вторник, 3 мая 2011 г.

New Article: Perspectives of the analysis of OFDM signals with CP.

Perspectives of the analysis of OFDM signals with CP. 

As usual, we assume that reader possesses some basic knowledge concerning principles of formation OFDM, and the reader is acquainted with our previous articles, as terminology and the main ideas remain former. 

There are some general provisions. 

We already were being considered and showed in the previous articles, that at formation of OFDM signals the basic/main/key parameters are LS, LU and LG (CP), which are having dimensional samples. Basically, each one of these two parameters from these three (LS LU LG), unambiguously set the third parameter, as there is a simple correlation, namely: 

LS = LU + LG; 

We add one more, the dimensionless parameter, coefficient k = LG/LU or k = ((Sh/Br) - 1). This parameter allows to receive correct LS, LU and LG for specific conditions, besides k possesses mass of other remarkable properties, but it is beyond this article. 

In a general view the scheme of formation of OFDM signal with CP looks as follows: 








As we already considered, and I once again underline this moment, that there is no any Hertz and-or seconds! LS, LU and LG have at a stage of formation dimensionality of samples/samplings. We name it Fundamental/primary/key parameters of OFDM signal, these parameters are core of OFDM signal. All is equal to these parameters (samples), with what speed they will be transferred, needless to say, that transmission/transfer speed should be a constant.


As soon as some speed of following is given to samples (sampling rate of formation of OFDM signal OFDM), then earlier faceless values LS, LU and LG acquire/get dimensionality in Hertzs and-or seconds. But! They don't lose, and can't lose their main/fundamental properties. For example, as there was duration LS = 100, LU = 60 and LG (CP) = 40 samples, so it remains, irrespective of sampling rate.


There is one nuance in these transparent and logical enough conclusions. All what has been told above, concerns to so-called sampling rate of formation of OFDM signal.


In practice, to form a signal at once on operational frequency it is not convenient, and frequently it is not even possible. Normally, the signal should be formed on sampling rate Х, and further whole spectrum of the signal should be transferred on operational frequency Y. Thus, sampling rate X can't change duration LS, LU and LG, as it (sampling rate) is a consequence of existence of these parameters, and frequency of transfer Y can't destructively influence these parameters as it is not connected to them.


Let's sum up the told...


Full version of this article you may read here.


The arcitle contain examples on the real signals, schemes, detailed pictures, explanations and other interesting information.