Conformity Magazine - April 2008 - (Page 41)

ervices utilizing next-generation mobile wireless technology (like WiMAX or 802.11n Wi-Fi and, in the future, LTE, UMB, and 802.16m) represent an important next step in the drive to broaden end-user access to high-speed wireless communication, information and advanced data, voice and video services. Multiple-input multiple-output (MIMO) RF technology is the foundation of this next generation of mobile wireless broadband products. By leveraging multiple transmit and receive antennas to employ techniques such as spatial multiplexing, and adaptive antenna systems (AAS) such as beamforming, MIMO-enabled WiMAX and Wi-Fi products deliver the greater throughput and range that drives costeffective, high-speed wireless products and services. For engineers, the pressure is on to design, develop and test products and services that deliver the robust quality of communications (performance and interoperability) necessary to drive sustained consumer demand. As both the mobile WiMAX and Wi-Fi standards are in the midst of a MIMO technology transition, great incentive exists to find design and test tools that can accelerate the delivery of high performance products. In-lab controlled channel emulation, using a channel emulator, is central to accurately characterize the effect of multi-channel RF interactions on the conformance, performance and interoperability of WiMAX and Wi-Fi systems for both MIMO and SISO (single-input single-output) implementations. This article discusses the critical test requirements of MIMOenabled WiMAX and Wi-Fi devices, and identifies channel emulator features that are required for effective and efficient testing of MIMO-enabled devices. Using Channel Emulation for Accurate Measurement of Over-the-Air Conditions The role of the channel emulator in wireless test is to recreate the complex, constantly changing, over-the-air conditions (often called impairments), so that the transmitting and receiving sides of the communication can be subjected to the real life signal quality of many different open air locations. The channel emulator uses statistical models to recreate the effects of radio transmissions in real-world setups, and can realistically reproduce the effects of disturbances, interference, reflections, noise, motion and more. To achieve this effectively, the channel emulator must have: • Dynamic emulation to replicate the constantly changing over-the-air channel conditions; • A bidirectional real-time path to precisely represent the inherent bi-directional nature of the client device and base station path. S Channel emulation technology utilizes sophisticated channel models to recreate conditions that occur in a real-world wireless transmission. These channel models serve as statistical characterizations of specific environments in which the wireless devices may be used. The conditions provided by the channel model are based on random processes that create specific instances of a channel condition caused by signal fading, signal multipath and antenna correlations. The models are dynamic in the sense that the conditions (phase of reflections and signal strength) are always changing. To accurately represent the dynamic channel conditions, the emulator must also be able to run endless dynamic models in order to change the channel conditions in time. To provide a reasonable statistical representation similar to a real-world channel, a channel emulator must provide long intervals of non-repeating channel conditions. This provides the devices under test with a very large number of unique channel instantiations similar to real-world conditions, resulting in adequate test coverage. Standards bodies and industry forums define channel models to represent certain classes of channel conditions typical to their usage scenarios. There are a number of channels defined by standards organizations to create a baseline for testing; current baseline testing of WiMAX devices use the ITU M.1225 Pedestrian B and Vehicular A channel models, April 2008 Conformity 1 http://www.monroe-electronics.com http://www.monroe-electronics.com

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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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