Channel emulation supports mobile MIMO
Rick Nelson, Editor in Chief -- Test & Measurement World, 2/1/2009 2:00:00 AM
MIMO (multiple-input multiple-output) technology stands as the foundation of next-generation mobile broadband wireless products, including those based on 3GPP LTE. MIMO technology, already in use in fixed IEEE 802.11n home wireless networks, can leverage multiple transmit and receive antennas in mobile environments as well as take advantage of techniques such as spatial multiplexing, adaptive antenna processing, and beam forming.
Bringing mobile MIMO products to market will require extensive laboratory and real-world OTA (over-the-air) testing. In the paper “Improving 4G Wireless Broadband Product Design through Effective Channel Emulation Testing,” Azimuth Systems reports that lab testing produces repeatable results, while OTA testing is not generally repeatable and is expensive to perform. To bridge the gap between the lab and the real world, the paper recommends the use of channel emulators, which “replicate real world channel propagation conditions in a controllable and repeatable fashion through the use of complex channel models and multiple, programmable parameters.”
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The paper notes that successful LTE channel emulation requires high dynamic range and a low noise floor—for example, an emulator may have to accommodate a PAPR (peak to average power ratio) greater than 10 dB and support better than 20-dB signal-to-noise ratio for a 64QAM signal. In addition, an emulator must not degrade a unit under test’s EVM (error vector magnitude), the term that best describes signal quality. Also, an emulator must be able to provide fast fading conditions that mimic real-world effects.
Channel emulation should also support multiple antenna connections for MIMO spatial multiplexing, STC (space time coding), and MRC (maximal ratio combining) techniques as well as AAS (adaptive antenna systems). Finally, channel emulation should be sufficiently flexible to accommodate channel models such as the 3GPP EPA (extended pedestrian A), EVA (extended vehicular A), and ETU (extended typical urban) models. The table lists the key parameters for the channel models in 3GPP E-UTRA (evolved UMTS terrestrial radio access).
You can download the full paper at www.azimuth.net/company-white-papers.htm.
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