Analysis on the characteristics of VDSL2 technology and its present situation

In fact, many people hope that the 2007 3G licences will be able to distribute digital trunking licences to some of the emerging operators, such as railcom, so that even if the 2008 Olympic Games cannot replace the digital trunking system in time, So can also make the domestic digital trunking communication standards can have more powerful support and European and American standards a high and low.


VDSL2 Technical Features

In recent years, with the rapid development of broadband Internet technology and broadband services, broadband users have been gradually from a single application of high-speed Internet access to VoIP, IPTV, visual communications and other integrated application development, therefore, access to bandwidth will put forward higher requirements, is expected in the next few years, User's bandwidth demand will reach downlink 6mbps-20mbps, uplink 1mbps-5mbps.

At present, telecom operators mainly use their rich copper resources, using adsl/adsl2+ access technology to provide broadband access. adsl/adsl2+ effective transmission distance of 5~6 km, ADSL downlink rate of up to 8Mbps, uplink rate of 640kbps, and adsl2+ downlink rate of the highest for 24Mbps, the uplink rate of 1Mbps. From the transmission rate, ADSL is difficult to meet the high bandwidth users access requirements, adsl2+ in the near future can basically meet the bandwidth needs, but the uplink bandwidth is low.

Following the first generation of VDSL, the ITU passed the VD-SL2 in May 2005 (second generation VDSL) The standard G.993.2,VDSL2 has good application foreground by extending spectrum and improving transmit power spectral density, supporting higher transmission rate and longer transmission distance, satisfying the demand of future users for high bandwidth.

According to the standard, VDSL2 has the following characteristics:

With high speed transmission capability.

The VDSL2 standard provides a bandwidth of up to 30MHz, which enables high-speed data transmission of bidirectional symmetric 100mbit/s in a short distance.

Ability to transmit over long distances. The VDSL2 standard stipulates the enhanced downlink transmit power (20.5dBm), with the uplink U0 band and the use of ECHO suppression and time domain equalization technology, so that the transmission distance can reach more than 2.5 kilometers.

Have a flexible profile configuration scheme.

The maximum cut-off frequency of the VDSL2 is 30MHz, the itu-tg.993.1 Plan997 and Plan998 are still used between the 1mhz~12mhz, and the 12mhz~30mhz can be divided into one or more upper and lower frequency bands to meet the needs of different applications.

Compatible with adsl/adsl2+.

The VDSL2 modulation method is unified to DMT, supports STM and PTM mode based on IEEE802.3AH64/65 byte encapsulation, and supports the ATM encapsulation mode adopted by adsl/adsl2+.

With better video business support capabilities.

According to the characteristics of video service, VDSL2 realizes impulse noise protection through interleaving technology, and can change the interleaving depth dynamically according to the error rate, and stipulates the double delay channel, and provides different service for different kinds of services (especially video service) on the difference of packet loss and delay sensitivity.

In addition, the VDSL2 also has the perfect PSD control, the loop diagnosis and the on-line reconfiguration and so on function.

Current situation of VDSL2 technology

Through the analysis of VDSL2 chip and equipment, the current VDSL2 technology is not mature enough, the present situation is as follows:

--The support for profile is not perfect. At present, VDSL2 equipment generally does not support the high spectrum profile (30a), and the degree of support to 8a~8d997/998 varies. This is not conducive to interoperability between various devices, and operators can not be based on the actual use of flexible choice.

The transmission performance of the equipment can basically meet the requirements. In the 12M spectrum with crosstalk noise 0.4mm diameter environment, the use of Plan998, 500 meters up and down the line can reach 15mbps/45mbps,1 kilometers up and down the line can reach 2.5mbps/25mbps,1.5 kilometers up and down to 0.5mbps/18mbps. And the use of the upper and lower line more symmetrical Plan997, 1 kilometers up and down the line can reach the 5mbps/20mbps, the basic ability to meet the business in the next few years demand for bandwidth.

--VDSL2 terminals and client-side devices using different chip manufacturers can not be interoperable. This is one of the important manifestations of VDSL2 immaturity at present. Interoperability will enable operators in the selection of equipment selection of the choice of a significantly reduced.

--some VDSL2 devices are not compatible with adsl2+, and ATM transfer mode is not supported. The adsl2+ support of ATM mode is also the characteristic that operators pay much attention to, can choose ADSL2+/VDSL2 access mode flexibly according to the need of actual business, it will greatly facilitate the initial business deployment, and reduce the cost of future upgrade.

--VDSL2 of new features. At present, the VDSL2 equipment can support pilot float, lattice code, frequency spectrum slot and so on, and can set the switch and frequency range of U0 frequency band. However, due to the standards in some aspects still need to be further improved and other reasons, the Delt/selt loop diagnostics, OLR, dual-delay channel and multiple-line binding, and other functional support is poor.

Application and analysis of VDSL2 technology

Although VDSL2 is not mature yet, as a competitive xDSL technology, it is still worth focusing on the technical characteristics and technical status of comprehensive VDSL2.

VDSL2 in a short distance (generally less than 1.5km), up and down row rate advantage is very obvious, especially the uplink rate is much higher than adsl2+, therefore, VDSL2 suitable for a short distance, high bandwidth demand and strong interactive business. With the DSLAM equipment close to the user, the VDSL2 and the FTTx combination of the application model can play its advantage.

VDSL2 and adsl2+ spectrum compatible, and can communicate with adsl2+, in short range of conditions can be used to support the characteristics of high bandwidth transmission, over a certain transmission distance, can directly switch to the adsl2+ mode, to achieve remote transmission, to ensure that adsl2+ to VDSL2 transition.

In terms of cost, the cost of VDSL2 will be higher than that of adsl2+, but the VDSL2 has obvious advantages over the economical cost and the convenience of using the fiber-pon. With the improvement of the maturity of VDSL2 equipment and the application of scale, the cost of it has been further reduced. VDSL2 is expected to be basically mature by the beginning of 2007, 2007 years can be tested commercially, operators through the deployment of VDSL2 will be able to provide greater access bandwidth to meet the needs of integrated access to multiple services. (Computer science)