FM-UWB for Communications and Radar in Medical Applications

Wireless Pers Commun (2009) 51:793–809DOI 10.1007/s11277-009-9772-6

FM-UWB for Communications and Radar in MedicalApplications

Ernestina Cianca · Bharat Gupta

Published online: 8 July 2009© Springer Science+Business Media, LLC. 2009

Abstract UWB technology is a useful and safe new technology in the area of wireless bodyarea network. There are many advantages of using UWB as a communication standard forbiomedical applications. Due to very low radiated power (−41.3 dBm/MHz), low power con-sumption, good coexistence with the other existing instruments, Robustness to interferenceand multipath. Moreover, one specific UWB technology, namely Frequency Modulated (FM)-UWB, has also an important advantage, which make it even more convenient for medicalapplications, such as simple low cost design (FM, no receive LO, no carrier synchronization asin IR-UWB). UWB technology has been also proposed radar applications such as: Non-Inva-sive Heart and Respiration Rate Monitoring; Detection of Cardiac Arrhythmias; Detectionof Pathological Respiratory Patterns, particularly in Sudden Infant Death Syndrome (SIDS)and Sleep Apnea; Multi-Patient Monitoring; Detection and Non-Invasive Imaging of BreastTumors. However, pulsed radar are mainly used for these applications. The main issue thatis addressed in this paper is the integration of sensing and communication using FM-UWBand radar technology so that a single device can be obtained for two different operationalmode. We have show that FM-UWB as radar can meet the requirements of typical biomedicalapplications such as Non-Invasive Heart and Respiration Rate Monitoring. Advantages andchallenges of this integration are shown. Future perspectives of this novel activity will bedrawn.

Keywords FM-UWB · Medical health · UWB-Communication · Radar · WBAN

1 Introduction

Wireless communication technologies have progress exponentially over last two decades.It is not only restricted to the mobile technology but also has demands in almost all areas

E. Cianca (B) · B. GuptaUniversity of Rome Tor Vergata, Via del Politecnico, 1, Rome, Italye-mail: [email protected]

B. Guptae-mail: [email protected]

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794 E. Cianca, B. Gupta

in some or other way. People are looking forward to use wireless technology in the field ofmedical health care sector. But, there is a need of extensive research work to make the medicalhealth system helpful and cost effective to the all patients across all age group and financialclass and even to the health-care providers. That is why, now a days people are looking forthe medical system, which provide health-care to everyone at door step in cheaper price andalso available everywhere.

Health-care providers are facing the problems in the area of transfer of information ofpatients to the domain experts, so that they can have the expert’s opinion on time and cansave as much causality as possible. Such a condition requires a real time monitoring systemwhich is possible with the advancement in wireless technology for medical field.

With the advancement in the wireless technology a new portal for the researchers and themedical industry has opened up. Now people are trying to sense the physiological changes inhuman body through the sensors which may be wearable or with non-wearable. Then, theycan replace the wired diagnosis system with the wireless system like ECG, EEG, body tem-perature measurement, blood pressure measurement, etc. There is also a thought of remotesensing (like tele-health care) and real time monitoring system. Real time monitoring systemin essence, is the system which can collect the physical changes of the patient’s body andtransmit the data to the medical server or to the concern place. The above feature requiresan increased accessibility to health-care provider, more efficiently tasks and processes and ahigher overall quality of health care services [1].

New generation of wireless medical health-care systems aim to provide flexible data ratesdepending on the applications e.g. medical images in case of breast cancer, medical data incase of blood pressure, heart beat rate, etc to the health provider. However, the goal mustbe achieved under the constraint of the limited available resources like spectrum and power.As wireless technology is growing with a lot of applications, there will be the consequenceslike spectral crowding, energy efficiency etc. So we have to find out the wireless technologywhich is able to provide the solution for above problems [2].

The first wireless system demonstrated by Gugliermo Marconi in the year 1897, meets thedescription of UWB radio. Marconi’s earliest spark-gap transmitters occupied a large portionof the spectrum, from very low frequencies up through the high-frequency (HF) band andbeyond. On the other hand, we could consider it has a first wireless communication systembased on UWB. Ultra-WideBand (UWB) technology has attract the attention of researcherbecause of the benefits like high data rate, low transmit power and low interference. The abovefeatures also attract the attention of people who are working in wireless medical system.

In early 1970s people had tried to monitor apnoea with the help of Radar to make itcontact-less. In 1976 and 1980 researches had tried to sense the respiratory motion of fatalthrough radar [3]. Development of this radar technology has stopped because of the highpower radiation concern for human safety, bulkiness of the apparatus and high cost.

