Information Technology Reference
In-Depth Information
Figure 11. The throughput comparison in a multi-hop scenario
when increasing the number of sending nodes;
and it goes no further than 1.59Mbps. This result
explains the advantage of the utilization of channel
diversity by H-MAC compared to Z-MAC which
uses one single channel.
We have simulated three protocols H-MAC,
LCM-MAC, and MMAC. For MMAC, the
specified values in (So and Vaidya, 2004) of 80ms
for data window and 20ms for the ATIM window
are used. Note that it is fair to compare the three
protocols H-MAC, LCM-MAC and MMAC to-
gether as they use one interface. LCM MAC
performs better than (or similar to) MMAC at all
times.
We noticed that, despite using time synchro-
nization, MMAC's performance is not improved
at low loads. This is due to the large data window
size. At low loads senders run out of packets
to send to the receivers present in their current
channel. As they cannot change channel until
the end of data window, this results in wastage of
bandwidth. LCM-MAC also does not give propor-
tional improvement with the increase in channels.
Contrary to LCM-MAC and MMAC, H-MAC
shows better performance in both simulations.
By its dynamic adaptation to the contention level
between CSMA and TDMA, H-MAC maintains its
good performance, and thus the data throughput
increases progressively with the increase in the
number of used channels.
CHANNEL DIVERSITY EVALUATION
In this simulation, we evaluated H-MAC and
compared it against two known multi-channel
protocols, LCM-MAC and MMAC. The simu-
lation scenario was performed with 100 nodes
placed randomly in 500m × 500m area. All the
radio parameters are being ns-2 defaults, and the
nominal bit rate of each channel is set to 1 Mbps.
There are 50 CBR flows with randomly selected
source-destination pairs. The shortest path routing
is used. The data packet sizes are 1000 bytes. The
data packet generation rate for each flow is varied
to vary the load in the network and simulations
are done for different number of channels. 6 and
13 channel results are presented in Figure 12 and
Figure 13.
Search WWH ::
Custom Search