基于SystemView的差错控制技术研究(13)

Marconi (1874-1937), Italian people, in 1894, the pilot at his father's estate. 1896, to London. In 1897, the company set up the radio reported. In 1899, the first time the British and French wireless communications. 1916, implementation of short-wave radio communications. 1929, set up a global wireless communications network. Kim won the Nobel Prize. Took part in the Fascist Party.

1.3 Classification of Communication Systems

According to type of information: Telephone communication system, Cable television system ,Data communication systems.

Modulation by sub: Baseband transmission,Modulation transfer.

Characteristics of transmission signals in accordance with sub: Analog Communication System ,Digital communication system.

Transmission means of communication system: Cable Communications,Twisted pair, coaxial cable and so on.

And long-distance telephone communication. Modulation: SSB / FDM. Based on the PCM time division multiple coaxial digital base-band transmission technology. Will gradually replace the coaxial fiber.

Microwave relay communications:Comparison of coaxial and easy to set up, low investment, short-cycle. Analog phone microwave communications mainly SSB / FM / FDM modulation, communication capacity of 6,000 road / Channel. Digital microwave using BPSK, QPSK and QAM modulation techniques. The use of 64QAM, 256QAM such as multi-level

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理工大学学士学位论文

modulation technique enhance the capacity of microwave communications can be transmitted at 40M Channel 1920 ~ 7680 Telephone Rd PCM figure.

Optical Fiber Communication: Optical fiber communication is the use of lasers in optical fiber transmission characteristics of long-distance with a large communication capacity, communication, long distance and strong anti-interference characteristics. Currently used for local, long distance, trunk transmission, and progressive development of fiber-optic communications network users. At present, based on the long-wave lasers and single-mode optical fiber, each fiber road approach more than 10,000 calls, optical fiber communication itself is very strong force. Over the past decades, optical fiber communication technology develops very quickly, and there is a variety of applications, access devices, photoelectric conversion equipment, transmission equipment, switching equipment, network equipment and so on. Fiber-optic communications equipment has photoelectric conversion module and digital signal processing unit is composed of two parts.

Satellite communications: Distance communications, transmission capacity, coverage, and not subject to geographical constraints and high reliability. At present, the use of sophisticated techniques Analog modulation, frequency division multiplexing and frequency division multiple access. Digital satellite communication using digital modulation, time division multiple road in time division multiple access.

Mobile Communications: GSM, CDMA. Number of key technologies for mobile communications: modulation techniques, error correction coding and digital voice encoding. Data Communication Systems.

1.4 Five basic types of data communication system:

（1）Off-line data transmission is simply the use of a telephone or similar link to transmit data without involving a computer system.The equipment used at both ends of such a link is not part of a computer, or at least does not immediately make the data available for computer process, that is, the data when sent and / or received are 'off-line'. This type of data communication is relatively cheap and simple.

（2）Remote batch is the term used for the way in which data communication technology is used geographically to separate the input and / or output of data from the computer on which they are processed in batch mode.

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理工大学学士学位论文

（3）On-line data collection is the method of using communications technology to provide input data to a computer as such input arises-the data are then stored in the computer (say on a magnetic disk) and processed either at predetermined intervals or as required.

（4）Enquiry-response systems provide, as the term suggests, the facility for a user to extract information from a computer.The enquiry facility is passive, that is, does not modify the information stored.The interrogation may be simple, for example, 'RETRIEVE THE RECORD FOR EMPLOYEE NUMBER 1234 'or complex.Such systems may use terminals producing hard copy and / or visual displays.

（5）Real-time systems are those in which information is made available to and processed by a computer system in a dynamic manner so that either the computer may cause action to be taken to influence events as they occur (for example as in a process control application) or human operators may be influenced by the accurate and up-to-date information stored in the computer, for example as in reservation systems.

2 Signal spectrum with bandwidth

Electromagnetic data signals are encoded, the signal to be included in the data transmission. Signal in time for the general argument to show the message (or data) as a parameter (amplitude, frequency or phase) as the dependent variable. Signal of their value since the time variables are or not continuous, can be divided into continuous signals and discrete signals; according to whether the values of the dependent variable continuous, can be divided into analog signals and digital Signal.

Signals with time-domain and frequency domain performance of the two most basic forms and features. Time-domain signal over time to reflect changing circumstances. Frequency domain characteristics of signals not only contain the same information domain, and the spectrum of signal analysis, can also be a clear understanding of the distribution of the signal spectrum and share the bandwidth. In order to rece …… 此处隐藏：8167字，全部文档内容请下载后查看。喜欢就下载吧 ……