1.1. What is communication (what is communication in layman's terms? a40)
1.1.1. Generalized communication (definition of generalized communication b40) (example of generalized communication c40)
1.1.2 Communication in a narrow sense (what aspects does narrow communication include? a41) (a brief description of telecommunications bc41) (a brief description of broadcasting a42) (a brief description of television? b42)
1.2. What is a communication system (the definition of communication system c42) (the development history of communication system d42)
1.2.1. Wired analog communication system (a brief description of the principle of sound transmission by telephone in ancient times a43) (the simplest composition of wired telephone communication system bc43, a44) (what is the function of the microphone? c43) (once in the telephone communication system The working principle of the widely used carbon microphone d43) (the function of the microphone a44) (the working principle of the common dynamic speaker b44)
1.2.2. Wireless analog communication system (the shortcomings of wired telephone communication a45) (the history of the invention of radio communication b45) (what equipment does the wireless telephone communication system consist of? c45) (what circuit does the analog communication system use to achieve? What is the transmission? What signal? d45) (The shortcoming of analog signal e45) (What is distortion? See supplementary notes)
1.2.3. Wired digital communication system (compared to analog signal, what are the advantages of digital signal? a46, d47, bd48, a49) (the principle description of binary digital signal b46) (if the transmission distance is too long, how to solve the binary digital signal Serious distortion problem? ac47) (Can the analog signal be amplified midway to solve the problem of serious distortion in long-distance transmission of analog signals? b47) (Schematic diagram of parallel transmission of 4 signals a48) (Schematic diagram of time slot exchange c48) (Working principle of symmetric encryption e48) (Summary of the advantages of digital circuits compared to analog circuits a50) (Schematic diagram of the principle of a wired digital telephone communication system b50)
1.2.4. Wireless digital communication system (Schematic diagram of wireless digital communication system a51)
1.3. Communication system model (a brief description of the communication process b51) (a schematic diagram of a one-way communication system model c51) (a schematic diagram of a two-way communication system model d51)
1.3.1. Source and sink (what is the source? What is the function of the source? a52) (what is the sink? What is the function of the sink? b52) (which part of the wireless microphone is the source and which part is the sink? c52) (Which parts in video surveillance are the source and which part is the sink? c52) (Which parts in the telegraph communication are the source and which part is the sink? a53) (What is Morse code? See supplementary notes)
1.3.2. Channel (What is a channel? b53) (Description about the requirements of the signal to be transmitted by the channel and the change of the signal during the transmission c53)
1.3.3. Transmitter and receiver (function description of transmitter a54) (function description of receiver b54)
1.4. Channel (From the perspective of transmission media, what two types of communication channels can be divided into? a55)
1.4.1. Wired channel (what are the transmission media of the wired channel? b55) (the description of the telephone line c55) (the description of the network cable d55) (the description of the optical fiber a56) (what is the core network? See supplementary notes)
1.4.2. Wireless channels (what are the transmission media of wireless channels? a57) (what are the transmission media mainly used in wireless channels in communication? b57) (for the description of frequency bands, see the supplementary notes) (about sky waves and ground waves) And the description of space waves, see supplementary notes) (Application of radio waves in communication c57) (Application of light waves in communication a60)
1.5. Signal conversion (what processing must the transmitter go through to convert the electrical signal of the source into a signal form suitable for channel transmission and what operations must the receiver go through to restore the signal transmitted by the channel? a61)
1.5.1. Source coding (a brief description of the function of source coding b61) (What is GSM? See the supplementary notes) (an example of the work flow of source coding c61)
1.5.2. Channel coding and interleaving (a brief description of the function of channel coding a62) (the defect of channel decoding b62) (an example of the work flow of channel coding and channel decoding c62) (a brief description of the function of interleaving and de-interleaving d62 ) (Illustration of interleaving and de-interleaving workflow e62)
1.5.3. Pulse shaping (a brief description of pulse shaping function a63) (an example of a rectangular pulse waveform corresponding to a digital signal b63)
