Prioritization of Patient Vital Signs Transmission Using Wireless Body Area Networks - E-Healthcare Systems and Wireless Communications - page 270

a different channel for transmitting and, thus,
interference will be greatly reduced. Therefore,
exposed terminal problem is better handled than
in other competing MAC protocols in the same
class. To show the advantage of our cognitive
radio approach, we compare our solution with the
standard one channel CSMA/CA MAC (denoted
by OC-MAC). Note that we didn't compare our
MQ-MAC protocol with the well-known proto-
cols such as S-MAC (Ye, Heidemann, & Estrin.,
2002) or B-MAC (Polastre, Hill, & Culler, 2004).
These protocols focus on minimization of energy
consumption while our protocol focuses on maxi-
mization of packet reliability, which makes the
protocol design totally different. Therefore such
comparison is not fair. The communication proto-
cols are implemented on TinyOS, the embedded
operating system designed for networked sensors.
These protocols are loaded into the TelosB sensors
and tested in our testbed (Sect. 5.1). Experiments
were carried on in the aisles of the floor (around
50×20 m 2 ) in our building with a sink node located
at one corner as shown in Figure 7(a).
In a multi-hop scenario, comparisons are made
with a network that routes on shortest paths, i.e.,
paths with the least number of hops to the sink.
The performance comparison is shown in Fig-

ure 3. Our results show that exploiting channel
diversity brings a lot of improvement. From the
results above, it is clear that our approach, which
exploits the channel diversity with measured chan-
nel quality, achieves higher packet delivery ratio
than those using only one channel.

Channel Quality Based Routing

The results in Figure 3 show that our MQ-MAC
protocol using multi-channel and measured chan-
nel quality information can achieve better MAC-
layer performance than competing schemes. We
are interested now in extending it into routing
and see how much improvement we can obtain.
Motivated by this, we propose a Channel Qual-
ity Based Routing (CQBR) algorithm that uses
multi-channels and measured channel quality
information for routing. Moreover, the MQ-MAC
scheme proposed in Sect. 4.2 is also incorporated
into the routing algorithm.
We aim at achieving full utilization of the
channels and robustness against interference. The
objectives of our CQBR protocol are:

1. Use measured channel quality to select a
route with the best quality;

Figure 3. One-channel MAC (OC-MAC) vs. MQ-MAC