Ultra Wide-Band Technology

(UWB)By: Mustafa Khaleel

Contents Introduction to UWB Narrowband, Wideband, and Ultra-Wideband UWB Signal Single Band and a Multi Band UWB Modulation Schemes Transceiver Architecture UWB antennas UWB-MIMO Applications Standardization Advantages - Limitations

Ultra Wide Band (UWB) Ultra Wide Band (UWB) is a technology for the transmission data by using techniques which cause a spreading of the

radio energy over a very wide frequency band. with a very low power spectral density. The low power spectral density limits the interference potential with

conventional radio systems (TV, GSM, UMTS, GPS, etc.). and the high bandwidth can allow very high data throughput for communications devices, or high precision for location

and imaging devices. UWB radios can use frequencies from 3.1 GHz to 10.6 GHz in USA and Asia and at least 6.0 to 8.5 GHz in Europe. The Federal Communications Commission in USA (FCC) has defined an UWB device as any device with a –10 dB

fractional bandwidth, greater than 20% or occupying at least 500 MHz of the spectrum Most narrowband systems occupy less than 10% of the center frequency bandwidth, and are transmitted at far greater

power levels. the FCC introduced severe broadcast power restrictions for UWB in order not interference other narrower band systems

nearby, such as 802.11a/g radio.

Narrowband, Wideband, and Ultra-Wideband

We can classify signal as Narrowband, Wideband, and Ultra-wideband by Fractional bandwidth and is defined by the ratio of bandwidth at –10 dB points to center frequency or The fractional bandwidth is defined as the radio of signal bandwidth to the center frequency.The –10 dB point represents the spectral power of a signal at 10 dB lower than its peak power.

Narrowband < 1% Wideband 1% < < 20% Ultra-Wideband > 20%

UWB-Signal

represents the time that the pulse exists and represents the time that the pulse is absent.

And duty cycle is the ratio of the time that a pulse is present to the total transmission time.

UWB systems use carrier less, short-duration (picosecond to nanosecond) pulses with a very low duty cycle (less than 0.5 percent) for transmission and reception of the information.

Low duty cycle offers a very low average transmission power in UWB communications systems. The average transmission power of a UWB system is on the order of microwatts.

the short-duration UWB pulses spread their energy across a wide range of frequencies—from near DC to several gigahertz (GHz)—with very low power spectral density (PSD) in in the frequency domain

UWB-Signal Impulse-radio (IR) UWB ,first systems were that utilized the concept of wideband communication in power limited system. IR UWB offers short duration pulses with fast rise and fall times, which results in wideband spectra. For example, a pulse signal which is centered at 6 GHz and occupies a bandwidth of more than 1.2 GHz (i.e. 20% fractional

bandwidth). These pulses are having very low energy because very low power level is permitted to UWB transmission. to carry the

information of one bit many such pulses are combined. The IR-UWB transceiver system has advantage of simplicity and low cost. A UWB signal can be any one of a variety of wideband signals, such as Gaussian, chirp, wavelet, or Hermite-based short-

duration pulses. Typical pluses Gaussian monocycle, and these pluses the first derivative of a Gaussian pulse and is given by:

where represents time and is a time decay constant that determines the temporal width of the pulse

In Figure above 500-picosecond pulse generates a large bandwidth in the frequency domain with a center frequency of 2 GHz.

the lowest and highest cutoff frequencies at –10 dB are approximately 1.2 GHz and 2.8 GHz, respectively, which lead to a fractional bandwidth of 80 percent; this is much larger than the minimum required by the FCC:

Single Band and Multi BandThe Single Band (Direct-Sequence UWB (DS-UWB)) :

supports the idea of impulse radio that is the original approach to UWB by using narrow pulses that occupy a large portion of the spectrum.

The Multi Band OFDM(MB-OFDM) approach divides the available UWB frequency spectrum (3.1 GHz to 10.6 GHz) into multiple smaller and no overlapping bands with bandwidths greater than 500 MHz .

Direct-sequence UWB is a single-band approach that uses narrow UWB pulses and time-domain signal processing combined with DSSS techniques to transmit and receive information.

The DS-UWB technique is scalable and can achieve data rates in excess of 1 Gbps.

This approach is similar to the narrowband frequency-hopping technique.

offers the advantage of avoiding transmission over certain bands.

UWB Modulation Methods

The modulation methods used in UWB systems are :

Pulse Position Modulation (PPM)On-Off Keying modulation (OOK)Pulse Amplitude Modulation (PAM)Pulse Width Modulation (PWM)

Pulse Position Modulation (PPM) : When the transmitted bit is 0, pulse does not shift. When bit is 1, pulse shift a specific amount δ, where δ is called modulation index.

