**5. UWB radar in medical applications**

94 Ultra Wideband – Current Status and Future Trends

**Figure 10.** Magnitude of the channel impulse response for each position of the walking cycle.

position six, where the left hand moves to the lowermost location.

spread ���� is estimated. The ���� is defined as,

where �� is the mean excess delay defined as,

variations of the amplitude is the Weibull distribution.

most prominent peak is clearly shown (Taparugssanagorn et al. 2011).

These experimental results indicate that the arm movements have a significant impact on the radio link A1 (Tx antenna on the left wrist and Rx antenna in the center of the front torso). For instance, when the hand moves to position three the strongest path arrives earlier than in the other positions due to the shorter distance between the antennas. There are also more significant paths due to the interaction of the electromagnetic waves with of the arm and the shoulder. The shadowing of the signal due to blocking by the body is evident in

Fig. 11 provides an alternative view of the channel impulse response where the delay of the

To evaluate the delay dispersion within the channel the root mean square (RMS) delay

���� <sup>=</sup> �� (�����)�|�(��)|� ��� ���

> �� <sup>=</sup> � ��|�(��)| � ��� ��� ∑ |�(��)| ��� � ���

�(�) is the channel impulse response, L is the number of paths and � is the delay. For the case discussed here the estimates for mean and the standard deviation of ���� are 0.1371 ns and 0.0670 ns respectively. Also the probability distribution function that best fits the

∑ |�(��)| ��� � ���

(5)

(6)

The potential use of UWB technology goes beyond transmitting information, collected by sensors, to a control station. The nature of the UWB signal is such that it can be used as in common radar applications, e.g. to detect and estimate dynamic parameters of an object. Fig. 12 shows the channel impulse responses for the case of subjects with and without an aortic valve implant (Taparugssanagorn et al. 2009). The Rx antenna was located at the middle of the front torso and the Tx antenna close to the heart, 10 cm away from the Rx antenna. P200 BroadSpecTM UWB antennas were used for this experiment.

It apparent that the responses are different, i.e. the one corresponding to the subject with an aortic implant has lower peaks. A possible explanation for the difference in the responses is the scattering caused by the metallic (titanium alloy) valve. Subsequent simulation studies carried out using a 3D immersive visualization environment has confirmed this type of results (Yang et al., 2011). Further investigations could lead to the use of the response to infer the nature of the implant behaviour.

The use of UWB signals to directly monitor vital signs is currently a very active research area. Thus for example, the estimation of the breathing rate and the heart beat frequency has been studied in (Lazaro et al., 2010). Using a mathematical model of the human body as related to its effect on the propagation of the UWB signals the feasibility of medical diagnosis using UWB radar technology has been assessed in (Pancera et al., 2011).

The UWB Channel in Medical Wireless Body Area Networks (WBANs) 97

The IEEE 802.15.4 standard and the industrial consortium supporting it, the ZigBee alliance, are widely used in wireless sensor networks (WSNs) applications. The IEEE 802.15.4 standard provides alternative physical layers for devices with precision ranging and extended range (IEEE Std 802.15.4, 2011). The UWB physical layer option of this standard provides for features that are desirable in medical applications such as very low power. The data rates supported are 110 kb/s, 851 kb/s, 1.70 Mb/s, 6.81 Mb/s, and 27.24 Mb/s. Whereas this standard has desired features to be used in medical applications it does not support the levels of safety, quality of service, and security features wanted in many of those applications. Thus, the remainder of this section deals with the IEEE 802.15.6 standard

The final version of this standard has been recently released (IEEE Std 802.15.6, 2012). It specifically deals with wireless communications in the vicinity of, or inside, a human body. It uses existing industrial scientific medical (ISM) bands and other bands. It allows devices to operate on very low transmit power and thus minimizes the specific absorption rate (SAR) into the body as well as increases the battery life. It also supports data rates up to 10 Mbs, quality of service (QoS) and it provides for strong security. The standard takes into

The default mode should support impulse radio UWB (IR-UWB) with a mandatory uncoded data rate of 487.5 kbs. It should also support, as optional PHY, wideband frequency

The standard provides specifications for the physical layer (PHY) and the medium access control (MAC) sublayer. Three PHYs are supported by the IEEE 802.15.6 as illustrated in

The UWB PHY layer constructs the PHY layer protocol data unit (PPDU) by concatenating the synchronization header (SHR), physical layer header (PHR), and the physical layer service data unit (PSDU). The SHR has two parts. The first part is a preamble, intended for timing synchronization, packet detection, and frequency offset recovery. The second part is the start-of-frame delimiter (SFD). Kasami sequences of length 63 are used to build the preamble. The usage of preamble sequences improves coexistence of WBANs and interference mitigation as different WBANs use different preamble sequences. The PPUD is

which has features specifically designed to support medical applications.

account the use of portable antennas in the presence of a human body.

modulation UWB (FM-UWB) with a mandatory uncoded data rate of 250 kbs.

**6.1. IEEE 802.15.4** 

**6.2. IEEE 802.15.6** 

Fig. 13.

**Figure 13.** IEEE 802.15.6 MAC and PHY layers

**Figure 12.** Average channel impulse response for subjects with and without aortic valve implant.

In summary UWB technology can be used not only to transmit information collected by sensors such as ECG electrodes and pulse oximeters but also to actively monitor vital signals and the behaviour of artificial implants.
