This is a follow up to the Cyclic Prefix (CP) I did here. There I gave a graphical explanation and here I will discuss how it happens theoretically. I recently came across the derivation in a text [1]. So here goes. Considering an N-point FFT system, a block of data points , is to be transmitted during a symbol time. The data vector is sent to an IFFT module. The operation of the FFT, i.e. the discrete Fourier Transformation (DFT) is given by the following matrix: where denotes the -th entry in the DFT matrix . Then the transmitted data vector after the IFFT operation is. . The normalization factor ...

Just yesterday got Ubuntu 9.10 installed on a iMac 27 incher. Here is small guide to the installation. Step 1: You need to partition your hard drive. Use the pre-installed Boot Camp Assistant program (Applications->Utilities->Boot Camp Assistant) for this. You probably will need to divide the drive in half because the other option of 32GB (I think) will not be enough. Step 2: Install rEFIT. This will give you a boot menu at startup where you can choose between Ubuntu and Mac OS X. Below is a screen shot of what you will see at start up (note: This is after Ubuntu installation). Step 3:...

This column will briefly explain how cyclic prefix (CP) in OFDM works by illustration. I decided to add this topic because the I seldom found a text that simply discussed the operation of CP and its usage. First, lets define a property of Discrete Fourier Transform (DFT) : If x(n) and h(n) time-domain signals, circular convolution between them x(n) © h(n) is equivalent to multiplication in the frequency-domain, X(k).H(k). That is, if we circularly convolve two time-domain signals, it is equivalent to multiplying the respective DFT’s of the time-domain signals in the frequency-domain. Now lets...

Do you even remember this? (http://www.mylivesearch.com/). I didn’t until a moment ago when I saw a cover of a TV series and remembered about this in an eerie way. Whatever became of this, I think I can safely say this is pretty much dead. It came out back in May 2007 and more than 2 years later it is still in beta. And a Google search gives less hits than it would give on my name (Don’t believe me? try it). This came as a direct opponent to Google search. It touted to redefine the way search results are found. It complained that Google results are outdated and it will give you the most...

Linux doesn’t always enjoy the love of hardware manufacturers. But it is blessed with an enthusiastic group of engineers who make life that much easier for the rest of us. BTNX-Button Extension (http://www.ollisalonen.com/btnx/) is such application. This nifty application maps mouse buttons with any combination of keys you want. Days of 3-button mouses are gone (except for Apple who are trying to do without buttons). Mouses now come with lot more buttons now.. I never realized the usefulness of this until I got myself a Logitech MX 1100 which has 8 buttons + scroller (except the 2 dpi buttons)....

Came along this handy web site on a Twitter post and thought it’s interesting to share. Started creating my own. It’s getting into shape. Why I thought of posting a short note on this is because I think this will get big. Soon. If you Google for “resume writing” it will give you a big list of pay sites where they provide you different levels of services. From resume writing templates to personal live assistance in providing you with a personalized resume. And these can cost you something around $1000! or more. For many of us starting out, what we need is a nice looking template...

This is a brief introduction to the Iptables. In the most basic terms, iptables can be thought of as a firewall. Basically, there are two components in an iptable: Chains Rules The incoming packets are flown through Chains. You can define many chains as you like and then connect the chains together so the packets are flown continuously. For the normal use, we can do without defining additional chains but I will show one with a chain to grasp the idea. First of all, there are few (among many) keywords that are of importance to learn. INPUT: All the incoming data packets come to this chain OUTPUT:...

I decided to add this little piece seperately becasue the last column was a little long. In this part-2 of securing the SSH connection, I will discuss how to further secure your SSH connection. To recap on the last part, we secured the (already secure) SSH connection by: Using RSA keys to login Disbaling the password login Restricting connections from Iptables We will pick up from there. So now nobody can log into your server (or computer) without having the private key. But this key is just a file that resides in your local computer. So suppose your local computer is in your office or your...

Tech journalists need not be completely unbiased. A real professional one needs to be in order to be ethical but that’s not usually the case. Everybody have their respective likes and nots and they somehow affect their writing. TG Daily is (although fast losing its credibility) a respectable tech news site. But once in a while some incompetent journalist (or so claims to be) comes with a very irresponsible article. I came across a few in recent time but this one made me want to write about it. The article in question is titled “Ubuntu is rubbish“. These kind of X OS is rubbish...

Today my first article got published on Akihabaranews.com. Pretty excited! Please do visit the link and have...