Gliffy Online

•February 7, 2009 • Leave a Comment

If you need to create a diagram but you don’t have a powerful tool like Visio (cause it’s expensive n it’s for windows :p ), or you have the tool but not comfortable with it (like ADA, well in my case :D ), you might want to try Gliffy Online. Through that website, you can create a very nice diagram easily (well again, for me it’s easy to use). And just like Visio and ADA, you can create any type of diagram like UML, network, flow chart, etc. After done creating your diagram, you can save it as jpeg or png. Or you can just publish it like this one.

First taste of Gliffy Online

First taste of Gliffy Online

Posted in internet
Tags: , ,

Easily Share Internet Connection in Ubuntu Ibex

•February 4, 2009 • Leave a Comment

So here is the case, you have more than one computers in your place, one internet connection, one of them (or all) has Ubuntu inside, and you want all of your pcs to be able to connect to internet through the Ubuntu pc. What you need to do in your Ubuntu pc (the gateway) is:

  1. Install dhcp server
    sudo apt-get install dhcp3-server
  2. Install firestarter
    sudo apt-get install firestarter
  3. Create symbolic link for dhcpd. Need to do this because firestarter looks for dhcpd, while in Ibex there’s only dhcpd3.
    sudo ln -s /usr/sbin/dhcpd3 /usr/sbin/dhcpd
  4. You might need to assign ipaddress to the network interface card that connect to your LAN.
    sudo ifconfig eth0 192.168.0.1
  5. Run firestarter
  6. firestarterwizard1
  7. firestarterwizard2
  8. firestarter3
  9. firestarter4
  10. Just connect your other pcs to the hub/switch

Note:

  1. I used Intrepid Ibex.
  2. I connected the pcs through cable. Haven’t tried this method for sharing internet connection over wireless (adhoc).

Posted in internet, linux
Tags: , ,

Name Your Dream Assignment

•January 30, 2009 • 1 Comment

Posted in news, photography
Tags: ,

Two Effecient Firefox Addons

•January 8, 2009 • Leave a Comment
  1. morningcoffee Morning Coffee.  There are some urls I always open everytime I start firefox like mail.google, mail.yahoo, ipv6mail, planet ubuntu id, planet el02, and detik.com. Although I have them all bookmarked in my toolbar, it still annoying (but I still do it P ) to do it everytime. But using this addon, I can add them to my everyday morning coffee, so that everytime I want to open them I just need to click once, and they all will be opened in tabs. 便利ですね。。。
  2. Fire Gesture. For this one, I got influenced by my japanese lab friends. I think all of them are using it. Using this addon, I can just hold right click than drag to the left to go back one page, or to the right to go forward one page. Another 便利 addon. There are also other gestures  we can set up.

Posted in internet, linux, software
Tags: , , , ,

Great Speech From Steve Job

•December 31, 2008 • Leave a Comment

Posted in internet, news, video
Tags: , ,

Gnome-ppp and Huawei 3G USB Modem

•December 23, 2008 • Leave a Comment
emobile modem

emobile modem

I had a problem connecting to internet using huawei 3G modem D02HW inUbuntu Intrepid Ibex before. The modem was detected, I already set the gnome-ppp to use this setting:
username: em
password: em
phone number: *99***1#
Deveice: /dev/ttyUSB0
Type: USB Modem
Speed: 460800
Phone Line: tone
Volume: High
InitString: init2=>ATH0E1
but it still couldn’t connect to the internet. It kept saying waiting for prompt and then permission denied on /usr/bin/pppd bla bla bla.
Here is the solution: change the user privilage in System -> Administration -> User and Groups -> Unlock -> Insert your password -> Properties -> User Privileges -> Check “Connect to internet using a modem” -> OK -> Logout -> Login -> Try connect again, it should be working now.

Posted in internet, linux
Tags: , , , , , ,

Firefox 3 Starts in Offline Mode Problem

•December 20, 2008 • 2 Comments

In my ubuntu, firefox always starts in offline mode. The solution is simple, in firefox, open new tab -> type “about:config” (without the double quotes) -> type toolkit.networkmanager.disable -> change the value to true. It should be working in online mode from now on.

Posted in internet
Tags: , , ,

Motivation For Research

•December 9, 2008 • 1 Comment
Tokyo tower

Tokyo tower

Japan is not only famous of its manga and anime, but also of the advance of technology. One of the reason of this advance is because of so many researches conducted in universities and companies. Recently I just found out about the reason why students and lecturers in Japan willingly conduct so many researches. Not only to add more entries on their curriculum vitae, but also because they want to go abroad. As you may know, there are so many international conferences about technology. And since it’s international scale, most of the time it’s held outside Japan. By doing research, they can submit papers, and if the papers passed the review, they will have the chance to go abroad. They also don’t have to worry about the money, because the university will pay for them, everything. For university, money is not a problem. The more papers produced by their students/lecturers, the more famous the university will be.

Researching is like racing here. In a meeting few days ago, my sensei listed the international conferences that will be held next year like PIMRC in Tokyo, VTC in Alaska, and APWCS in Seoul. He encouraged everyone to submit a paper to any of the conferences. Not only the master student or PhD students, but also the bachelor students as well. Even one of my friend who is still in bachelor degree is ready to submit paper to APWCS cause he wants to go to Seoul.

I believe this is one of motivation that universities in Indonesia should have to advance in technology. Especially to ITB, since I heard ITB is planning to be a research based institute. Hopefully more good quality papers are produced from ITB.

Posted in mumble, news
Tags: , ,

Probability of Error for BPSK over Rayleigh channel with Maximal Ratio Combiner

•November 13, 2008 • 1 Comment

Aside from deriving BER for BPSK over rayleigh channel, I also got another assignment to derive the equation of probability of error (BER) for BPSK over rayleigh channel with maximal ratio combiner (mrc). After searching here and there, I found the solution in Digital Communications by Proakis page 825. But just like the previous assignment, Proakis didn’t derive the equation in detail. Even Mr. Google couldn’t help me this time :( So I tried to solve it myself, but I’m stuck. So I posted here my unfinished work, maybe you can help me figuring it out.

For a certain value of time, the bit error rate probability is

P_b(\gamma_b)=Q(\sqrt{2\gamma_b})

where \gamma_b=\frac{E_b}{N_o}\sum_{k=1}^L {h_k}^2 = \sum_{k=1}^L \gamma_k . \gamma_k is the instantaneous SNR on the kth channel.

When k=1 , \gamma_b\equiv\gamma_1 and

P(\gamma_1)=\frac{1}{\bar \gamma_c} e^{-\frac{\gamma_1}{\gamma_c}}

where \bar \gamma_c=\frac{E_b}{N_0}E({h_k}^2) (average SNR per channel). So the characteristic function is

\psi_{\gamma_1}(jv) = E(e^{jv\gamma_1})
=\int_{-\infty}^{\infty} e^{jv\gamma_1}\frac{1}{\bar \gamma_c}e^{-\frac{\gamma_1}{\bar \gamma_c}}d\gamma_1
=\frac{1}{\bar \gamma_c}\int_{-\infty}^{\infty}e^{jv\gamma_1}\frac{1}{\bar \gamma_c}e^{-\frac{\gamma_1}{\bar \gamma_c}}d\gamma_1
=\left. -\frac{1}{\bar \gamma_c}\frac{\bar \gamma_c}{1-jv\bar \gamma_c}e^{-\gamma_1\left(\frac{1}{\bar \gamma_c}-jv \right) }\right|_{-\infty}^{\infty}
=\frac{1}{1-jv\bar \gamma_c}

Since the fading on K channels is mutually statistically independent
\psi_{\gamma_b}(jv)=\frac{1}{(1-jv\bar \gamma_c)^K}

Using inverse fourier transform,

p(\gamma_b) = \frac{1}{2\pi}\int_{-\infty}^\infty \psi_\gamma(jv)e^{-jv\gamma_b}

=\frac{1}{2\pi}\int_{-\infty}^{\infty} \frac{1}{(1-jv\bar \gamma_c)}e^{-jv\gamma_b}

=\frac{1}{{\bar \gamma_c}^K \Gamma(K)}{\gamma_b}^{K-1}e^{-\frac{\gamma_b}{\bar \gamma_c}}

=\frac{1}{(K-1)!{\bar \gamma_c}^K}{\gamma_b}^{K-1}e^{-\frac{\gamma_b}{\bar \gamma_c}}

So, the Bit error rate (error probability)

P_2=\int_{-\infty}^\infty P_2(\gamma_b)p(\gamma_b)d\gamma_b

=\int_{-\infty}^\infty Q(\sqrt{2\gamma_b})p(\gamma_b)d\gamma_b

To solve equation above, use integration by parts.
By definition, \int f(x)g(x)dx = F(x)g(x)-\int F(x)g'(x)
which is another way of rewriting the usual \int udv=uv-\int vdu

