OFDM是一种多载波调制技术，是LTE的关键技术之一。通过将单个信道划

OFDM is a multi-carrier modulation technology and one of the key technologies of LTE. By dividing a single channel into multiple mutually orthogonal sub-channels, OFDM completes the transmission of a single high-speed signal into multiple simultaneous low-speed signals. The mutual interference between the various sub-channels is reduced as the respective signals are coherently demodulated and separated at the receiving end. At the same time, since the bandwidth of the sub-channel is greatly reduced with the decomposition of the original channel, the inter-symbol crosstalk is reduced as each sub-channel can be regarded as a flat fading. At the same time, channel equalization becomes much easier because the bandwidth of each subchannel is much smaller than the original channel bandwidth. The main advantages of OFDM technology are: <br>(1) strong anti-interference ability, data can be efficiently transmitted in a multipath environment and fading channel; <br>(2) joint coding between sub-carriers, strong anti-fading; <br>(3) The orthogonal modulation and demodulation operations on sub-channels are completed by Fourier transform, and the technology is mature; <br>(4) Compared with other multiplexing technologies, orthogonal frequency division multiplexing technology is more compatible and can be used in multiple access modes Combine. <br>At the same time, OFDM also has some of its own shortcomings, mainly including: <br>(1) OFDM system is very sensitive to the frequency offset of carrier and the influence of phase noise, the tolerance to deviation of frequency offset is very low, and phase noise can also easily cause carrier The formation of inter-interference; <br>(2) The peak-to-average ratio of the OFDM system is relatively high. A peak-to-average ratio that is too high will increase the complexity of the analog-to-digital conversion process, and will also reduce the efficiency of the RF unit; <br>(3) The cost of the OFDM system is higher. Compared with the single carrier system, the OFDM system has much higher performance requirements on the linear scale of the amplifier, resulting in higher cost.

OFDM is a multi-carrier modulation technology and one of the key technologies of LTE. BY DIVIDING A SINGLE CHANNEL INTO MULTIPLE ORTHOGONAL SUB-CHANNELS, OFDM COMPLETES THE DECOMPOSITION OF SINGLE-WAY HIGH-SPEED SIGNALS INTO TRANSMISSION MODES OF MULTIPLE SIMULTANEOUS LOW-SPEED SIGNALS. The interference between the sub-channels decreases with the way in which the respective signals are separated by coherent dulce at the receiving end. At the same time, because the bandwidth of the sub-channel decreases greatly with the decomposition of the original channel, the intercode crosstalk is reduced with the flatness of each sub-channel. At the same time, channel balancing is much easier because the bandwidth per sub-channel is much smaller than the original channel bandwidth. The main advantages of OFDM technology are:<br>(1) Strong anti-jamming ability, data can be efficiently transmitted in multi-path environment and fading channel; <br>(2) the joint coding between the subcarriers, strong resistance to decay;<br>(3) Through the Fourier transformation to complete the orthogonal modulation and demodulation operation of the sub-channel, the technology is mature;<br>(4) Compared with other multiplexing technology, orthogonal separation and multiplexing technology is more compatible and can be combined with a variety of access methods.<br>At the same time, OFDM has its own shortcomings, mainly:<br>(1) OFDM system is sensitive to the frequency offset of the carrier and the noise effect of phase, the tolerance of frequency bias is very low, phase noise can also easily lead to the formation of intercarrier interference;<br>(2) THE PEAK RATIO OF OF OFDM SYSTEM IS RELATIVELY HIGH. High peak-to-average ratio will lead to increased complexity of the conversion processing of the modules, and will also lead to the reduction of the efficiency of rf units;<br>(3) The cost of OFDM system is high. OFDM systems require much higher performance requirements on the linear scale of amplifiers than single-carrier systems, resulting in higher costs.

OFDM is a multicarrier modulation technology and one of the key technologies of LTE. By dividing a single channel into multiple orthogonal subchannels, OFDM can decompose a single high-speed signal into multiple low-speed signals. The mutual interference of each subchannel decreases with the coherent demodulation and separation of each signal at the receiver. At the same time, because the bandwidth of the subchannel is greatly reduced with the decomposition of the original channel, the inter symbol interference is reduced with each subchannel as a flat fading. At the same time, channel equalization is much easier because the bandwidth of each subchannel is much smaller than the original channel bandwidth. The main advantages of OFDM technology are as follows:<br>(1) With strong anti-jamming ability, data can be transmitted efficiently in multipath environment and fading channel;<br>(2) Joint coding among subcarriers, strong anti fading;<br>(3) Through the Fourier transform, the orthogonal modulation and demodulation of the subchannel are completed, and the technology is mature;<br>(4) Compared with other multiplexing technologies, orthogonal frequency division multiplexing technology is more compatible and can be combined with a variety of access methods.<br>At the same time, OFDM has its own shortcomings, mainly including:<br>(1) OFDM system is very sensitive to the influence of frequency offset and phase noise. The tolerance of frequency offset is very low, and phase noise can easily lead to the formation of inter carrier interference;<br>(2) The peak to average ratio of OFDM system is relatively high. The high PAPR will increase the complexity of AD conversion and reduce the efficiency of RF cell;<br>(3) The cost of OFDM system is high. Compared with single carrier system, OFDM system requires much higher performance on linear scale of amplifier, which leads to higher cost.<br>