Prioritization of Patient Vital Signs Transmission Using Wireless Body Area Networks - E-Healthcare Systems and Wireless Communications - page 267

the power and channel information from these
sensors, selects the best available channel (i.e.,
the available channel with the best Link Quality
Indicator (LQI) (IEEE Computer Society, 2006)
with least interference from neighboring BANs)
and appropriate minimal transmission power
levels for them, and broadcasts control messages
requesting the sensors to tune their channels to
the specified channel and adjust their transmission
powers. The adaptive TDMA scheme uses the
same channel for one BAN, where the intra-BAN
slot is divided into sub-slots that are accessed
sequentially for data aggregation. The number of
sub-slots assigned to one sensor is decided by its
sampling frequency. The CH can also broadcast
other commands to change other parameters such
as sampling frequency of the sensor.

of functionalities by means of cross-layer design,
it is important to consider the ease of design by
following a modular design approach (Pompili,
Vuran, & Melodia, 2006). This will also allow
improving and upgrading particular functionalities
without the need to re-design the entire commu-
nication system. For these reasons, in our work
we rely on the above-mentioned design guidelines
and propose a cross-layer communication solu-
tion incorporating MAC, routing, and scheduling
functionalities. Our cross-layer solution is based
on current ZigBee standards and IMote2/TelosB
sensors, which means that it can be implemented
and deployed without the need for a new standard
or hardware platform.
Interactions between the scheduling, MAC,
and routing modules are shown as in Figure 1(c).
Basically, each module operates based on the input
from the other two modules and feeds back infor-
mation in the reverse direction so that the other
modules can adjust their operations. The MAC
module, which aims to select the channel with the
best quality for packet forwarding, collects the
channel quality information and passes it to the
routing module, which uses this information to
decide the route to the sink. The routing module ,
which aims to select a path to avoid intermediate
links of bad channel quality, estimates the number
of hops N sink , e2e reliability, and delay to the sink,
passing them to the scheduling module , which also
utilizes N tx (the average number of transmissions
to successfully send a packet) to select a proper
packet to transmit. Because of the close interaction
between these modules, the traffic is served with
different priority based on packet's emergency
state and vital sign requirements.

PROPOSED CROSS-
LAYER SOLUTION

In this section, we present our cross-layer inter-
BAN communication solution for in-hospital
triage. We first provide a brief overview of the
solution and then we present the solution in an
incremental way so that the rationale to adopt our
design for each component is made clear.

Overview

To maximize the network performance for in-
hospital triage, we adopt a cross-layer design
modular approach that jointly considers the
interaction of three modules: MAC, routing, and
scheduling. The goal of this cross-layer design is
to maximize the e2e reliability of the vital signs
with guaranteed e2e delays.
Cross-layer wireless communication solutions
allow for an efficient use of the scarce resources
such as bandwidth and battery energy. However,
although we advocate integrating highly special-
ized communication functionalities to improve
network performance and to avoid duplication

Multi-Channel Quality-Based MAC

Our Multi-channel MAC is designed to have
partial cognitive radio capability. In a cognitive
radio system, the cognitive process typically
starts with spectrum sensing, followed by chan-
nel identification and spectrum management