On-Off Keying modulation (OOK): When the transmitted bit is 1, a pulse is transmitted. When the bit is 0, no pulse is transmitted.

UWB Modulation Methods

UWB Modulation Methods

Pulse Amplitude Modulation (PAM) : When the transmitted bit is 1, a positive pulse is transmitted. When the bit is 0, a negative pulse is transmitted.

Pulse Width Modulation (PWM) : When the transmitted bit is 1, a wide pulse is transmitted. When the bit is 0, a narrow pulse is transmitted.

Transceiver ArchitectureUWB transmission is carrier less, meaning that data is not modulated on a continuous waveform

with a specific carrier frequency, as in narrowband and wideband technologies. Carrier less transmission requires fewer RF components than carrier based transmission.

The UWB transceiver architecture is considerably less complicated than that of the narrowband transceiver. The transmission of low-powered pulses eliminates the need for a power amplifier

There are Several Classes Of Transceivers ,The Coherent Transceivers:

On the transmitter side, the pulse generator has to control the transmitted pulse shape finely and is generally able to handle its polarity.

On the other side, the receiver is able to estimate the composite channel impulse response.

This estimation is then used as a comparison pattern to demodulate the received signal and all modulation schemes can be used.

Correct operation of the transceiver is ensured by a good quality time base on both the transmitter and receiver sides.

The Non-coherent Transceivers It is generally less efficient but more attractive if cost or power consumption Signal detection is based on energy detection performed on the incoming signal. Time base requirements are generally relaxed, allowing the use of low cost oscillators.

Differentially Coherent TransceiversOn the transmit side, a differential modulation scheme is used in order to resolve the resulting bit ambiguity.On the receiver to keep a delayed version of the incoming signal and use it as reference to be compared with the

current signal.

UWB AntennaThe antenna acts as a filter for the generated UWB signal, and only allows those signal components that radiate to

be passed.UWB antennas differ from their narrowband antennas in one basic concept.

In narrowband antennas tuned to particular center frequencies and have relatively narrow bandwidths.In contrast, UWB antenna designs seek much broader bandwidths and require no resonating operation.

UWB antennas should be linear in phase and should have a fixed phase center.

The antenna gain should be smooth across the frequency band in order to avoid dispersion of the transmitted pulse.

The Ringing EffectThe Ringing Effect : after the UWB antenna deform the transmitted signal . the antenna response to a plus

of very short duration, as is typical in UWB , is seen as ripple after the plus . this effect is consequence of the antenna geometry and translates into a frequency dispersion or time delay, which reduces the transmission speed.

To avoid ringing, resistive antennas with low Q-values should be used. The resistive loading will cause the unwanted signal component to die away quickly, leaving a pulse much closer to the desired shape.

where , , and are the center frequency and the upper and lower

The antenna bandwidth can also be increased by making the Q-value small.

the low Q-value implies that the efficiency of a resistive antenna is generally quite poor.

UWB AntennaThere are three types of antenna used with UWB:Base Station Antenna Its used for networks such as high speed data or for low data-rate systems, including location and tracking systems.

The base station antenna may be designed for indoor or outdoor the application.Base station antennas may be either directive or omnidirectional. Directional antennas(radio links) , or

omnidirectional antennas (mobile applications).Portable Antenna :

the antenna is small and low cost . the antenna is omnidirectional. And its can be constructed on a printed circuit board

Antenna Arrays In UWB radar applications, linear and planar antenna arrays may be formed with very sparsely spaced

elements.high resolution phased array antennas, with a beam which may be readily steered.The ratio of the wideband peak side lobe level to the peak main lobe level is a function of the number of

antenna elements rather than the element spacing.

There are several antenna topologies or types that are using in UWB such as horn antenna , Biconical antenna ,Helix antenna ,Bowtie antenna ,spiral antenna.

Antenna Topologies Out-Door Applications

In-Door Applications

Vivaldi antenna suitable Not-suitable1.has a directional radiation pattern.

log periodic and spiral AntennasOperate in the 3.1-10.6 GHz

suitable Not Recommended,1. hey have large physical dimensions.2. severe ringing effect.

planar or printed monopole antenna N/A Suitable.

Vivaldi antenna Spiral and conical spiral antenna

Log-periodic antennaMono-conical and bi-conical antenna

UWB-MIMOWe can using MIMO together with UWB helps in extending the communication range as well as

offers higher link reliability. The benefits of UWB-MIMO can be summarized as following:1. interference mitigation/suppression, 2. higher data rates, 3. improved link quality4. extended coverage, 5. reduced analog hardware requirements, and concurrent localization.

