IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 11, NOVEMBER

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1 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 11, NOVEMBER Experimental Study on the Dependence of Antenna Type and Polarization on the Link Reliability in On-Body UWB Systems Terence S. P. See, Member, IEEE, Tat Meng Chiam, Michael C. K. Ho, and Mehmet Rasit Yuce, Senior Member, IEEE Abstract An experimental study on the use of ultra-wideband antenna systems ( GHz) on the human body for wireless body area network (WBAN) applications is conducted. It has been found that the link reliability can be improved and transmit power can be reduced by properly selecting the transmit and receive antennas with different radiation properties (omni-directional, directional, pattern diversity) and polarizations (vertical and horizontal) at each location on the body. Moreover, when there is blockage by the body, it may be possible to achieve better transmission when the antennas are horizontally polarized. Also, antennas with pattern diversity can be used to enhance the overall reliability of the communication system. In order to eliminate the use of cables in the measurements, an on-body UWB system has been developed and the reliability can be assessed more practically in terms of the peak amplitude of the received waveform and the bit error rate. It has been observed that when the link quality is improved, the transmit power can be reduced by more than 20 db without compromising on the reliability, which will conserve the battery power. Index Terms Antennas, bit error rate, diversity, propagation measurements, RF transmission, ultrawide band, wireless body area network. I. INTRODUCTION I N recent years, the development of wearable communication devices on the human body have been extensively researched. The advantages of a UWB communication system are that it provides a potentially high transmission capacity and a low effective isotropic radiated power spectral density of less than dbm/mhz [1]. This results in a longer battery life for a body-centric network. The UWB antennas are researched and designed with the bandwidth, efficiency, gain, and group delay considerations within the limited antenna specifications Manuscript received November 30, 2011; revised April 03, 2012; accepted June 18, Date of publication July 13, 2012; date of current version October 26, T. S. P. See and T. M. Chiam are with the RF, Antenna and Optical Department, Institute for Infocomm Research, A*STAR, Singapore ( spsee@i2r.a-star.edu.sg; tmchiam@i2r. a-star.edu.sg). M. C. K. Ho was with the School of Electrical Engineering and Computer Science, University of Newcastle, Callaghan, NSW 2308, Australia. He is now with the Integrated Circuits and Systems Department, Institute of Microelectronics, Agency for Science, Technology and Research (A*STAR), Singapore ( hockm@ime.a-star.edu.sg). M. R. Yuce was with the School of Electrical Engineering and Computer Science, University of Newcastle, Callaghan, NSW 2308, Australia. He is now with the Department of Electrical and Computer Systems Engineering, Monash University, Victoria 3800, Australia ( mehmet.yuce@monash.edu). Color versions of one or more of the figures in this paper are available online at Digital Object Identifier /TAP [2], which is very different from the conventional narrowband antenna designs. Much effort to analyze the electrocardiogram (ECG), electroencephalography (EEG) and various physiological signals such as temperature, heartbeat, blood pressure, glucose level, SpO2, etc., has made it important to characterize the on-body RF transmission performance between the transmitter and receiver for medical research, pharmaceutical research, medical education, training, and healthcare applications. Communications from in-body implants and on-body sensors will allow for better diagnoses and improve therapy [3] [5]. In order to gather the various physiological signals of the human body, a wireless body area sensor network system can be implemented. The network system is a specific type of network structure which consists of fixed sensor nodes. As the sensor nodes are placed on a human body, various factors such as body movements, varying body orientations, and environment may degrade the link quality [6] [8]. Therefore, the antenna is one of the key elements in the wireless body area networks. Antennas with omni-directional radiation [9] [11] in free space and diversity [12] [16] are commonly used in body area networks However, the radiation patterns will be altered when the antennas are placed near the body. Therefore, by using antennas of different radiation characteristics, the overall system performance can be optimized. Instead of using the resource management schemes such as adaptive power control, routing, transmission scheduling, etc., the antenna selection in terms of the radiation properties and polarization for the different positions on the body can also be used to improve the quality of the communication link. In this paper, three different types of UWB antennas with different radiation characteristics will be used as the transmit and/or receive antennas. In order to facilitate the experimental study, the transmitter and receiver systems are developed to be mounted on the body. By understanding the effects of the polarization and position of the transmit and receive antennas on the system performance in terms of the peak amplitude of the received waveform and the bit error rate (BER), the link reliability can be enhanced without the need to increase the transmit power. II. MEASUREMENT SETUP Fig. 1(a) shows the measurement setup for the transmit-receive antenna system on the body inside the anechoic chamber. In Fig. 1(b), in order to verify the transmitter and receiver performance, both the transmit and receive antennas are first mounted X/$ IEEE

2 5374 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 11, NOVEMBER 2012 Fig. 1. (a) Wireless body area network measurement setup inside anechoic chamber; (b) measurement setup in free space; (c) transmit and receive antenna locations on the body (T: transmit antenna, R: receive antenna). on wooden tripods in free space at a distance of 1 m and oriented face-to-face with each other. The measurements are taken when the transmit and the receive antennas are vertically polarized. The UWB pulse generated by the transmitter is passed through the transmit antenna and picked up by the receiver front-end circuitry via the receive antenna. The locations of the transmit and receive antennas on the body are shown in Fig. 1(c). A 31-year old male adult of height 1.66 m and weight 67 kg is used in the measurements. The transmit antenna is placed on four different locations, namely the left chest area (for ECG application), the forehead area (for EEG application), left wrist (for temperature or heartbeat monitoring) and center waist (for glucose level monitoring). The receiver antenna is placed on three different locations, namely the right waist, left arm, and center chest. In order to avoid the impedance mismatch and significant absorption by the human body, direct contact between the receive antenna and the body should be avoided. Hence, the transmit and receive antennas are placed 10 mm away from the body. The UWB antennas used in this study are namely, the omnidirectional monopole antenna (Antenna A), directional L-plate antenna (Antenna B) and dual-port antenna with pattern diversity (Antenna C). The two ports of Antenna C are named CL and CR, respectively. When CL is excited, CR will be terminated using a 50 load, and vice versa. The peak-to-peak amplitude and waveform from the oscilloscope are recorded. The measurements will be divided into two parts. For the first part, the peak amplitude of the received waveform is recorded to determine which antenna is more suitable to be used as the transmit and receive antenna. From the results, the optimal receive antenna location and orientation with respect to the transmit antenna can be obtained. With this knowledge, the bit error rate of the antenna system can be determined in the second part of the measurement. Fig. 2. (a) Block diagram of UWB transmitter; (b) Photo of UWB transmitter; (c) Generated UWB pulse; (d) Spectrum of UWB pulse. A. Transmitter and Receiver Architectures The transmitter module generates the UWB pulse by using a 2 ns pulse generator. It is battery operated and can last for around 4 hours, which is sufficient for data collection at a particular receiver location. An overview of the transmitter circuit is as shown in Fig. 2(a). The transmitter module is assembled on a 4-layer printed circuit board with dimensions of cm as shown in Fig. 2(b), which is sufficiently compact for WBAN applications. The electrode is amplified before the input of the micro-controller. The micro-controller performs the analog-to-digital conversion, determines the transmission

