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TR41.9.2-03-05-017 Title: Proposed TSB-31C Test Procedure for Testing Signal Power Limitations for ADSL Equipment Distribution to: TIA TR41.9.2 Meeting Lake Buena Vista, Florida Location: May 5, 2003 Submitting Organization: Contact Peter Walsh, NCE Information: Paradyne Corporation: 8545 126th Ave. No. Largo, FL 33773 Phone Tel: (727) 530-8381 Fax: (727) 530-2428 E-mail: [email protected] Keywords: Part 68, TIA/TSB-31-C, ANSI/TIA-968-A Abstract: This contribution presents a draft proposal to update text in Sections 8.22 and 4.3 from the draft 4i version of TSB31C. The text has been revised to align with the current technical requirements in ANSI/TIA-968-A for ADSL modems; specifically those for signal power, power spectral density, and longitudinal output voltage. NOTICE: The contributor grants a free, irrevocable license to the Telecommunications Industry Association (TIA) to incorporate text or other copyrightable material contained in this contribution and any modifications thereof in the creation of a TIA Publication; to copyright and sell in TIA's name any TIA Publication even though it may include all or portions of this contribution; and at TIA's sole discretion to permit others to reproduce in whole or in part such contribution or the resulting TIA Publication. This contributor will also be willing to grant licenses under such copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing a TIA Publication, which incorporates this contribution. This document has been prepared by Paradyne Corporation to assist the TIA Engineering Committee. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on Paradyne Corporation. Paradyne Corporation specifically reserves the right to amend or modify the material contained herein and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of Paradyne Corporation other than provided in the copyright statement above. Page 1 of 19 TR41.9.2-03-05-017 1.0 Contribution Overview This contribution builds upon the test procedure set out in TR41.9-01-05-021R1 as accepted by Committee TR41.9 to facilitate testing of ADSL terminal equipment against the technical requirements of TIA/EIA/IS-883. With the adoption of ANSI/TIA-968-A by the ACTA, changes have been made with respect to the signal power limitations for ADSL modems. The most notable changes include an extension of the upper limit to which PSD is measured (now 30 MHz) and new limitations for longitudinal output voltage (LOV), based upon limits specified in ANSI T1.417-2001. This contribution presents a proposal to revise the Revision 4i draft of TSB-31C as follows. 2.0 List of Significant Changes Added a new test procedure to measure longitudinal output voltage. Eliminated references to the Alcatel Order, TIA/EIA/IS-883 and some references to ANSI T1.413. Added references to ANSI/TIA-968-A. Eliminated the list of commercially available equipment, which meets the specifications of the suggested equipment list referenced throughout the procedure. Eliminated the section containing sample PSD plots. Embedded sample plots showing an ADSL ATU-R’s PSD in each procedure that details the measurement for each segment of the mask. Previously, the sample plots were presented in a separate section and also, these were taken on a RADSL unit. ANSI T1.413 compliant equipment was used to generate these sample plots and they have been included with the procedure so that the user has some reference of the expected result. Extended the highest frequency to which PSD is measured to 30 MHz consistent with the current ANSI/TIA-968-A requirement. Changed the term, “total signal power” to “aggregate signal power” to be consistent with ANSI/TIA-968-A terminology. Moved the new SEL items to Section 4.3 since the procedure is no longer styled as a standalone appendix. Revised the new SEL items to reflect the need to test PSD out to 30 MHz. Page 2 of 19 TR41.9.2-03-05-017 8.22 SIGNAL POWER LIMITATIONS FOR ADSL TERMINAL EQUIPMENT 8.22.1 General This subclause provides a suggested test procedure to measure aggregate signal power, power spectral density (PSD), and longitudinal output voltage (LOV) for ADSL modems (ADSL ATU-R or similar CPE) against the applicable requirements specified in ANSI Standard ANSI/TIA-968-A-2002. 