Biomedical Engineering Reference
In-Depth Information
consumes very small power since it is only powered on when required (for
example, sleep mode operation in a periodic data transmission).
Compared to the transmit-only method a UWB WBAN system with narrow-
band feedback improves the network and reduces collisions. It also helps to
optimize the power consumption of the sensor node, introducing additional power
savings. In a system where both transmitter and the receiver use UWB, a turn-
around time should be used to switch from transmit state to receive state. In other
words, transmitter and receiver cannot operate at the same time due to the inter-
ference. Since we are using a narrow band receiver, it is possible to operate both
transmitter and receiver simultaneously; hence reducing the packet delay. Also,
independent downstream/upstream communication enables a much simpler MAC
design.
The MAC protocol presented in this chapter is unique in the sense that it is
developed to enhance the performance of a WBAN using the high data rate offered
by the UWB transmission while using a narrowband feedback path to avoid the
complexities given by a UWB receiver. In this MAC protocol, the priority of data
is taken into consideration and a guaranteed delivery mechanism is utilised to
transfer data with high priority. Different topologies are simulated in order to
investigate
various
performance
indicators
of
the
network
design
such
as
throughput, power consumption and delay.
3.2 Simulation Models
Simulations presented in this chapter are conducted in a co-simulation approach
using Matlab [
7
] and Opnet Modeler [
8
], which are commercially available sim-
ulation softwares. Physical layer simulations are done in Matlab. Matlab is linked
to Opnet Modeler using ''MX interface'' provided in Matlab. Opnet Modeler runs
in interactive co-simulation with Matlab for networking performance analysis and
it calls Matlab for physical layer performance. During a simulation, Opnet exe-
cutes as the master simulator, and invokes Matlab engine server to execute the
UWB transmitter developed in Simulink [
7
]. Opnet then takes back the control of
the simulation and executes networking functions. At the receiver stage, Opnet
again calls Matlab to execute UWB pulse receiver block. Output data bits of the
receiver stage are then used to generate the received data packets.
3.2.1 IR-UWB Pulse Generation
IR-UWB transmit pulse generation is achieved using Matlab, which is then used in
co-simulation with Opnet Modeler. This pulse generation technique is shown in
Fig.
3.2
. An IR-UWB signal with a bandwidth of 1 GHz centered at 4 GHz is
considered for the simulations. The pulse repetitive frequency (PRF), pulse width
