Study Notes on ADSL Access Technology

ADSL access technology is a common access method. Many people may not understand the principles and features of ADSL access technology. It does not matter. After reading this article, you will certainly have a lot of GAINS, I hope this article will teach you more things. ADSL access technology is another broadband access technology developed in recent years. It uses twisted-pair copper wires to provide users with bandwidth information services with asymmetry in two directions. The downlink speed is as high as 6-9 Mb/S, and the transmission distance is 3-5 km. Typical downlink speeds include T1, E1, DS26.312Mb/s), and E28.448 Mb/s ). The uplink speed is low, which varies with the products of different companies, usually 16-640kb/s.

The ADSL Access Technology transmits high-speed downstream data, low-speed data, and analog phones over a pair of telephone lines at the same time. Signals are divided and reused to occupy different frequency bands. Low-Frequency segments transmit voice messages. Intermediate Narrow-Band channels transmit upstream channel data and control information; other high-frequency segments transmit downstream channel data, images, or high-speed data.

ADSL access technology mainly uses DMT or CAP modulation methods. DMT is a discrete multi-frequency modulation. It divides all the frequencies into 256 sub-channels, and dynamically allocates the input data to them based on the instantaneous attenuation, group delay, and noise characteristics of the sub-channels. Adaptive distribution of sub-channel rates, and closure of sub-channels drowned by narrowband noise to achieve optimal use of transmission lines, minimizing the error code and noise, and improving the system transmission capacity. In addition, ADSL uses new developments in adaptive filtering, such as grid encoding and RS code, to improve noise resistance, and uses asymmetric echo cancellation technology to eliminate echo interference. The ADSL system sets up the ADSL modem on the local terminal and the client side respectively, and uses dmt fft to implement signal processing and modulation and demodulation. For telephone services from the telephone network, POTS is a common telephone service. The splitter is connected to a common telephone line in passive coupling mode. Exchange Bureau LEX) nodes are separated and inserted into the voice through the ADSL modem and POTS splitter, and transmitted to the user end together with high-speed data through twisted-pair copper wires, and then through the user end separator and ADSL modem, send the information to your PC or TV Terminal.

According to the T1.431 recommendation of the ecsa Standards Association), the ADSL access technology provides high-speed ticket and duplex channels. The express ticket channel uses the downlink channel to transmit 6 Mb/S data streams, 4 MPEG-1 images can be simultaneously transmitted, or 1-2 MPEG-2 images with better quality, or two 3 Mb/S digital broadcast TVs. The full-duplex ADSL channel can provide 160 kb/S and 576kb/S data streams for access to the ISDN network or high-speed link. ITU-T proposed three kinds of ADSL access technical standards: ADSL-1, ADSL-2 and ADSL-3 transmission rate were 1.544 Mb/S, 3.152 Mb/S and 6.32 Mb/S transmission distance were 5.5 km, 3.6 km and 2.5 km, respectively, can be used to transmit MPEG-1 and MPEG-2 images.

Using the existing twisted pair wire transmission broadband service, ADSL access technology can protect investment and reduce costs, which is especially suitable for a large number of scattered residential users. It is widely used for access and transmission of broadband services such as Internet access, remote LAN access, VOD, remote teaching, and multimedia retrieval. At present, the ADSL access technology and its applications are constantly developing, and the corresponding ADSL modulation and processing chips are also pushed to the market, telecom equipment manufacturers also produce different types of ADSL Access Technology modulation and demodulation products and actively explore the market, so that the ADSL Access Technology System is continuously expanded and used in the access network.

1. Wireless Broadband Access Technology "random" Application
2. Analysis of mainstream Broadband Access Network Technologies
3. Detailed explanation of application policies of optical fiber access technology
4. Comprehensive comparison of the two wireless access technologies
5. Introduction to Integrated Access Network