8.22.2 Conditioning the EUT to Transmit Continuously To properly measure aggregate signal power, PSD, and LOV, the EUT must be conditioned to transmit at its highest signal power level and line rate without a sustained connection to companion equipment. The method of testing with a companion device is impractical for ADSL equipment since the companion (ATU-C) equipment may present excessively high signal levels at frequencies at which the upstream PSD mask demands very low PSD levels. The amount of attenuation required to reduce the companion equipment’s signals below the upstream mask would be excessive to permit the link to come up at the maximum upstream line rate. This is because ADSL equipment automatically reduces the line rate over long loops to maintain an acceptable level of performance. There are two possible methods to achieve the required state for the ADSL modem. One method involves a test mode whereby the EUT’s transmitter is forced to enter the show time state without going through a training sequence. Show time refers to the state where the ADSL modem is transmitting a pseudo-random data pattern continuously. The other technique first involves bringing the link up over an artificial line whose characteristics effectively force the EUT into its maximum signal power and line rate and thus highest bandwidth state. Next, the EUT is strapped or conditioned to disable retrains so that once the show time state has been achieved, the EUT may be disconnected from the artificial line and connected to a 100 measurement termination. The artificial line may be either a commercial telephone line simulator or a simple 100 O-pad. In either case, the amount of through transmission attenuation must be set to maximize the EUT’s transmit power and bandwidth. This is necessary as most ATU-R’s utilize an adaptive transmit power scheme where power is cut back under short loop conditions. By the same token, if the line attenuation is excessive, then the link will not have sufficient margin to come up at its highest rate. The amount of line attenuation will vary from one vendor’s CPE to another and even with the same CPE if the start up margin is changed. Page 3 of 19 TR41.9.2-03-05-017 8.22.3 Aggregate Signal Power – ANSI/TIA-968-A Section 4.5.9.1 8.22.3.1 Background The aggregate signal power, or total power, of the ADSL modem must be limited to minimize near end crosstalk (NEXT) with other DSL systems that share the same cable binder. Crosstalk is widely recognized as a form of third party harm and represents the principal impairment to many DSL systems. 8.22.3.2 Purpose To verify that the signal power level transmitted to the network is properly limited. 8.22.3.3 Equipment True rms ac voltmeter SEL#41. 100 , 1 %, non-inductive resistor. NOTE: Refer to Section 4.3 for equipment details. 8.22.3.4 Equipment States Subject to Test Transmitting continuously at its highest signal power and upstream line data rate. 8.22.3.5 Procedure Condition the EUT to transmit at it highest upstream signal power level and line rate as described in 8.22.2. Connect the EUT to the test circuit of Figure 8.22.3.5-1. Measure and record the signal power level in dBm. If the ac voltmeter has its dBm scale referenced to 600 , then a correction factor of +7.8 dB must be added to the displayed reading to account for the measurement impedance of 100 . Page 4 of 19 TR41.9.2-03-05-017 FIGURE 8.22.3.5-1. AVERAGE SIGNAL POWER 8.22.3.6 Alternative Methods The total signal power may also be calculated by integrating the PSD over the operating band. This task consists of measuring the PSD over the operating band using a 10 kHz resolution bandwidth at discrete frequencies with a stepped interval of 10 kHz. The individual PSD readings are then converted to power readings by multiplying the PSD (in terms of watts/Hz) by the 10 kHz resolution bandwidth. This results in a power level for each 10 kHz window. These are then summed over the operating band to give the total power. The PSD measurement procedure is given in 8.22.4. 