1.5.4. Modulation (Brief description of the modulation function c63) (In wireless communication, why do you need to modulate the signal? d63) (In wired communication, why do you need to modulate the signal? a65) (What is ADSL? See the supplement notes)
1.5.5. Antenna technology (the signal obtained by modulation, that is, whether the modulated signal can be transmitted directly and propagated in space a66) (how does the electromagnetic wave move, that is, how does it propagate? b66) (about the propagation speed of the electromagnetic wave Description a67) (Description of electromagnetic wave wavelength b67) (Description of electromagnetic wave amplitude a68) (Description of function of transmitting antenna b68) (Description of function of receiving antenna c68)
1.6, multiplexing and multiple access technology
1.6.1. Multiplexing technology (Overview of multiplexing technology a69) (Common classification of multiplexing technology b69)
1.6.2. Multiple access technology (Overview of multiple access technology c69, b70) (Reconstruction classification of multiple access technology a70)
2. Signal and spectrum
2.1. Overview (What is the essence of information transmission? a71) (How to check the signal changes during information transmission? b71) (Overview of the spectrum c71) (What is the most common basic signal? d71)
2.2, sine signal
2.2.1. The waveform of the sine signal (a brief description of the sine signal waveform a72) (a brief description of the cosine signal waveform b72)
2.2.2. The characteristics of the sine signal (a brief description of the integral characteristics of the sine signal a73) (what is the fundamental wave? What is the harmonic? See the supplementary notes) (a brief description of the quadrature characteristics of the sine signal a74)
2.3. Complex exponential signal (why can the complex exponential signal replace the sinusoidal signal as the basic signal a77)
2.3.1. Euler formula (for the description of the three representation methods of complex numbers and some operations of complex numbers, see the supplementary notes) (Geometric meaning of Euler formula b77) (Proof of Euler formula c77)
2.3.2. How to understand complex numbers (the geometric meaning of exponential representation of complex numbers in the polar coordinate system a78) (an explanation of the nature of the imaginary number j a79)
2.3.3. How to understand the complex signal (the functional representation of the complex signal a81) (the geometric meaning of the complex signal a82) (a brief description of the principle of the oscilloscope generating Lissajous figures a85) (the X corresponding to various Lissajous figures Brief description of axis and Y axis input signal and electron beam trajectory function a86) (What is the nature of the complex signal? a87)
2.3.4, the characteristics of the complex exponential signal (integral characteristics of the complex exponential signal a88) (about two functions orthogonal) (the orthogonal characteristics of the complex exponential signal b88)
2.4, the phase and phase of the signal
2.4.1. Overview (Overview a90 about initial phase and phase)
2.4.2. What is Phase (what are the two meanings of the word Phase in physics? a91)
2.4.3. Phases and phases of the moon (instructions about the phases of the moon b91) (about the phases of the moon a92) (for a summary of the phases of the moon and the moon, see the supplementary notes)
2.4.4. What is a phase (about the phase of a sine wave, that is, a brief description of the state a93)
2.4.5. What is phase (a brief description of the phase of a sine wave a95) (how to determine the zero phase of a sine wave? b95) (a schematic diagram of the complete cycle of sine and cosine signals c95) (regarding the sign of phase Explain a99) (How is the phase of the sine wave taken? a100) (What is the initial phase of the sine wave? a101) (Use the rotation vector of the complex plane to compare and understand the phase of the sine wave a102)
2.4.6. What is phase difference (definition of phase difference a105) (an example of using three-phase alternating current to explain phase difference b105) (what are the characteristics of two co-frequency signals with a phase difference of 0? a106) (two signals " What is the meaning of "phase"? b107) (What are the characteristics of two co-frequency signals with a phase difference of plus or minus π? c107) (What are the characteristics of two co-frequency signals with a phase difference of plus or minus π/2? a109) (What are the characteristics of two co-frequency signals with an absolute phase difference less than π? b109) (What are the characteristics of two co-frequency signals with an absolute phase difference greater than π? a110)
2.4.7. Wave interference (a brief description of wave interference phenomenon a112) (what is a coherent wave? What are the conditions for wave coherence? Which waves produce interference phenomena? a114) (what is constructive interference? b114) (what Is it destructive interference? a115)
2.5. Signal decomposition and synthesis
2.5.1, Sine signal as the basic signal (a116 is an example of using a series of cosine signals to synthesize a square wave signal)
2.5.2, complex exponential signal as the basic signal (a120 is an example of using a series of complex exponential signals to synthesize a square wave)
2.6 Fourier series expansion of periodic signals
2.6.1. The definition of Fourier series expansion (for a brief description of the definition and related properties of the series, see the supplementary notes) (for the explanation of the Fourier series, see the supplementary document) (Fourier of periodic signals What is the definition of leaf expansion? a127)
2.6.2. The geometric meaning of the Fourier series expansion (what is the Fourier coefficient of the periodic signal? a127)
2.6.3. Fourier coefficient calculation formula (what is the Fourier coefficient calculation formula? a128) (the derivation process of the Fourier coefficient calculation formula b128)
2.6.4. Fourier coefficients of square wave signals (example of finding Fourier coefficients for square wave signals a129) (Description of sinc function a130)
2.6.5. Fourier coefficients of periodic rectangular signals (what is the calculation method of the Fourier coefficients of periodic rectangular signals? a131)
2.7. Discrete spectrum of periodic signals
2.7.1. Two types of frequency spectrum (how to use the three-dimensional frequency spectrum to describe the Fourier coefficients ck a132 of the periodic signal) (how to use the amplitude spectrum to describe the Fourier coefficients ck a133 of the periodic signal) (how to use the phase frequency spectrum to describe the Fourier coefficients ck a133) Fourier coefficients ck b133 constituting a periodic signal)
2.7.2. The frequency spectrum of commonly used periodic signals (how to draw the three frequency spectra of cosine signals? a134) (how to draw the three frequency spectra of sine signals? a135) (an example of drawing the frequency spectrum of a square wave signal a137) (about increasing or reducing the period Summary of the change rule of the periodic frequency spectrum of the rectangular signal a146)
2.8 Continuous spectrum of non-periodic signals
2.8.1. Discrete spectrum of non-periodic rectangular pulse signal (Description of the discrete spectrum of non-periodic rectangular pulse signal a144)
2.8.2. Continuous spectrum of non-periodic rectangular pulse signal (instructions for continuous spectrum of non-periodic rectangular pulse signal b146) (for a summary of solving the continuous spectrum of non-periodic rectangular signal, see the auxiliary document)
2.9, Fourier transform
2.9.1. Fourier forward transform (Description of the derivation process of the continuous spectrum of general non-periodic signal function a148)
2.9.2, Fourier negative transformation (Description of the process of deriving the general aperiodic signal function from the continuous spectrum of the general aperiodic signal function a149)
2.9.3. Fourier transform (what is Fourier transform? a151) (What is the representation form of Fourier transform with angular velocity w as an independent variable? b151)
2.9.4. Fourier transform of non-periodic signal (what is the function of rectangular pulse signal after Fourier transform? a152) (What is the function of sinc pulse signal after Fourier transform? b153)
2.9.5. Fourier transform of periodic signals (a brief description of Fourier transform method for DC signals a156) (a brief description of Fourier transform method for complex exponential signals a157) (Fourier transform method for cosine signals Brief description a159) (Brief description of the Fourier transform solution method for sinusoidal signals b159) (Brief description of the Fourier transform solution method for general periodic signals a160) (What is the essence of the Fourier transform of periodic signals? a161)
2.9.6. Symmetry of Fourier Transform (Explanation on the symmetry of the original function and the function after Fourier Transform a162)
2.9.7. Fourier transform of delayed signal (Summary of Fourier transform time-shift characteristic a165) (Proving process of Fourier transform time-shift characteristic a166) (Fourier transform analysis of sine pulse delayed signal b166)
2.9.8. Fourier transform of signal product (what is the relationship between the spectrum of the product of two signals and the two signals? a168) (what is the calculation process of general polynomial multiplication? b168) (the calculation process of convolution What is it? a169) (how to find the Fourier coefficient a170 of the signal after two signals are multiplied) (what is the convolution formula of any two discrete sequences? a171) (calculation process of the convolution of any two discrete sequences b171) (What is the convolution formula of two continuous functions? a177) (What are the convolutions of two discrete sequences and the convolution of two continuous functions called? What are the calculation processes of these two types of convolutions? b177) (What is the integral formula of the two continuous functions? c177) (Examples of the calculation process of the convolution of the rectangular function and the sawtooth function d177) (The law derivation process of the convolution of a continuous function and the unit impulse function a183) (a Summary of the law of convolution of continuous function and unit impulse function a185) (Illustration of the application of frequency domain convolution theorem in modulation a186) (Application of frequency domain convolution theorem in sampling a188)
