**1. Introduction**

84 Ultra Wideband – Current Status and Future Trends

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UWB is a technology that has several advantages when considered for a Wireless Body Area Network (WBAN). A WBAN is a network with its communications devices in very close proximity to the human body. In medical applications these devices are connected to sensors that can monitor vital signs such as ECG, temperature, and mobility. A WBAN allows for the remote monitoring of a patient's health minimizing the number of cables needed. The monitoring of vital signals usually require a relatively low data-rate which in the case of UWB translates into very small transmitting power, long battery life, and less potential side effects caused by electromagnetic radiation. All of these features are very desirable for devices that are close to the body and meant to be used for extended periods of time.

The human body is a complex structure and human tissues have different electrical properties which affect the propagation of electromagnetic signals. Moreover, as the human body moves, the characteristics of the radio links changes, e.g. the link from the chest to a wrist will change from line-of-sight to non-line-of-sight as a person walks.

To be able to design and develop UWB devices that can interface with WBANs it is then necessary to understand well the characteristics of the radio propagation channel at UWB frequencies and in close proximity to the human body. UWB measurements around a human body have been carried out by several researchers (Fort et al., 2006). There is however a lack of measurements, and subsequent analysis, carried out in real medical environment such as hospitals. The studies described in this chapter focus on scenarios most likely to be found in medical applications and as such they do not assume a large amount of antennas in close proximity to the skin. Among the several issues taken into account are the effects of mobility, and the interaction of the UWB signal with medical implants.

© 2012 Pomalaza-Ráez and Taparugssanagorn, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Pomalaza-Ráez and Taparugssanagorn, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **2. Hospital scenarios**

Fig. 1 shows a common hospital room scenario. Medical information is collected by sensors on the patient's body. The sensors are interfaced to a WBAN which transmit the information to be displayed on a bedside monitor. This information can also be transmitted to another hospital location for remote monitoring, e.g. a nurse's station. The radio links present in this type of scenario include the ones between sensor nodes (link A1), the links between the sensors and a gateway node (links A2), and the links from wireless devices carried by visitors or healthcare professionals (link A3). Other possible radio links are from the gateway to wireless networks such as 802.11 b/g/n and WiMAX.

The UWB Channel in Medical Wireless Body Area Networks (WBANs) 87

2 m high pole located 2 m away from the subject and the Tx antenna was on the left side of

the waist.

**Figure 2.** Floor plan of a regular hospital room.

**Figure 3.** Floor plan a surgery room

Figs. 2 and 3 show real hospital scenarios where measurements described in this chapter were taken (Taparugssanagorn et al. 2010). A regular hospital room is shown in Figure 2. This room's dimensions are: 6.3 m x 7.2 m x 2.5 m. A surgery room, with dimensions 6 m x 4.7 m x 2.5 m, is shown in Figure 3. Both radio links A1 and A2 were measured in each room. Within the hospital several scenarios were considered. Table 1 summarizes the measurements and scenarios in this study. A detailed description of the various experiments and the results can be found in (Taparugssanagorn et al. 2010). To illustrate the experiments and analyses performed the case of a subject standing in hospital room is discussed in more detail in the next section.

**Figure 1.** A typical hospital room scenario: A1 is a link between sensor nodes, A2 is a link between a sensor node and a gateway, and A3 is a link to other wireless networks.

To measure the A1 link, the receive (Rx) antenna was located at the centre of the front torso and the transmit (Tx) antenna was placed on the left wrist. These locations are comfortable for most patients and are also convenient places for sensors such as electrodes in the chest areas to generate an electrocardiogram (ECG) and a pulse oximeter on a finger trip to monitor the patient's oxygenation. To measure the A2 link, the Rx antenna was placed on a 2 m high pole located 2 m away from the subject and the Tx antenna was on the left side of the waist.

