Wireless Modem is Modulator (Modulator and Demodulator (Modem), is called in Chinese Modem (Hong Kong and Taiwan called data machine), according to the Modem of harmonics, called the "cat" intimacy. It is a device that converts a digital signal to a analog signal by modulating a digital signal at the sending end, and then converts the analog signal to a digital signal by demodulating at the receiving end.
The so-called modulation is to convert digital signals into analog signals transmitted over telephone wires; Demodulation: convert analog signals to digital signals. Call a modem.
MODEM English is MODEM, which functions as an interpreter for analog signals and digital signals. There are two kinds of electronic signals, one is "analog signal" and one is "digital signal". The telephone lines we use are analog signals, and the PCS transmit digital signals. So when you want to connect your computer to the Internet via a phone line, you have to use a modem to "translate" two different signals. After connected to the Internet, when PC send information to the Internet, as a result of the telephone line transmission is analog signal, so have to use a modem to the "translation" digital signal into analog signals, can be transferred to the Internet, this process is called "modulation". When the PC to get information from the Internet, because of the information coming from the Internet through a telephone line are analog signals, so the PC want to read them, also must use the modem "translate", this process is called "demodulation. In general, it's called modulation demodulation.
Basic principle: the average person's voice is 300-3400 hz frequency range, for the voice signal transmission in the ordinary telephone system, the online road assign it a certain bandwidth, international standard take 4 KHZ for a road (the band width of the occupied. In the transmission process: speech signal to a 300-3400 hz frequency input, the sender's telephone transform the voice signal into analog signals, the analog signal through a frequency division multiplexer to change, can transmit multi-channel analog signal at the same time on line, later when they arrive in the receiving end after a XiePin process to restore it to its original frequency range of the analog signal, again by the receiving party telephone converts analog signals into sound signal.
The information in the computer is composed of "0" and "1" to form a digital signal, while the transmission on the telephone line can only be analog electrical signal. Do not take any measures to use analog channel to transmit digital signals inevitably there will be a big mistake (distortion), therefore, in the ordinary telephone network to transmit data, it must to digital signal conversion to telephone network within the required when the original design of the audio spectrum (that is, 300 hz - 3400 hz).
Modulation is to control the carrier wave waveform with the baseband pulse, forming a signal suitable for the transmission of the line.
The demodulation is that when the modulated signal arrives at the receiving end, the analog signal that has been transformed by the modulator will remove the carrier and return to the original baseband digital signal.
A modem can also convert an audio signal into a higher frequency signal and convert a higher frequency signal into an audio signal. The other purpose of modulation is to facilitate line reuse so as to improve line utilization.
Based on the three main parameters of carrier signal, modulation can be divided into three kinds: amplitude modulation, frequency modulation and phase modulation.
Modem was originally used for data transmission only. However, with the increasing demand of users and fierce competition among manufacturers, there are more and more "two in one" and "three in one" Modem in the market. In addition to data transmission, these modems have facsimile and voice transmission functions.
1. Fax Modem
Through fax Modem, in addition to save the cost of a dedicated fax, benefits and there are many: can fax the documents in computer directly to the other side of the computer or fax machines, without having to print out the document first. It can be conveniently saved or edited with the fax received. It can overcome the problem that ordinary fax machine is gradually fading because of the use of heat sensitive paper; Because Modem USES the correct technique, the fax quality is better than the normal fax machine, especially for the graphic fax. The Fax Modem mostly follows the Fax protocol of v. 29 and v. 17. V.29 supports 9600bps fax rate, while v. 17 can support the fax rate of 14400bps.
2. Voice modems
The voice mode mainly provides voice mail message and full-duplex hands-free call function, which really makes the telephone and computer integrated. Here, it is mainly a new mode of phonetic transmission - DSVD (Digital Simultaneous Voice and Data). The DSVD is by Hayes, Rockwell,
In 1995, a speech transmission standard proposed by u.s.-based companies such as U.S.R. obotics and Intel is an expansion of the existing v. 42 error correction protocol. DSVD USES Digi Talk's digital voice and data transfer technology to enable Modem to communicate on the same side of the normal phone line as data transmission.