Biomedical Engineering Reference
In-Depth Information
Fig. 2.4 ER based UWB
communication
ER
Sensors
outside
the ER
Sensors
within the ER
Receiver
cause interference to each other. However, the transmitter sensor nodes that are not
located inside an ER do not cause interference at the targeted receiver. In this MAC
protocol, the data communication of sensor nodes within the same ER is resolved
temporally using Time Hopping codes (TH-codes), while the sensor nodes in dif-
ferent ERs are allowed to transmit data concurrently. All the sensor nodes transmit
data asynchronously. The main objective of this MAC protocol is to minimize the
interference that can occur in a multiple UWB transmission environment, while
optimizing the throughput using concurrent transmissions in mutually exclusive
ERs. Figure
2.4
depicts the sensor communication using the ERs.
Drawbacks: Although this MAC protocol addresses the issue of interference
mitigation in UWB multiple access, it does not investigate the efficiency of
important factors such as pulse synchronization and multiple access for sensor
nodes within the same ER. It also assumes that a sensor node can determine
whether it is within the range of a certain ER by accurate ranging capabilities.
2.6 UWB
2
The Uncoordinated Wireless Baseborn Access for UWB Networks (UWB
2
) pro-
tocol [
15
,
16
] utilizes orthogonal time hopping codes in order to achieve multiple
access in a shared medium. In this protocol, each node is identified using a unique
TH-code, which is generated using the method provided in [
17
]. A common TH-
code is used in order to communicate control messages and sensor initialization.
At initialization, a sensor node sends a Link Establishment (LE) frame shown in
Fig.
2.5
a, using the common TH-code. In this LE frame, the sensor node proposes
a TH-code to be used for communication between the sensor and the coordinator.
The coordinator node then replies with a Link Control (LC) message and listens
to the TH-code allocated for the sensor node. The sensor initialization is followed
by the data communication using the suggested TH-code and the data frame
format shown in Fig.
2.5
b. The UWB
2
MAC protocol supports both acknowledged
and un-acknowledged data communication. The main advantage of this MAC
