The spectrum of wireless communication is limited, the distribution is very strict, and the electromagnetic waves of the same bandwidth can only be used once. In order to solve the problem of many problems, engineers have developed a number of "modulation technology" (ModulaTIon) and "multi-technology" (MulTIplex) to increase Spectrum efficiency, so the invention of 3G, 4G, 5G different communication generation technology, then what components in our mobile phone are responsible for handling these technologies for us?
Modulation technology and multiplex technology
First of all, we need to understand that "ModulaTIon" and "MulTIplex" are completely different things. Let us first look at what is different?
Digital signal modulation technology (ASK, FSK, PSK, QAM): The analog electromagnetic waves are modulated into different waveforms to represent 0 and 1 different digital signals. ASK uses amplitude to represent 0 and 1, FSK uses frequency to represent 0 and 1, PSK uses phase (waveform) to represent 0 and 1, QAM uses both amplitude magnitude and phase (waveform) to represent 0 and 1.
Well, the digital signals 0 and 1 that each person's cell phone antenna is going to transmit become electromagnetic waves of different waveforms. The problem is coming again. So many different waveforms of electromagnetic waves are thrown into the air. How to distinguish those that are yours (and What are you talking about, those are my (and I am talking)?
Multiplex technology (TDMA, FDMA, CDMA, OFDM): Differentiate electromagnetic waves for different users. TDMA uses time to distinguish between yours and me. FDMA uses different frequencies to distinguish between yours and mine. CDMA uses different passwords (orthogonal spreading codes) to distinguish between yours and me. OFDM uses different positives. The subcarrier frequency is used to distinguish between yours and mine.
It is worth noting that digital signal modulation technology or multiplex technology is performed together when digital signals (0 and 1) are processed and processed. Generally, multiplex technology is used first to perform digital signal modulation technology. (except for OFDM), so multiplex technology and modulation technology must be used at the same time.
Digital modulation technology (Digital modulation)
The current mobile phone belongs to "digital communication", that is, the voice of our speech (continuous analog signal), which is first converted into discontinuous 0 and 1 digital signals by the mobile phone, and then converted into electromagnetic waves by digital modulation (analog signal) Carrying the digital signal), and finally transmitting it from the antenna, the principle is shown in Figure 1.
â–² Figure 1: Digital communication diagram. (Source:the Noun Project)
Digital communication system architecture
The architecture of the digital communication system is shown in Figure 2 (a). Users may use smart phones to make voice communications or access the Internet for data communication. We explain the following:
â–² Figure 2: Schematic diagram of the communication system architecture.
Voice upload (speaking phone): The sound is received by the microphone and then is a low frequency analog signal. It is converted into a digital signal by a low frequency analog-to-digital converter (ADC), and is subjected to data compression (Encoding) and cyclic processing via a "basic chip (BB)". Repeat check code (CRC), channel coding, inter-leaving, ciphering, and formatting, and then perform multi-bit processing such as multiplexing and modulation. , as shown in Figure 2 (b).
Next, it is converted into a high-frequency analog signal (electromagnetic wave) via an "IF chip" (IF), that is, a high-frequency digital analog converter (DAC); finally, electromagnetic waves of different time, frequency, and waveform are formed via a "radio frequency chip (RF)". It is transmitted by the antenna.
Voice download (listening to the phone): The antenna receives the electromagnetic waves of different time, frequency and waveform, and obtains the high frequency analog signal (electromagnetic wave) after processing by "radio frequency chip (RF)", and then passes the "IF chip" (IF). A high frequency analog digital converter (ADC) converts to a digital signal.
Next, de-modulation, de-multiplexing, de- formatting, de-ciphering, and de-interlacing are performed via "baseband chip (BB)". -inter-leaving), channel decoding, CRC, data decoding, etc., and finally converted to low frequency analog signals via low frequency digital analog converter (DAC) (Sound) is played back by the microphone.
Data communication (online): Basically, data communication is a digital signal regardless of uploading or downloading, so it can be directly processed into the baseband chip (BB). Other processes are similar to voice communication, and will not be repeated here.
Note: The principle of communication is a lot of mathematics. Since the mobile phone is something we use every day, most people are curious about the feeling of communication and want to know more, but often go into the first class of the classroom to see It is a lot of complicated digits: Fourier Transform, Laplace Transform, Discrete, and immediately retreat. In order to simplify the complexity, it is easy for everyone to understand. The above is for the digital communication system. The introduction is just a gesture, and there will be a gap with the actual situation. It is recommended that those who are interested in further understanding can base on the above concepts to further understand the technical details.
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