And design specifications for UWB-MIMO antenna :

UWB ApplicationsCommunications Devices. Imaging Devices.Vehicular Radar Systems.For communications devices, the FCC has assigned different emission limits for indoor and outdoor UWB

devices. The spectral mask for outdoor devices is 10 dB lower than that for indoor devices, between1.61 GHz and 3.1 GHz.

Vehicular radar systems are allowed to emit –41.3 dBm/MHz only in them 22 GHz to 29 GHz frequency range. The center frequency of their signal should be higher than 24.075 GHz.

Communications Devices

The high-data-rate capability of UWB systems for short distances has numerous applications for home networking and multimedia-rich communications in the form of WPAN applications. UWB systems couldreplace cables connecting camcorders and VCRs, as well as other consumer electronics applications, such as laptops, DVDs, digital cameras, and portable HDTV monitors. No other available wireless technologies—such as Bluetooth or 802.11a/b—are capable of transferring streaming video.

Radar Systems.Radar is considered one of the most powerful applications of UWB technology. The fine positioning

characteristics of narrow UWB pulses enables them to offer high-resolution radar (within centimeters) for military and civilian applications. Also, because of the very wide frequency spectrum band, UWB signals can easily penetrate various obstacles. This property makes UWB-based ground-penetrating radar (GPR) a useful asset for rescue and disaster recovery teams for detecting survivors buried under rubble in disaster situations.

Summarizes UWB applications in data communications, radar, and localization.

Standardization Wireless Personal Area Networks using UWB as PHY options

IEEE standard of 802.15.3a for high data rateDS-UWB vs. MB-OFDM-UWBProposal with drawn on Jan 2006

IEEE standard of 802.15.4a for low data rateCommunicationsHigh precision ranging and location

Advantages - Limitations

AdvantagesUWB technology has very high potential in real life applications, due to its high bandwidth

and low power.Very interesting application in wireless content transfer, especially for HD videos.Secure transmission, low probability of interception or detection and anti-jam immunity.

LimitationsEmissions below conventional level.Not appropriate for a WAN (Wide Area Network) deployment such as

wireless broadband access.

Thank You!

Reference

1) Advancement in Microstrip Antennas with Recent Applications,Chapter 6,UWB Antennas for Wireless Applications,Osama Haraz and Abdel-Razik Sebak.

2) Linardou, I., Migliaccio, C., Laheurte, J. M., & Papiernik, A. (1997). Twin Vivaldi an tenna fed by coplanar waveguide. ‐ Electron. Lett., 33(22), 1835-1837.

3) Kim, S. G., & Chang, K. (2004). Ultra Wideband Exponentially-Tapered Antipodal Vivaldi Antennas. IEEE Antennas and Propagation Society Symposium, Monterey, CA, June, 3, 2273-2276.

4) Sibille, A. (2005). Compared Performance of UWB Antennas for Time and Frequency Domain Modulation. 28th URSI General Assembly, NewDelhi, India.

5) Licul, S, Noronha, J. A. N., Davis, W. A., Sweeney, D. G., Anderson, C. R., & Bielawa, T. M. (2003). A parametric study of time-domain characteristics of possible UWB an tenna architectures. ‐ IEEE 58th Vehicular Technology Conference, VTC 2003-Fall, Octo ber, 5, 6-9.‐

6) Su, S. W., Wong, K. L., & Tang, C. L. (2004). Ultra-wideband square planar monopole antenna for IEEE 802.16a operation in the 2-11 GHz band. Microwave Opt. Tech-nol. Lett., 42(6), 463-466, Sept.

7) Kenny, S. Ryu, & Ahmed, A. Kishk. (2009). UWB Antenna with Single or Dual Bandnotches for Lower WLAN Band and Upper WLAN Band. IEEE Transactions on Anten nas and Propagations‐ , 57(12), 3942-3950, DEC.

8) Ultrawideband Antennas: Design and Applications.

9) Introduction to Ultra Wideband for Wireless Communications.

10) Ultra-Wideband: Past, Present and Future ,White Paper Presented by the EUWB consortium 2011-06-09.

11) UWB Theory and Applications,Ian Oppermann, Matti Hamalainen and Jari Iinatti All of CWC, University of Oula, Finland, 2004 John Wiley & Sons Ltd.

12) Essentials of UWB,Stephen Wood Roberto Aiello, Cambridge University Press 2008.

13) Introduction to Ultra-Wideband Communications,Nekoogar.book,August 2005.

14) A Comparison between Ultra-Wideband and Narrowband Transceivers,David Barras1, Frank Ellinger and Heinz Jäckel Laboratory for Electronics, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland.

15) ULTRA WIDEBAND SYSTEMS WITH MIMO,Thomas Kaiser and Feng Zheng ,Leibniz University of Hannover, Germany, 2010 John Wiley & Sons Ltd.