MindMap Gallery New digital bandpass modulation technology
Introduce new digital bandpass modulation technology from quadrature amplitude modulation, minimum frequency shift keying, Gaussian minimum frequency shift keying, and orthogonal frequency division multiplexing.
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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!
New digital bandpass modulation technology
quadrature amplitude modulation
QAM is a modulation method with joint amplitude and phase keying. It has high spectrum utilization and better anti-noise performance than MPSK. It is widely used in medium and large-capacity digital microwave communication systems, high-speed data transmission in cable TV networks, satellite communications and other fields. .
In multipath fading channels, the more signal amplitude and phase values, the greater the impact, so the star pattern is more attractive than the square pattern.
However, the generation and reception of QAM signals in square constellations are easier to implement.
In QAM, the amplitude and phase of the carrier are controlled by the baseband signal at the same time. Therefore, one of its symbols can be expressed as:
Generation of 16QAM signal
By superimposing two orthogonal 4ASK signals, a 16QAM signal can be formed
Square MQAM: Using two co-frequency orthogonal carriers to realize the transmission of two parallel LASK signals within the same bandwidth
Composite phase shift method: By superimposing two independent QPSK signals, a 16QAM signal can be formed.
Demodulation of 16QAM signal
Spectral zero bandwidth of MQAM signal
Minimum frequency shift keying and Gaussian minimum frequency shift keying
Minimum frequency separation of quadrature 2FSK signals
non-coherent demodulation
coherent demodulation
Basic principles of MSK signals
Frequency interval of MSK signal
The kth symbol of the MSK signal represents:
Minimum frequency difference:
Modulation index:
h=0.5
The number of cycles of the waveform in the MSK symbol
The MSK signal should satisfy the orthogonality condition:
Phase continuity of MSK signal
phase continuity condition
The phase at the end of the previous symbol = the phase at the beginning of the next symbol
Phase constraints
Orthogonal representation of MSK signals
Generation and demodulation of MSK signals
How to generate MSK signal
Demodulation method of MSK signal
Delayed decision coherent demodulation method
principle
block diagram
advantage
This method uses the information of the two symbols before and after to make a decision on the previous symbol, so it can improve the reliability of data reception.
Power spectrum of MSK signal
Error performance of MSK signals
The MSK signal uses half a sine (cosine) waveform with opposite polarity to modulate two orthogonal carrier waves.
Therefore, when each orthogonal component is received separately with a matched filter, the bit error rate performance of the MSK signal is the same as that of 2PSK, QPSK, OQPSK, etc.
However, if it is treated as an FSK signal and demodulated within each symbol duration TB using the coherent demodulation method, its performance will be 3dB worse than that of the 2PSK signal.
Main features of MSK signal
Gaussian Minimum Shift Keying (GMSK)
Gaussian low pass filter
Phase path of GMSK signal
∵ There is no phase turning point, ∴ The derivative at this moment is also continuous, that is, the frequency of the signal will not mutate, which will make the side lobe of the signal spectrum attenuate faster.
Power spectral density of GMSK signal
orthogonal frequency division multiplexing
single carrier modulation
It modulates the data stream that needs to be transmitted onto a single carrier for transmission. The various digital modulation methods introduced earlier belong to the single carrier system.
multi-carrier modulation
Orthogonal frequency division multiplexing (OFDM)
Features
The modulated signal spectrum of each subcarrier overlaps by 1/2 - improving frequency utilization and total transmission rate;
Each modulated signal is strictly orthogonal - making it easier for the receiving end to separate the signals and reduce mutual interference (ICI) between sub-channels;
The modulation system of each subcarrier can be different - different systems are adopted according to the advantages and disadvantages of the channel characteristics at each subcarrier.
shortcoming
Sensitive to frequency offset and phase noise generated by the channel
The ratio of signal peak power to average power is large, which will reduce the efficiency of the RF power amplifier
Strict requirements for synchronization
Basic principles of OFDM
Expression
orthogonality condition
Frequency domain characteristics of OFDM
OFDM frequency band utilization
OFDM implementation
OFDM signal modulation principle diagram based on IDFT/DFT:
OFDM signal modulation principle diagram based on IFFT/FFT:
OFDM signal reception schematic diagram based on IFFT/FFT: