1、 TECHNICAL REPORT ATIS-0600023 GUIDANCE FOR THE USE OF UPSTREAM POWER BACK OFF PARAMETERS FOR ITU-T RECOMMENDATION G.993.2 ANNEX A ATIS is the leading technical planning and standards development organization committed to the rapid development of global, market-driven standards for the information,
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4、ember and major U.S. contributor to the International Telecommunication Union (ITU) Radio and Telecommunications Sectors, and a member of the Inter-American Telecommunication Commission (CITEL). For more information, please visit . Notice of Disclaimer therefore this TR provides guidance in the foll
5、owing areas: Explanation of the technical meaning of these two parameters. Examples of the use of UPBO parameters a and b in a North American environment. Guidance on the configuration of these two parameters in North American implementations of VDSL2. Although this TR provides information on the co
6、nfiguration of these parameters, the guidance is of an explanatory nature. Specifically this Technical Report is not an ATIS Standard and values in examples and the guidance in this Technical Report are not requirements for either default values or the field configuration for parameters a and b . Th
7、e examples in this TR do not necessarily result in optimum values for either of these parameters in specific field situations and obtaining such optimum configuration for UPBO operation of VDSL2 may require field implementation specific information that is outside the scope of this TR. 1.2 Purpose T
8、his TR provides technical guidance to the Industry, that is network operators, and vendors of VDSL2 equipment and operations support software, on the meaning and usage of the VDSL2 UPBO a and b parameters for North American field implementations of VDSL2. Its purpose is to provide information on the
9、 technical meaning and guidance on the configuration of these two parameters. ATIS-0600023 2 1.3 Application This TR provides guidance to network operators and vendors on the proper usage of the G.993.2 UPBO parameters a and b . 2 NORMATIVE REFERENCES The following standards contain provisions, whic
10、h through reference in this text constitute a basis of technical discussion in this ATIS Technical Report. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this ATIS Technical Report are encouraged to investigate
11、 the possibility of applying the most recent editions of the standards indicated below. 1 ITU-T Recommendation G.993.2, Very High Speed Digital Subscriber Line Transceivers 2 (VDSL2), February 2006, including Amendment 1, July 2007 and Amendment 2, February 2008.12 ITU-T Recommendation G.993.1 Very
12、High Speed Digital Subscriber Line Transceivers, June 2004.13 ATIS-0600424.2004 (R2009), Interface Between Networks and Customer Installation, Very High Speed Digital Subscriber Line (VDSL) Metallic Interface (DMT Based)2. 4 ITU-T Recommendation G.997.1 Physical layer management for digital subscrib
13、er line (DSL) transceivers, June 2006 including Amendment 1, December 2006 and Amendment 2, November 2006.13 DEFINITIONS, ACRONYMS, & ABBREVIATIONS 3.1 Definitions 3.1.1 Reference Length: The Reference Length (RL) for Upstream Power Back Off is the electrical length of a loop for which no Upstream P
14、ower Back Off will occur if the actual electrical length of a particular loop is greater than the Reference Length. 3.1.2 Upstream Power Back Off: Upstream Power Back Off are the methods defined in ITU-T Recommendations G.993.1 2 and G.993.2 1 for reducing the transmitted power in the upstream direc
15、tion on shorter loops to reduce crosstalk into longer loops also transporting VDSL2 that are in the same cable/binder. 3.2 Acronyms & Abbreviations ATIS Alliance for Telecommunications Industry Solutions AWG American Wire Gauge 1This document is available from the International Telecommunications Un
16、ion. 2This document is available from the Alliance for Telecommunications Industry Solutions, 1200 G Street N.W., Suite 500, Washington, DC 20005. ATIS-0600023 3 FEXT Far End Crosstalk ITU-T International Telecommunications Union Telecommunications Standards Sector PSD Power Spectral Density RL Refe
17、rence Length TR Technical Report UPBO Upstream Power Back-Off VDSL2 Very High Speed Digital Subscriber Line 2 US0 The Upstream 0 band of the VDSL2 Recommendation US1 The Upstream 1 band of the VDSL2 Recommendation US2 The Upstream 2 band of the VDSL2 Recommendation US3 The Upstream 3 band of the VDS
18、L2 Recommendations 4 UPSTREAM POWER BACK OFF CONFIGURATION This Technical Report (TR) provides guidance on the configuration of the a and b values for UPBO for VDSL2 in North America. This TR provides guidance to the Industry in the following areas: Clause 4.1 discusses the meaning of the UPBO param
19、eters a and b for VDSL2 and the context in which they are used by a North American Operator. As the values of a and b can be used to optimize UPBO with respect to the specifics of a Network Operators plant in particular locations, the TR provides guidance as to the meaning of the parameters and the
20、general effects of changes in their values. However, specific techniques for optimizing the values are not in the scope of this TR. Clause 4.2 provides a discussion on optimum values for a and b . Clause 4.3 Provides examples of the use of a and b on sample loops of various gauges. This TR emphasize
21、s that in North America the values for a and b be configurable by the Network Operator, as is currently required in the ITU-T Recommendations, to enable optimization of UPBO. NOTE: The analysis that follows assumes the limit mask is flat for each upstream band (i.e. beyond the reference length used
22、for an upstream band Ui,), the PSD level will nominally be aiacross the entire band. 4.1 What are the UPBO a and b parameters In G.993.2 1, the PSD Mask for Upstream Power Back Off (UPBO), UPBOMASK, is defined in Section 7.2.1.3.2 of that recommendation by formulas which define the UPBOMASK as funct
23、ions of f , frequency, in Mhz, kl0, electrical length of the loop as defined in G.997.1 2, and two variables a and b . In the equations defining UPBOMASK in Section 7.2.1.3.2 of G.993.2, the term abf defines a reference PSD based on an assumed nominal transmit PSD and the loss on an assumed Referenc
24、e Loop of a particular Reference Length. The formulas that define UPBOMASK use a to set an assumed nominal transmit PSD and b to model a loop that corresponds to the Reference Length (RL) where ATIS-0600023 4 the loss on the reference loop is modeled as being proportional to f such that bf approxima
25、tes the loss of a loop of length RL. When a is set to the nominal transmit PSD3for a particular band, the effect of the term abf on the formula for UPBOMASK is that no upstream power back off is applied for loops whose electrical length, kl0, is greater than the RL that is determined by the setting
26、ofb . ITU-T Recommendation G.997.1 4 defines the parameter UPBOPSD-pb to allow the Network Operator to configure a and b for each upstream band except US0.4. Figure 1 illustrates the relationship between various settings of b and reference lengths of 26 AWG loops at 1000ft, 1500ft, 2000ft, 2621ft5,
27、and 3000ft and insertion loss modeled across the VDSL2 US1 band6. In general, the values of a and b are set to same values for all loops in a binder. As mentioned above, a is typically set to the Transmit Template PSD, which for the VDSL2 US1 and US2 bands is the Limit PSD Mask 3.5dB. The value of a
28、 is configurable to allow the Network Operator to tune the behavior of UPBO when a PSD Mask is set in the upstream direction that modifies the Transmit Template PSD for a modem to one below the Transmit Template PSD. 3The default nominal transmit PSD in VDSL2 is (LimitMask for the band 3.5) dB. This
29、 PSD is flat for US Bands in Annex A of VDSL2.) 4As the formula abf has units of dBm / Hz in the definitions of a and b in the ITU-T Recommendations and in the guidance provided in this TR, the values of a are in units of dBm / Hz and of b are in units of dB / Hz . 5This is equivalent to the value o
30、f b proposed for the default for the US1 band in ATIS-0600424.2004 (R2009) 3 for the F noise model and the M2 template. This graph indicates that such a value for b equates to a RL of 2621 ft. 6Clause 4.3 provides a examples of a and b settings for the US1 and US2 bands for both 26 AWG and 24 AWG lo
31、ops. ATIS-0600023 5 Figure 1 - Various Reference Lengths and Best Fit Values of b in the US 1 Band Increasing the reference length (RL, that is increasing b) in the UPBO formulas results in lowered upstream FEXT from shorter loops into the longer loops. However, the reduced power also leads to reduc
32、ing the maximum upstream bit rate available on the short loops to a rate at least equal to that which would be possible if the short loop length were equal in the length the RL. Increasing the value.of bthus reduces the upstream bandwidth achievable on all the loops shorter than the RL. 4.2 Issues o
33、n the Optimization of UPBO Determining the optimum setting of b for any particular implementation of VDSL2 involves evaluating the above trade off in terms of both particular characteristics of the Network Operators loop plant and their specific VDSL2 customer service models and requirements. Becaus
34、e of this, determining an optimum value of b for VDSL2 is likely to be dependent on conditions specific to particular Network Operators environments, possibly varying among different metropolitan areas or even in some cases from access node to access node. It must be assumed if UPBO is to be configu
35、red in a North American field implementation that equipment supporting VDSL2 is compliant with the ITU-T Recommendations G.997.1 and G.993.2 with respect to the ability to set the values of a and b . That is the values of a and b must be configurable by the Network Operator if they are to utilize UP
36、BO. ATIS-0600023 6 4.3 Examples of the a and b Settings for North American Loops The following tables provide a list of b values and the corresponding Reference Length (RL) - for example, 26 AWG and 24 AWG loops in the US1 and US2 VDSL2 bands. In all these tables a is set to a value of the Transmit
37、Template PSD as defined in G.993.2 section 7.2.1 and Annex A1 which for the VDSL2 US1 and US2 bands is the Limit PSD Mask 3.5dB. That is: US1 band: a 53dBm / Hz US2 band: a 54dBm / Hz The examples in these tables provide guidance as to acceptable initial values for b in North America for the example
38、 loops listed below. However, as discussed in 4.2, they are not necessarily optimal values for any particular field implementation of VDSL2 and are not recommended default values for b in North America. Guidance for the US0 and US3 bands is for further study. Table 1 - b vs Reference Length (RL) for
39、 26 AWG Loops in the US1 Band Value of b in dB / Hz Reference Length (RL) in feet 24.25 3000 20.21 2500 16.17 2000 12.13 1500 8.08 1000 Table 2 - b vs Reference Length (RL) for 26 AWG Loops in the US2 Band Value of b in dB / Hz Reference Length (RL) in feet 24.68 3000 20.57 2500 16.45 2000 12.34 150
40、0 8.23 1000 ATIS-0600023 7 Table 3 - b vs Reference Length (RL) for 24 AWG Loops in the US1 Band Value of b in dB / Hz Reference Length (RL) in feet 22.52 3500 19.30 3000 16.09 2500 12.87 2000 9.65 1500 6.43 1000 Table 4 - b vs Reference Length (RL) for 24 AWG Loops in the US2 Band Value of b in dB / Hz Reference Length (RL) in feet 22.76 3500 19.51 3000 16.26 2500 13.01 2000 9.76 1500 6.50 1000