2.9.9. Fourier transform of signal convolution (what is a unit impulse sequence? What is a unit impulse response sequence? a191) (input sequence x[n], unit impulse response sequence h[n] in a discrete system What is the connection with the output sequence y[n]? a192) (known input sequence x[n] and unit impulse response sequence h[n] to solve the output sequence y[n] example a193) (in a continuous system What is the relationship between the input signal, the unit impulse response and the output sequence? a196) (an example where the sampled signal passes through an ideal low-pass filter to reconstruct an analog signal b196) (the definition of time domain convolution theorem a199) (time domain convolution Derivation of the theorem b199) (application of the time domain convolution theorem in filtering a200)
2.10.1, Discrete Fourier Forward Transformation (definition of Discrete Fourier Transformation b201) (Example analysis of discrete Fourier transform of complex exponential signal a202) (Discrete Fourier transform of complex exponential signal X(k) The relationship with the ck of the discrete spectrum explains a205) (Fourier transform of cosine signal a206) (What is the essence of discrete Fourier forward transform? a207) (Derivation of discrete Fourier forward transform a208)
2.10.2, Discrete Inverse Fourier Transform (definition of Discrete Inverse Fourier Transform a214) (take 8 sampling points in one cycle as an example to understand the calculation process of Discrete Inverse Fourier Transform a215) (Discrete Fourier Transform What is the essence of ?a218)
3. Channel (schematic diagram of the position of the channel in the communication system model a221)
3.1. Noise and interference (what are the noise and interference in the channel? a221) (what are the effects of noise and interference on the channel? b221)
3.2. Channel bandwidth (what factors determine which signals can pass through the channel and which signals cannot pass through the channel? a221) (the definition of channel bandwidth b221) (if the signal bandwidth, that is, the frequency of the signal, exceeds the channel bandwidth, what will happen to the signal Phenomenon? c221)
3.3. Channel capacity (definition of data capacity a222) (calculation formula of channel capacity, namely Shannon’s formula b222) (the relationship between signal-to-noise ratio and the ratio of signal power to noise power, see the auxiliary document) (known signal-to-noise ratio and bandwidth Example of seeking channel capacity c222)
3.4. Mobile fading channel (What are the three types of attenuation or loss suffered by radio waves during propagation? a223)
3.4.1. Path loss (the definition of path loss a224)
3.4.2. Large-scale fading (the definition of large-scale fading b224) (The difference between large-scale fading and small-scale fading, see the auxiliary document)
3.4.3. Small-scale fading (definition of small-scale fading c224) (what is multipath? d224) (taking wireless TV signals as an example, what impact does multipath have on communication quality? a225) (multipath propagation affects mobile communications What is the influence of radio waves? b225) (what is fading? a226) (an example of in-phase superposition of signals in multipath b226) (an example of reverse superposition of signals in multipath a227) (signal in the same direction and inversely in multipath To summarize a228) (in general, description of multipath superposition a228) (what is coherent bandwidth? a230) (what is frequency selective fading? a231) (what is flat fading? b231) (what is Doppler effect? a232) (What is Doppler frequency shift? b232) (Interpretation of the principle of Doppler frequency shift between the mobile receiving station and the wave source in a straight line a233) (About the Doppler frequency shift where the mobile receiving station and the wave source are not in a straight line Explanation of the principle of frequency shift b233) (The principle explanation of Doppler frequency shift in the case of multipath propagation, that is, Doppler spread, a235) (what is the coherence time? a238) (what is fast fading? a239) (what Is it slow fading? b239)
4. Source coding (the position a240 of the source coding in the communication system model) (what does the source coding process include for analog sources? b240)
4.1. A/D conversion (what is the process of A/D conversion? c240)
