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1、Introduction to Communication SystemIt is ofte n said that we are living in the in formatio n age. Communi cati on tech no logy is absolutely vital to the gen erati on, storage, and tran smissi on of this in formatio n.Any com muni cati on system moves in formatio n from a source to a dest in ati on
2、 through a cha nn el. Figure 1 illustrates this very simple idea. The in formatio n from the source will gen erally n ot be in a form that can travel through the channel, so a device called a transmitter will be employed at one end and a receiver at the other.Figure 1 simple com muni catio n systemT
3、he source or in formatio n sig nal can be an alog or digital. Com mon examples are an alog audio, video signals and digital data. Sources are often described in terms of the frequency range that they occupy. Telepho ne-quality an alog voice sig nals, for in sta nee, contain freque ncies from 300Hz t
4、o 3kHz, while an alog high-fidelity music n eeds a freque ncy range of approximately 20Hz to 20kHz.Digital sources can be derived from audio or video sig nals can have almost any ban dwidth depe nding on the nu mber of bits tran smitted per sec ond, and the method used to convert binary ones and zer
5、os into electrical sig nals.A com muni cati on cha nnel can be almost anything: a pair of con ductors, an optical fiber or a free space that we live. Sometimes a channel can carry the information signal directly. For example, an audio signal can be carried directly by a twisted-pair teleph one cable
6、. On the other hand, a radio link through free space cannot be used directly for voice signals. Such situation require the use of a carrier wave will be altered, or modulated m, by the information signals in such a way that the information can be recovered at the destination. When a carrier is used,
7、 the information signal is also known as the modulating signals.Tech no logy is at the core of many new and emerg ing digital in formati on products and applicati ons that support the information society. Such products and applications often require the collection, sometimes in real time. The abilit
8、y of tech no logy to han dle real world sig nals digitally has made it possible to create affordable, inno vative; and high quality products and applicati ons for large con sumer market for example: digital cellular mobile pho ne, digital televisi on and video games. The impact of is also evide nt i
9、n many other areas, such as medicine and healthcare. For example: in patient monitors for intensive care, digital X-ray appliances, advaneed cardiology and brain mapping systems and so on, digital audio, for example: CD players; audio mixers and electro nic music and so on. And pers onal computer sy
10、stems for example: disks for efficie nt data storage and error correct ion, moder ns, sound cards and video conferencing and so on.Most of the major cities in the domestic bus stop artificial voice. Every one of the key points from the driver or atte ndant to stop by voice. But sometimes due to vari
11、ous factors such as weather, vehicle con gesti on, flight attendants are feeling the effects of the changes. There being given the stations reporting stations, especially for passengers not familiar with the topography of the city, causing a lot of unnecessary trouble. Well thus affect the image of
12、a city construction window, then developed automatic stop system inevitable. As required before the docking system bus GPS information (latitude and longitude information, etc.), longitude and latitude information generated by the distance between bus stops with the message that this is going to exp
13、erience the tedious, use the micro-controller difficult to achieve, and when using chips, the proper solution of this problem.Using radians per second in the mathematics dealing with modulation makes the equation simpler. Of course, frequency is usually given in hertz, rather than in radians per sec
14、ond, when practical devices are being discussed. It is easy to convert between the two systems per second, when practical devices are being discussed. It is easy to convert betwee n the two systems by recalli ng from basic AC theory, w =2 nIn modulation, the parameters that can be changed are amplit
15、ude E, frequency w, and phase 0 . Combinations are also possible. For example, many schemes for transmitting digital information use both amplitude and phase modulation.Multiplexing is the term used in communications to refer to the combining of two or more information signals. When the available fr
16、equency range is divided among the signals, the process is known as frequency-division multiplexing (FDM).Radio and television broadcasting, in which the available spectrum is divided among many signals, are everyday examples of FDM. There are limitations to the number of signals that can be crowded into a given frequency range because each requires a certain bandwidth, For example, a television channel only occupies s given bandwidth of 6MHz in 68MHz bandwidth of V
