PCM Definition
PCM Chinese called pulse code modulation, composed of. rivers proposed in 1937 that this concept laid the foundation for digital communication. In 1960s, it began to be applied to the local telephone network to expand the capacity, so that the transmission capacity of most existing audio cable core lines was increased by 24 ~ 48 times. By the middle and end of 1970s, various countries have successfully modulated pulse codes for large and medium-sized transmission systems such as Coaxial Cable Communication, microwave transmission, satellite communication, and optical fiber communication. At the beginning of 1980s, pulse code modulation was used in telephone relay transmission, large-capacity trunk transmission, and digital programmable switches. Working Principle
Pulse coding modulation converts a continuous analog signal with a continuous value to a discrete time, and transmits the discrete digital signal in the channel. Pulse coding modulation is the process of first sampling the analog signal, then quantifying the sample value amplitude and coding.
Sampling is to periodically scan analog signals and convert time-based continuous signals into time-based Discrete Signals. After sampling, the analog signal should also contain all information in the original signal, that is, the original analog signal can be restored without distortion. The lower limit of the sampling rate is determined by the sampling theorem. The sampling rate is 8 kbit/s.
Quantization refers to discretization the instantaneous values obtained after sampling, that is, using a set of defined levels to represent the instantaneous sampling values with the nearest level value.
After a simulated signal is sampled and quantified, a quantified pulse amplitude modulation signal is obtained, which is only a finite number.
Encoding: a set of binary code groups are used to represent each quantified value with a fixed level. However, quantization is actually completed in the encoding process at the same time. Therefore, the encoding process is also called a modulo/number transformation and can be recorded as A/D.
