Conformity Magazine - April 2008 - (Page 44)

channel bandwidth) is given by -174 dBm/Hz * 20 MHz = 101 dBm. A receiver with a real noise figure of 10 dB would then have a noise threshold or noise floor of -91 dBm at 20 MHz. As such, the channel emulator should have a noise floor of -91 dBm (or better) at 20 MHz. Advanced Channel Control Simplifies Problem Troubleshooting As previously discussed, effective WiMAX and Wi-Fi testing requires running channel models for long periods of time, often several hours or even days. Effective testing will incorporate running long samples or selecting random points in time to begin the channel model sampling, and so full control of the channel model operation will be highly beneficial to the user to provide this flexibility, as well as for the troubleshooter who may want to review a sample of the model and evaluate results a second time or multiple times to understand the behavior in a test. Simple control to start, pause, resume and stop the channel is not sufficient; in addition the ability to skip forward or backward in the model, to select a portion of the model and loop through that, and then finally to single step through the model will assist the user in identifying, honing in on, and finding exact conditions of the channel which may be good or bad for their unit under test. Channel control commands enable the engineer to start the emulator and immediately fast forward to the time period of interest (which may have occurred hours or days earlier in a test run). Once the channel conditions under investigation are being run, the engineer may need to debug the radio by looping on a point in time, single stepping the channel, and observing the actual channel parameters during those steps. At such a point, the channel information should be readily available to allow the user to take that scenario and analyze the channel conditions. Figure 2 shows the results of a throughput vs. time performance test conducted on a SISO device. The test plot identifies significant throughput reductions at multiple points throughout the test. Using advanced channel emulator controls, the user “plays” the specific time periods of interest to help diagnose the cause(s) of the throughput reductions. Automation Enhances Channel Emulation Test Systems The need to run long statistically significant tests with a channel emulator has been outlined above. That, coupled with the need to run several models, as well as the need to adjust parameters like range (of the client device from the base station/access point) and motion, can mean that many hours or days of testing effort is required to achieve full test coverage. Programmatic control of all the advanced functionality allows complete automation of the test, and eliminates the need for engineers either to be physically present or to frequently log in to the test set-up to make all the necessary changes. A channel emulator that is completely coupled to a test automation Figure 1: SISO, MISO, SIMO and MIMO antenna configurations Conformity April 2008

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Conformity Magazine - April 2008 NewsBreaks Editor’s Note Mandatory Analog Cellular Service Ends FCC Releases Quarterly Reports on Consumer Inquiries and Complaints New Standards List Released for The EU’s Low Voltage Directive FDA Issues Notification on Unretrieved Device Fragments FDA Offers Guidance on Waivers for In-Vitro Diagnostic Devices ESD Open Forum Emerging Issues in Standards Challenges in Testing Design Fundamentals Focus on... New Products Product Reviews Premarket Approval Application Guidance Issued by FDA New Jersey Enacts Electronic Waste Recycling Regulations A New U.S. Standard for Workstation and Computer Design Might the CPSC Hold Retailers Accountable for Safe Products? CPSC Loses “Sole Toy Tester” CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - April 2008

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