3 SEE et al.: EXPERIMENTAL STUDY ON THE DEPENDENCE OF ANTENNA TYPE AND POLARIZATION 5375 Fig. 3. Block diagram of UWB receiver front-end circuitry. format, modulation scheme and sets the data rate. As the UWB pulse rate is independent of the data rate, this enables the system to vary the number of UWB pulses per data bit. The narrow pulse generator is formed using a variable voltage-controlled oscillator (VCO), delay circuitry and an XOR gate. It is able to produce a narrow pulse ranging from 0.5 ns to 2 ns, with a variable pulse repetitive frequency of between 17 MHz to 170 MHz. The narrow pulse and 4 GHz VCO are combined to form the UWB signal centered at 4 GHz with a 500 MHz bandwidth. The generated narrow pulse passes through a bandpass filter, which shapes the pulse spectrum to conform to the UWB requirement. After passing through the filter, the UWB pulse is amplified using a wideband low noise amplifier (LNA) to meet the dbm/mhz effective isotropic radiated power spectral density level requirement. The digital output of the micro-controller and the UWB signal are combined using the logic gates before transmitting the information via the UWB antenna. The generated UWB pulse and its corresponding spectrum are shown in Fig. 2(c) and (d), respectively. The system has been designed to operate in the GHz frequency band using direct modulation technique (i.e., no carrier is used). From the output of the transmitter, the peak-to-peak amplitude of the pulse is 190 mv with a pulse width of 2 ns. The block diagram of the receiver frontend circuit is shown in Fig. 3. The receiver antenna is placed on the body while the receiver front-end circuitry can be placed away from the body. The received signal entering the receiver passes through a 3 5 GHz bandpass filter to eliminate the unwanted out-of-band signals. The filtered signal is amplified by 48 db using three wideband LNAs before down-converting to the baseband signal using a mixer and a 4 GHz VCO. The baseband signal passes through a low-pass filter with 100 MHz bandwidth before going through the baseband amplification stage and recorded using the oscilloscope. B. Antenna Designs The UWB antennas used in this study are shown in Fig. 4. The dielectric substrate used for the antennas is Rogers 4003C with an and a thickness of mm. The width of the 50 microstrip line used to excite the antennas is 1.86 mm. The Antenna A is an omni-directional printed monopole antenna. The size of the antenna is mm [17]. The Antenna B is a directional antenna of the same size as Antenna A. It is made up of an L-shaped radiator that is connected to the ground plane on the front side of the PCB via a shorting wall. The feeding plate is located beneath the radiating plate and soldered to the microstrip line on the reverse side of the PCB [18]. The Antenna C is a dual-port antenna with pattern diversity characteristics and has a size of mm. The notched radiators are positioned in a and 135 configuration. The isolation between Fig. 4. Antenna designs (a) Antenna A; (b) Antenna B; (c) Antenna C (units in mm). the two radiating elements is more than 20 db, which has been effectively enhanced by having a central strip that extends vertically from the ground plane [19]. In the figures, the orientation of the Antennas A and C correspond to the vertical polarization, while Antenna B corresponds to the horizontal polarization. III. RESULTS AND DISCUSSIONS A. Received Signal Measurements As a reference, the received waveform is recorded as shown in Fig. 5 when the transmit and receive antennas are separated at a distance of 1 m in free space. The peak amplitude is around 13 mv and 30 mv when a pair of Antenna A and B is used as the transmit and receive antennas, respectively. All the measurements are conducted inside the anechoic chamber with the human subject standing in an upright position. The transmitter is located on the left chest, forehead, left wrist, and center waist. The simulated 3D radiation plots are obtained for the total electric fields when the transmit antenna is placed on the left chest and receive antennas are placed near the right waist/left arm/center chest at selected polarizations. The various parts of the human body are modeled as homogeneous layers of tissues and their compositions and parameters at 4 GHz are given in Table I based on the parametric model [20]. It must be noted that in the simulations, the effect of the transmitter that is connected to the transmit antenna has not been taken into account.

