Medium Access Control (MAC) Protocols for Ultra-Wideband (UWB)-BasedWireless Body Area Networks (WBAN) - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 135

Fig. 3 The IEEE802.15.4a standard super frame structure
the inspiration for many UWB based MAC implementations that can be found in the
literature.
The main application of IEEE802.15.4a is for low data rate UWB applications
and ranging applications. Similar to the IEEE802.15.6 standard, the IEEE802.15.4a
standard also uses a beacon-enabled super frame structure for UWB PHY layer
communication. The maximum number of time slots is limited to 16. The super frame
is divided into a contention access period (CAP) and a contention free period (CFP).
The CAP supports random access using ALOHA, whereas the CFP offers guaranteed
time slots (GTS) for high-priority data traffic. The IEEE802.15.4a standard super
frame structure is shown in Fig. 3 .
The performance of the IEEE802.15.4a standard for WBAN applications has
been intensively studied in [ 24 ] and [ 25 ]. MAC layer for IEEE802.15.4a standard
is almost identical to that of IEEE802.15.4. 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 [ 24 ], the delay performance of the IEEE802.15.4a standard for WBAN ap-
plications is evaluated on the basis of two categories of physiological signals:
continuous and routine signals. Physiological data such as electrocardiography and
electroencephalography require continuous monitoring, hence they are considered