Customer Solutions

LabWindows/CVI Ensures Production of High-Quality ADSL Modems

Author(s):

Kjell Olovsson, Wandel & Goltermann

Industry:

Telecommunications

Product:

GPIB & Instrument Control, LabWindows/CVI, NI TestStand

The Challenge:

Designing an asymmetric digital subscriber line (ADSL) tester to meet the high-volume, multiunit requirements of telecommunications production testing.

The Solution:

Using National Instruments LabWindows/CVI and Test Executive to create an IMPACT ADSL test system, a high-speed, multichannel test system for effectively testing ADSL modem systems.

Introduction
ADSL is an asymmetrical service that provides up to 9 Mbps of data from the telephone company to the subscriber and 640 Kbps of data from the subscriber back to the central office. Asymmetrical data is well suited for Internet traffic, where large files and graphics are transmitted downstream to the user and small amounts of data are returned from the user.

ADSL is a digital service that encodes information, then transmits it as a digital bit stream. Discrete multitone (DMT) is a technique for transmitting ADSL data over 256 discrete channels between 20 kHz and 1.2 MHz. Further, ADSL is a subscriber line service. Subscriber line refers to the twisted pair copper wire that runs from a neighborhood telephone cabinet to individual homes and businesses. Because ADSL does not include frequencies below 20 kHz, plain old telephone service (POTS) and ADSL can be transmitted on the same physical pair of wires connected to the home or business.

Production Testing
We previously used a Unix-based test system with an internally designed controller to test ADSLs. After converting to a National Instruments Test Executive, with LabWindows/CVI and a GPIB controller on Windows, we now produce a high-speed, user-friendly ADSL tester capable of testing several modems simultaneously. The IMPACT test system also uses a VXI-based ADSL test head that comprises a physical layer test module, a datacom test module, and an optional POTS module.

We must perform production testing at both the datacom/backbone interface, located in telephone company central offices, and the copper line interface, connected to homes and businesses. The National Instruments Test Executive manages a suite of high-speed tests, including backbone/datacom and copper line interfaces tests, load and stability tests, as well as return loss, longitudinal conversion loss, and power spectrum density tests.

Results
LabWindows/CVI ensures that we can quickly configure the test solution and optimize it for user-friendliness. The LabWindows/CVI design makes the IMPACT platform open and facilitates integration of the system into existing test environments. We can perform the software integration process or users can. In either case, the IMPACT platform is easily adapted to customer requirements for high-volume, multimodem ADSL testing.

For more information, contact:

Kjell Olovsson at kjell.olovsson@wage.de

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