4.1.1. Sampling (instructions on sampling principle a241) (instructions on reconstruction principle b241) (instructions on Nyquist sampling theorem c242) (taking the transmission of voice signals on the telephone line as an example of Nyquist sampling theorem Carry out time domain and frequency domain image description a242) (What is frequency aliasing phenomenon? a246) (Frequency aliasing phenomenon in real life? b246) (Using rotation vector to simulate wheel rotation to explain frequency aliasing phenomenon a247) (ideal sampling What is the difference between the actual sampling process and the actual sampling process? a249)
4.1.2. Quantization (what is quantization? a250) (what is quantization level? b250) (what is quantization error? c250) (what is quantization signal-to-noise ratio? d250) (what is uniform quantization? The properties of uniform quantization are Which? e250) (What is non-uniform quantization? What are the properties of non-uniform quantization? a252) (How to achieve non-uniform quantization in practice? a253) (On the principle of using compressors, uniform quantizers and expanders to achieve non-uniform quantization Instructions, see supporting documentation)
4.1.3. Coding (the definition of coding b253) (how to code the quantized signal c253)
4.1.4. Realization (which instruments are used to complete the analog/digital conversion function and digital/analog conversion function in the communication system a254) (the description of the working principle of the analog-to-digital converter b254, not read the content) (digital-to-analog converter The working principle of a257, did not read the content)
5. Channel coding and interleaving
6. Transmission and reception of baseband signals (what is a baseband signal? See the supplementary notes) (the location of baseband signal transmission and reception in the communication system model a302)
6.1 Pulse forming
6.1.1. Rectangular pulse (instructions about rectangular pulse a302)
6.1.2, sinc pulse (instructions about sinc pulse a304)
6.2, baseband filter
6.2.1. Ideal low-pass filter (relevant instructions about ideal filter a305)
6.3.1. What is an eye diagram (a brief introduction to the eye diagram and how the eye diagram reflects the strength of crosstalk between codes and the influence of noise a310)
6.3.2. The principle of eye diagram generation (how the eye diagram is generated a311)
7. Frequency band signal transmission and reception (what is the position of frequency band signal transmission and reception in the communication system model? a316)
7.1. Analog modulation (what type of target signal is analog modulation? b316) (what are the three types of analog modulation? c316)
7.1.1. Standard amplitude modulation (what is the basic idea of amplitude modulation? a317) (what is standard amplitude modulation? b317) (what is the modulation principle of standard amplitude modulation? a319) (what is the demodulation principle of standard amplitude modulation? a320) (Analysis on the frequency spectrum of the standard amplitude modulation signal a321) (Description on the modulation efficiency of the standard amplitude modulation a322)
7.1.2 Double-sideband modulation (instructions on the principle of double-sideband modulation a322) (instructions on the demodulation principle of double-sideband modulation a323) (instructions on the frequency spectrum appearing in the process of double-sideband modulation and modulation of the baseband signal a325) (about bilateral Description of the upper and lower sidebands of the modulated signal in band modulation a326)
7.1.3, single sideband modulation (what is the modulation principle of single sideband modulation a327) (what is the demodulation principle of single sideband modulation? a328) (about the frequency spectrum that appears in the process of single sideband modulation modulating the baseband signal Description a325)
7.1.4. IQ modulation (what is IQ modulation? a331) (what is the modulation principle of IQ modulation? b331) (why can IQ modulation be called quadrature modulation? c331) (what is the demodulation principle of IQ modulation? a332) (Analysis of the frequency spectrum of IQ modulation in the process of modulation a333)
7.2, digital modulation
7.2.1. Digital modulation (what is the basic idea of digital modulation? a335) (what are the two common digital modulations? b335)
7.2.2. PSK modulation (what is PSK? c335) (what is BPSK? a336) (what is QPSK? b336) (what is 8PSK? a337)
7.2.3, QAM modulation (what is a symbol? See the auxiliary document) (what is QAM quadrature amplitude modulation a338) (what is 16QAM? b338)
7.2.4. Realization of digital modulation (instructions about BPSK modulation principle a339) (instructions about BPSK demodulation principle a340) (instructions about QPSK modulation principle a341) (instructions about QPSK modulation principle a343) (about 8PSK modulation Principle description b343) (Description of the principle of 8PSK demodulation a346) (Description of the modulation principle of 16QAM b346) (Description of the principle of 16QAM demodulation a348) (Description of the principle of digital modulation and demodulation b348)