**Figure 2.** Floor plan of a regular hospital room.

86 Ultra Wideband – Current Status and Future Trends

Fig. 1 shows a common hospital room scenario. Medical information is collected by sensors on the patient's body. The sensors are interfaced to a WBAN which transmit the information to be displayed on a bedside monitor. This information can also be transmitted to another hospital location for remote monitoring, e.g. a nurse's station. The radio links present in this type of scenario include the ones between sensor nodes (link A1), the links between the sensors and a gateway node (links A2), and the links from wireless devices carried by visitors or healthcare professionals (link A3). Other possible radio links are from the

Figs. 2 and 3 show real hospital scenarios where measurements described in this chapter were taken (Taparugssanagorn et al. 2010). A regular hospital room is shown in Figure 2. This room's dimensions are: 6.3 m x 7.2 m x 2.5 m. A surgery room, with dimensions 6 m x 4.7 m x 2.5 m, is shown in Figure 3. Both radio links A1 and A2 were measured in each room. Within the hospital several scenarios were considered. Table 1 summarizes the measurements and scenarios in this study. A detailed description of the various experiments and the results can be found in (Taparugssanagorn et al. 2010). To illustrate the experiments and analyses performed the case of a subject standing in hospital room is discussed in more

**Figure 1.** A typical hospital room scenario: A1 is a link between sensor nodes, A2 is a link between a

To measure the A1 link, the receive (Rx) antenna was located at the centre of the front torso and the transmit (Tx) antenna was placed on the left wrist. These locations are comfortable for most patients and are also convenient places for sensors such as electrodes in the chest areas to generate an electrocardiogram (ECG) and a pulse oximeter on a finger trip to monitor the patient's oxygenation. To measure the A2 link, the Rx antenna was placed on a

sensor node and a gateway, and A3 is a link to other wireless networks.

gateway to wireless networks such as 802.11 b/g/n and WiMAX.

**2. Hospital scenarios** 

detail in the next section.

**Figure 3.** Floor plan a surgery room


The UWB Channel in Medical Wireless Body Area Networks (WBANs) 89

This setup corresponds to a measurement of the S21 parameter where the device under test (DUT) is the radio channel. The range of the frequency spectrum covered was from 3.1 GHz to 10.6 GHz. For each experiment setup 100 frequency responses were measured. The

The measured transfer function frequency values were converted to the time domain (channel impulse response) using an inverse Fast Fourier Transform. A Hamming window

Fig. 5 shows the average of the channel impulse response, corresponding to link A1, when

The effect of the human body and the environment can be clearly differentiated. These results are significantly different than the ones obtained in an empty hospital room (Hentilä et al, 2005). In Fig. 5 the first region of the IR shows a fast decay of the energy during the first 5-6 ns due to the effects of the human body. The decay of the second region in the response is slower and contains the diffuse multipath components and a few subclusters caused by the reflections coming from the room. In this particular case the first of such subclusters, arriving at around 8 ns, is due to a measuring equipment (VNA) which was

For each particular hospital scenario listed in Table 1 the measurements obtained share the

Fig. 6 corresponds to the case when the subject is lying down on bed in a hospital room. Fig. 7 corresponds to the case when the subject is lying down on a bed in a surgery room and two other people are randomly walking around the bed. The Least Squares (LS) fitted lines shown in these figures are used to model the variability of the amplitudes as described in

measurement parameters are summarized in Table 2.

**Table 2.** Measurement parameters

was used to reduce sidelobes.

**3.1. Channel impulse response** 

the subject is standing in the hospital room shown in Fig. 2.

located 1.3 m in front of the subject when is standing.

general characteristics shown in Fig. 5.

Section 3.2.

**Parameter Value**

Bandwidth 6.9 GHz VNA IF bandwidth 3.0 kHz Number of samples per sweep 1601 Maximum detectable delay 231 ns Sweep time 800 ms Average noise floor - 120 dBm Transmit power 0 dBm Tx and Rx cables' loss 7.96 dB

Frequency range 3.1 to 10.6 GHz

**Table 1.** Measurements and scenarios.
