ULTRA WIDEBAND TECHNOLOGY

By :The student Kareem AA Difar

ETTI-AWT11/1/2016

CONTENTS 1.IEEE 802 Organization. 2.What is UWB? 3.Power Spectral Density of UWB. 4.Hardware Features and Bandwidth . 5.Bandwidth Property of UWB signals and channel Model. 6.Power delay Profile in UWB. 7.Probability Density Function of UWB system. 8.Delay Dispersion 9.Modulation Schemes. 10.Advantages 11.Disadvantages. Figures Lists References

Fig.1 IEEE 802.organization

1.IEEE 802 Organization

2.WHAT IS UWB?

Fig.2 General Application

Frequency operation 3.1 to 10.6 GHz.Data range from 110Mbps to Gbps. UWB is ideally up to 10meters .Modulation in Time and Frequency Domain .Better sensitivity it can Recover one tenth of the reference signal because we do not Send one pulse but Million of pulse . The effect of the number of resolved paths and bandwidth on reduced-complexity rake symbol-error probability (SEP). Multipath resolution, however, increases as the bandwidth increases. An ultra wideband (UWB) system is therefore capable of resolving individual multipath arrivals with path length differences on the order of centimeters or , on the other hand, the very short duration of UWB pulses makes them less sensitive to the multipath effect. Because the transmission duration of a UWB pulse is shorter than a nanosecond in most cases.The analog circuits will consume a large of current in order to process the signal at a high rate , with digital circuits we can build receivers with energy consumption of less than 20nj/bit and fast power up circuits especially clock reference circuits we reduce the power drain considerable ,additionally PLL circuits with 1mA have been achieved .

To reduce the potential interference from UWB transmissions and provide multiple access capability, a randomizing technique is applied to the transmitted signal. This makes the spectrum of the UWB signal more noise like. The two main randomizing techniques used for single band, UWB systems are time hopping (TH) and direct-sequence (DS). THSS systemwhich is usually utilizing Pulse-Position-Modulation (PPM) as a modulation schemeand the DS approach is based on continuous transmission of pulses composing a single data bit. The DS-UWB scheme is similar to conventional DS spread-spectrum systems where the chip waveform has a UWB spectrum.

Fig.3 Frequency allocation of UWB and other existing wireless system [power spectral density is Fourier transform ].

3.Power Spectral Density of UWB.

4.Hardware Features and Bandwidth Ultra wide band system have special hardware

consideration Antenna must capable of transmitting or receiving GHz Bandwidth signals with minimum dispersion , distortion and . attenuation .There response can not be peaked with using LC resonant circuit , because it use for narrow bandwidth and causes phase distortion .When we 3-10 GHz frequency range , these 50 OHM antennas are approximately 4x3cm2 in area gain approximately 2 dBi .Antenna gain is low for omni-directional designs and received power is proportional to [1/ f ^2 ] so attenuation[path-loss] over 10 meter link can be greater than 30 dB. Broadband amplifiers are needed to compensate the path-loss between transmitter and receiver .A low noise pre-amplifier topology suitable for CMOS integration . The input and the output matching networks must cover a much wider range in frequency compared to narrower preamplifier. [example: A dipole antenna has a gain of 2.15 dBi. An isotropic radiator has a gain of 0 dBi. ]

Fractional Bandwidth is the ratio of signal bandwidth (10 dB) to center frequency: .

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Fig.4 The frequency band bounded

Fig.5 Throughput vs Distance .

5.Bandwidth Property of UWB signals .

Fig 6. Shows the Gaussian family in time and its corresponding power spectral density .The fourth derivative is centered at 6GHz and has a -10 dB Bandwidth between 3 and 10.5 GHz.

As can be seen in the pulse waveforms, the Gaussian impulse has no zero crossing point, while the Gaussian monocycle pulse and Gaussian doublet pulse have one and two zero crossings, respectively, which help define the bandwidth characteristics of these pulses. It is also observed that the spectral responses of these pulses contain no side-lobes beyond the zero-crossing frequency points which are desirable for signal transmission.

