суббота, 27 июня 2009 г.

The classical analysis of OFDM signals. Possibilities and limitations.

The classical analysis of OFDM signals

The arctile is written by SergUA6.

Thist article is big enough to put it whole in the blog. Below there will be little bit information from the article, and whole text with pictures and examples you can read here.

The Classical OFDM analysis surely represents difficulty. Before analyze the real signals we will consider the main methods and principles on the synthesized signals. It is typical enough and very productive method.

For synthesis of OFDM signals the OCG program is used. As usually, I underline, you can use any other program both for the analysis and for synthesis, it is important that results would not call doubts, could be verified and have been repeated.

It is supposed that some bases of OFDM creation are known, it does not demand special substantiations as the analysis it is not simple and not only usage of this or that analyzer.

Extensively, it is experience and knowledge of an analyst, it is an ability to generalise, to draw the conclusions etc. Before appearance of OCG, the analysis of OFDM of signals, at least, for me, carried chaotic, unsystematic and extremely not productive character, but the possibility of synthesis of the various by parameters signals has allowed to develop certain techniques and the common approaches. In practice all it does work and does work good enough.

Standardly the task of OFDM analysis is to define:

  • the clock frequency of manipulation,
  • the value of frequency spacing of channels
  • quantities of the channels,
  • modulation in the channels
  • definition of the presence and length of the cyclic prefix (CP),
  • features of the signal if the such are exist.

Advantages of the classical analysis:

  • it doesn’t matter how many frequencies in the analyzed OFDM signal, 3-30-300 or 3000
  • it is also, generally, doesn’t matter if the signal is generated on even or odd harmonics it does not influence results
  • for the score of the very strong averaging-out, the classical analysis is insensitive to separate/single/some anomalies in the signal

Disadvantages of the classical analysis are:

  • impossibility to work correctly with short signals
  • impossibility of reception of a bit stream (while the universal demodulator can provide it)
  • impossibility to allocate the necessary channel in the pure state
  • the extremely big problem is to work with the signals having very short CP.

Despite minuses, the classical analysis, in most cases, allows to receive quite good results at the analysis of overwhelming majority of OFDM signals. I hope this article in some measure will help with it.

Auhtor SergUA6 from MSM team.