Lesson 02: Basics of Data Communication (1)
Basic concepts : information source, channel, and sink; digital signal, analog signal; analog communication, digital communication (transmission in channel).
Analog channel bandwidth calculation: W=f2-f1, where f1 is low frequency and f2 is high frequency.
Digital channel bandwidth calculation: Nyquist theorem (no noise)
Nyquist theorem : B=2W (B symbol rate, baud rate) information amount n (bit) and symbol type N: n=log<2 >N
Data rate R=Blog<2>N=2Wlog<2>N
Digital channel bandwidth calculation : Shannon's theorem (noisy)
Shannon's theorem : C=Wlog<2>(1+S/N)
where C is the data rate, W is the channel bandwidth, S is the average power of the signal, and N is the average noise Power, S/N is the signal-to-noise ratio (usually expressed in decibels dB). The relationship between decibels and signal-to-noise ratio: dB=10lg(S/N).
Unit conversion : communication conversion rate is 1000, such as 1G=1000M (bit bit)
storage conversion rate is 1024, such as 1G=1024M (Byte byte)
1 byte=8 bit
Channel delay: cable channel delay 200m/us (200km/ms, 200000km/s)
satellite channel delay : 270ms
Transmission medium: twisted pair: divided into unshielded twisted pair UTP, shielded twisted pair STP. It can reach 100Mb/s
through 100 meters : T568B-T568B T568A-T568A, computer-switch, switch-router
cross : T568A-T568B, computer-computer, computer-router, switch-switch, router-router
Coaxial cable : It is divided into thick coaxial cable and thin coaxial cable. Long transmission distance, stable signal, often used in TV, surveillance system, video signal.
Optical fiber (optical cable): Divided into single-mode optical fiber SMF, multi-mode optical fiber MMF.
Wireless channel: divided into radio waves and infrared light waves.
Analog channel modulation: divided into amplitude modulation ASK, frequency modulation FSK, phase modulation PSK, quadrature amplitude modulation QAM.
Digital channel coding: It is divided into three steps : sampling (analog channel bandwidth 2 times), quantization (level), and coding (binary).
Modulation technology and number of symbols: n=log<2>N.
Polar code: Divided into unipolar, polar, and bipolar.
Return-to-zero code: return-to-zero code, non-return-to-zero code (1 flip), bi-phase code (level flip).
Mann code and differential Mann code: Mann code drops 0 to 1 (down 1 to 0), and the efficiency is 50%; differential Mann code breaks 0 to level 1, and the efficiency is 50%.
Various coding efficiency:
4B/5B efficiency 80%, used for Fast Ethernet;
8B/10B efficiency 80%, used for Gigabit Ethernet;
64B/66B efficiency 97%, used for 10 Gigabit Ethernet;
Manchester code and The efficiency of differential Mann code is 50%, used in Ethernet.