The early history of digital communication is linked with the development of telegraph. 1937, British A.H. Reeves proposed pulse code modulation (PCM), which promoted the digitization of analog signals. 1946, French e.m. delorean invented incremental modulation. 1950 C. C. Cutler proposed differential coding. From 65438 to 0947, Bell Laboratories developed a 24-channel electronic tube pulse code modulation device for experiments, which proved the feasibility of PCM. 1953 invented the feedback comparison encoder without coding tube, which expanded the dynamic range of the input signal. 1962, the United States developed a 24-channel transistor 1.544 Mbit/s pulse code modulation device, which was used between local telephone networks. Compared with analog communication, digital communication has obvious advantages. Strong anti-interference ability, communication quality is not affected by distance, which can meet the requirements of various communication services, facilitate the use of large-scale integrated circuits, and facilitate the realization of secure communication and computer management. The disadvantage is that the occupied channel frequency band is wide. In the 1990s, digital communication developed towards ultra-high-speed, large-capacity and long-distance, and efficient coding technology became more and more mature. Speech coding has been put into practical use and new digital intelligent terminals will be further developed.
Chapter II Modulation and Demodulation of Analog Signals
Modulation: converting various digital baseband signals into digital modulation signals (modulation signals or frequency band signals) suitable for channel transmission; Demodulation: At the receiving end, the received digital band signal is restored to a digital baseband signal.
Chapter III Digital Transmission of Analog Signals
Mainly through three steps, sampling, quantization and coding.
Chapter 4 Multiplex and Digital Multiplex
Chapter V Quasi-synchronous and Synchronous Digital Transmission Systems
Chapter VI Baseband Transmission of Digital Signals
Chapter VII Frequency Band Transmission of Digital Signals
Chapter VIII Synchronization Principle
Chapter 9 Error Control Coding
10 pseudo-random sequence and its application
Chapter 1 1 Broadband Access Network Technology
refer to
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