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This lesson talks about the receiving and transmitting principles of the 4G frequency band

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Let's use the framework diagram to see the specific channels of these lines

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in the 4G frequency bands of the three major operators

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The first thing to know is that China Mobile, China Unicom,

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and China Telecom in the 4G frequency band use different frequency bands.

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B1 and B3 frequency bands belong to the middle frequency band

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B38, 40, 41 belong to the high frequency band

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B1 and B3 are the 4G frequency bands used by China Unicom and China Telecom

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B38, 40, 41 are 4G frequency bands for mobile use

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Let's first look at it in its entirety

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Regardless of whether it is Mobile, China Unicom or Telecom,

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the frequency band components they pass through are almost the same,

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but not necessarily the same components

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They pass through the frequency band of the same component type

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For example, everything has to go through the power amplifier, the antenna switch,

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the filter, and the receiving chip.

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Let's first look at its reception

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The received signal is the electromagnetic wave emitted by the base station in the air,

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which is sensed by the antenna and becomes a received electrical signal.

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This high frequency electrical signal it passes through this coaxial switch

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The coaxial switch is always on, and then the filter filters out the clutter

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After filtering the clutter, hand it over to the big antenna switch.

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The big antenna switch is only switched on here.

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Turn on the receiving signal at the antenna end to the specific frequency band for this reception

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For example, China Unicom uses band 1 or band 3

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We can also say that after the reception, the reception of the B1 frequency band

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or the reception of the B3 frequency band is formed.

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Of course, if you are mobile, it is the reception of the B41 frequency band.

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After the antenna switch turns on the received signal at the antenna end

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and forms a specific frequency band signal

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This received signal needs to be amplified by the receiving chip, and then output after amplification.

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The output frequency band signal continues to go, the purpose is to go to the RF transceiver

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Because such a high-frequency carrier signal is added to picture and video,

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this high-frequency carrier is unnecessary

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It goes to the radio frequency, and the radio frequency performs receiving mixing,

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which is to remove the carrier and demodulate the basic picture and video signals

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Through the IQ bus to the baseband CPU or the baseband CPU contained in the large CPU

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The baseband CPU performs the final demodulation, decodes the pictures and videos,

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and sends them to the large CPU circuit for processing

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and sends them to the large CPU circuit for processing

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This is receiving

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We can also find the root of the launch from the baseband CPU

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The communication between the baseband CPU and the radio frequency is to transmit IQ or Qlink bus

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Its transmission is called UL, and its reception is DL

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Let's move on to launch

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The transmitted IQ or UL signal is modulated by the baseband CP and sent to the RF transceiver

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This one is a low-frequency signal, including pictures and videos are all low-frequency signals

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It cannot be directly transmitted in the air for a long distance and fast, only by turning it into a high frequency

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This low-frequency signal is sent to the RF transceiver,

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and the RF transceiver performs mixing to generate a high-frequency carrier

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The carrier carries information such as pictures and videos, forming a transmission signal

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The transmitted signal is specific to certain frequency bands, that is,

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the high frequency is generated from the radio frequency transceiver

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For example, the middle frequency band is the 1 and 3 frequency bands.

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The high frequency bands are B38, 40, 41

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After the transmitted signal comes out, the electric power is very weak

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and needs to be amplified by the transmitted power amplifier.

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It can only be given to the antenna end after amplification

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Antenna switch At this time, it will switch to transmit and send it to the filter

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The so-called switch is connected, it is to switch the transmission and reception,

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so that the transmission and reception do not interfere with each other

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We can also think that the reception is stopped at the moment when it is transmitted

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Of course, the switching frequency of this switch is very high.

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This antenna switch turns on the transmit signal to the filter

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The filter filters out the clutter and sends the transmit signal to the coaxial switch

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The first pin and the second pin of the coaxial switch are conducting

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After the electrical signal reaches the antenna,

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the antenna converts the electrical signal into electromagnetic waves and transmits them into the air

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At this time, electromagnetic waves in specific frequency bands in the air are formed.

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This is the 4G band

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We found that whether it is 4G frequency band or 2G frequency band,

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it is only the frequency band that is different,

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but the components that the frequency band passes through are basically the same,

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and they must pass through the same type of power amplifier and the same type of receiving amplifier

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And the same type of radio frequency

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That's all for this lesson