Friday, November 29, 2013

Aqua-Sim For Simulating Underwater Acoustic Sensor Networks

When working on terrestrial wireless sensor networks (WSN), we are dealing with electro-magnetic waves to propagate our signals from a sender to a receiver. However, underwater sensor networks are significantly different from their terrestrial counterpart due to the usage of acoustic signals for communication. In underwater environments we are unable to depend on radio signals for communication in long distances since higher attenuation of radio signals when traveling through water. Therefore acoustic signals is the only or most prominent and practical solution so far.

Simulating underwater acoustic sensor networks (UASN) requires special propagation models and other considerations specific to the unique features of acoustic physical medium . Due to this reason, its not possible to simulate UASNs using simulators used for terrestrial WSNs with same configurations. That means we need simulators which specifically support UASNs. Aqua-Sim is such a simulator which is based on NS-2 and therefore I found it easier to use than learning a completely new simulator. Today I installed it and ran a test TCL script to initiate using it for my simulation requirements of UASN. Since its a modified version of standard NS2 simulator, there's nothing new to be done to install it. However since I faced some error during the installation, I decided to write down the steps I followed for future reference.

First I had to download the source files of Aqua-Sim from the following link. At the end of the page pointed by this link, they have provided a download link for 1.0 version of Aqua-Sim. After downloading I extracted the compressed folder to the desktop of my Ubuntu 12.04 system. Entered the following commands in the terminal to install Aqua-Sim on my system.

cd Desktop/Aqua-Sim-1.0/

After running the installation process for a while, suddenly it turned out with an error saying "ld: hidden symbol `__stack_chk_fail_local' isn't defined". After searching in the web for this error I found the solution mentioned in this blog. According it, I had to edit a configuration file, so I opened the file Aqua-Sim-1.0/otcl-1.12/configure and searched for the line SHLIB_LD="ld -shared" inside it. Then I commented and added a different line as shown below.

#SHLIB_LD="ld -shared"
SHLIB_LD="gcc -shared"

Then I ran the command "./install" again and this time it worked. At the end of the installation process, as usual in NS2 installation, it asked for setting some environmental variables in my system. So I opened the "/etc/profile" file and added the following lines at the end of the existing content and saved.

export PATH=$PATH:/home/asanka/Desktop/Aqua-Sim-1.0/bin:/home/asanka/Desktop/Aqua-Sim-1.0/tcl8.4.13/unix:/home/asanka/Desktop/Aqua-Sim-1.0/tk8.4.13/unix

export LD_LIBRARY_PATH=/home/asanka/Desktop/Aqua-Sim-1.0/otcl-1.12:/home/asanka/Desktop/Aqua-Sim-1.0/lib

export TCL_LIBRARY=/home/asanka/Desktop/Aqua-Sim-1.0/tcl8.4.13/library

Now we are done with installation. Just to make sure that the installation went fine, I ran the validation script as follows. It takes a long time for the validation scripts to complete.

cd Aqua-Sim-1.0/ns-2.30

After the validation script finished the execution, I ran a sample TCL simulation script as shown below.

cd /ns-2.30/underwatersensor/uw_tcl
ns tmac-example.tcl

This script executed successfully indicating that everything is OK and Aqua-Sim is ready for my future simulations of UASN networks. Cheers!

Wednesday, November 6, 2013

Invited talk of Professor C. K. Toh at DGIST

Professor C. K. Toh
At the end of last month, I got a chance to attend to an interesting talk conducted by Professor C. K. Toh from National Tsing Hua University in Taiwan. In his visit to Korea, he conducted this invited talk at the DGIST (Daegu Gyeongbook Institute of Science and Technology) where I got the opportunity to attend with my lab mates. Professor C. K. Toh is a collaborator and an advisor to our Monet research lab and therefore he is more important to us. However it was the first time I met him in person. The topic of his talk was "The Green Internet" where he talked about the modern trends he observed in the Internet and how it is going to effect the energy crisis of our century. DGIST institute is located in a beautiful place in Daegu, far away from the main city area. It took nearly an hour for us to drive to their place. In addition to us from Monet lab in KNU, there were some other attendees mainly from DGIST itself.

My lab mates and me in front of DGIST building
In his talk, Professor Toh showed how our modern Internet is going to face a challenge from the energy crisis. The number of users of Internet is rapidly increasing and therefore the number of computers connected to the Internet is also increasing. Due to this always connected nature of the Internet, users expect all the network resources to be available anytime anywhere. Data centers has to run 24/7 making them consume power always. Almost all the networked devices including user PCs, routers and servers are powered on all the time even when nobody is using them. The ultimate result of this trend is a huge energy crisis in the near future due to the Internet. He showed that as the Internet bill, actually what we are paying is mainly an energy bill. When the energy consumed to run the Internet infrastructure gets increased, the cost for Internet access also can go higher. In conclusion, he suggests to take proactive actions to reduce the excess energy wasted on Internet related devices. One simple suggestion is to turn of the computers when not in use. He suggested some more interesting ideas as solutions for this issue.

After his lecture we all had lunch with him. He has got his PhD from  University of Cambridge. I didn't know that he is such a giant in the field until I read his profile. He has even worked on some DARPA research projects.