MindMap Gallery Communication Principles-Channel Mind Map
It introduces wireless channels, wired channels, digital simulation, channel capacity, noise in the channel, and the impact of channel characteristics on signal transmission.
Edited at 2024-02-18 11:20:57Avatar 3 centers on the Sully family, showcasing the internal rift caused by the sacrifice of their eldest son, and their alliance with other tribes on Pandora against the external conflict of the Ashbringers, who adhere to the philosophy of fire and are allied with humans. It explores the grand themes of family, faith, and survival.
This article discusses the Easter eggs and homages in Zootopia 2 that you may have discovered. The main content includes: character and archetype Easter eggs, cinematic universe crossover Easter eggs, animal ecology and behavior references, symbol and metaphor Easter eggs, social satire and brand allusions, and emotional storylines and sequel foreshadowing.
[Zootopia Character Relationship Chart] The idealistic rabbit police officer Judy and the cynical fox conman Nick form a charmingly contrasting duo, rising from street hustlers to become Zootopia police officers!
Avatar 3 centers on the Sully family, showcasing the internal rift caused by the sacrifice of their eldest son, and their alliance with other tribes on Pandora against the external conflict of the Ashbringers, who adhere to the philosophy of fire and are allied with humans. It explores the grand themes of family, faith, and survival.
This article discusses the Easter eggs and homages in Zootopia 2 that you may have discovered. The main content includes: character and archetype Easter eggs, cinematic universe crossover Easter eggs, animal ecology and behavior references, symbol and metaphor Easter eggs, social satire and brand allusions, and emotional storylines and sequel foreshadowing.
[Zootopia Character Relationship Chart] The idealistic rabbit police officer Judy and the cynical fox conman Nick form a charmingly contrasting duo, rising from street hustlers to become Zootopia police officers!
channel
Overview
narrow channel
cable channel
Open wire, cable, fiber optic
wireless channel
free space or atmosphere
Generalized channel
modulation channel
Study modulation and demodulation issues
constant parameter channel
Characteristics do not change over time
random parameter channel
Characteristics change over time
coded channel
Study encoding/decoding problems
There is a memory channel
There is a dependency relationship between the preceding and following code elements
memoryless channel
The preceding and following code elements are independent of each other
wireless channel
How electromagnetic waves propagate
ground wave
Frequency: <2MHz Characteristics: Diffraction capability Distance: hundreds or thousands of meters Used for: AM broadcasting
Tianbo
Frequency: 2~30MHz Characteristics: Reflected by the ionosphere Distance: <4000km (one hop) Used for: long-range, short-wave communication
Line of sight spread
Frequency: >30MHz Characteristics: Straight line propagation, penetrating ionosphere Usage: Satellite and outer space communications, ultra-short wave and microwave communications Distance: Depends on antenna height
radio relay
Advantages: large capacity, low investment, easy maintenance, and stable transmission quality. Application: Transmission of voice and television signals over long distances.
satellite relay
Advantages: large communication capacity, stable transmission quality, long transmission distance, and wide coverage area. Disadvantages: large transmission delay, large signal attenuation, and high cost.
scatter communication
Ionospheric scattering frequency: 30~60MHz Distance: above 1000km Tropospheric scattering frequency: 100~4000MHz Distance: <600km Meteor trace scattering characteristics: height 80~120km, length 15~40km Retention time: less than 1 second to several minutes Frequency: 30 ~100MHz distance: more than 1000km use: low-speed storage, high-speed burst, intermittent transmission
cable channel
Symmetrical cable
Features
Each pair is twisted to reduce mutual interference between pairs
shortcoming
Large transmission attenuation, long distance, and crosstalk interference between adjacent channels
application
Transmission media in telephone lines, local area networks and integrated wiring projects
coaxial cable
composition
Composed of two coaxial conductors. Inner core: metal wire. Outer conductor: metal braid.
