Introduction to VDSL2 technical standards

/ June 12, 2020

What is vdsl2

DSL technology uses existing copper wire resources (telephone lines) to provide high-speed and low-cost network access services to end customers, and has achieved great success in the market in the past few years. The VDSL technology in the DSL technology family will be transmitted The bandwidth has been greatly expanded, and ultra-high-speed (100 megabytes) services are provided over short distances.With the popularity of video services, it is expected that there will be great market growth in the coming years.

VDSL2, ITU officially numbered G.993.2, developed based on ITU G.993.1 VDSL1 and G.992.3 ADSL2, agreed at the ITU meeting in May 2005, the trial version was approved in February 2006, November 2006 The R1 version of G.993.2 will be released. The current trial version band is defined up to 12MHz, and the R1 version will expand the band to 30MHz

Vdsl2 band plan

VDSL2 defines three Annexes for frequency allocation plans, corresponding to the needs of different regions.

Annex A, North America, the spectrum allocation is shown in Figure 1, where USx corresponds to the upstream frequency band, DSx corresponds to the downstream frequency band, and the starting frequency point of US0 varies from 4 kHz to 25 kHz, depending on whether there is POTS (traditional voice service), The stop frequency changes from 138KHz to 276 kHz, depending on whether a higher rate is required for upstream.

Figure 1: Annex A band plan

The frequency division of more than 12MHz is still under study.The preliminary definition in G.993.2 R1 is shown in Figure 2:

Figure 2 Annex A extended band plan:

Annex B, Europe, this Annex defines two frequency band plans, the 997 plan is shown in Figure 3, and the uplink and downlink symmetric bandwidth is provided, and the 998 plan is shown in Figure 4, which provides uplink and downlink asymmetric bandwidth. The frequency band above 12MHz needs to be further studied.

Figure 3 Annex B Plan 997 Symmetrical Bandwidth

Figure 4 Annex B Plan 998 asymmetric bandwidth

Annex C, a frequency plan customized specifically for the Japanese market, as shown in Figure 5

Figure 5 Annex C: Japan, the frequency allocation diagram is shown below:

Vdsl2 transmission profile (profile)

VDSL2 also defines 8 transmission profiles (profile 8a, 8b, 8c, 8d, 12a, 12b, 17a, 30a) for all frequency band plans. Corresponding to different needs, each transmission profile defines a set of parameters, including Transmission power, sub-channel bandwidth, maximum bandwidth, rate and other settings. Products that support the VDSL2 standard can only support at least one of the transmission templates according to local specifications, simplifying the complexity of design implementation. Table 1 lists 8 transmissions Partial transmission parameter table of the template-Partial parameters of VDSL2 transmission template

Some parameters Parameter value
8a 8b 8c 8d 12a 12b 17a 30a
Maximum downlink transmit power (dBm) +17.5 +20.5 +11.5 +14.5 +14.5 +14.5 +14.5 +14.5
Sub-channel width (kHz) 4.3125 4.3125 4.3125 4.3125 4.3125 4.3125 4.3125 8.625
Support US0 band Claim Claim Claim Claim Claim Does not require Does not require Does not require
Minimum bidirectional rate capability 50 Mbit / s 50 Mbit / s 50 Mbit / s 50 Mbit / s 68 Mbit / s 68 Mbit / s 100 Mbit / s 200 Mbit / s
Other new features of Vdsl2

Compared to VDSL1, VDSL2 adds many new features.

VDSL2 determines that DMT is the only modulation method. In the era of VDSL1, the dispute between the two modulation modes of CAP and DMT has not ceased, and each manufacturer makes products according to their own preferences. The era of VDSL2 has put an end to this dispute and has provided manufacturers The solution to the interconnection problem has laid a solid foundation. Compatible with ADSL1, ADSL2 +, and VDSL band plans, meaning that VDSL2 and other standards are transmitted in the same bundle of cables, and there will be no near-end interference due to inconsistent frequency bands used. Relative VDSL1 has a 2dB performance enhancement using 30MHz bandwidth, and the maximum capacity is 200Mb / s in both directions. It is a high-speed access in the true sense. However, the short range, the one-way 100Mbps service requirement is within 200 meters, and the rate is 1 kilometer away. Fast attenuation, reliable maximum distance of about 1.8 kilometers. The actual use of VDSL2 will be fiber to the community or building, and then VDSL2 access to individual homes or unit users. Increase the maximum downlink transmit power to 20.5dBm (transmission template 8b), When nearby cables are not sensitive to noise, this template can increase the transmission distance or transmission rate. Force support trellis coding to increase the resistance Disturbance capability compulsorily supports up to 15-bit QAM modulation, supports all-digital mode, and can increase the bandwidth for lines that do not require traditional voice. Supports multiple data link layer encapsulation of ATM, STM, and PTM, compared to ATM and VDSL in the ADSL world The PTM in can improve the efficiency of large packets, and improve the initialization of the seamless connection line with the IP network, including the channel discovery phase and the line diagnosis mode, support a wider range of test parameters (mainly refer to the G.992.3 ADSL2 standard), the increased line Diagnosis capabilities, reduce operating costs, support cyclic expansion of CE (CYCLIC EXTENSION) length to 1/4 (16/64), further reduce intersymbol interference (intersymbol) based on G.992.3 enhanced flexible frame structure, reduce redundant management channels, Improve channel transmission efficiency Support stronger INPULSE NOISE PROTECTION capability, with a maximum depth of 16 SYMBOLS network management interfaces modified according to G.997.1, standard MIB supports MIB controlled PSD power spectrum (POWER SPECTRUM DENSITY) Mechanism to support in-band power spectrum template control Support US0 band to 276kHz Enhanced FEC forward error correction capabilities, including a wide range of Reed-Solo mon coding and interleaving summary

On the basis of VDSL1, VDSL2 has absorbed many new features of ADSL2, and has made more definitions of frequency plans and transmission templates for different needs. With the expansion of video services in the future, VDSL2 technology will gain more in the market. Big success.

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