First attempt of using UWB radar in medical applications is in human body monitoringand imaging in 1993 [4]. On August 9, 1994, the first US Patent application was filed formedical UWB radar. One year later, MIT began an educational project for the “Radar Stetho-scope” [5]. In 1996, the biomedical use of UWB radars is better described with photo andsample tracings, and in the same year, the US Patent [4] was awarded. Since then, UWB isoften considering as a possible alternative to medical remote sensing and medical imaging.U.S. patents emphasize that the average emission level used (1 µW) is about 3rd orders ofmagnitude lower than most international standards for the continuous human exposure tomicrowave making devices medically harmless [6]. Thus is suitable to be a potentially effec-tive way of human body imaging, especially in real time imaging. By 1999 many works havebegun for UWB medical applications in cardiology, obstetrics, breath pathways and arteries.

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FM-UWB for Communications and Radar in Medical Applications 795

UWB radar application in medicine is nowadays being researched in several Universities[7]. The first attempt to make a prototype for Heart Rate Monitoring based on UWB radarwas done at the University of Rome, Tor Vergata [3]. The propagation model is based onconsidering the parameters like thickness, impedance, linear attenuation and wave speed ofsix superimposed living tissues. Along with this work, UWB radar application are being orwere studied at the University of California Davis in breath and speech, at the University ofCalifornia Berkeley in speech, University of Iowa in speech [3,7].

State of the art in the wireless medical field is that, people are sensing the physiologicalsignal coming form the body through the UWB technology. Pulsed UWB radar has beenconsidered to sense the movement of body since it meets the resolution requirements [7–9].

To make the real time monitoring medical system, we require the integration of com-munication technology and the sensing technology. The integration of technology is stillmissing in the future health care system. We are trying to investigate the requirements of theintegrated medical system, then proposing that integrated medical system on the based ofnew technology. Organization of rest of the paper is as follows, basics of UWB technologyis explained in Sect. 2, Sect. 3 explains the required UWB features in medical application,Information and Communication technologies (ICT) and its application in medical field isexplained in Sect. 4, FM-UWB principle and its advantage for the short range communicationis explained in Sect. 5, how radar is used in medical application specially for UWB and newproposed method are explained in Sect. 6, proposed integrated block diagram for sensingand communication and its feasibility study are shown in Sect. 7 and finally, conclusion andfuture prospective is given in last section.

2 Ultra-WideBand Technology

Ultra-WideBand (UWB) technology has recently received significant attention in both aca-demic field and industry for the application in communication as well as in radar because ofhigh data rates, high range resolution up to centimeter, penetration capability and low powerconsumption device, etc.

By definition, the −10 dB RF bandwidth BRF of a UWB signal centered at a frequencyfc should be at least 25% of the central frequency or at least 500 MHz for operation above3.1 GHz. UWB characterizes transmission systems with instantaneous spectral occupancy inexcess of 500 MHz or a fractional bandwidth of more than 20%. The fractional bandwidth isdefined as

Fractional Bandwidth (FB) = B/ fc (1)

where, B = fH − fL denotes the −10 dB bandwidth and center frequency fc = ( fH + fL)/2with fH being the upper frequency of the −10 dB emission point, and fL the lower frequencyof the −10 dB emission point.

On 14 February 2002, the Federal Communications Commission (FCC) in the UnitedStates unleashed huge “new bandwidth” (3.1–10.6 GHz) at the noise floor, where UWBradios overlaying coexistent RF systems can operate using low-power ultra-short informa-tion bearing pulses [10]. The FCC approved the use of 7500 MHz of spectrum for the UWBdevices for the communication application in the frequency range of 3.1–10.6 GHz band,which is an unlicensed and used for the indoor applications. The power spectral density(PSD) of the modulated UWB signal in the above mentioned band must satisfy the spectralmasks specified by FCC. The spectral mask specified by the FCC is shown in Fig. 1.

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Fig. 1 FCC spectral mask for indoor applications

According to the Shannon’s Channel Capacity, the capacity of a communication channelis expressed as:

C = B · log2(1 + S/N ) (2)

where, C = channel capacity (bps), B=Channel bandwidth (Hz), S=Signal power (Watts),N=Noise power (Watts). This ultra large bandwidth opens the door to high capacity wirelesscommunication systems, where data rates of hundreds of Mbps are possible. Alternatively,very large numbers of LDR and MDR users and their devices can be supported [11]. How-ever, the channel capacity is proportional to either B or S/N. It is seen that the capacity canbe increased by increasing bandwidth (B) as well as S/N ratio. In general, depending on theapplication, we have to do trade off between the data rate and average power, like in medicalapplication we have high bandwidth but low transmitted power.

Generally, UWB technology has many advantage because of its Ultra-WideBand nature,which are as follows [12]:

– High data rate: UWB technology could provide high data rates in short and mediumrange (20–50 m) wireless communications because of its high bandwidth.

– Multipath resistance: UWB signal is having a very small pulse width (order of nanosec-ond), and if the pulse arrive at the receiver are separated at least by one pulse width, andthen there will be no interference. Finally, the multipath pulses are filtered out in timedomain. The fine-time resolution of UWB signals facilitates the receiver to coherentlycombine multipath signal component.

– Low-cost: The transceiver structure may be very simple due to the absence of the carrier.Hence, don’t need the much hardware to design the transmitter and receiver.

