Spread Spectrum Communications

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called spread spectrum communication, spread spectrum communication is short. It is used to transfer the information bandwidth of the RF bandwidth is much greater than the information itself as a means of communication, spread spectrum communication-systems, is known as a major breakthrough in communications technology.  
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About the type of direct sequence spread spectrum technology background carrier frequency hopping spread spectrum time hopping (TH) pulse frequency modulation characteristics of mongrel spread spectrum advantages: The main technical publish outline of ultrashort wave communication is usually (in 10 watt radio station, for instance) can pass 20-30 km away, while the pseudo-code spread spectrum device 10 mW that is capable to pass 30
the elementary principles of spread spectrum communication
-50 km. In additional words, spread spectrum systems can endow 30 dB of SNR promotion, the interference reduced 1000 times. Familiar communications human know, for decades, folk must pay for the signal to ruckus ratio improved a excellent handle of effort, to 1 dB, 1 dB pat 2-3 dB breakthrough is a meaningful contribution. The breakthrough moment came, the G P S signal to noise ratio improved to convert a reality, this is indeed a huge bound amenable,Antelope, merely can be said on this point has been spread spectrum communication is a new contemporary communications technology completions. It has an important role in anti-interference effects, but will also send a range of spread spectrum communication revolutionary clash. Use than the original signal (source generated signal) itself much RF signal frequency bandwidth communications, stands for spread spectrum communications. In spread spectrum communication system, letters end with a specific modulation usage will be inflated bandwidth of the original signal to get spread spectrum signal. Side and then arranged to receive the received spread spectrum signal to be addressed, put it back to the original bandwidth of the signal. Spread spectrum signal bandwidth and the ratio of the original signal bandwidth, shrieked the processing acquire of spread spectrum communication system GP, it is the spread spectrum communication system is an important parameter. Most spread-spectrum communication system of the GP merit is much greater than 10. Technical background of traditional analog telegraph communication commonly used FM (FM) and extent modulation (AM) in 2 ways, can not meet the high-speed data communications Spread Spectrum Communications Introduction to

requirements. Into the 80's, digital wireless data communication into the fashion,Pharmacology, with its amplitude shift keying modulation (ASK), frequency shift keying (FSK) and phase shift keying (PSK), their vantage is to assist the use of advanced digital signal processing techniques, such as equalization, coding, etc., to improve the data displacement rate and transmission reliability. Practical systems such as GSM, IS-54 and so on. But there are some flaws of these systems. On the one hand, the wireless communication channel open, communication context, there is inevitably a broad range of accidental interference,Wanyanliang, production the reliability of signal transmission to reduce at the same time, channel time domain and frequency domain selective fading, making the data transmit rate of increase is limited; the other hand, with the quick growth of wireless services, wireless networks have necessitated considerable flexibility to adjust to alterations in commerce development. These are accustomed wireless digital communications complicated to determine. These factors contributed to the demand for new technology to improve data transfer rates and further improve transmission reliability. Type of straight sequence spread spectrum referred to as the DS (DS). The message sent along the pseudo-random series of characters (alternatively pseudo-noise code) encoded on the carrier modulation. Pseudo-random sequence is many greater than the rate of the rate information to be sent, so the modulated signal spectrum breadth will be greater than the width of the spectral transmission of information. Referred to the carrier frequency hopping spread spectrum frequency hopping (FH). Load information of the carrier signal frequency along the pseudo-random sequence of control quickly in a given band in conversion, this transition is much larger than the band breadth of the spectral width of the transmission of information. Hopping (TH), when the timeline is divided into intermittent frames, each frame is divided into a digit of time pieces. When the movie in a skeleton which sends a signal by the pseudo-code control, due to signal when the chip is much smaller than the width of the period of the signal spectrum in order to achieve the expansion. Pulse FM radio frequency pulse signal final letter in every pulse wheel frequency changes in a definite course. Receipt of the letter ended with the dispersion filter in the demodulation signal to the pulse width into the filter before and after the same time through another postpone to the output, so that every pulse compression to put the instantaneous power is high, but much of the timer pulse width , thus increasing the channel interference ratio. This modulation is effectively used for radar, but also has applications in communications. Hybrid spread spectrum spread spectrum several differ ways of mingling applications, such as: the fusion of DS and frequency hopping (DS / FH), a alignment of frequency hopping and time hopping (FH / TH), and the DS, when frequency hopping and jumping The combination of (DS / FH / TH), etc. Characteristics of spread spectrum communication channel occupied band is much wider than other means of communication. Uses spread-spectrum communication because it has the following characteristics:
spread-spectrum communication key features
① mighty ability to suppress interference, the marker processing via the receiver, the aisle tin increase with the spread-spectrum semaphore into the overlapping of various orchestra interference marker intensity decreased to approximately the incipient 1/GP, thereby channel interference percentage increased nearly GP-fold. Spread spectrum communication did no suppress the self-noise interference, but can be mainly depressed the interference of narrow-band signals; ② signal power spectral density is very cheap; ③ Signal intention of concealment and confidentiality; ④ can be secondhand to accomplish the aptitude to code a haphazard site department multiple way communications (watch multiple access); ⑤ when using scatter spectrum communication signals can be high-resolution ranging. Advantages: anti-interference anti-noise anti-multipath fading privileged and cheap power spectral density, with covert and low probability of intercept high-precision dimension can be any multi-site reuse and situation of the cardinal technical issues to achieve the main technical problems scatter spectrum communication are: ① address code pattern, rate and signal spectrum, interference between the signal specifics are directly related, so how to elect the address code is normally a special research topic; ② the use of wideband RF signals, and the modulation ought be famous modulator, demodulator requirements; ③ receiver must resolve the address signal code period and conveyor frequency to demodulate the signal, thus the absence because agreeable synchronization; ④ development and presentation of fashionable devices and components (such as the matched percolate, frequency synthesizer and micro-computer control, etc.) have an major role in amending the appliance extravaganza. In the modern ground-based communications and satellite communications is warmhearted used in spread spectrum communications, in mandate to achieve multiple access communications and improved anti-jamming and so above. Spread-spectrum technology is likewise usually used in dimension, control, positioning and navigation and so on. Spread spectrum communication system with frequency division, period division multiple systems attach constitute the communication web system to meet the requirements of naval and civilian communications. Further reading: 1
interference Category: communication, communication technology, aviation technology, avionics and onboard computer systems, wireless access to improve my