8.22.3.7 Suggested Test Data Signal Power Level. Line Data Rate and Baud Rate if applicable. 8.22.3.8 Comments It is recommended that the voltmeter provide a high-impedance balanced input particularly if the EUT has intentional paths to ground. The resistor value in the above figure is in ohms. Page 5 of 19 TR41.9.2-03-05-017 8.22.4 Power Spectral Density – ANSI/TIA-968-A Section 4.5.9.2 8.22.4.1 Background As is the case for the ADSL modem’s total power, its PSD must be limited to minimize crosstalk. PSD is limited by the imposition of a PSD mask, which specifies a limit as a function of frequency. The mask permits a reasonable level in the operating band while restricting the ADSL modem’s PSD below the operating band to protect POTS and above the operating band both to minimize interference both with the downstream spectrum as well as other DSL systems potentially affected by crosstalk. The mask presents measurement challenges because it specifies such a broad range of signal levels which can’t practically be made in a single sweep due to limitations in the spectrum analyzer’s dynamic range. For this reason and resolution bandwidth considerations, the mask is broken into segments. Either low pass or high pass filtering techniques are employed, as necessary, to allow the spectrum analyzer to effectively measure low PSD levels in the presence of high PSD level conditions associated with the operating band. 8.22.4.2 Purpose To verify that the PSD is below the mask. 8.22.4.3 Equipment Spectrum analyzer SEL#57. 100 , 1 % non-inductive resistor. Differential amplifier with 10X passive probe set and built in LPF SEL#58. 100:50 balun transformer SEL#59. 10 dB, 50 pad SEL#60 500 kHz High Pass Filter SEL#61 8.22.4.4 Equipment States Subject to Test Transmitting continuously at its highest signal power and upstream line data rate. Page 6 of 19 TR41.9.2-03-05-017 8.22.4.5 Procedure The test procedure is broken down into four sections associated with making the PSD measurements in a given frequency range segment. 8.22.4.5.1 Procedure for Segment 1 Condition the EUT to transmit at it highest upstream signal power level and line rate as described in 8.22.2. Connect the EUT to the test circuit of Figure 8.22.4.5.1-1. Set the differential amplifier for unity gain and a low pass cut-off frequency of 10 kHz. Set the spectrum analyzer as follows: Resolution bandwidth: 100 Hz Video bandwidth: 3 Hz Attenuation or range: Set for minimum without overload Reference level: -40 dBm dB/div: 10 dB Start frequency: 200 Hz Stop frequency: 4000 Hz Marker Function: Noise dBm/Hz Limit test: On with limit line programmed with the mask’s peak limit Measure and record the PSD over the first segment of the mask, which covers the voice frequency band. NOTES: The PSD readings must be adjusted by a net correction factor of 17 dB derived from the 10X probe which introduces 20 dB of loss and the 100:50 ohm impedance correction factor of –3 dB. The resistor value in Figure 8.22.4.5.1-1 is in ohms. Page 7 of 19 TR41.9.2-03-05-017 FIGURE 8.22.4.5.1-1. PSD CONNECTION DIAGRAM FOR SEGMENTS 1 & 2 FIGURE 8.22.4.5.1-2. SAMPLE PSD PLOT FOR SEGMENT 1 Page 8 of 19 TR41.9.2-03-05-017 8.22.4.5.2 Procedure for Segment 2 Condition the EUT to transmit at it highest upstream signal power level and line rate as described in 8.22.2. Connect the EUT to the test circuit of Figure 8.22.4.5.1-1. Set the differential amplifier for unity gain with no filtering Set the spectrum analyzer as follows: Resolution bandwidth: 1 kHz Video bandwidth: 30 Hz Attenuation or range: Set for minimum without overload Reference level: -20 dBm dB/div: 10 dB Start frequency: 4 kHz Stop frequency: 26 kHz Marker Function: Noise dBm/Hz Limit test: On with limit line programmed with the mask’s peak limit Measure and record the PSD over the