OFDM:How frequencies become orthogonal

[bhq]

how frequencies orthogonal

In OFDM how the frequencies become orthogonal.

Example i have a signal cosine 5 KHz, how many orthogonal frequencies can i have for OFDM in that case.

 

[m_pourfathi]

how frequency become orthogonal to each other

Imagine, each OFDM symbol time is T seconds. It is composed of two time intervals one is called Guard time or Guard interval which is Tg and the other one is Orthogonality period demonstrated by Tort.
The relationship between these three parameters is as follow:

T = Tg + Tort

Tg is usually less than 25 % of the symbol time and is defined as amost the transient time of the signal for each symbol in the channel. The inverse of the orthogonality Period or 1/Tg is called the frequency spacing of the OFDM Modulation the carriers placed 1/Tg in frequency apart are orthogonal to each other. The mathematical description of the orthogonality is as follow:

∫cos(2* pi*fc*t + n* Δf)*cos(2*pi*fc*t + k *Δf)dt the integral is from Tg to T

the cosine can be replaced by sin function as well.

if Δf = 1/Tg then the above integral shall equal to 0 if n ≠ k which describes the orthogonality of the carriers in the OFDM.

Refer to books on Modern Digital Communications and see OFDM. you get a more detailed view on the subject.

 

[zio_nneo]

orthogonal in ofdm

Do you have e-book that you have mention?????can you give us link for the book mention?

 

[m_pourfathi]

orthogonality in ofdm books

Yeah sure, These are some ebooks in ebook upload and download forum of edaboard. enjoy!







Added after 3 minutes:

About your example, what frequency is 5 kHz? is it your carrier frequency?

 

[xulfee]

frequencies are orthogonal

every frequency other than 5kHz is orthagonal to it,u can see it by taking inner product of any two frequencies