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Digital Signal Processing
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Digital Signal Processing
1?Introduction
Digital signal processing (DSP) is concerned with the representation of the signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing. DSP includes subfields like audio and speech signal processing, sonar and radar signal processing, sensor array processing, spectral estimation, statistical signal processing, digital image processing, signal processing for communications, biomedical signal processing, seismic data processing, etc.
Since the goal of DSP is usually to measure or filter continuous real-world analog signals, the first step is usually to convert the signal from an analog to a digital form, by using an analog to digital converter. Often, the required output signal is another analog output signal, which requires a digital to analog converter. Even if this process is more complex than analog processing and has a discrete value range, the stability of digital signal processing thanks to error detection and correction and being less vulnerable to noise makes it advantageous over analog signal processing for many, though not all, applications.
DSP algorithms have long been run on standard computers, on specialized processors called digital signal processors (DSP)s, or on purpose-built hardware such as application-specific integrated circuit (ASICs). Today there are
additional technologies used for digital signal processing including more powerful general purpose microprocessors, field-programmable gate arrays (FPGAs), digital signal controllers (mostly for industrial applications such as motor control), and stream processors, among others.
In DSP, engineers usually study digital signals in one of the following domains: time domain (one-dimensional signals), spatial domain (multidimensional signals), frequency domain, autocorrelation domain, and wavelet domains. They choose the domain in which to process a signal by making an informed guess (or by trying different possibilities) as to which domain best represents the essential characteristics of the signal. A sequence of samples from a measuring device produces a time or spatial domain representation, whereas a discrete Fourier transform produces the frequency domain information that is the frequency spectrum. Autocorrelation is defined as the cross-correlation of the signal with itself over varying intervals of time or space.
2?Signal Sampling
With the increasing use of computers the usage of and need for digital signal processing has increased. In order to use an analog signal on a computer it must be digitized with an analog to digital converter (ADC). Sampling is usually carried out in two stages, discretization and quantization. In the discretization stage, the space of signals is partitioned into equivalence classes and quantization is carried out by replace the signal with representative signal values are approximated by values from a finite set.
The Nyquist-Shannon sampling theorem states that a signal can be exactly reconstructed from its samples if the samples if the sampling frequency is greater than twice the highest frequency of the signal. In practice, the sampling frequency is often significantly more than twice the required bandwidth.
A digital to analog converter (DAC) is used to convert the digital signal back to analog signal.
The use of a digital computer is a key ingredient in digital control systems.
3?Time and Space Domains
The most common processing approach in the time or space domain is enhancement of the input signal through a method called filtering. Filtering generally consists of some transformation of a number of surrounding samples around the current sample of the input or output signal. There are various ways to characterize filters, for example: Alinear filter is a linear transformation of input samples; other filters are non-linear. Linear filters satisfy the superposition condition, i.e. if an input is a weighted linear combination of different signals, the output is an equally weighted linear combination of the corresponding output signals.
A causal filter uses only previous samples of the input or output signals; while a non-causal filter uses future input samples. A non-causal filter can usually be changed into a causal filter by adding a delay to it.
Atime-invariant filter has constant properties over time; other filters such
as adaptive filters change in time.
Some filters are stable, others are unstable. A stable filter produces an output that converges to a constant value with time, or remains bounded within a finite interval. An converges to a constant value with time, or remains bounded within a finite interval. An unstable filter can produce an output that grows without bounds, with bounded or even zero input.
AFinite Impulse Response (FIR) filter uses only the input signal, while an Infinite Impulse Response filter (IIR) uses both the input signal and previous samples of the output signal. FIR filters are always stable, while IIR filters may be unstable.
Most filters can be described in Z-domain (a superset of the frequency domain) by their transfer functions. A filter may also be described as a difference equation, a collection of zeroes and poles or, if it is an FIR filter, an impulse response or step response. The output of an FIR filter to any given input may be calculated by convolving the input signal with the impulse response. Filters can also be represented by block diagrams which can then be used to derive a sample processing algorithm to implement the filter using hardware instructions.
