"Communication Principles" Final Review Notes

Chapter One

1. Communication system composition

2. Classification

Transmission quality: wired communication and wireless communication

Whether to modulate: baseband communication system and frequency band communication system

3.Method of communication

4. Information amount (I), average information amount (H), code transmission rate, transmission rate

5. Bit error rate, error rate

500 * 20000*10^(-6)

other

1000*4=4000

2^(4)=16

Chapter 23

The signal undergoes Fourier transform to obtain the spectral density.

The energy spectral density is the square of the energy signal spectral density.

1. Energy signal, power signal and their Fourier changes

The power signal is a special periodic signal, and the corresponding Fourier change is the discrete spectrum, Baseval's theorem

2. Wiener-Xinqin theorem

Maybe a picture

Output power spectral density = input power spectral density * square of H (w)

Wiener's emerging theorem means: Power = Fourier transform of autocorrelation function (both input and output are acceptable)

third chapter

example

Solution 1

Solution two suggestion

Both the noise and the channel are generally stationary.

Chapter 4 (√)

1. Classification of channels

Narrow sense and broad sense, modulation and coding, wired and wireless, constant parameters and random parameters, amplitude frequency distortion and phase frequency distortion in constant parameter channels, multipath effect in random parameter channels, that is, two-path effect

2. Gaussian white noise

Noise power: times bandwidth

White noise characteristics:

Gaussian means: the probability density distribution is a normal distribution

What is white: The power spectral density conforms to a uniform distribution in the entire frequency domain

3. Channel capacity

Replenish

Shannon's formula: (important for discussion) signal power, noise power spectral density, signal bandwidth. As S tends to infinity, what will happen to the channel capacity. etc.

Chapter 5 (Key Points) (Half √)

5.1 AM, DSB, SSB, VSB, time domain waveform diagram, frequency domain spectrogram and expressions in linear modulation.

1.AM (Features)

2.DSB (Features)

3.SSB (Features)

4.VSB (Features)

5.2 FM and PM expressions in nonlinear modulation, comparison of broadband, narrowband FM and AM, demodulation methods (coherence and envelope detection), threshold effect

Nonlinearity—FM bandwidth, expression of frequency modulation bandwidth., fm is the baseband signal

Small signal-to-noise ratio----the threshold is less than

FDM (Frequency Division Multiplexing)

See screenshot

Exercises in the book (5-8 5-9)

5-8

Replenish

AM is inefficient,

Frequency division multiplexing is required - à minimum bandwidth (SSB), equipment complexity - "Simple (AM)

Time domain waveform graph (AM, DSB) | Review

Frequency domain spectrogram (AM, DSB, SSB) | Review

Expression (AM, DSB, SSB)

SSB subtracts up and adds down, with a small tip

basic concept

DSB=2,SSB=1. Noise immunity performance is consistent. There are differences because the input conditions are not equal.

Chapter Six (√)

Basic code, differential code, AMI code, HDB3 code, how to encode HDB3 code? (Must know it)

In any case, the spectrum of the basic code (frequency domain characteristics of the baseband signal) does not have a discrete spectrum (x)

The steady state term is 0

Baseband system characteristics without inter-code crosstalk, partial response system (maximum code transmission rate, easy to implement)

(Judgment of no inter-code crosstalk)

HDB3 only encodes and does not modulate. The baseband signal shown is

Conditions for discrete spectrum-free classification: equal probability and bipolarity

Chapter 7 (√)

7.1 Able to draw ASK, 2FSK, 2PSK/DPSK waveform diagrams, understand spectrograms, (modulated signals, FSK has f1-f2, others are twice) bandwidth, modulation method and demodulation method principle block diagram (important!)

7.1.1 2ASK

7.1.2 2FSK

7.1.3 2PSK

Coherent demodulation: coherent, low pass

Envelope detection: rectification, low pass

(All demodulation drawings and demodulation process diagrams)

7.2 System block diagram

Page 255/225 in the book? 7-1/7-2

(The demodulation block diagram must be tested)

Replenish

It is known that the digital signal {an}=1011010, if the symbol rate is 1200 baud and the carrier frequency is 1200Hz, draw the waveforms of 2PSK, 2DPSK and relative code {bn} (assuming that code 0 corresponds to phase 0, 1 in the 2PSK system The code corresponds to the phase π. In the 2DPSK system, the 0 code corresponds to the phase difference 0, the 1 code corresponds to the phase difference π, and it is assumed that the starting reference symbol is 1).

Chapter 10 (√)

1. Low-pass sampling theorem

fs is greater than or equal to twice fh

2. Bandpass sampling theorem formula:

Learn to pass

set of formulas

3. Ideal sampling does not exist. What are the two actual samplings: natural sampling and flat-top sampling?

4.A law (the value of A), u law (the size of A)

A rate: 13 lines and 87.6

u rate: 255, which is a 15-fold line equivalent to 94.18 of A

5.PCM encoding

6. Conditions for incremental modulation not to be overloaded

7.Basic structure of E1 signal:

30 transmission signal channels, 2 control signals

8. Transmission rate:

2.048Mbit/s

Attached, some words about this subject

For the course on Communication Principles, my suggestion is that you still need to listen carefully in class, and if you only talk about the final exam, you still need to read the questions in the study pass carefully, and have some understanding of some things, etc., and master the big questions HDB3码、FSK\ASKPSK\DPSK、PCM编码.