4 5376 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 11, NOVEMBER 2012 Fig. 5. Measured received waveforms in free space. Fig. 6. Simulated normalized 3D patterns of the total electric fields for Antennas A and B on the body when the transmit antenna is placed on the left chest and the receive antenna placed on the right waist/left/arm/center chest. TABLE I TISSUE PARAMETERS AND COMPOSITION FOR THE VARIOUS PARTS OF THE 4 GHz Fig. 7. Simulated normalized 3D patterns of the total electric fields for Antennas A and B on the body when the transmit antenna is placed on the forehead and the receive antenna placed on the right waist/left/arm/center chest. It can be observed that the radiation plots that are normalized to 6 dbi are able to correspond well with the amplitude of the received waveforms, which is dependent on the positions of the transmit and receive antennas on the body as well as their relative positions and the distance between them. From Fig. 6, it can be seen that in the case of Antenna A, the gain is relatively weak and the maximum radiation (yellow region) is directed outwards from the body and is elliptical in shape. This implies that when the receive antenna is placed far away from the transmit antenna, e.g., on the right waist, a higher received signal strength can be achieved with the receive antenna horizontally polarized. Furthermore, when the transmit antenna is placed on the left arm, the radiation null which occurs due to the absorption by the body is directed towards the transmit antenna on the left chest. Hence, it will be expected that the received signal to be extremely weak. In the case of Antenna B, it can be seen that the gain is higher and the radiation is more directional than Antenna A. Also, it can be observed that it is possible to improve the transmission by directing the maximum radiation direction towards the transmit antenna when the receive antenna is placed on the right waist or the antenna is horizontally polarized when placed on the center chest. Fig. 7 shows the simulated 3D radiation plots for the total electric fields when the transmit antenna is placed on the forehead. For each location of the transmitter, the peak amplitude of the received waveforms when the receiver is placed on the right waist, left arm, and center chest are recorded for the vertical and TABLE II CHEST WHEN TRANSMITTER IS PLACED ON THE LEFT CHEST horizontal antenna polarizations. In this study, Antenna A or B is the transmit antenna, while either Antenna A, B, CL, or CR has been chosen to be the receive antenna. Table II shows the peak amplitudes of the received signals at different receive antenna locations when the transmitter is placed on the left chest. In the case where the monopole-type Antenna A is used as the transmit antenna and the receive antenna placed on the center chest, it can be seen that the strongest signals occur when both the transmit and receive antennas are vertically polarized. Also, strong signals can generally be achieved when the transmit antenna is vertically polarized. However, the signal gets weaker when the transmit antenna is horizontally polarized. On the other hand, when the directional-type Antenna B is used as the transmit antenna, stronger signals can be achieved generally due to the higher gain of Antenna B as shown in Fig. 6. Moreover, when the

5 SEE et al.: EXPERIMENTAL STUDY ON THE DEPENDENCE OF ANTENNA TYPE AND POLARIZATION 5377 TABLE III CHEST WHEN TRANSMITTER IS PLACED ON THE FOREHEAD monopole-type Antennas A and C are used as the receive antennas, the signals obtained when they are horizontally polarized are weaker than when they are vertically polarized. On the other hand, when Antenna B is used as the receive antenna, strong signals can be achieved for the different transmit-receive antenna polarization combinations. When the receive antenna is placed on the left arm and Antenna A used as the transmit antenna, weak signals are obtained for most of the different transmit-receive antenna polarizations despite the closer proximity between the antennas. This is mainly because of the weak line-of-sight propagation between the antennas due to the blockage by the arm. Generally, at all the three receiver locations, reasonable signal strength can still be achieved when the receive antenna is horizontally polarized. This observation can be deduced from Fig. 6, where the directional radiation property of Antenna B as well as its relative position with respect to Antenna A makes it possible for the horizontal polarization to achieve better RF transmission than the vertical polarization. When Antenna B is used as the transmit antenna, the received signals on the left arm are generally weaker than the received signals on the center chest, but still relatively strong due to the higher gain of Antenna B. When the receive antenna is placed on the right waist, the waveform amplitude is generally lower as the signal needs to propagate a longer distance from the chest to the waist. Generally, higher signal strength can be obtained when the transmit antenna is vertically polarized. The optimum location of the receive antenna is found to be at the center chest when the transmitter is placed on the left chest. In cases where there is weak line-of-sight between the transmit and receive antennas, the receive antenna be horizontally polarized. The gain of Antenna C is comparable to that of Antenna A. Moreover, it is able to receive higher signal strength from at least one of the ports at most of the receiver locations as compared to Antenna A. This suggests that diversity can be used to enhance the received signal strength, especially in cases where the link quality is poor. Table III shows the peak amplitudes of the received signals at different receiver locations when the transmitter is placed on the forehead. It can be observed that when Antenna A is used as the transmit antenna and the receive antenna is placed on the center chest, stronger signals can be received when the transmit and/or receive antennas is horizontally polarized. This can be predicted from Fig. 7, where the radiation pattern of the transmit antenna on the forehead is directed downwards when it is horizontally polarized. On the other hand, when Antenna B is used as the transmit antenna, better signal reception can be obtained when Antenna B is vertically polarized, which is due to the radiation being directed downwards as shown in Fig. 7. Due to the higher gain of Antenna B, it can be seen that good transmission can be achieved for all the antenna polarization combinations when it is used as both the transmit and receive antennas. Also, due to the difference in the tissue thickness and composition on the forehead and on the left chest, the radiation patterns when the same antennas are placed on the forehead and on the left chest will be different. The advantage of using Antenna C over Antenna A is more prominent when Antenna B is used as the transmit antenna. From the table, it can be seen that when the receive antenna is placed on the center chest, the signal received by at least one of the ports of Antenna C is stronger than that of Antenna A. Similar observation can be made when the Antenna C is horizontally polarized and placed on the left arm. From the results, it can be seen that the optimum location of the receive antenna when Antenna A is used as the transmit antenna will be on the left arm and when both antennas are horizontally polarized. However, when Antenna B is chosen as the transmit antenna, the optimum location of the receive antenna will be at the center chest due to the closer proximity and reduced blockage between the transmit and receive antennas. On the other hand, when the transmit antenna is placed on the forehead, the signal strength when the receive antenna is placed on the left waist will be considerably weaker due to the longer propagation distance from the forehead to the waist as well as some degree of blockage by the body. From the study conducted above, it can be seen that the transmission using the directional antenna is generally stronger due to the higher antenna gain. Hence, it will be useful to examine if this phenomenon is still valid when the gain of Antenna B is reduced to that of Antenna A. The effect on the received signal strength when the gain of Antenna B is reduced by around 6 db in order to match the gain of Antenna A will be studied. The FCC has placed stringent requirement on UWB transmission, allowing a peak transmission power limit of 0 dbm and an average limit of dbm. Therefore, it is important to maximize the transmission power to enhance the system performance. In practice, the measurement of the average and peak power can be calculated easily using a spectrum analyzer. For the average power measurement, the resolution bandwidth is 1 MHz with an integration time of 1 msec. A resolution bandwidth of between 1 to 50 MHz can be used for the measurement of the peak power. The peak transmission limit is dependent on the resolution bandwidth of the spectrum analyzer according to (1) [21] Hence, with a 3 MHz resolution bandwidth of the spectrum analyzer, in order to obtain a stronger received signal for a more accurate analysis, the transmit power has been adjusted to dbm, which is the maximum permissible transmit power level. (1)

