Biomedical Engineering Reference
In-Depth Information
Fig. 3.12 Different network
topologies used in the
simulations
Topology 2
Topology 1
Patient: n
Patient: n
Coordinator
Coordinator
Patient: n+1
Patient: n+1
3.4.1 Network Topologies and Interference Model
Two different network topologies are simulated in order to investigate the effect of
using intermediate router nodes on the network performance (Fig.
3.12
). Topology
1 uses a router as an intermediate node between sensor nodes and coordinator
node. The router node gathers data sent by the sensor nodes using a UWB receiver
and transmits them to the coordinator node using a UWB transmitter. The router
node uses a 433 MHz ISM band receiver to receive control messages related to
router-coordinator interface from the coordinator node and transmits control
messages related to router-sensor node interface using a narrowband transmitter
operating in the same frequency band. Router nodes have the ability to store and
forward data. Router nodes use the MAC protocol and super frame structure for its
data communication with both sensor node side and the coordinator node side of
the network. Data communication between router nodes and sensor nodes uses
both CAP and CFP while data communication between router nodes and coordi-
nator node uses only CFP with several GTS allocated per a router node depending
on the data transmission requirement. Cluster tree routing [
23
], which is used for
Zigbee is adapted for the use of UWB based data transmission and is implemented
as the routing protocol in Topology 1. The motivation behind using a router as an
intermediate node is to decentralize the coordination within the network by
dividing it into sub networks. It also helps to optimize the power consumption in
the sensor nodes. In Topology 2, sensor nodes directly communicate with the
coordinator.
All the nodes are contained in a 10 m 9 10 m Opnet simulation environment.
The router nodes are kept at a distance of 0.5 m in Topology 1. An average
separation of 1.5 m is assumed between the subnets in this topology. The router
nodes are kept at an average distance of 1.5 m from the coordinator node. In
Topology 2, each sensor node is placed at an average distance of 2 m from the
coordinator node.
The interference between the subnets is minimized using two methods. As the
first method, the pulse transmit power of the sensor nodes are set at a lower value,
such that the power leakage between subnets is minimized. The power levels are
