Biomedical Engineering Reference
In-Depth Information
(a)
Sense -
Idle channel
detected
Sense -
Busy channel detected
+ Back-off
Preamble +
Data
Beacon n
Beacon
n+1
(b)
No
Data to send
Yes
Yes
Data
transmission
Waits for
random back-off
time
No
No
Preamble
detected
Back-off timer
expired
Yes
Preamble
detection
Fig. 2.3 PSMA based medium access proposed in [
12
], a data transmission using a super frame
structure; b channel access mechanism
Drawbacks: The major drawback of this MAC protocol is that it assumes the
presence of an IR-UWB based receiver at the sensor node end in order to sense the
channel using PSMA mechanism. Hence, it ignores all the complexities that involve
in using an IR-UWB receiver at WBAN sensor nodes that are mentioned above. It
also does not provide a solution for the case where two or more sensor nodes perform
preamble sense simultaneously, which leads to an eminent collision scenario.
2.5 MAC Protocol Based on Exclusion Regions
A MAC protocol developed based on transmit and receive antenna patterns and the
antenna directionality is proposed in [
14
]. An Exclusion Region (ER) is defined as
an area surrounding a receiver, such that the transmitter sensor nodes within an ER
