Hello,
Today I would like to share with you the VDSL2 technology status application analysis.
VDSL2 technical characteristics
In recent years, with the rapid development of broadband Internet technology and broadband services, broadband users have gradually evolved from a single application for high-speed Internet access to comprehensive applications such as VoIP, IPTV, and visual communication. Therefore, higher access bandwidth will be proposed. Requirements, it is expected that in the next few years, users' bandwidth requirements will reach 6Mbps~20Mbps in the downlink and 1Mbps~5Mbps in the uplink.
At present, telecom operators mainly use their rich copper wire resources to provide broadband access using ADSL/ADSL2+ access technology. The effective transmission distance of ADSL/ADSL2+ is 5~6 kilometers, the downstream rate of ADSL is up to 8Mbps and the upstream rate is 640kbps, while the downstream rate of ADSL2+ is up to 24Mbps and the upstream rate is 1Mbps. In terms of transmission rate, ADSL is difficult to meet the access requirements of high-bandwidth users. ADSL2+ can basically meet the bandwidth needs in the near future, but the upstream bandwidth is relatively low.
Following the first-generation VDSL, the ITU passed the VDSL2 (second-generation VDSL) standard G.993.2 in May 2005. VDSL2 supports higher transmission rates and longer transmission rates by spreading the spectrum and improving the transmit power spectral density. The transmission distance meets the needs of users for high bandwidth in the future, and has a good application prospect.
According to the standard, VDSL2 has the following characteristics:
●With high-speed transmission capability.
VDSL2 standard stipulates the frequency band division up to 30MHz, can realize bidirectional symmetrical 100Mbit/s high-speed data transmission within a short distance.
●With long-distance transmission capability
The VDSL2 standard specifies an enhanced downlink transmit power (20.5dBm), with the use of the uplink U0 frequency band, echo suppression, and time domain equalization technology, so that the maximum transmission distance can reach more than 2.5 kilometers.
●It has a flexible profile configuration scheme.
The maximum cut-off frequency of VDSL2 is 30MHz. The frequency band plans of Plan997 and Plan998 of ITU-TG.993.1 are still used between 1MHz and 12MHz. One or more uplink and downlink frequency bands can be divided between 12MHz and 30MHz to meet different application requirements.
● Compatible with ADSL/ADSL2+.
VDSL2 modulation mode is unified as DMT, supports STM and PTM mode based on IEEE802.3ah64/65 byte encapsulation, and supports ATM encapsulation mode adopted by ADSL/ADSL2+.
●Has better video service support capabilities.
According to the characteristics of video services, VDSL2 implements impulse noise protection through interleaving technology, and can dynamically change the interleaving depth according to the bit error situation, and provides dual delay channels, which are sensitive to packet loss and delay for various services (especially video services) Different sexes provide different services.
In addition, VDSL2 also has complete PSD control, loop diagnosis and online reconfiguration functions.
VDSL2 technology status
Through the analysis of VDSL2 chips and equipment, the current VDSL2 technology is not mature enough, and its current status is as follows:
Profile support is not perfect. Currently, VDSL2 equipment generally does not support high-spectrum Profile (30a), and the degree of support for 8a~8d997/998 varies. This is not conducive to the intercommunication between various devices, and it is also difficult for operators to choose flexibly according to actual use needs.
The transmission performance of the equipment can basically meet the requirements. In a 0.4mm wire diameter environment with crosstalk noise in the 12M spectrum, when Plan998 is used, the uplink and downlink of 500 meters can reach 15Mbps/45Mbps, the uplink and downlink of 1 km can reach 2.5Mbps/25Mbps, and the uplink and downlink of 1.5 kilometers can reach 0.5Mbps/18Mbps. When using Plan997 with more symmetrical uplink and downlink, the uplink and downlink of 1 km can reach 5Mbps/20Mbps, which can basically meet the bandwidth requirements of the business in the next few years.
The VDSL2 central office and user-end equipment cannot communicate with each other when using chips from different manufacturers. This is one of the important manifestations of the immaturity of VDSL2 at present. Poor interoperability compatibility will greatly reduce the choice of operators when selecting equipment.
Some VDSL2 devices are not compatible with ADSL2+ and do not support ATM transmission mode. ADSL2+ support for ATM mode is also a feature that operators are very concerned about. The ADSL2+/VDSL2 access mode can be flexibly selected according to actual business needs, which will greatly facilitate the initial service deployment and reduce the cost of future upgrades.
New features of VDSL2. At present, VDSL2 equipment can generally support pilot floating, trellis coding, spectrum slotting, etc. At the same time, the U0 frequency band switch and frequency range can be set. However, due to the reasons that the standard still needs to be further improved in some aspects, the support for functions such as DELT/SELT loop diagnosis, OLR, dual delay channels, and multi-pair bonding is poor.
VDSL2 technology application analysis
Comprehensive VDSL2 technical characteristics and technical status. Although VDSL2 is not yet mature, as a competitive xDSL technology, it is still worth paying attention to.
VDSL2 has obvious advantages in uplink and downlink rates in short distances (generally less than 1.5km), especially the uplink rate is much higher than ADSL2+. Therefore, VDSL2 is suitable for short-distance services with high bandwidth requirements and strong interactivity. As DSLAM equipment approaches users, the combined application mode of VDSL2 and FTTx can give more play to its advantages.
VDSL2 is compatible with the ADSL2+ spectrum and can interoperate with ADSL2+. Under short-distance conditions, VDSL2 can support high-bandwidth transmission. After a certain transmission distance, it can be directly switched to ADSL2+ mode to realize medium and long-distance transmission to ensure ADSL2+ Transition to VDSL2.
In terms of cost, the cost of VDSL2 will be higher than that of ADSL2+, but compared to fiber PON access, VDSL2 still has obvious advantages in terms of economic cost and ease of use. As the maturity of VDSL2 equipment increases and its scale is applied, there is room for further reduction in its cost. Operators will be able to provide greater access bandwidth by deploying VDSL2 to meet the needs of multi-service integrated access.
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