Let f(\gamma_b)=p(\gamma_b) .
And by definition

\int x^ne^{ax}dx=\frac{e^{ax}}{a^{n+1}}\left[ (ax)^n-n(ax)^{n-1}+n(n-1)(ax)^{n-2}-\dots+(-1)^nn!\right]

So we have

F(\gamma_b) = \int f(\gamma_b)d\gamma_b = \int \frac{1}{(K-1)!{\bar \gamma_c}^K}{\gamma_b}^{K-1}e^{-\frac{\gamma_b}{\bar \gamma_c}}

=\frac{1}{(K-1)!{\bar \gamma_c}^K} \int {\gamma_b}^{K-1}e^{-\frac{\gamma_b}{\bar \gamma_c}}

=\frac{e^{-\frac{\gamma_b}{\bar \gamma_c}}}{(-1)^K(K-1)!}\left[ \left(-\frac{\gamma_b}{\bar \gamma_c} \right)^{K-1}-(K-1)\left(-\frac{\gamma_b}{\bar \gamma_c} \right)^{K-2}+\right.

\left.(K-1)(K-2)\left(-\frac{\gamma_b}{\bar \gamma_c} \right)^{K-3}-\dots+(-1)^{K-1}(K-1)!\right]

Let g(\gamma_b)=Q(\sqrt{2\gamma_b}) also

\frac{d}{dx}\int_{u(x)}^{v(x)} f(t)dt=f(v(x))v'(x)-f(u(x))u'(x)

So

g'(\gamma_b)=\frac{d}{d\gamma_b}Q(\sqrt{2\gamma_b})=\left( -\frac{1}{\sqrt{2\pi}}e^{-\gamma_b}\right)\left( \frac{1}{\sqrt{2}}\gamma_b^{-\frac{1}{2}}\right)

Probability of error becomes

P_2=\int_0^\infty Q(\sqrt{2\gamma_b})p(\gamma_b)d\gamma_b=\left. F(\gamma_b)g(\gamma_b)\right|_0^\infty-\int_0^\infty F(\gamma_b)g'(\gamma_b)

=\frac{1}{2}-\frac{1}{(-1)^K(K-1)!}\frac{1}{2\sqrt{\pi}}\int_0^\infty \gamma_b^{-\frac{1}{2}}e^{-\gamma_b\left( 1+\frac{1}{\bar \gamma_c} \right)}\left[ \left(-\frac{\gamma_b}{\bar \gamma_c} \right)^{K-1}-(K-1)\left(-\frac{\gamma_b}{\bar \gamma_c} \right)^{K-2}\right.

\left.+(K-1)(K-2)\left(-\frac{\gamma_b}{\bar \gamma_c} \right)^{K-3}-\dots+(-1)^{K-1}(K-1)!\right]d\gamma_b

And somehow the equation becomes

P_2=\left[ \frac{1}{2}(1-\mu)\right]^K\sum_{k=0}^K \binom{K-1+k}{k}\left[ \frac{1}{2}(1+\mu)\right]^k

where
\mu=\sqrt{\frac{\bar \gamma_c}{1+\bar \gamma_c}}

So that’s it. Anybody can help me on the last part of the derivation? You can download the pdf version of that equation here.

Posted in math
Tags: , , , , ,

PSP and Linux

•November 12, 2008 • 2 Comments

For Linux(nix) users, creating psp compatible files is so easy. Use the following.

How to convert videos to psp compatible format:
ffmpeg -i InputVideo -f psp -r 29.97 -b 768k -ar 24000 -ab 64k -s 320x240 outputvideo.mp4

How to convert pdf to image(s):
convert nani.pdf nani.jpg
or you can use ghostscript instead using this script:
#!/bin/bash
if [ $# -ne 2 ];then
echo “Usage: $0 input.pdf outfile”
exit
fi
INPUT=$1
OUTFILE=$2
gs \
-dSAFER \
-dBATCH \
-dNOPAUSE \
-sDEVICE=jpeg \
-r150 \
-dTextAlphaBits=4 \
-dGraphicsAlphaBits=4 \
-dMaxStripSize=8192 \
-sOutputFile=${INPUT}_%d.jpg \
${TARGET}

To be able to execute convert and ffmpeg, you need to install them first of course.

Posted in linux, psp
Tags: , , , ,

« Previous Entries