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    Analysis of communication components: baseband, intermediate frequency and RF parts

    We know that the spectrum of wireless communication is very limited, the distribution is very strict, the same bandwidth of electromagnetic waves can only be used once, in order to solve the problem of fewer congee, engineers developed a lot of "modulation" and "multi-task technology" (Multiplex), to increase spectral efficiency, so only 3G, 4G, 5G not. With the invention of communication generation technology, what components are responsible for handling these technologies for us in our mobile phones?
    1, modulation technology and multitasking Technology
    First, we need to understand that Modulation and Multiplex are totally different things. Let''s see how they are different.
    Digital signal modulation technology (ASK, FSK, PSK, QAM): The modulation of analog electromagnetic waves 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 amplitude and phase (waveform) to represent 0 and 1.
    Well, everybody''s cell phone antenna is going to send out digital signals 0 and 1 that have become different waveforms of electromagnetic waves, and the problem is, with so many different waveforms thrown into the air, how can you tell which ones are yours (talking to you) and which ones are mine (talking to me)?
    Multi task technology (TDMA, FDMA, CDMA, OFDM): the electromagnetic wave is distributed to different users. TDMA uses time to distinguish between you and me, FDMA uses different frequencies to distinguish between you and me, CDMA uses different passwords (orthogonal spread spectrum codes) to distinguish between you and me, and OFDM uses different orthogonal subcarrier frequencies to distinguish between you and me.
    It is noteworthy that both digital signal modulation technology and multi-task technology are carried out together when the digital signal (0 and 1) is operated and processed. Generally, multi-task technology and digital signal modulation technology (except OFDM) are carried out first, so multi-task technology and modulation technology must be used simultaneously.

    2. Digital modulation is now a kind of "digital communication", that is, the voice of our speech (continuous analog signal), first converted from the mobile phone into a discontinuous 0 or 12 digital signals, then through digital modulation into electromagnetic waves (analog signals carrying digital signals), and finally transmitted from the antenna. Out, the principle is shown in Figure 1.

    Digital communication system architecture
    The architecture of the digital communication system is shown in Figure 2 (a). Users may use their smartphones to make voice calls or to communicate data over the Internet. We explain the following:

    Voice Upload (Voice Call): A low-frequency analog signal received by a microphone is converted to a digital signal via a low-frequency analog-to-digital converter (ADC). Data compression (Encoding), cyclic repetitive check code (CRC), channel coding, interleaving, and addition are performed via a baseband chip (BB). Ciphering, Formatting, Multiplexing, Modulation, and other digital signal processing, as shown in Figure 2 (b).
    Then the high frequency analog signal (electromagnetic wave) is converted to the high frequency analog signal (electromagnetic wave) by the intermediate frequency chip (IF), which is also called the high frequency digital analog converter (DAC). Finally, the electromagnetic wave with different time, frequency and waveform is transmitted by the antenna through the radio frequency chip (RF).
    Voice Download (Phone): The antenna receives electromagnetic waves of different time, frequency and waveform, then processes them into high-frequency analog signals (electromagnetic waves) via the RF chip, and then converts them into digital signals through the IF chip, or high-frequency analog-digital converter (ADC).
    Digital signal processing, such as De-modulation, De-multiplexing, De-formatting, De-ciphering, De-inter-leaving, Channel decoding, CRC, Decoding, etc., is performed via the "BB" chip. Finally, the low-frequency analog signal (sound) is converted to the low-frequency analog signal (sound) by the low-frequency digital analog converter (DAC) and played out by the microphone.
    Data Communication (Internet): Basically, data communication, whether uploaded or downloaded, is a digital signal, so directly into the baseband chip (BB) processing can be, other processes and voice communications similar, no longer described here.
    Note: The principle of communication is a lot of math. Since cell phones are something we use every day, most people are curious to know more about the sense of communication, but they often go into the classroom and see a lot of complicated numbers in the first class: Fourier Transform, Laplacian transformation. Laplace Transform, Discrete, immediately back down, in order to simplify the complexity of easy to understand, the above introduction of digital communication system is only a hint, and the actual situation will fall, it is suggested that interested in further understanding of the concept can be based on the above to further understand the technical details.
    3. The architecture of wireless communication system is based on the previous introduction. Let''s look at several important integrated circuits (IC) in smartphones. They mainly include three parts: baseband (BB), intermediate frequency (IF) and radio frequency (RF). As shown in Figure 3, each part may have one or more integrated circuits (IC) or several integrated circuits (IC). Package into one, called "System in a Package (SiP)", or integrate several chips into one, called "System on a Chip (SoC)".

    Baseband chip (Baseband, BB): belongs to
    date2018-8-23 Read271second
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