers between 0.5 and 1.0 are proposed Fractional bandwidth Relative bandwidth Narrowband: conventional comm wideband: 3G cellular technology ultra wideband: wide bandwidth and carrierless

UWB BASIC CHARACTERISTICS High spatial capacity: bits/sec/m 2 Low power portable device needed b Bluetooth a UWB range (m) BW (MHz) data rate (Mbps) spatial cap (b/s/m 2 )1,000 30,000 83,000 2,000,000 All systems are bounded by the channel capacity which says that the capacity increases linearly with bandwidth but only logarithmically with S/N.  None can not reach the speed of UWB. C = B log (1 + S/N)

UWB BASIC CHARACTERISTICS Relatively simple in transceiver architecture Transmitter: pulse generator + antenna Receiver: antenna + LNA + receiver (matched filter or correlator) + detector no power amp, no transmit filter, no VCO, no mixer, no PLL, no ref osc. etc Low cost and power consumption Simple hardware entails low cost Due to low semiconductor cost and power consumption for signal processing : makes UWB technology practical

UWB BASIC CHARACTERISTICS LOW PROBABILITY OF INTERCEPT (LOI)

CHARACTERISTICS FOR UWB COMM. Very low power level below kT thermal noise level < 10uW average transmit power Short duration pulse less than 1 nsec Ultra wide bandwidth larger than 20% of carrier frequency High data rate achieved higher than 110 Mbps High processing gain: the ratio of the RF bandwidth of the signal to the information bandwidth of the signal For ex., 7.5 GHz channel bandwidth with 100 MHz information bandwidth has a processing gain of 75. The duty cycle of the transmission of 1 % yields a processing gain of 100 (20 dB) Low probability of intercept and detection Low-cost digital signal processing hardware is often used in modern digital radios to generate several modulation methods: These systems can step down the information density in their signal to serve users at greater distances (range) A UWB radio can use several pulses to send one information bit thereby increasing SNR in the receiver: Under software control, the UWB system can dynamically trade date rate, power consumption, and range. Enable the power constrained portable computing applications of the future.

ADVANTAGES OF UWB OVER NARROWBAND Potential advantages Low cost, low power: simple implementation Carrierless, direct baseband signal Low duty cycle operation Potential for high capacity: high throughput Large effective processing gain Share the spectrum with many users Low noise power spectral density Improved co-existence Ideally no frequency planning Good propagation quantities Multipath resistant, cm location High penetration (high BW, low freq.) Fine time resolution Potential issues Regulatory Limits, thresholds, bands Noise aggregation issues Wireless internet connectivity issues Lack of standards In development, but lengthy process Utility not clear in all cases Performance and implementation Synch., jitter, sampling, etc. Susceptibility to interference Short range (a few meters to a few km) Low power direct pulse operation Low antenna transmit efficiency (BW-1/QF) Amount of digital computation

UWB vs SPREAD SPECTRUM Both tech for spectrum spread Direct sequence Frequency hopping Pulsed-FM or chirp Time hopping

CHALLENGES FOR UWB REALIZATION Regulatory issues Finding a way to make the technology legal without causing unacceptable interference to other users that share the same frequency bands Power efficient and low cost implementation Fulfillment of spectral mask, but full exploitation of allowed power: Interference suppression Technique which adaptively suppress interference from other systems

CHALLENGES IN TECHNICAL AREAS Susceptible to being unintentionally jammed by traditional narrowband transmitter Filter matching accuracy [FOER01] Extreme antenna bandwidth requirements Accurate timing synchronization for a correlated- based receiver due to short pulse durations Amount of energy in the multipath components caused by reflections in the channel: Rake receiver is a candidate Noise from on-board microcontroller

GOALS FOR UWB IMPLEMENTATION Fulfillment of spectral mask, but full exploitation of allowed power. Interference suppression Cheap implementation Robustness to multipath Scalability

UWB PHY LAYER COMPONENTS Transmitter Source coding / channel coding Pulse generation Code sequence generation for multiple access Modulation Power control Antenna Receiver Low noise amplifier Synchronization detection Demodulation Cross correlation detection (using template) or matched filtering Channel decoding / source decoding

