Friday, September 24, 2010

Line Coding RZ-NRZ and 128 QAM Modulation

I don't know why i am so enthusiastic to write on my blog tonight. Well, it's not a problem, isn't it?

Couple minutes ago, i had an exploration on my netbook's files, and i found sort of assignment of my last semester lecture. It is not a bad thing to share right?

Actually the subject of the project is Digital Communication. It is all about digitalized communication with all advantages compare to analog communication. According to my assignment, I won't tell about the communication system. Yet, it's about small parts of the system.

The assignments that i want to share is the two big assignments which is assigned for mid semester and final semester in the last term. Line coding RZ - NRZ was for the mid semester and 128 QAM Modulation was for the semester.

Firstly, line coding is a technique that is used in digital communication system where the data that is transmitted are in certain codes as representation of digital data (bit). These codes will be related to the necessary voltage that is generated by the generator. There are so many methods to encode data into line code or even you can establish your own line codes. That's why, on my assignment will introduce the basic line coding that is used in communication system, that are RZ and NRZ. RZ is stand for Return Zero which means for a time bit, the voltage are return to the zero '0' voltage at exact time within the time bit. Besides, NRZ- Non Return Zero - makes the voltage steady on the assign voltage as long as a time bit. Both of them have its own advantages. Furthermore, from these two line codes, there are so many developed line codes.

Secondly, the assignment is about modulation, specifically 128 QAM modulation. Modulation is a technique that varying properties of waveform of high frequency in order to carry the pure information signal (line code mode) so that it can be transmitted through certain medium where pure information signal is unable to be transmitted. For example, when you make a call via cellphone, your voice (analog) is converted into digital data, and then converted into certain line coding, then modulated into high frequency. Without the modulation scheme, the information can't be transmitted through the air. The three basic digital modulations are ASK-amplitude varying-, PSK- phase varying, FSK- frequency varying. From three of them are able to develop to several modulation schemes, one of them is QAM ( Quadrature Amplitude Modulation) which is combined ASK-PSK modulation scheme. For 128 QAM, there are seven bits which are have 128 possibilities each, that can be transmitted at one time. It means this modulation is very efficient. There are definitely difficult calculations to construct this modulation scheme as well.

Those are some descriptions of my assignment of last terms. It was pretty satisfied score of the assignment,haha..