– Low transmit power and low interference: According to the FCC, the average powerof pulses transmitted for short duration with a low duty cycle is very low. Hence, thepower spectral density of UWB signals is extremely low because of the higher spectrumbandwidth. This gives the possibility for UWB system to work simultaneously with thenarrowband systems in the same spectrum without causing interference.

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Because of the low power transmissions, less interference, coexistence with the otherexisting radio technology, short-range communication, gives the potential to UWB technol-ogy to work in medical health-care field.

3 UWB Features for Medical Application

It is needed to know the answer of some important questions before apply UWB techniquein the medical field. For example, Find the possible type of problems in medical field whichcan be resolved with the help of this new technology. what could be the reasonably solutionof these problems? Is UWB technology able to address yet unresolved medical problems [3].

Firstly, the new technology should have these feature for the application in medical field,like—non-invasiveness, low power, non-contact remote operation, bio-compatibility, bio-friendliness, etc. [13]. In addition to the above mention UWB technology features, the accu-racy detection and localization is also needed for medical monitoring application and highresolution imaging is required for pathologic imaging. The UWB technology is having allabove stated features which are very much suitable for medical applications. Most importantUWB technology features are explained are as follows:

1. Penetration capability: UWB uses RF ranges from 3.1 to 10.6 GHz means a bandwidth of7.5 GHz and has high gain, which means that for lower frequencies are able to penetrateinto the target because of the higher wavelength. This makes UWB viable for wide areaapplications where obstacles are certain to be encountered. The feature makes it easy toimage organs of human body for medical application.

2. High precision ranging: Most desirable feature of UWB is high precision ranging atcentimeter level because of ultra short pulse characteristic. This feature also gives strongmultipath resolving capability. The UWB pulse is much shorter, which provides verygood temporal and spacial resolution which is suitable for the localization and monitor-ing in the medical applications.

3. Low electromagnetic radiation: The FCC has allotted the low radio power pulse lessthan −41.3 dB/MHz for indoor environment, because of this radiation power is low. Thelow radiation influences the environment very less, which make it suitable for hospitalapplications. Moreover, the low radiation is safe for human body exposure, even at shortdistance, which makes it possible to apply UWB technology in the medical application.

4 Information and Communication Technologies (ICT)

Information and Communication Technology (ICT) is defined as reflecting all forms of tech-nology used to create, store, exchange and use information in its various forms. Example:Tele-health involves using Information and communications technologies to deliver healthinformation, services and expertise over short and long distances. Within health care, ICTis an essential enabler for improving client care, enhancing provider capacity and effective-ness and achieving appropriate utilization of the health system.Technology in the home andcommunity setting can and will play an increasingly important role in enabling and empow-ering patients and their families to manage their own condition more effectively and liveindependently in their homes.

According to [14], worldwide predicted population of older people will be about 761 mil-lion by 2025, which is more than the population in the year 1990. If the trend follows in near

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future, the percentage needed for care demand is increased extraordinary than the percentageof health care providers. It might be the worst situation in near future. People have alreadystarted working in the direction to develop a system which can provide information aboutthe patient’s health condition and communicate it to the desired destination depending on thesituation, it should be independent of time and place. This is only possible with the mergingof-the-shelf communication technologies and developing new era in the medical field.

Technologies are well developed in their individual fields, requirement is to merge themand develop the new systems. There are so many basic issue when thinking a project likethis—how we can collect the patient’s health data?, how we can analysis the patient’s healthcondition?, how is possible to sent this data to the medical server?, how is possible to makethe application in real time scenario?. Basic need is to integrate the different technologies andconcepts, to provide the health care anywhere and anytime. Thats provide the much degreeof freedom to the patients and elder people don’t have to come to the hospital for medicalregular checkup.

By introducing, Wireless Body Area Network (WBAN) to monitor the vital sign of phys-iological changes in human body through Sensor networks in hospital, smart home caresystem, can reduce the load up to some extent. The pervasive health-care concerns technolo-gies and concepts that integrates health-care more seamlessly to our daily life, wherever weare and whenever we need [15]. Main purpose of integration is to obtain and to transmit vitalsigns from sensors to repositories or other units, in real time. These medical data have to betransmitted with high security and reliability to the destination i.e, where it is needed. Thecombination of these technologies will develop a real time monitoring health-care system tosupport the patients, elderly people and handicap person in hospital and home.

Key to ICT enabled integration for the health-care system

1. Inter-operability: The ability to share data accurately, securely and reliably betweendifferent systems regardless of the applications within individual organizations.

2. Implementation of electronic medical records: Capturing relevant clinical data electron-ically within a sector, service or organization is an important step to sharing informationelectronically.

3. Linkages to an electronic health record: determining the key elements within health-carethat must be shared in order to ensure the best care for the individual and then linking toan electronic record accessible by health-care practitioners anywhere in the country.