As seen, the monocyle has a single zero crossing .If additional derivatives of the Gaussian function are used , the relative bandwidth decrease and the center frequency increases for fixed time delay. If the Gaussian monopulse is used as transmit impulse function , then the second derivative of the function is what we is received .If the third derivative is used as the impulse function then the received impulse is the fourth derivative , and so on

5.1 The Range of fractional bandwidth [0 to2]

To understand the effect of the fractional bandwidth on the performance of the UWB system, we now present a class of pulses that can be used to produce waveforms with a wide range of fractional bandwidths.Narrowband Bf < 1% : Wideband 1% < Bf < 20% : Ultra-Wideband Bf > 20%UWB transmitter: A UWB transmitter is an intentional radiator that, at any point in time, has a fractional bandwidth equal to or greater than 0.20 or has a UWB bandwidth equal to or greater than 500 MHz. The fractional bandwidth varies between 0 and 2, and is often quoted as a percentage (between 0% and 200%). The higher the percentage, the wider the bandwidth.Note : The largest Fractional BW of a[ Capacitor connected Grid] achieved was up to 193.5%, which closely approximates the 200% maximum limit of an UWB channel.[Capacitor-Connected Grids as One-Dimensional UWB Data Transfer Channels]

Fig.7 Fractional Bandwidth versus measurement point in dB for mono-pulse derivative

5.2 Derivative As we know the frequency in this law is center

frequency but in UWB is not ?UWB is defined as any radio technology having a spectrum that occupies a bandwidth

greater than ¼ the center frequency or a bandwidth of greater than 500 MHz. Simple examples of an ultra-wideband transmission would be an RF (Radio Frequency) transmission with a bandwidth of at least 250 MHz having a center frequency of 1GHz or a transmission with a bandwidth of greater than 500 MHz having a center frequency of 6 GHz. The 200% fractional bandwidth is not achievable because it is correspond Fl=0 and the minimum value correspond to monochromatic signal and antenna only support single frequency radiation.

5.3Channel Capacity: Shannon’s capacity

Shannon’s theorem tells us the communication efficiency limit but does not specify how to achieve this limit. One possible method is the application of coding techniques to UWB signaling for the purpose of achieving high the capacity grows largely as we increase the bandwidth and UWB system based on Shanon’s law.

) and the SNR (of the system. shows this situation using bandwidths: 500 MHz,1000 MHz different 2000 MHz, 2500 MHz and 3500 MHz, which are typical UWB bandwidths.

If we were to compare the capacity of UWB systems with other existing radio systems,

the difference would be enormous .

Fig.8 Shanon's Theorem Capacity vs SNR

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To characterize the UWB channel for applications HDR-WPAN three indoor channel models have been proposed the Rayleigh tap delay line model (same as the one used in 802.11 standard) , Nakajami Channel Model and Saleh-Valenzuela (S-V) (Saleh, 1987) models:.

5.4.1:.Rayleigh Channel Model . where “r” is the envelope amplitude of the combined multipath signals, and 2a2 is the expected value of the envelope power of the combined multipath signals. because it has zero mean and there are no line of sight and the signal uniformly distributed . Rayleigh is caused by reflection and scattering and diffraction.The common model: 2-ray Rayleigh fading X, y two objects because the signal narrow band system.Rayleigh is Power Distribution not Rayleigh amplitude distribution the power is additive because the power is more significant than amplitude in Random signals.

5.4 IEEE 802.15.3a channel model Small scale characteristic

Hint[The Rayleigh model process narrow band system not UWB system when m=1]

5.4.2 :Nakajami Channel Model . It is a generalized distribution which can model different fading environments and It has greater flexibility and accuracy in matching some experimental data than the Rayleigh, lognormal or Rice distributions . So the Nakagami-m channel model is of more general applicability in practical fading channelsFor the emerging networks, operating at VHF and UHF frequencies, Rayleigh distributed fading model is inadequate to analyze the channel. Therefore, Nakagami m-distribution is used for analysis purpose . Nakagami distribution of the envelope of instantaneous received signal power, “m” is fading or shape factor, that denotes the severity of fading As special cases, Nakagami-m includes Rayleigh distribution when m = 1, and one-sided Gaussian distribution for m = 1/2. This basically means that, if m < 1, the Nakagami-m distributed fading ismore severe than Rayleigh fading, and for values of m > 1, the fading circumstances are less sever. To capture the clustering property, an approach that models multipath arrival times using a statistically random process based on the Poisson process has been considered , specifically , the multipath arrival times can be characterized by a Poisson process with a constant arrival rate as is known that with increase of bandwidth, more multi-paths can be resolved and the severity of fading decrease.Where “r” is the envelope amplitude of the signal received and Ω is the average signal power also received .

