Biomedical Engineering Reference
In-Depth Information
Fig. 2.2
The IEEE 802.15.4a standard super frame structure
802.15.4a standard also uses a beacon enabled super frame structure for UWB
PHY layer communication. The maximum number of timeslots is limited to 16.
The super frame is divided into a Contention Access Period (CAP) and a Con-
tention Free Period (CFP). The CAP supports random access using ALOHA, while
the CFP offers Guaranteed Time Slots (GTS) for high priority data traffic. The
IEEE 802.15.4a standard super frame structure is shown in Fig.
2.2
.
The performance of the IEEE 802.15.4a standard for WBAN applications has
been intensively studied in [
9
,
10
]. MAC layer for the IEEE 802.15.4a standard is
almost identical to that of IEEE 802.15.4. The main difference is that mandatory
channel access mechanism is changed to ALOHA or slotted ALOHA rather than
CSMA/CA. This amendment is necessary, as it is difficult to perform CCA on the
low power UWB signal.
In [
9
], the delay performance of the IEEE 802.15.4a standard for WBAN
applications is evaluated based on two categories of physiological signals: con-
tinuous and routine signals. Physiological data such as Electrocardiography (ECG)
and Electroencephalography (EEG) require continuous monitoring: hence, they are
considered as continuous signals. The routine signals include body temperature
and blood pressure, which are monitored periodically. The time delay is analysed
based on the performance of ALOHA and slotted ALOHA channel access
mechanisms on these two types of signals. The results show that the worst-case
