Dear community friends, hello!
Today I'm going to share with you the principles of OFDM.
First, let me introduce the concept of OFDM.
OFDM is a frequency division system in essence. However, conventional FDM requires a wide guard band between adjacent carriers, resulting in low spectral efficiency, OFDM greatly improves spectral efficiency by orthogonalizing subcarriers.
Principles of OFDM
OFDM is developed based on FDM technology.
OFDM is implemented through the fast Fourier change (FFT) technology.
OFDM is developed through DSP (digital signal processing) chips and can be applied.
The OFDM technology differs from the traditional FDM technology in the following aspects:
OFDM uses multi-carriers to transmit information streams. Therefore, OFDM can be regarded as a multi-carrier transmission technology.
OFDM subcarriers are orthogonal to each other so that in the same radio link, multiple signals can be here transmitted in parallel, and the overall rate can be increased to M times.
OFDM processing flow
Structure of the OFDM transmitter
Two core modules of an OFDM transmitter
IFFT (Inverse FFT): A large number of narrowband (subcarrier) frequency-domain signals are converted into time-domain signals after the IFFT.
The CP (cyclic prefix) is added to copy the tail of each OFDM symbol to the front of the symbol.
Advantages and disadvantages of OFDM
Advantages
The long symbols of OFDM can almost completely resist multipath interference.
Provides higher spectral efficiency for wideband channels.
Flexible bandwidth.
Implementation via FFT and FFT is relatively simple.
Disadvantages
Frequency offset and phase noise can cause serious problems.
Doppler shift affects subcarrier orthogonality.
Some OFDM systems have higher PAPR.
Precise frequency and time synchronization are required.
In general, OFDM technology supports the development of LTE. It provides a basis for various LTE services.
That's all I've shared about OFDM.
All community friends are welcome to read and comment. I will share OFDMA and SC-FDMA in my next post.