second segment of the mask, which covers the frequencies between the voice band and the ADSL operating band. Page 9 of 19 TR41.9.2-03-05-017 FIGURE 8.22.4.5.2-1. SAMPLE PSD PLOT FOR SEGMENT 2 8.22.4.5.2 Procedure for Segment 3 Condition the EUT to transmit at it highest upstream signal power level and line rate as described in 8.22.2. Connect the EUT to the test circuit of Figure 8.22.4.5.3-1. Set the spectrum analyzer as follows: Resolution bandwidth: 10 kHz Video bandwidth: 300 Hz Attenuation or range: Set for minimum without overload Reference level: -20 dBm dB/div: 10 dB Start frequency: 25 kHz Stop frequency: 525 kHz Marker Function: Noise dBm/Hz Limit test: On with limit line programmed with the mask’s peak limit Page 10 of 19 TR41.9.2-03-05-017 Measure and record the PSD over the third segment of the mask, which covers the ADSL operating band on up to 525 kHz. FIGURE 8.22.4.5.3-1. PSD CONNECTION DIAGRAM FOR SEGMENT 3 Page 11 of 19 TR41.9.2-03-05-017 FIGURE 8.22.4.5.3-1. SAMPLE PSD PLOT FOR SEGMENT 3 8.22.4.5.4 Procedure for Segment 4 Condition the EUT to transmit at it highest upstream signal power level and line rate as described in 8.22.2. Connect the EUT to the test circuit of Figure 8.22.4.5.4-1. Set the spectrum analyzer as follows: Resolution bandwidth: 10 kHz Video bandwidth: 300 Hz Attenuation or range: Set for minimum without overload Reference level: -70 dBm dB/div: 10 dB Start frequency: 525 kHz Stop frequency: 30 MHz Marker Function: Noise dBm/Hz Page 12 of 19 TR41.9.2-03-05-017 Limit test: On with limit line programmed with the mask’s peak limit and above 1221 kHz the dashed line mask limit from ANSI T1.413 which will ensure compliance with the –50 dBm total power in a 1 MHz sliding window. Measure and record the PSD over the fourth segment of the mask, which covers the high frequencies above the ADSL operating band. NOTE: The 10 dB pad may be omitted if the high pass filter can withstand high input levels without introducing distortion products. The PSD readings must be adjusted to take into account losses introduced by the balun, pad and filter. FIGURE 8.22.4.5.4-1. PSD CONNECTION DIAGRAM FOR SEGMENT 4 Page 13 of 19 TR41.9.2-03-05-017 FIGURE 8.22.4.5.4-2. SAMPLE PSD PLOT FOR SEGMENT 4 8.22.4.6 Alternative Methods A balun transformer may be used instead of the differential amplifier as long as its frequency response and return loss are acceptable. Also, more than one type of balun may be used to cover the entire frequency range of interest. If the PSD exceeds the dashed limit in the mask at any point above 1221 kHz, measurements must be made to calculate the total power in a 1 MHz sliding window. This concept was discussed in 8.22.3.6. The peak limit of –90 dBm/Hz, above 1221 kHz, must never be exceeded by any individual spectral component. However, noise may exceed the dashed line limit provided that the power integrated over a 1 MHz bandwidth is less than –50 dBm. As the procedure given in 8.22.4.5.4 suggest, the sliding window calculation is not necessary if the PSD never exceeds the dashed line. As an example, the dashed line in ANSI T1.413-1998 Figure 32 reaches a noise floor of –110 dBm/Hz, which over a 1 MHz band is equivalent to –50 dBm. Page 14 of 19 TR41.9.2-03-05-017 8.22.4.7 Suggested Test Data Plots of the PSD for each segment with the limit line shown on each graph Line Data Rate and Baud Rate if applicable. 8.22.4.8 Comments Care must be taken to ensure that measurement errors are kept to a minimum. Sources of error may include the following: Impedance deviations from the ideal 100 termination Differential amplifier loss or gain Balun loss Attenuator pad loss over the ideal loss High pass or low pass filters’ frequency response Limited dynamic range of the differential amplifier Limited amplitude accuracy of the spectrum analyzer PSD measurement errors caused by excessively fast sweep times or not averaging enough samples when making a swept average measurement Page 15 of 19 TR41.9.2-03-05-017 8.22.5 Longitudinal Output Voltage – ANSI/TIA-968-A Section 