UWB MAC LAYER COMPONETS Initially MAC protocol is to be applied. UWB MAC questions Are standard MAC protocols applicable to UWB (e.g., and b)? What, if any, UWB specific features may be required within the MAC? Can the UWB MAC facilitate co-existence with other systems (e.g., WLAN and )? MAC design considerations Scalability of personal operating space based on UWB localization Improved co-existence with other systems Reduced power consumption Scalability in terms of range and throughput trades PRF and peak power can vary inversely providing for constant average power This enables signaling of different data rates on a per packet or link basis based on the range [FOER] Synchronization of received packets at different receivers Receivers in a multicast network based on UWB localization [FOER]

UWB APPLICATIONS Radar Passive target identification Target imaging and discrimination Signal concealment from electronic warfare and anti-radiation missile Detection or remote sensing Ground penetration radar Locating Communications

UWB APPLICATIONS FOR COMM Home Entertainment Proximity detectors Tracking Industrial Automotive Military Law enforcement/rescue

FCC ACTIVITIES NOI (Notice of Interest): Sep Ask feedback from the industry regarding the possibility of allowing UWB emission on an unlicensed basis following power restrictions described in the FCC Part 15 rules. More than 500 comments have been filed. P = E 2 4 R 2 / whereP: emitted power (W) E: electric field strength (V/m) R: radius of the sphere (m) : characteristic impedance of a vacuum (=377 ohms) NPRM (Notice of Proposed Rule Making): May 2002 Ask feedback from the industry on specific rule changes that could allow UWB emitters under the Part 15 rules. First R&O (Report and Order): Feb Frequency assignments: 3.1 – 10.6 GHz Frequency mask: indoor and outdoor

FCC MASK Factors which affect how UWB impacts other narrowband systems Separation between the devices Channel propagation losses Duty cycle Modulation techniques Pulse repetition frequency (PRF) employed by the UWB system Receiver antenna gain of the narrowband receiver in the direction of UWB transmitter Three types of UWB devices Imaging systems (medical, surveillance, ground penetrating radar) which may operate either below 960 MHz or between 1.99 and 10 GHz Vehicular radar systems (above GHz) Communications and measurements systems restricted to Indoor networks or hand-held devices working on a peer-to-peer basis Operating between 3.1 to 10.6 GHz, FCC 15 rules applied (limits) FCC mask ETSI limits are expected to be similar [SORENSEN]

FCC MASK (cont ’ d)

FCC FREQUENCY ASSIGNMENT Feb Assigned frequency band of GHz :7.5 GHz Bandwidth To be deployed on an unlicensed basis following the Part rules for radiated emissions of intentional radiators With frequency mask which constrains the transmit power

OPPONENTS Airlines GPS Cell phone companies Department of Defense Baby monitor companies

IEEE802 STANDARD ACTIVITIES IEEE802: standards for LAN/MAN IEEE802.15: WPAN (Wireless Personal Area Networks) Deals with short range comm. Including Bluetooth IEEE : high rate short range communications up to 55 Mbps IEEE a: task group for alternate PHY for high rate short range communications higher than 110 Mbps IEEE802.18: coexistence between wireless applications: currently study coexistence between & a

IEEE a For alternate PHY for high rate WPAN ( ) Date rate: Higher than 110 Mbps up to 480 Mbps (possibly 1 Gbps) Key Applications: multimedia and imaging PHY: UWB MAC: modified IEEE15.3 MAC Became a formal task group (TG) in Jan Leading companies: XtremeSpectrum (Motorola), Time Domain, General Atomics, Intel, Texas Instruments, CRL (Japan), STMicronics (Switzerland), etc

a STANDARD ACTIVITIES PHY requirements Low power consumption Small form factor MAC requirements Modified high rate MAC Target applications indoor application for short range less than 10 m Coexistence with other narrowband systems: x, , Bluetooth, HomeRF, HyperLAN, GPS, PCS, future satellite, etc

a TARGET APPLICATIONS Short range indoor comm. Up to 10 m range Video and imaging applications: digital camera, DVD, MP3, video streaming, etc

a TECHNICAL REQUIREMENTS

IEEE AND RELATED ORGANIZATIONS

BLUETOOTH (IEEE )

ZIGBEE (IEEE ) Low rate wireless personal area networks (LR-WPAN) in residential and industrial environments Connectivity among inexpensive fixed, portable, moving devices Other home networking attempts: wired and wireless HomePNA Homeplug Powerline Alliance CEA R-7 HomeRF Echonet Wireless for home networking: reduction in installation cost Internet connectivity Multi-PC connectivity Audio/video networking Home automation Energy conservation Security Relaxed throughput requirements for home automation, security, and gaming Eliminate complexity of heavy protocol stacks Needs power consumption Eliminate to utilize too many computational resources

