Communication system structure of lifting emergency data communication

Time：2020-12-11 View：

Communication System

 

Offline data transmission
It simply uses telephone or similar links to transmit data, excluding computer systems. The devices used at both ends of such a link are not computer components, or at least not immediately provide data to the computer for processing, that is, the data is offline when it is sent or received. This kind of data communication is relatively cheap and simple.

 

Remote Batch Processing
The term applies to such a method: data communication technology is adopted to make the input and output of data geographically far away from the computer that processes them in batch mode.

 

Online data collection
It refers to the method of using data communication technology to instantly provide the newly generated input data to the computer. Data is then stored in a computer (such as a disk) and processed at predetermined intervals or as needed.

 

Interactive System
As the name implies, it provides users with the function of extracting information from computers. The query function is passive. That is, it does not modify the stored information. Questions can be simple, for example, "retrieve records with employee number 1234" can also be complex. Such systems may use terminals that can generate hard copies and/or visual displays.

 

Real-time system
It is such a kind of system, in which the computer system obtains and processes information under dynamic conditions so that the computer can take actions to influence the ongoing events (for example, in process control applications) or it can affect people (operators) through accurate and constantly updated information stored in computers, such as in pre-sale systems.

Spectrum and bandwidth
The signal is the electromagnetic code of data, and the signal contains the data to be transmitted. The signal usually takes time as the independent variable, and a certain parameter (amplitude, frequency or phase) representing the message (or data) is the dependent variable. Signals can be divided into continuous signals and discrete signals according to whether the values of independent variable time are continuous. According to whether the values of dependent variables are continuous, signals can be divided into analog signals and digital signals.
The signal has two basic forms and characteristics: time domain and frequency domain. Time domain characteristics reflect the changes of signals over time. The frequency domain characteristics not only contain the same amount of information in the time domain of the signal, but also can clearly understand the spectrum distribution and occupied frequency span of the signal through the spectrum analysis of the signal. In order to obtain the requirements of the transmitted signal on the receiving equipment and channel, it is not enough to know only the time domain characteristics of the signal, but also the spectrum distribution of the signal. The time domain characteristic of the signal indicates the change of the signal with time. Since most of the energy in the signal is concentrated in a relatively narrow frequency band, we call the frequency band where most of the energy of the signal is concentrated as the effective bandwidth, which is called the bandwidth for short. Any signal has bandwidth. Generally speaking, the larger the bandwidth of the signal, the higher the data transmission rate using this signal, and the larger the bandwidth of the transmission medium is required.
Next, we will briefly introduce the spectrum and bandwidth of common signals. The spectrum of the sound signal is roughly in the range of 20 Hz to 2000 kHz (the signal below 20 Hz is infrasound, and the signal above 2000 kHz is ultrasonic), however, the reproduction of acceptable voice can be generated with a much narrower bandwidth, so the standard spectrum of voice signal is 300 Hz ~ 3400Hz, and its bandwidth is 3 kHz. The spectrum of TV signal is 0~4 MHz, so its bandwidth is 4 MHz. As a special example, the bandwidth of the monostable pulse signal is infinite. For binary signals, the bandwidth generally depends on the exact shape of the signal waveform and the order of 0 and 1. The greater the bandwidth of a signal, the more faithfully it represents a sequence of numbers.