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OFDM Lecture 16 - OFDM

2022-07-26 09:25:00 【Bai Xiaosheng in Ming Dynasty】

Preface ：

      The main reference of this article  Sunny Classroom OFDM The direction of the PPT.

Catalog

  1.     FDM
  2.     OFDM

OFDM :Orthogonal Frequency Division Multiplexing

One   FDM（Frequency Divison Multiplexing）

          The channel is divided into multiple non overlapping subchannels

         

          advantage ： Strong anti-interference ability

          shortcoming ： Low bandwidth utilization

Two   OFDM

     2.1 Application scenarios

            

    2.2  Follow FDM differences

           

            No, Guadrd Band, The subchannels overlap

            advantage :

                      High bandwidth utilization

        How about the interference between subchannels ？

       

 2.3 Anti interference principle

     

      A signal sends three orthogonal subcarriers , The waveform is shown in the right figure

  Orthogonality is in a period , The inner product between different signals is 0 .

  For example, the three groups of signals are

     cosw_1 t, cosw_2t ,cosw_3t, The inner product between any group of signals is 0, such as ：

\int_{-T/2}^{T/2}cos (w_1 t) cos (w_2 t) dt=0

    front Modulation know , Each waveform represents a symbols, If it doesn't 0, Then know its

Corresponding Bits Stream composition .

  Sending signal :

 s= cosw_1 t +cosw_2 t +cos w_3 t

 

2.4 Decoding principle

      Using the orthogonality between subcarriers , For example, restore  cos w_1 t

      Multiply the signal by  cos w_1 t

     r= \int cosw_1t cos w_1t dt + \int cosw_1tcosw_2tdt +\int cos w_1t cos w_3tdt

         =\int cos^2w_1tdt

       =\int \frac{cos 2w_1t +1}{2}dt

  

  3、 ... and Complementary cosine formula

 

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