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Hint [1:Nakagami fading is known to be a special case of Rayleigh fading and it possesses good auto correlation properties and Within any one cluster, the phases of individual reflected waves are random, but the delay times are approximately equal for all waves.2 .”m “is called also Gamma distribution[[http://www.wirelesscommunication.nl/reference/chaptr03/ricenaka/nakagami.htm]]

The Saleh-Valenzuela (S-V)model was introduced for a wideband indoor channel .In the S-V model multipath arrivals are grouped in to different categories : cluster arrival and a ray arrival within a cluster. Parameters are provided to characterize the clusters and ray arrival rates (Λ and λ), as well as the inter and intraluster exponential decay constants ( η and γ). Four sets of parameters are provided to model the four following channel types: In most indoor environments, however, objects are not distributed uniformly in space but rather are clustered. Roughly speaking, a cluster is a group of objects that are close together and are separated from other objects by a considerable distance . Many variations on the SV model have been proposed in the literature according to the considered environment, frequency band and transmission range. It is valid for UWB systems irrespective of their data rate and their modulation format. Based on measurements and simulations in various environments, proposed statistical models : a frequency dependent path gain is used. The multipath components are defined in “clusters” and “rays” as described previously. Cluster arrivals are Poisson distributed with “Cluster arrival rate” ( ). And within each cluster; the ray arrivals are also Poisson distributed with “Ray arrival rate” ( ), and >> shapes of power delay profiles (PDP) are assumed to better reflect the line-of-sight (LOS) or non-line-of sight (NLOS) configurations and poisson process characterized by constant arrival rate .

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5.4.3 Saleh-Valenzuela Formalism

Fig.9 Saleh-Valenzuela formalism [Clusters]

[Hint]The number of clusters is a function both of the measurement bandwidth and of the considered environments.

The power delay profile (PDP) gives the intensity of a signal received through a multipath channel as a function of time delay Power delay profiles are generally represented as plots of relative received power as a function of excess delay with respect to a fixed time delay reference.S-V and Two-Cluster Model.This model is based on S-V model, but the only difference is that instead of several clusters with randomtime of arrival, only two clusters are considered with deterministic time of arrival (Figure 11.b). Also, instead ofdetermining the gain of first ray of each cluster stochastically in S-V model, the gain of first ray in first andsecond clusters are computed deterministically. The other model components, i.e., gain and time of arrival of nextrays in each two cluster are modeled statistically. The channel has the following response.

M is the number of paths in the first cluster, and N is the number of paths in the second cluster. The parameters ofthis model can be divided into deterministic and stochastic parts. In order to calculate the deterministic parameters, it is enough to have length, width and height of the room, electromagnetic properties of reflecting surface,polarization and bandwidth of transmitted and received signal. The statistical parameters are modeled like S-Vmodel.

Fig.10 (a) The power profile Delay of UWB system is the decay time constant Fig.11(b) only two clusters are considered with deterministic time of arrival and Average power delay profile versus excess delay in semi-logarithmic scale

6.The Power Delay profile [PDP] of UWB system

6.The Power Delay profile [PDP] of UWB system

Fig.12Complex impulse response as a function of ToA and AoA

Fig.11 Multi-Path Component Hint[ Performance in rake receiver improved in in resolvable path].

Fig.13 Change the probability density function with increase the signal Bandwidth

For DS-UWB, the effects of multipath fading are very different. Because of its wide signal bandwidth, the DS-UWB receiver is able to separately resolve multipath components to largely prevent the destructive combinations from occurring. The result is that the "deep fades" that occur in narrowband or OFDM systems do not occur for DS-UWB systems.The shape of a pdf determines the performance of a wireless receiver in the presence of noise and interference. Proper characterization of fading pdfs also impacts the design and use of diversity schemes method ,but larger bandwidth overcome multipath but not ISI.

7.Probability Density Function of UWB system

Hint[PDF is a useful tool in defining the statistical structure of communication channels]

8.Delay Dispersion The amplitude of the summed signal will undergo fast variations due to the constructive

and destructive combining of the nonresolvable multipath components Wideband channels have resolvable multipath components the parameters change

slowly Narrowband channels tend to have nonresolvable multipath components the

parameters change quickly Each multipath component can lead to delay dispersion by itself but we can assume no significant multipath fading due to fine time resolution in UWB signals. Fig.14 illustrates the in small-scale spatial variation of the measured channel energy

and small-scale fading for narrow band and the UWB channel. It is apparent that the narrowband channel is far more susceptible to multipath and interference and small scale fading than UWB system . Statistically, the fade depth is related to the standard deviation, σ, of the channel energy expressed in dB scale. In order to cover a range of system performance levels.

Fig.14 Fading in Narrow Band and Ultra Wide Band hint [MRC diversity MAX SNR ]

There are two common UWB modulation types that are used in UWB systems. First type of modulation is based on a single-band processing (there is no intermediate frequency used) or impulse radio (IR) systems. The second type of modulation is based on multiband processing and do have carriers, such as Multiband UWB and Orthogonal Frequency Division Multiplexing (OFDM) (supported by the Multiband Group –WiMedia Alliance).

1.Single Band UWB Modulation.Gaussian pulse.1:PPM a 1 is sent at the beginning, whereas the 0 is sent in the middle of the period.2:PAM3:OOK4:Bi-PSK pulse position modulation is one of the most used techniques

in UWB systems. Pulse position modulation was first introduced by Time Domain Corporation in the late 1980s . In PPM pulses are generated at high rates.

