Biomedical Engineering Reference
In-Depth Information
delay performance for Slotted ALOHA is better than that for the ALOHA when
continuous signal data is transmitted. The performance further improves for slotted
ALOHA when the number of GTS increases. The results show that when the
number of GTS for slotted ALOHA is increased from 7 to 12, worst case delay
drops from 75 to 25 ms. However, ALOHA has better delay performance as
compared to slotted ALOHA for routine data. The results also show that the
performance of slotted ALOHA degrades for routine signal as the number of GTS
increases. In terms of delay, slotted ALOHA performs better for continuous signal
monitoring, but not for routine signal monitoring.
Bit Error Rate (BER) analysis for on-body WBAN sensor nodes that commu-
nicate using IEEE 802.15.4a is analysed in [
10
]. The results show that the BER
increases significantly as the number of on-body sensor nodes increases. The
analysis shows that in order to maintain an acceptable BER of 10
-3
, the maximum
number of attached on-body sensor nodes has to be limited to six. The analysis is
carried out based on a single user scenario where all the sensor nodes are attached
to a single patient. The performance of the WBAN system will significantly
degrade if there are other users in the same vicinity.
Drawbacks: The IEEE 802.15.4a standard has similar drawbacks as the IEEE
802.15.6 standard, such as the frequent use of a UWB receiver at the sensor nodes
and disregarding the dynamic power control capability achievable through UWB
physical layer manipulations. In addition, it does not support high data rate
communication; hence restricts the extraction of the benefits provided by the UWB
communications.
2.4 PSMA-Based MAC
The work presented in [
11
,
12
] analyses the performance of an IR-UWB MAC
protocol for medical data monitoring in terms throughput and power consumption.
It presents a MAC protocol based on a medium access protocol called Preamble
Sense Multiple Access (PSMA), where the WBAN sensor nodes sense a preamble
in order to detect a busy channel or an idle channel condition. Every sensor node
attaches a preamble sequence at the beginning of a data packet. The presence of
this preamble code in the channel indicates a busy channel condition. The
objective of using a preamble sequence is to minimize the false alarms and miss
detections that can occur in traditional energy or feature based CCA methods [
13
].
The suggested MAC protocols in [
11
,
12
] also uses a beacon enabled super frame
structure inspired by the IEEE 802.15.4a standard. The operation of the proposed
medium access method is depicted in Fig.
2.3
.
The throughput and energy consumption analysis presented in [
11
] compares
the performance of the PSMA based MAC with the slotted ALOHA based IEEE
802.15.4a standard. The comparison shows that the suggested MAC protocol
performs better in terms of throughput and energy consumption for WBAN s
consisting of large number of sensor nodes.