6 5378 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 11, NOVEMBER 2012 TABLE IV CHEST WHEN TRANSMITTER IS PLACED ON THE LEFT CHEST TABLE VII EXPERIMENTAL SETTINGS TABLE V CHEST WHEN TRANSMITTER IS PLACED ON THE FOREHEAD arm, which is due to the reduced line-of-sight between the transmitter and receiver. TABLE VI CHEST WHEN TRANSMITTER IS PLACED ON THE LEFT WRIST AND CENTER WAIST (USING ANTENNA B) Furthermore, in order to ensure that the antennas do not exceed the peak transmit power limit, attenuators are connected to the output of the transmitter to compensate for the antenna gain. As shown in Table IV, the peak amplitudes of received signal on the right waist, left arm, and center chest are recorded when the transmitter is on the left chest. For antenna B, an attenuator of 6 db is connected to the output of the transmitter in order to match the gain to that of Antenna A. When the receiver with Antenna B is placed on the right waist, strong signals for almost all the polarizations are obtained when using Antenna A as the transmit antenna. However, when the receiver is placed on the left arm, stronger signals are obtained when using Antenna B as the transmit antenna, and when the Antenna B is horizontally polarized. When the receiver is placed on the center chest, strong signals could be obtained for almost all the polarizations when either Antenna A or B is used at the transmitter. The peak amplitudes of received signal are recorded as shown in Table V with the transmitter located on the forehead. When the receiver is placed on the right waist as well as the center chest, strong signals are obtained when either Antenna A or B is used at the transmitter. The optimum transmit-receive antenna polarization is found to be V-H. However, when the receiver is placed on the left arm, stronger signals are obtained when using Antenna A as the transmit antenna. The optimum transmit-receive antenna polarization is found to be H-V. In addition, the transmitter is also placed on the left wrist and center waist. For brevity, only Antenna B is used on both the transmitter and receiver. The results are shown in Table VI. When the transmitter is placed on the left wrist, the best receiver location will be on the left arm, since there is significant blockage by the body when the receiver is placed on the right waist and center chest. On the other hand, when the transmitter is located on the center waist, good transmission can be achieved when the receiver is located on the center chest and right waist, but becomes significantly weaker when it is placed on the left B. Bit Error Rate Analysis The recovered UWB pulse is digitized using a high-speed analog-to-digital converter (ADC) and processed by the FPGA before transferring the data to the laptop using a serial cable. The function of the FPGA is to process the received multiple UWB pulses and for a certain threshold, determine whether it is bit 1 or bit 0 before sending to the laptop as well as to set the appropriate baud rate for data transfer to the laptop. Preprocessing is necessary as the data transfer rate via the serial cable is much lower than the rate of data transfer from the sensor nodes to the UWB receiver using the gating method. After the processing by the FPGA, the data is transferred to the laptop and the BER is computed based on a known pseudo-random data sequence from the transmitter. The bit error rate is calculated based on the experimental settings shown in Table VII. The UWB pulse rate is selected to be much higher than the actual data rate in order to allow for processing gain and ease the synchronization process. The sensor nodes have been designed to perform gating operation, which allows the transmitter to transmit at the maximum peak power of dbm based on a 3 MHz resolution bandwidth. Four different transmitter locations, namely the left chest, forehead, left wrist and center waist, which are commonly used for physiological signal monitoring, have been chosen to evaluate the performance of the UWB WBAN. The measurements are conducted in the anechoic chamber where the human subject remains stationary. For each measurement scenario, 5 sets of reading are taken and each set of reading consists of data bits. Fig. 8 shows the BER curve when the transmitter is placed on the left chest. For instance, AB Waist VH refers to the case where transmitter Antenna A is placed on the left chest and vertically polarized; receiver Antenna B is placed on the right waist and horizontally polarized. The transmit power can be varied by using RF attenuators and the corresponding BER is calculated. As it can be seen from Fig. 8, when the transmit antenna is vertically polarized, the lowest transmit power is required to achieve a low BER when the receiver is placed on the center chest. However, when the receiver is placed on the arm, a much higher transmit power is required in order to achieve a low BER. From Fig. 8, it is able to deduce the minimum transmit power that is required in order to achieve zero BER for the various

7 SEE et al.: EXPERIMENTAL STUDY ON THE DEPENDENCE OF ANTENNA TYPE AND POLARIZATION 5379 TABLE IX OPTIMUM TRANSMIT POWER (IN dbm) TO ACHIEVE ZERO BER WHEN ANTENNA C IS USED AS THE RECEIVE ANTENNA TABLE X SUMMARY ON THE OPTIMUM TRANSMIT-RECEIVE ANTENNA TYPES AND POLARIZATIONS AT DIFFERENT LOCATIONS ON THE BODY Fig. 8. No. of error bits at different transmit power levels when transmitter is placed on the left chest. TABLE VIII OPTIMUM TRANSMIT POWER (IN dbm) TO ACHIEVE ZERO BER antenna types and polarizations at the different receiver locations. This information will be very useful to conserve the battery power. Table VIII summarizes the minimum transmit power that is required in order to achieve zero BER for the different transmitter locations. It can be seen that when the transmitter is placed on the head, a higher transmit power is generally required for most of the cases as compared when the transmitter is placed on the left chest. When Antenna A is used as the transmit antenna, the receiver located on the center chest requires a lower transmit power as compared to the right waist. However, when the transmit antenna is changed to Antenna B, the reverse occurs. This shows that for different types of transmit antennas, the location of the receiver can be optimized in order to minimize the transmit power. When the transmitter is placed on the wrist, the least transmit power is required when the receiver is located on the arm. On the other hand, a much higher transmit power is needed when the receiver is placed on the right waist. This is due to the significant blockage between the right waist and the left wrist by the body. Last, when the transmitter is placed on the center waist, due to the close proximity to the receiver, the lowest transmit is required. On the other hand, the highest transmit power is needed when the receiver is located on the arm, which is due to the long distance between the transmitter and receiver as well as certain extent of blockage by the body. On the receiver end, Antenna B is replaced by Antenna C and the optimum transmit power required is recorded in Table IX. Both the transmit and receive antennas are vertically polarized. When the transmitter with Antenna A is placed on the left chest and forehead, a lower transmit power is required for Antenna CL as compared to Antenna CR. However, when Antenna B is used at the transmitter, Antenna CR requires a lower transmit power than Antenna CL. In the table, there are some null entries as the required transmit power in those cases is larger than the allowable peak limit of dbm. From this study, it can be seen that for the different types of transmit antenna, the Antenna C is able to make use of its diversity in order to achieve a low BER with a low transmit power. Based on the BER results obtained, a summary of the optimum transmit-receive antenna types and polarizations at the different locations on the body is summarized in Table X. The information shown suggests that in order to achieve the optimal system performance in terms of the BER with a low transmit power, the antenna type and polarization should be properly selected. IV. CONCLUSION This paper presents an experimental study to locate the optimal types and polarizations of the transmit and receive antennas at the various locations on the body. The typical transmitter locations where useful physiological signals can be obtained have been chosen. The antennas with different radiation properties have been used on the transmitter and receiver and the peak amplitude of the received waveform and the bit error rate of the system have been used to evaluate the system performance. From the study, it can be seen that there is good correlation between the radiation patterns of the antennas in the presence of the body and the amplitude of the received waveform for the different locations on the body. The horizontally polarized antennas may be used to improve the transmission in scenarios where there is poor line-of-sight due to body blockage. Moreover, it has been shown that the pattern diversity antenna has been effective in providing another degree of freedom to enhance the link reliability in on-body systems. By properly selecting the type and polarization of the transmit and receive antennas for the different body locations, the system performance can be optimized in terms of reducing the transmit power by more than 20 db while maintaining a very low bit error rate, which will in turn translate to an increase in the life span of the battery.

8 5380 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 11, NOVEMBER 2012 REFERENCES [1] Federal Communications Commission (FCC), Feb. 14, 2002, First report and order. [2] K. Y. Yazdandoost and R. Kohno, Design and analysis of an antenna for ultra-wideband system, presented at the 14th IST Mobile and Wireless Communications Summit, Dresden, Germany, [3] K. Y. Yazdandoost and R. Kohno, UWB antenna for wireless body area network, in Proc. IEEE Asia-Pacific Microw. Conf., 2006, pp [4] E. Jovanov, A. O Donnell-Lords, D. Raskovic, P. Cox, R. Adhami, and F. Andrasik, Stress monitoring using a distributed wireless intelligent sensor system, IEEE Eng. Medicine Biol. Mag., vol. 22, no. 3, pp , May/Jun [5] Y. Hao and R. Foster, Topical review: Wireless body sensor networks for health-monitoring applications, Physiol. Meas., vol. 29, no. 11, pp. R27 R56, [6] K. Kim, I.-S. Lee, M. Yoon, J. Kim, H. Lee, and K. Han, An efficient routing protocol based on position information in mobile wireless body area sensor networks, in Proc. NETCOM, 2009, pp [7] T. S. P. See, Z. N. Chen, and X. M. Qing, Proximity effect of UWB antenna on human body, in Proc. IEEE Asia-Pacific Microw. Conf., Dec. 2009, pp [8] T. S. P. See and Z. N. Chen, Experimental characterization of UWB antennas for on-body communications, IEEE Trans. Antennas Propag., vol. 57, no. 4, pp , Apr [9] W.-T. Chen and H.-R. Chuang, Numerical computation of human interaction with arbitrarily oriented superquadric loop antennas in personal communications, IEEE Trans. Antennas Propag., vol. 46, no. 6, pp , Jun [10] A. Alomainy, Y. Hao, C. G. Parini, and P. S. Hall, Comparison between two different antennas for UWB on-body propagation measurements, IEEE Antennas Wireless Propag. Lett., vol. 4, pp , [11] J. A. Ruiz and S. 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Wireless Technolology Conf., Paris, France, Sep , [17] T. S. P. See and Z. N. Chen, Characterization of received pulses by antennas in proximity of human body, presented at the 2nd Eur. Conf. on Antennas and Propagation, Edinburgh, U.K., Nov , [18] T. S. P. See and Z. N. Chen, An electromagnetically coupled UWB plate antenna, IEEE Trans. Antennas Propag., vol. 56, no. 5, pp , [19] T. S. P. See and Z. N. Chen, An ultra-wideband diversity antenna, IEEE Trans. Antennas Propag., vol. 57, no. 6, pp , [20] C. Gabriel, Compilation of the Dielectric Properties of Body Tissues at RF and Microwave Frequencies, Occupational and Environmental Health Directorate, Radiofrequency Radiation Division, Brooks Air Force Base, TX, Rep. N.AL/OE-TR , Jun. 1996,. [21] US Code of Federal Regulations, Title 47, Chapter 1, FCC, Part 15 Subpart F Ultra-Wideband Operation, Section (g), Oct. 1, 2011 [Online]. Available: Terence S. P. See was born in December 1977 in Singapore. He received the B.Eng. and M.Eng. degrees from the National University of Singapore, in 2002 and 2004, respectively. In 2004, he joined the Institute for Infocomm Research, Singapore, as a Research Engineer, and is currently a Senior Research Engineer in the Antenna group, RF, Antenna and Optical Department. His main research interests include antenna design and theory, particularly in small and broadband antennas and arrays, diversity antennas, antennas for portable devices, and antennas for body-centric wireless communications. Since 2004, he has authored and coauthored more than 30 papers published in international journals, conferences, and three book chapters. He currently holds four granted and filed patents. Mr. See was a recipient of an NUS graduate scholarship in Tat Meng Chiam received the B.Eng. degree in electronic engineering from the Singapore Institute of Management, SIM University, in In 2005, he joined the Institute for Infocomm Research, (I R, A*STAR), Singapore, where he is currently a Research Engineer in the RF, Antenna and Optical Department. Michael C. K. Ho received the B.S. degree and Ph.D. degree in electrical engineering from the University of Newcastle, Australia, in 2006 and 2011, respectively. In 2011, he joined the Institute of Microelectronics, Agency for Science, Technology and Research (A*STAR), Singapore, where he is currently a Scientist in the Integrated Circuits and Systems Department. His research interests include UWB communication scheme, body channel communication, implantable and wearable biomedical devices, ASIC design, wireless power and data link, sensor interface, integrated ASIC and MEMS biomedical device development and wireless communications Mehmet Rasit Yuce (SM 12) received the M.S. degree in electrical and computer engineering from the University of Florida, Gainesville, in 2001 and the Ph.D. degree in electrical and computer engineering from North Carolina State University (NCSU), Raleigh, in December From August 2001 and October 2004, he was a Research Assistant with the Department of Electrical and Computer Engineering, NCSU. In 2005, he was a Postdoctoral Researcher in the Electrical Engineering Department, University of California at Santa Cruz. He was a Senior Lecturer in the School of Electrical Engineering and Computer Science, University of Newcastle, New South Wales, Australia, until July In July 2011, he joined the Department of Electrical and Computer Systems Engineering, Monash University, Australia. His research interests include wireless implantable telemetry, wireless body area network (WBAN), bio-sensors, MEMs sensors, integrated circuit technology dealing with digital, analog and radio frequency circuit designs for wireless, biomedical, and RF applications. He has published more than 80 technical articles in the above areas. He is an author of the book Wireless Body Area Networks published in Dr. Yuce is a member of the IEEE Solid-State Circuit Society, IEEE Engineering in Medicine and Biology Society, and IEEE Circuits and Systems Society. He received a NASA group achievement award in 2007 for developing an SOI transceiver and a research excellence award from the Faculty of Engineering and Built Environment, University of Newcastle in 2010.