Biomedical Engineering Reference
In-Depth Information
as continuous signals. The routine signals include body temperature and blood pres-
sure, which are monitored periodically. The time delay is analyzed on the basis of
performance of ALOHA and slotted ALOHA channel access mechanisms on these
two types of signals. The results show that the worst-case 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 with 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 communicate
using IEEE802.15.4a is analyzed in [
25
]. 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
on the basis of 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
IEEE802.15.6 standard, such as the use of a UWB receiver at the sensor nodes and
disregarding the dynamic power control achievable through UWB physical layer ma-
nipulations. Also, it does not support high data rate communication, hence restricts
the extraction of the benefits provided by the UWB communications.
Preamble Sense Multiple Access-Based MAC
The work presented in [
26
] and [
27
] analyzes the performance of an IR-UWB MAC
protocol for medical data monitoring in terms throughput and the 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 [
28
].
The suggested MAC protocols in [
26
] and [
27
] also uses a beacon-enabled su-
per frame structure inspired by the IEEE802.15.4a standard. The operation of the
proposed medium access method is depicted in Fig.
4
.
The throughput and energy consumption analysis presented in [
26
] com-
pares the performance of the PSMA-based MAC with the slotted ALOHA-based
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