4. Standardized documentation systems: standardization of medical data and terminologyenhance inter-operability and minimize duplication of effort

4.1 ICT for Wireless Body Area Network

The UWB technology can be used for wireless body area network for the medical applica-tion. It gives all the advantage which is required to develop a medical system. To monitorthe patient’s suffering from chronic diseases, such as diabetes and asthma, permanent moni-toring is an important part. Long term monitoring of patient’s ECG data is required for earlyindicators about heart attacks and in depth diagnosis of patient’s health condition. In general,demand of continuous patient’s monitoring is essential. Wireless Body area network is oneof the basic infrastructure for the ICT. The requirements of a WBAN for medical applicationinclude:

– Low Power Consumption– Low Emission Level for safety of human body

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– Reliability and High Security in medical data transmissions– Low cost and user friendly– Compatibility with other existing network technologies

Lots of projects are going and some have done to make the medical system feasible [14].In Body Area Network project, has designed the integration of body sensor through internet,which facilitate much degree of freedom to the patients. In Human++ project, realization ofbody area network consisting of sensors communicating with a PDA to monitors a person’shealth. In CodeBlue project, exploring application of WSN technology in medical scenariolike pre-hospital and in-hospital care. Telemedicare is the project, which is trying to improvethe home based care and medical treatment in a 24 h real time medical monitoring. Therewere lots of project which try to improve the condition of patients through the technology.Now, MELODY, which will deal with the Ultra-WideBand technology for the improvementof wireless health technology [16].

Primary requirement for all the above mentioned related to medical health care are lowpower transmission, low interference with the other existing technologies, low cost, easilyavailable, secure and safe, etc. The Frequency Modulated Ultra-WideBand (FM-UWB) willhave the potential to fulfill all the primary need of the medical system.

5 FM-UWB Technology

FM-UWB is defined as an analog implementation of a spread-spectrum system with a spread-ing gain equal to the modulation index (β) [17]. In particular, FM-UWB is a low complexityconstant envelope low data rate UWB communication technology with lower power con-sumption than Impulse Radio (IR) and good robustness to interference and multipath [18].UWB technologies can ensure low data rate (1–100 Kbps) and medium data rate (100 Kbps–10 Mbps) [11]. According to the Carson’s rule:

BRF = 2(� f + fm) = 2(β + 1) fm (3)

Above equation says that the Bandwidth of a RF signal in frequency modulation is not onlydepend on the central frequency fm , but also depend on the modulation index (β). So, wehave the freedom to choose modulation index (β) to get higher bandwidth. FM has the uniqueproperty:

– β < 1: for narrowband FM signals– β � 1: for wideband FM signals

Assume an FM signal V(t) with amplitude A and carrier frequency fc (ωc = 2π fc)modulated by a sinusoidal signal m(t) of frequency fm(ωm = 2π fm) such that [17]

m(t) = Vm sin(ωmt) (4)

An RF oscillator sensitivity of k0[rad/s] yields derivation �ω = 2π� f

�ω = koVm

resulting in an FM signal V(t):

V (t) = A sin(ωct + ϕ(t))

V (t) = A sin(ωct + K0

t∫

∞Vm sin(ωmτ)dτ)

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V (t) = A sin(ωct − β cos(ωmt) + ϕ0) (5)

where, β = K0Vm/ωm, ϕ(t) is the instantaneous phase excursion due to the FM, ϕ0 is anarbitrary but time-dependent constant, and β is the modulation index defined by

β = � f

fm= �ω

ωm

Equation 1.5 can be expressed as a sum of Bessel functions Jn(β) of the first kind (ordern) of the argument β

V (t) = A∞∑

n=−∞Jn(β) sin(ωc + nωm)t (6)

Theoretically, the spectrum of an signal is infinitely large, The higher order Bessel functionJn(β) decay rapidly for (n > β) as shown in Fig. 2.

The fast decay of the Bessel functions for n > β, the bandwidth of a wideband FM signalcan be controlled by adapting the modulation index β. When the modulation index β � 1, awideband spectrum is obtained in which no carrier can be distinguished. The spectral roll-offof this FM-UWB signal is very steep. This strongly improves the coexistence of FM-UWBsystems with other RF systems operating in adjacent frequency bands. Analog FM can thus beused as a spreading mechanism to generate an unmodulated constant-envelope UWB signalof appropriate bandwidth.

FM-UWB is a novel wireless communications system using double FM modulation. Thesystem is envisioned for LDR: 1–100 kbps and MDR: 100–1000 kbps and short range WPANsystem and WBAN. This large bandwidth leads to new interesting possibilities for both com-munications and radar applications. For this reason, integrated systems using UWB tech-nology have been investigated for a decade. The main advantages of the UWB technologyare:

– Power consumption: The Federal Communications Commission (FCC) power require-ment for UWB systems is −41.3 dBm/MHz in the reference band for indoor applications.These low power levels are safe for human exposure.

Fig. 2 Amplitude of the Bessel functions (20 log10(Jn(β)) for various values of the modulation index β

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Fig. 3 FM-UWB transmitter

– High security: Because of their low average transmission power, UWB communicationsystems have an inherent immunity to detection and interception.