4.5.9.3 8.22.5.1 Background Longitudinal output voltage (LOV) limits complement PSD limits by restricting the amplitude of common mode signals much like the PSD limits restrict the amplitude of the equipment’s differential mode signals. LOV limits are necessary as common mode signals tend to couple more readily than differential mode signals in multi-line, twisted pair cable plant. In other words, LOV limits are necessary to limit crosstalk. LOV limits have been crafted to allow higher levels around the equipment’s operating band. This is necessary as a common mode image of the desired differential mode signal results through imbalance in the line interface, cabling and the measurement circuitry. A tighter limit applies above the equipment’s operating band where the LOV source is usually not associated with any signal intended to be applied to the line. ADSL modems must also meet certain LOV limits for voiceband terminal equipment. These measurements should be made using the procedure set out in Sections 8.15 and 8.17. 8.22.5.2 Purpose To verify that the longitudinal output voltage is below the limit. 8.22.5.3 Equipment Spectrum analyzer SEL#57. LOV Test fixture shown in Figure 8.22.5.5-1 8.22.5.4 Equipment States Subject to Test Transmitting continuously at its highest signal power and upstream line data rate. 8.22.5.5 Procedure Condition the EUT to transmit at it highest upstream signal power level and line rate as described in 8.22.2. Connect the EUT to the test circuit of Figure 8.22.5.5.1-1. Resolution bandwidth: 3 kHz Video bandwidth: 300 Hz Attenuation or range: Set for minimum without overload Page 16 of 19 TR41.9.2-03-05-017 Reference level: -30 dBV dB/div: 10 dB Start frequency: 10 kHz Stop frequency: 844 Hz Marker Function: Voltage dBV Limit test: On with limit line programmed with the LOV limit Measure and record the LOV averaging the readings over several sweeps. NOTES: The resistor values in Figure 8.22.5.5.1-1 are in ohms. A resolution bandwidth (RBW) of 3 kHz is typically used as most spectrum analyzers support this RBW. FIGURE 8.22.5.5.1-1. LOV TEST FIXTURE & CONNECTION DIAGRAM Page 17 of 19 TR41.9.2-03-05-017 FIGURE 8.22.5.5.1-2. SAMPLE LOV PLOT 8.22.5.6 Alternative Methods None 8.22.4.7 Suggested Test Data Plot of the LOV with the limit line shown Line Data Rate and Baud Rate if applicable. 8.22.4.8 Comments Care must be taken in the construction of the LOV test fixture. Resistor values must be matched as previously mentioned. Test leads from the fixture to the EUT should be kept as short as possible to minimize RF ingress. The ground connection to the fixture should be of a low inductance, kept short, and connected directly to the chassis ground Page 18 of 19 TR41.9.2-03-05-017 of the EUT. For EUT’s without an earth ground, a ground plane should be used as discussed in Section 9.1.8. Amend Section 4.3 as follows: (57) Spectrum analyzer: input impedance 50 ohms, frequency range from 20 Hz to at least 30 MHz, sensitivity of –130 dBm/Hz or better, resolution < 1 Hz, absolute amplitude accuracy +1.5 dB or better, RBW of 100 Hz, 1 kHz, 3 kHz, and 10 kHz. (58) Differential amplifier with 10X passive probe set: amplifier gain 1,10, gain accuracy +1%, bandwidth DC to 10 MHz, output impedance 50 ohms, input resistance 1 megohm, input capacitance 20 pF, bandwidth limit filter upper cutoff frequency 10 kHz, filter response 6 dB/octave, minimum common mode rejection ratio 10000. (59) 100:50 balun transformer: frequency range 10 kHz to 30 MHz minimum. (60) 10 dB 50 pad: frequency range DC to 30 MHz minimum. (61) High Pass Filter: fc 3 dB cut off frequency 500 kHz, f/ fc ratio 0.40:1, stop band attenuation –50 dBc. Update the Table of Contents as follows: 8.22 SIGNAL POWER LIMITATIONS FOR ADSL TERMINAL EQUIPMENT 8.22.1 8.22.2 8.22.3 8.22.4 8.22.5 General Conditioning the EUT to Transmit Continuously Aggregate Signal Power – ANSI/TIA-968-A Section 4.5.9.1 Power Spectral Density – ANSI/TIA-968-A Section 4.5.9.2 Longitudinal Output Voltage – ANSI/TIA-968-A Section 4.5.9.3 Page 19 of 19