7.2.5. Constellation diagram (a brief overview of the constellation diagram a349) (the constellation diagram description for BPSK modulation a350) (the constellation diagram description for QPSK modulation b350) (the constellation diagram description for 8PSK modulation a351) (the constellation diagram for 16QAM modulation Description a352)
7.2.6. The mapping relationship of digital modulation (why the input data of QPSK modulation is mapped to π/4, 3π/4, 5π/4, 7π/4 in the order of 00, 01, 11, 10 instead of Mapping in the order of 00, 01, 10, 11 a353) (What is Gray code? a355)
7.2.7. Modulation efficiency (under the same symbol rate, what is the change rule of the modulation efficiency of different orders of digital modulation? b355) (How many kinds of symbols are there in common digital modulations, each symbol What is the number of bits carried? c355) (what is a symbol? a356) (what is the baud rate? a357)
7.3 Frequency conversion technology
7.3.1. Direct frequency conversion (what is direct frequency conversion? a358) (examples of direct frequency conversion b358)
7.3.2. Indirect frequency conversion (what is indirect frequency conversion? a359) (in the case of indirect frequency conversion, the baseband IQ signal waveform, intermediate frequency signal waveform and radio frequency signal waveform diagram b359) (indirect up-conversion principle description a360) (The principle of indirect down conversion a362)
7.3.3. Digital frequency conversion (the principle diagram of digital up-conversion a363) (the principle diagram of digital down-conversion a364)
7.3.4. Band-pass sampling (what is a band-pass signal? a364) (what is the band-pass sampling theorem a365) (the derivation of the band-pass adoption theorem b365) (about the band-pass sampling theorem between the sampling frequency fs and the highest frequency fH A369) (What is the relationship between the band-pass signal sampling theorem and the Nyquist sampling theorem? a371) (Instructions on over-sampling and under-sampling a372)
8. Antenna technology (the schematic diagram of the position of the antenna in the wireless communication system model a375)
8.1. The function of the antenna (what is the function of the antenna? b375)
8.2. Principle of electromagnetic wave radiation (when will electromagnetic wave radiation occur? c375)
8.2.1. The relationship between the radiation ability and the shape of the wire (the relationship between the radiation ability of electromagnetic waves and the shape of the wire a376)
8.2.2. The relationship between radiation ability and wire length (the relationship between electromagnetic wave radiation ability and wire length b376)
8.3. Half-wave symmetrical oscillator (a brief description of half-wave symmetrical oscillator c376, b377)
8.4. Omni-directional antenna (what are the characteristics of omni-directional antenna? a377) (a brief description of vertical four-element antenna array b377)
8.5. Directional antenna (what are the characteristics of directional antenna? a378) (schematic diagram of directional antenna b378)
8.6. Multi-antenna technology (a brief overview of the difference between multi-antenna and single antenna a379)
8.6.1. Diversity technology (disadvantages of single antenna sending and receiving modulated signals b379) (what is diversity receiving technology? c379) (what are the commonly used algorithms for combining multiple signals? a380) (application examples of diversity receiving technology b380)
8.6.2. MIMO (what is a MIMO system? a380, c381) (what is a SISO system? a381) (what is a SIMO system? b381) (analysis and explanation on the limitation of SISO system information transmission rate a382) (why can MIMO be improved? Transmission rate? b382) (taking dual input and double output as an example to illustrate the relationship between MIMO input baseband data, output baseband data and channel gain a383) (taking multiple input and multiple output as an example to illustrate MIMO input baseband data and output baseband data And the channel gain a385) (instructions about the MIMO channel matrix a386) (instructions about the MIMO channel matrix when the distance between the transmitting and receiving antennas is large enough a387) (about the MIMO channel matrix when the distance between the receiving antennas is very small The description a389) (the description of the MIMO channel matrix when the distance of the transmitting antenna is very small a390) (taking a dual-input and double-output MIMO system as an example, how to judge how many channels of data can be paralleled by a MIMO system? a391) (using four-input Take the four-out MIMO system as an example. How to judge how many channels of data can be paralleled by a MIMO system? a391) (How many channels of data can the MIMO system transmit in parallel by solving the rank of the matrix? a397) (The relationship between the rank of the matrix and the system of equations, see Supplementary Notes ) (Explanation on the meaning of the rank of the channel matrix a399) (Explanation on spatial multiplexing a401) (Explanation on transmit diversity b401)
8.6.3. Beamforming (What is beamforming? a402) (Description of the principle of beamforming a402) (How is beamforming realized? a407)