MindMap Gallery Digital baseband transmission system
Introduced digital baseband signals and their spectrum characteristics, common code patterns for baseband transmission, digital baseband signal transmission and inter-symbol crosstalk, baseband transmission characteristics without crosstalk, anti-noise performance of baseband transmission systems, eye diagrams, partial responses and time domain equalization
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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!
Digital baseband transmission system
introduction
system characteristics
Direct transmission of baseband signals without modem
The composition of the baseband transmission system
Channel: Provides a transmission channel for baseband signals. Transmit filter, i.e. channel signal former: Function: Original baseband signal → Baseband signal suitable for channel transmission Purpose: Match the channel, reduce the code string, and facilitate synchronization extraction. Receive filter: Function: Filter out-of-band noise and equalize channel characteristics. Purpose: Make the output baseband waveform conducive to sampling decisions. Sampling decision maker: Function: Make sampling decisions on the output waveform of the receiving filter. Purpose: Determine the transmitted signal code sequence and regenerate the baseband signal. Synchronous extraction: Extract bit timing pulses for sampling.
Waveforms at each point of the baseband transmission system
Digital baseband signals and their spectrum characteristics
Six basic signal waveforms
(a) Unipolar waveform
---Characteristics: Single polarity, DC component and low-frequency component. ——Application: Inside equipment and in digital modulators.
(b) Bipolar waveform
——Advantages: No DC component (equivalent), strong anti-interference ability. ——Application: V.24, RS-232C interface standard and digital modulator.
(c) Single return-to-zero code
——Features: bit timing signals can be directly extracted from it, ——Application: used as a transition pattern for extracting synchronization clocks from other patterns.
(d) Double return-to-zero code
- It has the characteristics of both bipolar and return-to-zero waveforms
(e) Differential waveform (relative code waveform)
——Features: Use the transition/invariance of adjacent symbol levels to represent signal symbols. Signal difference (1 changes, 0 remains unchanged) Space number difference (0 changes, 1 remains unchanged - Advantages: It can eliminate the impact of uncertainty in the initial state of the equipment.
(f)Multi-level waveform
——Features: One pulse can carry multiple bits of information. ——Advantages: When the code transmission rate is constant, the transmission rate of multi-level waveforms is high. ——Application: High data rate transmission system.
Four-level waveform: 00—— 3E 01—— E 10—— - E 11—— -3E
expression
If the waveforms of each symbol are the same but have different values, it can be expressed as:
s(t) Random pulse sequence an The level value of the nth symbol TB symbol duration g(t) A certain pulse waveform
Generally:
Spectral characteristics of baseband signals PSD
Purpose
Signal bandwidth
Bit timing component, DC component, etc.
method
From the definition of power spectral density
Ideas
Steady state wave v(t)——periodic signal
The statistical average component of the random sequence s(t), the statistical average waveform of each symbol is the same:
Power Spectral Density
Alternating wave u(t)
Power Spectral Density
s(t) =u(t) power spectral density of v(t)---Ps( f )
bilateral spectrum
One-sided spectrum
Common code patterns for baseband transmission
Code selection principle
①No DC component and small low-frequency component;
② Rich timing information;
③The main lobe width of the power spectrum is narrow;
④ Not affected by the statistical characteristics of the source;
⑤Have self-checking ability
⑥Easy to compile and decode.
Several common transmission code patterns
AMI code
encoding rules
“1” —— 1, -1 alternately “0” —— 0
Features
Does not contain DC components and has few low-frequency components
three levels
The encoding and decoding circuit is simple and has macro self-checking capabilities.
shortcoming
When the letter code has a long string of zeros, it is difficult to obtain timing information.
application
PCM24 road base group (North American series) 1.544Mb/s line pattern.
HDB3 code
encoding rules
When the number of consecutive "0"s does not exceed 3, the encoding rules of AMI will be followed.
When the number of consecutive "0"s exceeds 3, change the fourth "0" to a non-"0" pulse and record it as V or V-, which is called a destruction pulse.
The polarity of adjacent V codes must appear alternately (to ensure no DC)
The polarity of the V code should be the same as the polarity of the previous non-"0" pulse, otherwise, change 0000 to B 00V or B-00V-. B is called the regulatory pulse
The polarity of the transmission number after the V code must also be alternated.
Features
In addition to maintaining the characteristics of the AMI code, it also limits the number of consecutive "0" codes to less than 3, which is beneficial to the extraction of bit timing signals.
application
A-law PCM line interface pattern below quartic group
Biphase code (Manchester code)
encoding rules
“0”——01; “1”——10
Features
Two levels (opposite polarity);
No DC component;
Rich bit timing information
The encoding and decoding circuit is simple
The number of consecutive codes does not exceed 2
shortcoming
The bandwidth is 1 times larger than the original code.
application
Transmission patterns in local area networks.
CMI code
encoding rules
"1"——1 1, 0 0 alternate "0"——01
Features
Bipolar two-level code, the number of consecutive codes does not exceed 3.
application
A-law PCM quartic group interface pattern;
In optical cable transmission systems with rates lower than 8.448Mb/s
nBmB code (m>n)
n-bit binary code (original code group) combinations 2^n→m-bit binary code (new code group) combinations
Select allowed code groups from 2^m types, and the rest are prohibited code groups
advantage
Provides good synchronization and error detection capabilities
cost
The required transmission bandwidth increases with m
Usually choose m=n 1, such as 1B2B, 4B5B, 5B6B code, etc.
nBmT code (m≤n)
4B/3T code, converts 4 binary codes into 3 ternary codes, - an improved version of 1B/1T code
At the same code rate, the information capacity of 4B/3T codes is greater than 1B/1T, thus improving frequency band utilization.
4B/3T codes, 8B/6T codes, etc. are suitable for high-speed data transmission systems, such as high-order group coaxial cable transmission systems
Digital baseband signal transmission and inter-code crosstalk
System composition and transmission model
Baseband transmission system model
Baseband transmission system composition
Waveforms at each point of the baseband transmission system
Quantitative analysis
Baseband transmission overall characteristics
The baseband signal corresponding to {an}
Receive filter output signal
Partial response and time domain equalization
Category I partial response system
The current symbol only generates inter-symbol crosstalk for the next symbol
If g(t) is the waveform of the transmitted signal, and the interval between transmitted symbols is TB
Then the sampled value of this symbol is only subject to crosstalk from the same amplitude sample of the previous symbol.
Highest band utilization without ISI
Category IV partial response system
The current symbol only generates inter-symbol crosstalk for the next symbol
Notice
shortcoming
Eye
definition
It refers to a pattern observed at the receiving end with an oscilloscope; when transmitting a binary signal waveform, the pattern displayed on the oscilloscope is very similar to the human eye - hence the name "eye diagram". The size of ISI and the strength of n(t) can be observed from it; In order to intuitively evaluate the performance of the system; Adjustments to the receive filter may also be indicated to reduce ISI.
Observation method
Without ISI - big "eyes", the stitches are thin and clear; with ISI - small "eyes", and the stitches are messy. When there is noise, the eye diagram traces become blurred strip lines; the greater the noise, the wider and blurrier the lines are, and the smaller the "eyes" open, or even close.
Noise immunity performance of baseband transmission systems
Binary Bipolar Baseband System Pe
Analytical model
nR(t)Characteristics
x(t)Characteristics
For a bipolar baseband signal, its sampling value is (A,-A), then the value of the synthetic wave x(t)=s(t) nR(t) at the sampling time is:
Bit error rate Pe
Assume the decision threshold is Vd, and the decision rule is: x(kTB) > Vd, it is judged as a "1" code - wrong x(kTB) Vd, it is judged as a "0" code - correct
Total bit error rate of bipolar baseband system: (the value of Pe depends on P(1), P(0), A, and Vd)
optimal threshold level
The decision threshold level that minimizes Pe
Binary Unipolar Baseband System Pe
Compared
Baseband transmission characteristics without inter-code crosstalk
time domain conditions
Meaning: This code element has a value at the sampling time; other code elements are 0 at the sampling time.
Frequency domain conditions
"Cut, translate/fold, superimpose" When the ideal LPF transmits at a rate of Re=1/Te, there is no inter-code crosstalk.
Design of H(w)
Ideal low pass characteristics
Nyquist bandwidth (narrowest bandwidth)
Nyquist rate (highest baud rate without ISI)
Highest band utilization for ISI-free baseband systems
Cosine roll-off characteristic
Describe the degree of roll-off