– Resistance to interference: UWB is robust to narrowband interference.– Penetration ability: Unlike narrowband technologies, UWB systems can penetrate effec-

tively through different materials; UWB technology can provide through-the-wall com-munications and ground-penetrating radar.

To get the FM-UWB using double FM as shown in Fig. 3: digital FSK followed by highmodulation index analog FM to create a constant envelope UWB signal: (1) The data signald(t) modulates a low-frequency sub-carrier using narrowband FSK techniques. (2) Then thesub-carrier signal m(t) modulates the RF oscillator using analog FM with high modulationindex [17].

The receiver demodulates the FM-UWB signal without requiring local oscillator and car-rier synchronization (as in the case of IR UWB) which makes the device simpler and cheaper.Figure 4 shows the block diagram of the FM-UWB receiver.

6 UWB Radar for Medical Application

The Micro-power Impulse Radar invented at LLNL, in the year 1994 had given a new potentialto work with ultra low power radar, besides being extremely compact and inexpensive [6].This open the new opportunities in area of medical health-care field to diagnosis the patient asa contact-less. Electromagnetic waves coming from radar are able to probe the human bodythanks to reflection and diffraction phenomena due to different impedance values of humantissues. This technology could have lots application in the medical field, mainly monitoringand the medical Imaging. Monitoring applications could be wireless vital signs monitoring ofhuman body (like—Heart rate monitoring, blood Pressure, Blood Oxygenation, ECG, etc),patient motion monitoring (like—movement of patient in ICU, watch on handicap and olderperson at home, etc ) and the medicine storage monitoring.In the medical Imaging, we coulduse in the following case—Cardiology Imaging, Pneumology Imaging, Obstetrics Imaging,

Fig. 4 FM-UWB receiver

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and Ear–Nose–Throat Imaging. some method of heart monitoring with the different UWBradar techniques—like Pulse radar and Continuous radar.

6.1 Pulse Radar

Pulse radar operates by sending short pulses and by receiving the echoes reflected by thetarget. The time delay between the transmitted pulse and the received one is proportional tothe distance R0 (range) from the target to the radar [19]:

R0 = c�t

2(7)

where, R0 is the range at the particular time t0,�t is the total round time and c is the speedof light. The range resolution is:

�R = cτ

2(8)

where τ is the pulse duration. This pulse width must be in the nanosecond to get the resolu-tion in centimeter accuracy. To get the pulse width in nanosecond, requirement of complexcircuitry at the transmitter and to get the synchronization at the receiver again we need themore circuitry, this is at the expense of high power consumption. Collecting the range valuesat different instants and processing them, it is possible to rebuilt the dynamic motion of thetarget (i.e. the heart, in case of Heart Rate Monitoring) [8].

6.2 Continuous Wave (CW) Radar

There are two different methods to measure range by CW radar:

– Frequency Modulation (FM-CW) radar(Chirping);– Multiple-Frequency CW radar(Phase measurement).

6.2.1 FM-CW

The frequency of the transmitted electromagnetic wave changes as a known time function(chirping) as shown in Fig. 5. The range is:

R = c fr

4�F fm(9)

where, fr is the difference between the received and the transmitted frequency, fm is themodulation rate, �F is the modulation range. In this case, the range resolution is:

�R ∼= c

2�F(10)

However, typical continuous wave FM radars do not meet the resolution requirements ofsome biomedical applications. For heart motion detection we need a millimeter resolution.Using FM-CW radar, we could get a resolution of the order of centimeters also using all thehuge bandwidth available for UWB technology (�F = 7.5 GHz).

In addition, using FM-CW Radar, in the frequency range �F = 7.5 GHz, we get a reso-lution of �R = 2 cm; not enough for biomedical applications.

Therefore, we need to develop some thing which gives the resolution requirement and lowpower consumption together.

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Fig. 5 (a) Frequency modulation, (b) beat frequency fb

6.2.2 Multiple-Frequency CW Radar

The transmitted two continuous sine waves of frequency f1 and f2 separated by an amount� f = f2 − f1. The form of the doppler-shifted signals echoes at each of the two frequenciesare [19]:

V1R = sin

(2π( f1 ± fd1)t − 4π f1 R0

c+ ϕ1

)(11)

V2R = sin

(2π( f2 ± fd2)t − 4π f2 R0

c+ ϕ2

)(12)

where, fd1 and fd2 are the doppler frequency shift associated to f1 and f2, respectively. Thedifference � f is usually very small, then fd1 and fd2 are approximately equal. The receiverseparates the two components of the echo signals and heterodynes each received signal com-ponent with the corresponding transmitted waveform and extracts the two doppler-frequencycomponents. Finally we get the phase difference �φ and the range:

R0 = c�φ

4π� f(13)

The resolution depends on the minimum value of �φ which receiver can differentiate and,potentially, we get the desired range resolution for biomedical applications. The unambigu-ous measurement of �φ is possible only if �φ is less than 2π . This puts limitations on themeasurement of the maximum range distance:

Runamb = c

2� f(14)

In case of non-invasive heart monitoring, Runamb should be bigger than the average distancefrom the heart tissue to the human skin (∼= 4 cm). To see the feasibility of range resolution,

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keep the radar 1 meter away from the body to make the application as noninvasive and con-tact-less. Put the value of Runamb in Eq. 14, to get the frequency span for the operation. Then,� f come 150 MHz. If radar is potential to measure the phase difference equals to 1◦, thenthe range resolution could be 3 mm. Possible to measure smaller, depending on the how smallphase difference can be measured.

