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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

FDM
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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