Advantages (compared to twisted pair)
Strong anti-electromagnetic interference capability, wider bandwidth and higher speed
shortcoming
The cost is higher; solution: use optical cable instead
optical fiber
Structure: core, cladding Classification by refractive index: step type, gradient type Classification by mode: multimode fiber, single-mode fiber
advantage
Wide transmission bandwidth, large communication capacity; small transmission attenuation, long transmission distance without relay; anti-electromagnetic interference, good transmission quality, anti-eavesdropping, corrosion resistance; small size, light weight, saving non-ferrous metals, environmental protection
shortcoming
Fragile, expensive interfaces, installation and maintenance require specialized skills
application
In the main lines of long-distance telephone networks, cable TV networks, etc.
digital model
modulation channel model
Model
Superposition of noisy linear time-varying/time-invariant networks
commonality
There is a pair (or multiple pairs) of input terminals and output terminals; most channels satisfy the linear superposition principle; there are fixed or time-varying delays and losses for signals; when there is no signal input, there may still be output (noise)
Entry and exit relationship
Additive noise is always present
Classification
constant parameter channel
Characteristics basically do not change over time
accompanying channel
Characteristics change randomly and rapidly over time
coded channel model
Model
It can be described by transition probability.
Channel capacity
Discrete Signal Capacity
The average amount of information sent by the source (entropy)
Average amount of information lost due to channel noise
Information transmission rate R
The average amount of information transmitted by the channel per second
r ‒The number of symbols transmitted by the channel per second is (symbol rate) [H(x) – H(x/y)] ‒It is the average amount of information obtained by the receiving end
Channel capacityCt
Maximum information transmission rate: probability distribution of all possible information sources
Meaning: The maximum average amount of information that each symbol can transmit
Equivalence
continuous channel capacity
Shannon formula S - signal average power (W); B - bandwidth (Hz) n0 - noise single-sided power spectral density; N = n0B - noise power (W)
Equivalence
meaning
When the average power of the signal and channel noise is given, the theoretical limit value of the amount of information that can be transmitted per unit time on a channel with a certain frequency bandwidth.
significance
If R, ≤ C, then a channel coding method can always be found to achieve error-free transmission; if the transmission rate is greater than the channel capacity, error-free transmission is impossible.
in conclusion
Channel capacity C depends on B, S and n0
Increasing S can increase C. If S →∞, then C→∞
Decreasing n0 can increase C. If n0 → 0, then C→∞
application
When C is constant, the channel bandwidth B and signal-to-noise ratio S/N can be converted to each other.
Increasing B can lead to a decrease in S/N; vice versa
Noise in the channel
definition
Unwanted electrical signals are present in the channel
It always exists independently of the signal, so it is also called additive interference.
Distort the signal, cause code errors, and limit the transmission rate
type
By noise source
man-made noise
natural noise
Internal noise (thermal noise)
Thermal movement of electrons from all resistive components
Evenly distributed in the frequency range of 0~10^12Hz
Properties: Gaussian white noise
According to the nature of noise
impulse noise
Narrowband/Single Frequency Noise
power spectrum
Noise equivalent bandwidth
Physical meaning: The noise power passing through the rectangular filter with width Bn = the noise power passing through the actual receiving filter.
average power
Ripple noise
The impact of channel characteristics on signal transmission
Characteristics of constant parameter channels (time-invariant systems) and their impact on signal transmission
Transmission characteristics
Distortion-free transmission
Impulse response of ideal constant parameter channel
Distortion-free transmission (ideal constant parameter channel) characteristic curve
Distortion effects
Amplitude frequency distortion
Impact: For analog signals, it causes waveform distortion → the signal-to-noise ratio decreases. For digital signals, it causes inter-code crosstalk → the bit error rate increases.
phase frequency distortion
Impact: Little impact on voice signals, great impact on video signals, digital signals: inter-code crosstalk → increased bit error rate
Parametric channel characteristics and their impact on signal transmission
Parametric channel characteristics
Attenuation changes with time Delay changes with time Multipath propagation
multipath effect
Multipath propagation causes Rayleigh fading of signals
Frequency dispersion caused by multipath propagation
Measures to reduce frequency selective fading
Diversity reception
spread spectrum technology
OFDM etc.