6.2.3 Proposed Approach for Radar

Our proposed approach for the radar sensing, applies the Multi-frequency CW radar tech-nique with the FM-UWB principle. So in place of two sine waveforms, we are transmittingthe two FM signals simultaneously. The modulating signal is:

ms(t) = At sin(ωmt)

where, At is the amplitude of the sinusoidal signal of frequency fm (ωm = 2π fm). Therefore,the transmitted frequency modulated signal of carrier frequency fc is:

Vt (t) = At sin(ωct − βcos(ωmt) + φ0) (15)

where, the modulation index β = � f/ fm . The received echo of this transmitted FM-CWsignal, reflected from the target is:

Vr (t) = Ar sin

[(ωc ± ωd) t − βcos(ωmt) + φ0 − 4π fc R0

c+ βcos

(ωm2R0

c

)](16)

The receiver heterodynes the signal, and with some approximations, we get:

Vd(t) = Ar At sin

[±ωd t − 4π fc R0

c+ β

](17)

In the proposed approach, we transmit simultaneously two FM signals of carrier frequen-cies fc1 and fc2. After the phase detector, we obtain the following expression for the phasedifference:

�φ = 4π( fc2 − fc1)R0

c(18)

The above Eq. 18, gives you the range means it would show the movement of heart by chang-ing the distance between the heart and the device. But if need to understand the motion ofheart carefully and diagnosis the patient’s health more closely. It is required to measure thesmall displacement at every instance of time. Then, the required parameter is the small dis-placement x of the moving target (in this application: heart), it is necessary to evaluate �φ

twice, at two different time instants t1 and t2. The phase difference at the instant t1:

�φt1 = 4π( fc2 − fc1)R0

c

and at the instant t2:

�φt2 = 4π( fc2 − fc1)(R0 + x)

c

Taking the difference of these two “phase differences”, we get the small displacement xof the target:

x = c(�φc2 − �φc1)

4π( fc1 − fc2)(19)

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While drawing the displacement at every instant of time, we would get a short of waveform.This we could establish the correlation between the ECG and output waveform based on thedisplacement, which would help health provider to get heart condition remotely.

7 Common Technology Used for the Integration of Communication and Sensing

A possible FM-UWB integrated communication/sensing transceiver is presented in Fig. 6.In the integrated transceiver, the sensing is performed by using a multiple frequency methodwhere two different frequencies fc1 and fc2 are simultaneously transmitted. The dash linesand blocks are related to the FM-UWB transmitter and receiver components for the com-munication part whereas the solid lines and blocks show the FM-UWB CW transmitter andreceiver components for the sensing part. The double dash lines and blocks are common toboth the communication and the sensing part.

The complexity issue is of utmost importance for terminal dedicated to those applicationsand FM-UWB gives great advantages. However, only a slight increase of the transmitter isrequired with respect to a pure communication transceiver (two FM Modulators are neededinstead of one).Frequency modulated signal technique is used in the integration to get highsecurity and robustness in communication [20]. We can obtain communication/sensor device:highly integrated, small and power efficient; something that has been wanted for long time inthe medical field. We found that small increase in the hardware make it possible to design acompact and cost effective, integrated communication/sensing device because of the commonblock elements.

Fig. 6 Block diagram of a possible integrated transceiver based on FM-UWB: communication and sensingparts are integrated using switching functions to connect convenient processing blocks

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7.1 Feasibility Study

This section aims to test the possibility of using an FM-UWB communication/sensing systemwith available commercial power is able to probe the sensing with the desirable range, tomake the system contact-less. Since there is no commercial FM-UWB transceiver is availableso far, we took a prototype developed by CSEM (Switzerland) within the MAGNET project[18]. The data sheet of prototype FM-UWB communication transceiver specifies:

– Transmit output power: Pt = −14 dBm– Center frequency: f = 4.5 GHz– Bandwidth: B = 500 MHz– Receiver sensitivity: Smin = −80 dBm– RF frequency range: 4.25 GHz ≤ f ≤ 4.75 GHz

The FCC restricts the value of power spectral density (PSD) to −41.3 dBm/MHz for indoorapplication. So, the effective isotropic radiated power for the prototype FM-UWB commu-nication transceiver must also follow power restriction by the FCC. Having a bandwidthof 500 MHz, the Effective Isotropic Radiated Power (EIRP = PSD ∗ B) is −14.31 dBm.This shows that the transmitted output power Pt of the prototype FM-UWB communicationtransceiver is approximately equal to the FCC’s maximum allowed EIRP for the consideredfrequency range. Hence, the transmitting antenna gain Gt is unity (E I R P = Pt ∗ Gt ).

