**6. Standards**

For WBANs to become widely adopted it is important to have standards. The IEEE 802.15 group of standards focuses on short range communications, low complexity, and low power consumption making them suitable for use in WBANs. Two standards from this group have specifically addressed the use of UWB technology with medical applications in mind. This section describes UWB features of the IEEE 802.15.4 standard of the recently approved IEEE 802.15.6 standard.

The IEEE 802.15 task group 6 (TG6) developed a UWB channel model as part of the process of developing the IEEE 802.15.6 standard (Yazdandoost & Sayrafian-Pour, 2009). A comparison of the IEEE 805.15.6 channel model and the one described in this chapter can be found in (Viittala et al., 2009).

### **6.1. IEEE 802.15.4**

96 Ultra Wideband – Current Status and Future Trends

and the behaviour of artificial implants.

**6. Standards** 

802.15.6 standard.

found in (Viittala et al., 2009).

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).

**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

For WBANs to become widely adopted it is important to have standards. The IEEE 802.15 group of standards focuses on short range communications, low complexity, and low power consumption making them suitable for use in WBANs. Two standards from this group have specifically addressed the use of UWB technology with medical applications in mind. This section describes UWB features of the IEEE 802.15.4 standard of the recently approved IEEE

The IEEE 802.15 task group 6 (TG6) developed a UWB channel model as part of the process of developing the IEEE 802.15.6 standard (Yazdandoost & Sayrafian-Pour, 2009). A comparison of the IEEE 805.15.6 channel model and the one described in this chapter can be 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 which has features specifically designed to support medical applications.

### **6.2. IEEE 802.15.6**

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

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

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 Fig. 13.

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

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

illustrated in Fig. 14. The PPUD bits are converted into RF signals for transmission in the wireless medium.

The UWB Channel in Medical Wireless Body Area Networks (WBANs) 99

To provide or support time reference allocations a hub establishes a time base that divides the time into beacon periods (superframes). A hub transmits a beacon in each superframe, except in inactive superframes, or does not transmit a beacon in any superframe. A hub can

Fig. 16 shows the superframe structure when the hub operates in the beacon mode with superframes. A node can obtain, and initiate frame transactions, in the EAP1, RAP1, EAP2, RAP2, and CAP periods in any active superframe using CSMA/CA or slotted Aloha based

The EAP1 and EAP2 periods are used for the highest priority traffic, i.e. emergency information. The RAP1, RAP2, and CAP period are used for regular traffic. In a MAP period a hub can arrange scheduled uplink, downlink, and bilink allocation intervals. It can also

In non-beacon mode with superframes the entire superframe period is a MAP phase. In the non-beacon mode without superframe boundaries the hub provides polled allocations whose length is specified in terms of the number of frames granted for transmission (type-II

According to this standard all nodes and hubs can choose the following three security levels:

• Level 0 – unsecured communications. The messages are transmitted in unsecured frames. There are no measures for data authentication and integrity validation,

• Level 1 – authentication only. Messages are transmitted in secured authenticated but

• Level 2 – authentication and encryption. Messages are transmitted in secured authenticated and encrypted frames. Confidentiality, privacy protection, and replay

**Figure 16.** Layout of access phases in a superframe period for beacon mode

confidentiality and privacy protection, and replay defense.

not encrypted frames. Confidentiality and privacy is not supported.

provide unscheduled bilink allocation intervals.

operate in one of the following modes:

• Beacon mode with superframes • Non-beacon mode with superframes • Non-beacon mode without superframes

random access protocols.

polled allocation).

defense are supported.

**Figure 14.** IEEE 802.15.6 UWB physical layer protocol data unit (PPDU)

The PHR contains information about the data rate of the PSDU. The coded bit rates supported are shown in Table 3.


**Table 3.** IEEE 802.15.6 UWB-PHY coded bit rates.

According to the IEEE 802.15.6 standard all nodes and hubs are organized into logical sets called body area networks (BANs) as illustrated in Fig. 15. There is one and only one hub in a BAN. The number of nodes in a BAN ranges from zero to nMaxBANSize=64.

**Figure 15.** Network Topology

To provide or support time reference allocations a hub establishes a time base that divides the time into beacon periods (superframes). A hub transmits a beacon in each superframe, except in inactive superframes, or does not transmit a beacon in any superframe. A hub can operate in one of the following modes:

• Beacon mode with superframes

98 Ultra Wideband – Current Status and Future Trends

supported are shown in Table 3.

FM 202.5

**Figure 15.** Network Topology

**Table 3.** IEEE 802.15.6 UWB-PHY coded bit rates.

**Data rate 0 (kb/s)** 

**UWB - PHY** 

**Figure 14.** IEEE 802.15.6 UWB physical layer protocol data unit (PPDU)

Synchronization Header

Preamble SFD

**Data rate 1 (kb/s)** 

wireless medium.

illustrated in Fig. 14. The PPUD bits are converted into RF signals for transmission in the

The PHR contains information about the data rate of the PSDU. The coded bit rates

S� S� ... S� S�� PHR PSDU

PHY Protocol Data Unit (PPDU)

DBPSK/DQPSK 487 975 1950 3900 7800 15600 557 1114

According to the IEEE 802.15.6 standard all nodes and hubs are organized into logical sets called body area networks (BANs) as illustrated in Fig. 15. There is one and only one hub in

**Data rate 3 (kb/s)** 

**Data rate 4 (kb/s)** 

**Data rate 5 (kb/s)** 

**Data rate 6 (kb/s)** 

**Data rate 7 (kb/s)** 

**Data rate 2 (kb/s)** 

On-Off 394.8 789.7 1579 3159 6318 12636

a BAN. The number of nodes in a BAN ranges from zero to nMaxBANSize=64.


Fig. 16 shows the superframe structure when the hub operates in the beacon mode with superframes. A node can obtain, and initiate frame transactions, in the EAP1, RAP1, EAP2, RAP2, and CAP periods in any active superframe using CSMA/CA or slotted Aloha based random access protocols.

**Figure 16.** Layout of access phases in a superframe period for beacon mode

The EAP1 and EAP2 periods are used for the highest priority traffic, i.e. emergency information. The RAP1, RAP2, and CAP period are used for regular traffic. In a MAP period a hub can arrange scheduled uplink, downlink, and bilink allocation intervals. It can also provide unscheduled bilink allocation intervals.

In non-beacon mode with superframes the entire superframe period is a MAP phase. In the non-beacon mode without superframe boundaries the hub provides polled allocations whose length is specified in terms of the number of frames granted for transmission (type-II polled allocation).

According to this standard all nodes and hubs can choose the following three security levels:


Security starts with a negotiation of the desired security suite between a node and a hub. Once the security selection is negotiated the two communicating parties activate a preshared or generate a new shared master key (MK).

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