Basic introduction
General definition
Baseband and band corresponds, band: on baseband signal which occupy frequency modulated signal bandwidth (a possession of from the lowest to the highest frequency frequency difference).
The most simple definition of a
A signal of baseband bandwidth is its former bandwidth modulation and reuse, or in multi-channel separation and demodulation.
The composite video signal devices have created this new most VCR, playstation and DVD player is a common baseband signal.
modulation
Usually need to put a baseband signal to higher frequencies of the carrier modulation, in order to wireless transmission. Results the modulated signal was moved to a higher frequency (RF) to go up, for bilateral belt modulation, modulation signal bandwidth greaten doubled. Namely, from the lowest frequency (is not zero frequency) to the highest frequency distance is baseband bandwidth twice. Can use single side band modulation to minimize this impact. With communication, highest frequency general far exceeded baseband bandwidth. Some signal depends whether for baseband signal. For example, the simulation telephone switching network connection will use band-pass filters filter under 300 KHZ and 3400 hz above the waveform, because no signal is very close to zero frequency, it can't be considered baseband signals, but in the telephone system frequency division multiplexing hierarchical structure, it is often regarded as a baseband signal.
Baseband Signal
Source (information source, also say to send terminal) issued without modulation (frequency shift and transform) original signal, its characteristic is lower frequency, signal spectrum from zero frequency starting near, has the low-pass form. According to the original signal characteristics, baseband signal can be divided into digital baseband signal and analog baseband signal (correspondingly, source also is divided into digital source and simulation source. The decision by the source. Said the popular point, baseband signal is sent to the direct expression of the transmission of information signal, such as we speak of sound waves is baseband signal. (if one signal contains a frequency reached the infinity of exchange ingredient and possible dc component, criterion this signal is baseband signals.
Because at point-blank range baseband signal attenuation is not big, thus signal content will not change. Therefore in the transmission distance is close, computer network are adopted the baseband transmission mode. As from a computer to monitor, printer and other peripheral signal is frequency-hand mode. Most of the LAN using frequency-hand mode, such as Ethernet, token ring. Common network design standards 10BaseT use is baseband signal.
Band signal (bandpass signal)
In communication, the baseband signal has a very low frequency spectrum of anti-jamming and improve the component is proposed.in consider should not be commonly direct transmission, needing the baseband signal transformation into its band suits in the channel, the change of signal transmission of the signal frequency signal is (if one signal only contains a kind of frequency exchange ingredients or limited several frequency exchange ingredients, we call this signal called frequency signals).
It is mainly used in the cable TV network television and video broadcast.
Frequency-hand mode
In the channel of baseband signal transmitted directly, called frequency-hand mode. The system is called for frequency-hand mode baseband transmission system. Transmission medium of the whole channel by a baseband signal occupation. Frequency-hand mode need not modems, equipment, with low cost and high speed of ber advantages, suitable for short. The data lose, the transmission distance in the 100 metres inside, in audio city telephone, computer network communication is widely used. As from a computer to monitor, printer and other peripheral signal is frequency-hand mode. Most of the LAN using frequency-hand mode, such as Ethernet, token ring.
In the cable channel, to directly communicate with teletypewriter signals is baseband signal transmission. A company, factory, this kind of means can be used to large terminal connected to the main computer. Baseband data transfer rate is 0 ~ 10 Mb/s, more typically 1Mb/s ~ 2.5 Mb/s, normally used for transmitting digital information.
Band transfer:
In the channel in direct transmission frequency band signal, called frequency transmission. Can be transmitted over a long distance. Its disadvantages are rate is low, ber high.
Say commonly band is digital baseband signal transmission by modulation transform, become can in the public telephone wire transmission of analog signals, analog signals via analog transmission media delivered to the recipient, then reductive into the original signal transmission. This band transmission not only overcame the at present a lot of long-distance telephone lines can't direct transmission baseband signal flaws, but can realize multiplexed communication lines, thereby improving the utilization ratio. But frequency transmission in the sender and receiver should set modem, will baseband signal is transformed into bandpass signal retransmission. The advantages of transmission bandwidth can be conducive to the existing large analog channels (such as analog switched telephone network) communications. Cheap, easy implementation. Home users dial-up could fall into this category communication
Broadband transmission Broadband
Is relatively general said band of broad-spectral-bandwidth transmission in transmission. Broadband refers to the wider than audio bandwidth frequency band, it includes most electromagnetic spectrum. Use this broad-spectral-bandwidth transmission system, called broadband transmission system. Its frequency transmission through the help, can will link capacity is decomposed into two or more channels, each channel can carry different signals, which is broadband transmissions. All the broadband transmission channel can also send signal. Such as CATV, ISDN, etc. Transmission bandwidth in 128kbps > = very wide
Broadband is transmission analog signals, the speed of data transmission range of 0 ~ 400Mb/s, and often use the transmission rate is 5 Mb/s ~ 10 Mb/s. It can hold all radio, and can make the high-speed data transmission. Broadband transmission system is more analog signal transmission system.
Say commonly, broadband transmission and frequency-hand mode compared has the following advantages:
(1) can be in a channel transmission of voice, images and data information and enables the system with a variety of utility;
(2) a broadband channel can be divided into multiple logical baseband channels, realize multiplexing, thus greatly increased the capacity of the channel,
(3) broadband transmission distance than baseband far, because the digital baseband transmitted directly digital, transmission rate is higher, the shorter the distance transmission. Don't confuse baseband, baseband signals frequency-hand mode these concepts.
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