Microwave Engineering Europe - April 2008 - (Page 11)

TEST & MEASUREMENT 11 Comprehensive WiMAX and Wi-Fi product design demands effective channel emulation By Graham Celine, Senior Director of Marketing, Azimuth Systems Inc. s WiMAX and Wi-Fi become increasingly popular, the stakes increase for vendors servicing the market and the engineers developing new products. Both standards are in the midst of a MIMO technology transition, providing further incentive to ﬁnd new design and veriﬁcation tools that can accelerate development of higher performance products. Multiple-Input Multiple-Output (MIMO) technology is the foundation of the next generation of mobile WiMAX and Wi-Fi products. By leveraging multiple transmit and receive antennas to employ techniques such as spatial multiplexing, adaptive antenna processing, and beam forming, MIMOenabled products deliver greater wireless throughput and range enabling ubiquitous high-speed voice, video and data services. In-lab controlled channel emulation, using a channel emulator is required to accurately characterize the effect of multi-channel RF interactions on the conformance, performance and interoperability of MIMO and SingleInput Single-Output (SISO) WiMAX and Wi-Fi systems. This white paper explains the critical test requirements for comprehensive design of MIMO-enabled WiMAX and Wi-Fi devices. The understanding of key technical requirements and features that increase test effectiveness will assist engineers and engineering managers in the selection of the channel emulator that best meets their needs. Using channel emulation to accurately measure over the air conditions To accurately test real-world, over-the-air conditions in a controlled lab environment, a channel emulator that reproduces these conditions is required. A channel emulator therefore must have: • dynamic emulation to mimic the constantly changing over-the-air channel conditions; • a real-time path to precisely represent the inherent bi-directional nature of the device and base station path. Over-the-air conditions are constantly changing due to many variables, including device movement, the environment, people, A cars etc. Channel emulation technology utilizes sophisticated channel models to recreate conditions that occur in real-world wireless transmission. Standards bodies and industry forums deﬁne channel models to represent certain classes of channel conditions, which serve as statistical characterizations of speciﬁc environments. The conditions provided by the channel model are based on random processes that create a speciﬁc instance of a channel condition due to fading, multipath and correlations. The models are dynamic in the sense that the conditions are constantly changing. To accurately represent all the conditions, the emulator must also be dynamic in order to change in time, and provide long intervals of non-repeating channel conditions, as the real world would. This provides the devices under test with a very large number of unique channel instantiations similar to real-world conditions, resulting in more test coverage. There are a number of channels that are deﬁned by standards organizations to create a baseline. For example, ITU M.1225 Pedestrian B and Vehicular A channel models provide a baseline for testing WiMAX devices today while IEEE 802.11n channel models A through F form the baseline of Wi-Fi testing. Table 1 below provides key parameters of the ITU M.1225 Pedestrian B and Vehicular A channel models with proposed changes by the WiMAX forum for spatial correlations. Table 2 provides key parameters of IEEE 802.11n channel models A through F. In addition, test organizations, product development labs and others may have their own models that they feel better represent the conditions in which devices are expected to operate. A channel emulator must have the ability to use standard models as well as custom, user-deﬁned models. In the case of standard models, channel emulators should offer them as a built-in feature. To allow for extensible emulation of channels, a channel emulator must offer the ability to program both spatial and temporal parameters as part of deﬁning custom model parameters. In real-world device operation, a bidirectional channel exists between the mobile Table 1: Parameters of ITU M.1225 Pedestrian B and Vehicular A channel models. Table 2: Parameters of IEEE 802.11n channel models. Microwave Engineering ● April 2008 ● www.mwee.com 011-012-014-016_MWEE.indd 11 28/03/08 18:10:10 http://www.mwee.com

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Microwave Engineering Europe - April 2008 News Contents Comment Test and Measurement: Comprehensive WiMAX and Wi-Fi Product Design Demands Effective Channel Emulation Military/Aerospace Focus: Hardware Needs Limit Software Radio Interview — Mitsubishi Electric Europe: GaAs Technologies Spanning High-End Space and Radar Through to Cost-Sensitive Handset and LNB Applications How Do You Test ZigBee Transmitters? Advanced Receiver Design Boosts Performance CMOS PAs Pave the Way for One-Chip Phones Products Calendar

Microwave Engineering Europe - April 2008

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