Modulation Of Three Xdsl Technology And Applications Introduction
With the rapid development of Internet, communication technology is undergoing a tremendous change
, due to rapid increase in the number of network users; access network as a communication network connected to the network and end users, network technology has become a hot topic.
Present, the main access technologies are hybrid fiber / coaxial (HFC) access technology, optical fiber access technology, copper access technologies and wireless access technology. In which access to existing copper telephone lines to transmit the media, using advanced digital signal processing technology and the modulation and demodulation technique to improve transmission remonstrance dry rate and distance. There are HDSL (high-speed digital subscriber loop), ADSL (Asymmetric Digital Subscriber Loop) and VDSL (ultra-high-speed digital subscriber loop). XDSL technology uses twisted-pair copper wire and equipped with separate high-frequency audio signal splitter, the 4kHZ the following audio signal with high frequency xDSL modulated signal separated by the filter, so that voice and high-speed data can also transfer. XDSL technology uses twisted-pair copper wires as transmission line cost savings, economic and easy, it can be used as an early use of broadband access technologies. The following will introduce the three kinds of XDSL modulation technology and application technology.
1, HDSL HDSL uses echo suppression, adaptive filtering and high-speed digital processing techniques, line coding using 2B1Q code. Two pairs or three pairs of modules (central office machine) and network terminal module (user machine), each of the twisted pair transmission rate of 1168kb / S; two pairs of wire to provide 2Mb / S of E1 services. HDSL unrepeated transmission distance of 3-5km.
American National Standards Institute (ANSI) to develop the T1E1.4/94-006 and the European Telecommunications Standards Institute (ETSI) proposed DTR/DM-0.3036 defines the electrical and physical characteristics of HDSL, frame structure, transmission methods and communication regulations and other standards. As a result of echo suppression adaptive equalization techniques to enhance the anti-interference ability, to overcome inter-symbol interference, enabling longer transmission distances without repeaters. HDSL central office switching systems are placed and the client, the system by the transceiver, multiplexing and mapping components and E1 Interface circuit. Transceiver, including the transmission and reception of two parts, is the HDSL core of the system. Send some of the input code stream by single HDSL line coding conversion, through the D / A waveform exchange and the formation and processing, send amplifier, sent by the outside. Some use of echo cancellation devices to receive, to leak part of the transmitted signal and impedance mismatch of the reflected signal for echo cancellation, and then by a balanced treatment to restore the original data signal, by decoding transformation for the HDSL line stream, and then to reuse with the mapping part of the deal. Which echo cancellation device and adaptive equalizer as a system and track changes in outside properties, the dynamic adjustment of system parameters, so on behalf of the system transmission performance.
HDSL system, multiplexing and mapping the completion of the data stream multiplexing and demultiplexing. Send some to 2Mb / S of the PCM stream is divided into two parts, the cost of adding bits of the frame structure HDSL, HDSL frames into the transmission stream, sent to the line through the transmitter. Correspondingly, the receiving part will receive the two-way 1168kb / S of HDSL stream, remove the frame structure of HDSL overhead bits, and then multiplexed into a 2Mb / S of the PCM stream, sent through the interface circuit FCM2Mb / S, G.703 interfaces. Interface part of the implementation system and PCMG.703 HDSL interface conversion and adaptation, complete with NRZ HDB3 stream stream one another, and to achieve electrical and impedance adaptation. HDSL line coding are mainly two or 2B1Q code and CAP codes. 2B1Q code is the 4-level pulse amplitude modulation code, two bits per symbol bit, 4 level +3, +1, -1, -3, respectively, 10,11,01,00, thereby enhancing the transmission of bits rate. CAP is a non-carrier amplitude and phase modulation, the data signal via two orthogonal modulated superimposed, respectively, and will not carry out useful information for carrier suppression. Two kinds of coding for improving the transmission efficiency is very useful. Many have already achieved HDSL digital modulation and signal processing chips and come on the market.
Modulation Of Three Xdsl Technology And Applications Introduction
By: wuwu
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