The transmitted power density uniformly distributed at a distance R from the source is

Ptd = Pt · Gt

4π R2 (20)

and the power intercepted by the target (heart) is

Pi = Ptd · σ (21)

where, σ is the radar cross section of the heart. For the feasibility study, we took the assump-tion same as [7]. The radar cross section (RCS) value is defines as the product of the area ofthe target (A), reflectivity of the target() and the antenna gain (G),

σ = A · · G

Calculated value σ = 0.001 m2, [7]. However, the effective radiated by the heart (con-sider to be spherical) is σ/4π R2. Some power would be captured by the receiving apertureAe = Gr · λ2/4π , where Gr = 0 [dBi].

so far, the received power is expressed as

Pr = (Pt Gt ) ·( σ

4π R2

)·(

Ae

4π R2

)(22)

Equation 22, is basically a radar equation in lossless medium. According to [3], the prop-agation loss during the round trip of EM radiation from heart to radar receiver is 20 dB.This is not the correct approximation here, because the operating frequency is 4.5 GHz, butthe propagation loss values is based on the 1.5 GHz. This open the future prospective to doexperiments in UWB frequency to know the electrical property of human tissues. So that,exact model for the propagation loss can be designed.

Considering propagation loss, the received power at the radar is:

Pr = (Pt Gt ) ·( σ

4π R2

)·(

Ae

4π R2

)·(

1

L

)(23)

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– (Pt Gt ) is the EIRP of the radar in the direction of the heart where Gt is the antenna gain.– (σ/4π R2) is the fraction of EIRP intercepted and backscattered by the heart assuming it

has a spherical cross-section σ [7].– (Ae/4π R2) is the fraction of the scattered power where Ae is the receiving aperture.– L is the total round trip loss [3].

The maximum range for keeping the device away from the heart is:

R =(

c2

64π3 · Pt

Smin· σ

f 2 · 1

L

) 14

(24)

– Pt = −14 dBm = 39.8 µW– Smin = −80 dBm = 10 pW– σ = 0.001 m2

– f = 4.5 GHz– L = 20 dB = 100– c = 3 × 108 m/s

Putting all the value in Eq. 24, we get R ∼= 10 cm, which is greater than the average dis-tance between the center of the heart and the skin (4 cm) [7]. This result allows us to say thatour integrated system can be use as a non-invasive and contact-less support for Heart RateMonitoring. It is worth noting that this range is shorter than IR-UWB distance calculated in[7] because in our approach we transmit lower power. If transmitting power is increased thenproportionally the range can be increased.

For heart Beat monitoring on continuous basis, develop a accurate shape model for theheart, so that exact power budget analysis would be done. Secondly, according to [21], there isa heart’s motion during the respiration. While monitoring the heart beat continuously, heart’smotion is also consider. At the receiver, some filtering technique is to be defined to separatethe signal coming from the heart, breathing and reflection from the other organs. Define theexact propagation loss and echo loss model is designed on the basis of electrical propertiesof human tissue at the UWB frequency range.

8 Conclusions and Future Prospectives

In this chapter, we propose the use of FM-UWB for sensing purposes in biomedical applica-tions. We show that the proposed approach allows to get the desired resolution for biomedicalapplications such as Heart Rate Monitoring. Moreover, we show that it is possible to imple-ment a device which integrates both sensing and communication capabilities and use the sameFM-UWB technology. The integrated device is not much more complex than one single sens-ing or communication device since most of the components are common to the two schemes.A preliminary feasibility study shows that the integrated device can meet the requirements ofboth sensing and communication purposes. The further development of this work will haveto consider the following considerations:

1. Only measuring the heart beat is not solving the purpose in diagnosis the patient’s condi-tion. We should be able to draw the exact movement of heart to make it comparable witha ECG signal. Monitoring the patient’s condition from remote means that only when itis strictly needed the health provider will call the patient for hospitalization. However,this requires contact-less ECG system with a good accuracy.

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2. Generally, we get the signal from the movement of chest, which contains the informa-tion about the respiration rate and heart beat. Here, one point to be considered is thatthe percentage of displacement produced by the heart is very less in comparison to thedisplacement produced by the respiration rate. Moreover, a signal processing techniqueis needed to take care of filtering out the signal because of the heart beating. This ispossible to do also with the measurement of signal directly coming from the heart: thiscould be a big step forward in biomedical field. In this direction, we have to developthe model of propagation of EM wave inside the human body. And secondly, we haveto model the movement of the heart at the time of breathing condition in such as waythat continuous monitoring of the patient could be possible. Till now people are takingmeasurement only in the breath hold condition.

To summarize, many other issues must be solved. Nevertheless, so far there is no inte-grated device available which is able to measure the heart beat continuously and transmit theinformation to the desired location i.e. medical server, health care provider’s PDA. Proposedintegrated device could be the one which could be waiting for long in the medical field.