ZIGBEE (IEEE ) Key features Low throughput: 250 Kbps Low cost: module cost estimated >$2 Ultra low complexity Low installation cost Low power consumption: last between 6 months and 2 years with AA batteries according to applications Bluetooth and IEEE High throughput Zigbee and IEEE IEEE Define PHY and MAC layer specifications Zigbee Define application profiles and interoperability Products availability Initial release of IEEE standard First integrated circuits to implement draft standard: early 2003 First Zigbee embedded products : Q3 2003

ZIGBEE (IEEE ) Applications Industrial control and monitoring Public safety Sensing and location determination at disaster sites Automotive sensing Tire pressure monitoring Smart badges and tags Precision agriculture Sensing of soil moisture, pesticide, herbicide, and pH levels Home automation and networking PC peripherals: wireless mice, keyboards, joysticks, low-end PDA ’ s, and games Consumer electronics; Radio, TV, VCR ’ s, CD ’ s, DVD ’ s, remote controls Home automation: heating, ventilation, and air conditioning (HVAC), security, lighting, and control of objects such as curtains, windows, doors, and locks Health monitoring: sensors, monitors, and diagnostics Toys and games: PC-enhanced toys and interactive gaming between individuals and groups propertyrange Raw data rate868 MHz: 20 Kbps 915 MHz: 40 Kbps 2.4 GHz: 250 KHz range10-30 m latency15 ms for PC peripherals; 100 ms for home automation applications Channels868 MHz: 1 channel 915 MHz: 10 channels 2.4 GHz: 16 channels Frequency bandTwo PHY ’ s: 868MHz/915MHz and 2.4GHz addressingShort 8-bit or 64-bit IEEE Channel accessCSMA-CA and slotted CSMA- CA temperatureIndustrial temperature range -40 to +85 C Technical parameters

ZIGBEE (IEEE ) Network topology Star network Peer-to-peer network (mesh network) PAN cordinator User device

ZIGBEE (IEEE ) IEEE /915 MHZ Physical layer IEEE GHZ Physical layer Data link layer Network layer Upper layers IEEE MAC layer SSCS IEEE802.2 LLC type 1 Other LLC Zigbee spec

UWB vs x vs Bluetooth bBluetooth802.11aUWB Range(m) Bandwidth(MHz) Data rate (Mbps) Spatial capacity (b/s/m 2 ) ,00083,0002,000,000 modulationGFSKPPM/PAM/ biphase/s pectral keying Transmit power (mW) 10.01

IEEE a vs WiMedia

IEEE a vs IEEE

UWB RELATED INDUSTRIES XtremeSpectrum Time Domain General Atomics AetherWire & Location Multispectral Solutions (MSSI) Pulse-Link Appairent Technologies Pulsicom Staccato communications Intel TI Motorola Perimeter players Sony Fujitsu Philips Mitsubishi Broadcom Sharps Samsung Panasonic

COEXISTENCE Coexistence with other narrowband systems: x, , Bluetooth, HomeRF, HyperLAN, GPS, PCS, future satellite, etc reviews this issue

PRODUCSTS RELEASED XtremeSpectrum Trinity chip set: 2 chips RF + baseband, digital control, MAC Time Domain PulseOn 100: PPM PulseOn 200: PPM and other modulation PulseOn 300: other modulation

GLOBAL INTEREST

ACADEMIA INVOLVED University of Southern California, Ultra Lab Dr. Scholtz: initiated time hopping PPM (TM-PPM) One member of MURI University of California, Berkley, Berkeley Wireless Research Center Mainly interested in ASIC implementation One member of MURI University of Massachusetts Mainly research on antenna One member of MURI University of California, Davis Ohio Stat University Antenna Georgia Tech Antenna Texas A&M antenna Virginia Polytech New Jersey Institute of technology, Center for Telecommunication Mainly interested in transceiver

RELATED ORGANIZATIONS UWB Working Group NTIA published a report analyzing the impact of UWB emissions on GPS and suggested an additional dB attenuation beyond the power limits described in the FCC Part Department of Commerce Department of Defense FCC NIST

MARKET FORECASTS

MATHEMATICAL BACKGROUNDS

OPTIMAL BASEBAND WAVEFORMS

CHANNEL CHARACTERISTICS FOR UWB COMMUCATIONS

UWB CHANNEL MODELING In-door propagation modeling and measurements: propagation and energy transfer Cluster Multipath Path loss model Multipath model