4?Frequency Domain
Signals are converted from time or space domain to the frequency domain usually through the Fourier transform. The Fourier transform converts the signal information to a magnitude and phase component of each frequency. Oft
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1 ???? communication and signal
2 ???? signal engineering
3 ???? signal design
4 ?? signal
5 ???? signal theory
6 ???? signalling system
7 ???? signal wiring
8 ???? signal circuit
9 ???? lighting circuit
10 ???? warning circuit
11 ???? interface circuit
12 ???? testiing circuit
13 ???? directional circuit
14 ???? circuit design
15 ???? circuit analysis
16 ???? succesive route;succesisve route
17 ??? signal box;signal tower
18 ???? control center
19 ???? relay house;relay room
20 ??? power supply roon;power supply room
21 ?? section
22 ???? signal construction
23 ??? signal shop
24 ????? industrial construction
25 ???? cable connecting
26 ???? cable laying
27 ????? cable laying machine
28 ???? ;???? railway signalling
29 ???? fixed signal
30 ???? movable signal
31 ???? vision signal;visual signal
32 ???? flashing light signal;flash signal;flashing signal 33 ???? acoustic signal;whistle signal
34 ??? hand signal
35 ???? protecting signal;protection signal
36 ???? cab signalling
37 ???? hump signal;humping signal
38 ???? section signaling;wayside signaling
39 ???? running signal;train signal
40 ???? shunting signal ???? calling-on signal
42 ???? trackside signal;ground signal
43 ???? home signal
44 ???? station signal;signaling at stations
45 ???? starting signal
46 ???? alarming signal
47 ???? accident signal
48 ???? colour light signal
49 ???? signal colour fidelity
50 ???? signal indicator
51 ???? signal visibility;signal aspect and indication
52 ???? crossing signal
53 ?????
? crossing automatic signal;automatic level crossing signal
54 ?????
? crossing announcing signal;highway level crossing announcing device 55 ????? crossing controller
56 ???? crossing barrier;cross barrier at grade crossing 57 ???? crossing protection
58 ???????
? remote control crossing;remote surveillance and telemetering for highway l
59 ???? crossing safety
60 ???? level crossing accidents
61 ???? track circuit
62 ?????? a.c.track circuit;ac track circuit
63 ?????? pulse track circuit
64 ??????? jointless track circuit
65 ?????? value-type track circuit;valve type track circuit 66 ?????? audio frequency track circuit
67 ?????
? polar freguency coded track circuit;polar-frequency pulse track circuit
68 ?????
? frequency shift track circuit;frequency-shift modulated track circuit 69 ????? long track circuit
70 ?????? track circuit district
71 ?????? track circuit testing
72 ????? track sensor
73 ??? axle counter
74 ???? rail impedance
75 ???? ;??? rail insulation;insulation section
76 ???? polar reversal;polar transposition
77 ????? rail bond
78 ????? ;????? rail bond;rail bond
79 ???? broken rail protection
80 ???? ;???? broken rail protection;broken rail protection ??? track occupied
82 ???? shunting effect
83 ???? normal state
84 ?? interlocking
85 ???? centralized interlocking
86 ?????? relay system interlocking
87 ?????? electric interlocking
88 ?????? electronic concentration interlocking ?
89 ?????? microcomputer-based interlocking
90 ????? non-centralized interlocking
91 ????
? interlocking with electric lock;interlocking by electric locks 92 ???????
colour light interlocking system with electriclock;interlocking by electric locks with color light-si
93 ??????
? interlocking system of semaphore signal;interlocking by electric locks with semaphore
94 ???? interlocking equipment
95 ??? electric lock
96 ??? switch
97 ???? pipe installation
98 ???? locking device
99 ???? indication panel;display board
100 ???? signal indication
101 ?? locking
102 ?? release
103 ?? blocking;block system
104 ???? manual block
105 ???? section block;section blocked
106 ????? semi-automatic block;semi-automatic block system 107 ??????
? all-relay semiautomatic block;all-relay semi-automatic block system 108 ???? automatic block;automatic block system
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发表于 2019-9-13 23:46:11