References

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2. Arslan, H., Chen, Z. N., & Benedetto, M. G. D. (2006). Ultra wideband wireless communication. NewYork: Wiley..

3. Staderini, E. M. (January, 2002). UWB radar in medicine. IEEE Aerospace and Electronic SystemsMagazine, 17(1).

4. McEwan, T. E. (November, 1996). Body monitoring and imaging apparatus and method. US Patent5,573,012.

5. Staderini, E. M. (July, 2008). Oral presentation: Medical applications of UWB radars.6. McEwan, T. E., & Azevedo, S. (January/February, 1996). Micropower impulse radar. Science and

Technology: Review, 16–29.7. Carlos, G. B. (29 November–1 December, 2006). Bio-medical sensing using ultra wideband commu-

nications and radar technology: A feasibility study. In First international conference on pervasivecomputing technologies for healthcare, pp. 1–9.

8. Staderini, E. M., & Varotto, G. (27–30 November, 2007) Optimization criteria in the design of medicalUWB radars in compliance with the regulatory masks. In IEEE conference on biomedical circuitsand systems, BIOCAS 2007, pp. 53–58.

9. Zito, D., Pepe, D., Neri, B., & De, R. D. (4–8 June, 2007). Feasibilty study os a low-cost system-on-a-chip UWB pulse radar on silicon for heart monitoring. In International conference waveformdiversity and design, pp. 32–36.

10. Yang, L., & Giannaki, G. B. (November, 2004). Ultra wideband communication—an idea whose timehas come. IEEE Signal Processing Magazine, pp. 26–54.

11. Gerrits, J. F. M., Farserotu, J. R., & Long, J. R. (21–23 September, 2004). UWB considerations forMAGNET systems. In Thirtieth European conference on solid-state circuits, ESSCIRC-04, pp. 45–56.

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13. Pan, J. (2007). Medical applications of Ultra-WideBand (UWB). Survey Paper.14. Thraning, B. M. (July, 2005). The Impact of ZigBee in a Biomedical Environment. Master thesis

submitted in Agder University College.15. Korhonen, I., & Bardram, J. E. (September, 2004). Guest editorial introduction to the special section

on pervaisve healthcare. IEEE Transactions on Information Technology in Biomedicine, 8(3).16. http://www.melody-project.info.17. Gerrits, J. F. M., Kouwenhoven, M. H. L., Van der Meer, P. R., Farserotu, J. R., & Long, J. R. (2005).

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Author Biographies

Ernestina Cianca received the in Electronic Engineering Laureadegree cum laude at the University of L’Aquila nel 1997. She got thePhD at the University of Rome Tor Vergata in 2001. She has beenemployed by the University of Aalborg, Denmark, in the Wireless Net-working Groups (WING), as Research engineer (2000–2001) and asAssistant Professor (2001–2003). Since Nov. 2003 she is Assistant Pro-fessor in Telecommunications at the URTV (Dpt. of Electronics Engi-neering), teaching DSP, Information and Coding Theory and AdvancedTransmission Techniques. She has been the principal investigator ofthe WAVE-A2 mission, funded by the Italian Space Agency (ASI).She currently the coordinator of the scientific activities for severalprojects with the European Space Agency (ESA) and ASI. She hasbeen involved in several European and national projects. Main researchinterests: Novel Air Interfaces for future wireless systems, in particu-

lar MIMO in Single carrier systems with Frequency Domain Equalization, Multicarrier Systems, satellitecommunications is EHF bands (in particular, W-band), energy efficient wireless systems, power control andresource management, heterogeneous networks, UWB for biomedical applications. She is currently TPCCo-Chair of the conference European Wireless Technology 2009 (EuWIT2009), joint event with the Euro-pean Microwave Week 2009. She is also TPC Co-Chair in the conference Wireless Vitae 2009 (http://www.wirelessvitae2009.org). She is author of about 50 papers, on international journals/transactions and proceed-ings of international conferences.

Bharat Gupta has got his Bachelor’s of Engineering degree in Elec-tronic and Communication from Vikram University, India in the yearof 2000. He did his Master in honours from the Birla Institute ofTechnology in year of 2003. He got the M.Tech degree in Remote Sens-ing. He stood first in M.Tech and got 3rd in Univeristy. He has sub-mitted his master’s thesis in ‘Thermal Microwave Remote sensing’.He has carried out a six month training in Digital Image Processingat RRSSC, ISRO, Jodhpur, India. Presently, he is working as a lec-turer in department of Electronics and Communication Engineering atBirla Institute of Technology, Mesra, Ranchi, India since 2004. And,he is persuing his research work at University of Rome, Tor Vergat-a, Italy. He has enrolled as a PhD Scholar in Electronics Department.His research interest is FM-UWB Communication and UWB in Bio-medical Application. He has presented papers in International/Nationalconferences.

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FM-UWB for Communications and Radar in Medical Applications

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