INDOOR CHANNEL MODELING Objective Path loss and multipath charateristics of typical operational environments Help to evaluate the performance of the system Fundamental parameters Path loss Multipath RMS delay spread Power decay profiles Number of path components: number of multipath arrivals considered (e.g., those within 10 dB of the peak multipath arrival Associated thresholds Environment Indoor office and residential Line-of-sight (LOS) and non line-of-sight (NLOS)

INDOOR NARROWBAND CHANNEL MODEL IEEE CHANNEL MODEL Model using an exponentially decaying Rayleigh fading tap delay line (TDL) Assume that each of the channel taps is drawn from an independent complex Gaussian random variable with an average power profile that decay exponentially The probability distribution of the kth tap of the channel impulse response hk

OPTIMIZATIONS OF TRANSIENT WAVEFORMS AND SIGNALS Various solutions for the optimum transmit antenna generator waveform are required to: Maximize receive antenna voltage amplitude (with constrained input energy and bandwidth) Provides the “ sharpest ” received antenna voltage waveform (with constrained input energy and bandwidth) Maximize received energy (with an inequality constrained on the radiated power spectral density) Results are derived for arbitrary antennas Effects of generator and load impedances are included Rigorous EM solutions via moment method Closed-form results for short antennas for some special cases

OPTIMAL BASEBAND WAVEFORMS Gaussian impulse Monocycle Polycycle Doublet others

UWB WAVEFORM IMPLEMENTATION Implementation via active pulse shaping techniques By combining several readily implementable and scaled functions, a good approximation of Gaussian wavelets can be achieved

ONE EXAMPLE (GAUSSIAN PULSE)

ANOTHER EXAMPLE

MULTIPLE ACCESS TECHNIQUES

MULTIPLE ACCESS TECHNIQUE TDMA CDMA FDMA Time hopping random/pseudorandom TH sequence Using orthogonal functions Walsh functions and other functions Analog impulse radio MA receiver (AIRMA) Digital impulse radio MA receiver (DIRMA)

MODULATION SCHEMES Pulse position modulation (PPM) (or Time-modulated) Pulse amplitude modulation (PAM) On-off keying (OOK) Biphase (or BPSK or antipodal) M-ary Spectral Keying (SK)

DETECTION Template Zero crossing detection Correlator using coded sequences: cross- correlation peak calculated Maximal sequence codes Complementary codes Time-integrating correlator Time-domain filtering (matched filtering) Selective Rake receiver

SYNCHRONIZATION Clocks and timing Protocols for synchronization Sync. & Training Sequence Central timing control + timing logic Fast acquisition at receiver [Mitsubishi proposal] template signal and received signal need to be aligned standard method: serial search (chip by chip) but: chip duration very short in UWB, takes long time Block search algorithm For LOS For NLOS Channel estimation needed?

CHANNEL CODING One example [mitsubishi] rate ½ convolutional code; requires 4dB SNR for 10^-5 BER Improvement by 3dB possible by turbo codes

POWER CONTROL To overcome near-far problem of CDMA

EFFICIENT ANTENNA

ANTENNA IN COMMUNICATION SYSTEMS At transmitter Antenna is modeled as a circuit component; real part in it determines the radiated power (for ) Current in the antenna determines E rad At receiver E-field at the Rx is translated to a voltage source By reciprocity theorem, Z ant,rx =Z ant,tx Transmitterreceiver

UWB ANTENNA CONSIDERATIONS Parameters Broadband: Low Q: low selectivity Antenna matching: impedance Gain Polarization Antenna efficiency = P radiated / P applied Directivity Small size VSWR Differentiation effect Antenna can no longer be optimized at the carrier frequency (no carrier in UWB) Frequency-independent antenna is needed Requirements of UWB antenna Two dimensional Omni-directional field pattern Small size Low cost

CHALLENGES IN UWB ANTENNA DESIGN EM aspects of UWB communication systems have not been studied adequately Most of the conventional antenna analyses assume harmonic time dependent (not the case in UWB) Time-domain EM analysis/simulation are needed Issues in UWB antenna design Efficient pulse generation/reception Pulse dispersion problem Matching/ringing problem

SYSTEM DESIGN PERSPECTIVE UWB antenna is not likely to be a purely resistive load and may strongly influence the transmitter circuits Antenna/circuit co-design is necessary Efficient pulse-shape design Taking pulse-shape design into account adds one more dimension to improve the performance of the antenna Pulse generatorbonding wire transmission line antenna

MONOPOLE ANTENNA (1) FREQUENCY RESPONSE:s11 The smaller the s11, the larger the radiation Resonant at f=c/(0.5lamda), which leads to freq. hump Two ways to avoid ringing & flatten the freq. response Make the conductive wire more resistive Shorten the dipole For 6cm monopole, freq. hump at 1.4GHz For 2cm monopole, no freq. hump in 0-3 GHz freq. range

MONOPOLE ANTENNA (2) FAR-ZONE ELECTRIC FIELDS OF THE MONOPOLE When L is much smaller than lamda/e, no ringing happens Radiated energy is decreased, but it ’ s OK sometimes Undetectable UWB system transmits at noise level

MONOPOLE ANTENNA (3) SHORT MONOPOLE: INPUT V/I CHARACTERISTICS The input V/I behavior resembles that as driving a capacitor Radiation is too small ” energy stored in near-field Modeling a 2cm monopole by a pF capacitor Given the same V s & R s, I s in two cases overlap perfectly

MONOPOLE ANTENNA (4) SHORT MONOPOLE: RADIATION The radiated field is the time-derivative of the input current The dimension is small. Phase difference between I(z) at each part is ignorable  quasi-static condition

DIPOLE ANTENNA Consists of two straight wires Simple scheme, easy to analyze, mechanism is well-known Popular in narrowband systems “ hump ” in frequency domain Resistively loaded dipoles exibit very broad BW since reflection on the antenna is suppressed, but Radiation efficiency is reduced Termination is a problem

LOOP ANTENNA Circular turns of wire To meet the 2D geometry spec only 1 turn is used Used for AM radio Radiate normally/axially if the loop is small/large relative to a wavelength A modified version, large current radiator, is adopted by Aether Wire & Location, Inc., an UWB localizer company. Large radiation power can be delivered, but its shape is 3D.

MICROSTRIP ANTENNA Metallic patches sit on a dielectric substrate Usually made on PCB Low profile, conformable to various surface, inexpensive, durable, but narrow-band Modify the shape to broaden the bandwidth, e.g. bowtie antenna antenna patch dielectric substrate ground

UWB ANTENNA The E field strength in UWB systems proportional to the d/dt of the drive current regardless of the waveform: ideal antennas The antenna can perform filtering functions in some cases. txrx antenna  antenna i di/dt d 2 i/dt 2 Key issue Electrically small, adequately efficient antenna design

TPYES OF ANTENNAS Bow-tie Relatively high input impedance Requires a matching balun to make it usable with 50 ohm system Tapered slot Two dimensional microstrip Resister loaded dipole Low gain and low efficiency Diamond dipole: developed by Time Domain Corp. Emits a waveform similar to a Gaussian third derivative 75 % efficiency with about 3:1 VSWR Discone High performance 3-D structure: difficult to manufacture Bicone High performance 3-D structure: difficult to manufacture Log-periodic Spiral Transverse electromagnetic (TEM) horn Most commonly used for UWB radars Relatively high gain Wideband Unidirectional radiation Little distortion

ANTENNA, ONE EXAMPLE One example Time Domain Corp. BroadSpec 102 Planar antenna Smaller than a standard business card Well matched from GHz with max return loss -15 dB and VSWR below 1.5:1 Dipole like pattern with gain 0-3 dBi Impedance 50+j0 ohm Efficiency above 90 %

TRNASMITTER STRUCTURE Antenna Pulse generator Clock generator Control Power control Modulator: switch

RECEIVER STRUCTURE Efficient receiver processing Coherent signal processing Matched filtering Use matched filter with processing gain to improve SNR Analog impulse radio MA receiver (AIRMA) Digital impulse radio MA receiver (DIRMA)

Rake receiver

RECEIVER STRUCTURE Low noise amp Variable gain amp Sample/hold A/D converter Sampling clock generator Pulse generator Template generator

MAC LAYER

UWB NETWORKING (NETEX) Overlapped Piconet Each piconet has one piconet controller (PNC). Intra- and inter-piconet operation Multihop operation to reach far region

PERFORMANCE EVALUATION Interference AWGN Multipath S/N Multiple access performance Multiple user interference calculation for analog impulse radio Throughput QoS Power control

FUTURE RESEARCH ISSUES UWB imaging algorithm Handling on-chip interference Computationally efficient ranging algorithms Interference excision over ultra wide bandwidths UWB node teaming for long-distance transmission Efficient pulse shape design