Another unique characteristic is that pulses are not evenly spaced in time, but randomly spaced (pseudo noise) in time intervals. This pseudorandom process reducesthe discrete lines on the power spectral density of the PPM signal more than those of the PAM or OOF. This is a very important characteristic especially given the restrictions by the FCC EIRP limited mask. These spectral lines could cause severe interference to existing narrowband radios, and various techniques such as random dithering could be applied in PPM to lower these discrete spectral lines and smoothen the spectrum .

PPM is also less sensitive to noise than is PAM or even PSK signals because information is carried in the time shift of the pulses.

δ = The time between two states of the PPM modulation and they orthogonal

Fig.15 Modulation schemes in UWB

Fig.16 PPM with hard and smooth spectra lines

9.Modulation 9.1Modulation [time domain]

Hint[The WiMedia Alliance was a non-profit industry trade group that promoted the adoption, regulation, standardization and multi-vendor interoperability of (UWB) technologies]

Each MB-OFDM band is only 528MHz wide , this reduces the demands on the bandwidth of the signals which the transmitter and receiver must process .A guard interval is inserted between OFDM symbols in order to sufficient time to with between channels ,however , switching must be achieved within 9 ns.The proposed standard for high data rate applications using UWB technology (IEEE 802.15.3a) is multiband OFDM ,which offers bit rates ranging from 55 to 480 Mbit/s .In the proposed standard , the 3-10 GHZ spectrum approved for indoor use is divided into 14 band that are 528MHz wide. For the first generation of MB-OFDM systems ,potential interference from WLAN and other commercial sources are limited . These bands lie between the 2.4 GHz ISM bands used by and 5-6GHZ Bnads are used by 802.11 WLAN .MB_OFDM is therefore scalable and channel capacity can be added as technology improves or capacity requirements increase by adding more 528MHz wide band to the system .On the transmit side , OFDM produce Peak to average ratio 21 dB for the transmit signal the required

RF output =-41.25+10log(528)=-14 dBm

9.2.UWB with MB-OFDM [frequency domain]

1:Low power consumption2:Interference Immunity3:High Security4:Reasonable Range5:Low Complexity, Low Cost6:Large Channel Capacity7:Scalability .

8:Processing Gain Potentiality it is a measure of anti-jamming [High Performance rake receiver].

Where Bc the RF bandwidth and it is 1.2288 Mcps and Rb = 9.6 Kbps is the baseband before

spreading .

9:Co existence with wireless personal network (802.15)and Wireless local area Network( 802.11) and quantify the mutual interference

10: The center frequency of the UWB signal can be used to estimate propagation loss for the signal without incurring a significant error in the calculation of received power :

Fig.16 The estimating propagation loss

10.Advantage

12: It has been noted, conventional narrowband communications signals must use higher carrier frequencies in order to implement a wider bandwidth. As the frequencies of these signals increase, the propagation losses that they experience becomes greater, as illustrated in Figure.18 .but the shorter pulse width lesser attenuation so that there is possible to penetrate thicker layer of material

Figure.18 The Penetration of obstacles.

10.Advantage

Since UWB pulses are very short in time domain, high-speed ADC (Analog to Digital Converter) and high-speed DSP are essential for UWB systems to digitize and process UWB signals.

UWB antenna is more expensive than narrow-band antennas.

The low output power leads to smaller coverage area. In general, with high gain antenna, UWB signals may cover up to one kilometer. But with regular antennas, the range of UWB signals is usually from ten to twenty meters.

11.Disadvantages

Fig.1 IEEE 802.15 organizationFig.2 General Application Fig.3 Frequency allocation of UWB and other existing wireless system .Fig.4The frequency band boundedFig.5 Throughput vs Distance . Fig6. Shows the Gaussian family in time and its corresponding power spectral

density .The fourth derivative is centered at 6GHz and has a -10 dB Bandwidth between 3 and 10.5 GHz.

Fig.7Fractional Bandwidth versus measurement point in dB for the monopulse derivative

Fig.8 Shanon's Theorem Capacity vs SNRFig.9 Saleh-Valenzuela formalism [Clusters]Fig.10 The power profile Delay of UWB system Fig.11Multi-Path Component.Fig.12Complex impulse response as a function of ToA and AoAFig.13Change the probability density function with increase the signal Bandwidth Fig.14Fading in Narrow Band and Ultra Wide Band Fig.15 Modulation schemes in UWB Fig.16PPM with hard and smooth spectra linesFig.17 The estimating propagation lossFigure.18 The Penetration of obstacles.

Figure List

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