Tips for testing MIMO, LTE, and 802.11ac devices

You can learn more about MIMO testing from two articles available in the “Designlines” section of the EE Times Website.

Martin Rowe, Senior Technical Editor -- Test & Measurement World, 1/20/2012 3:21:21 PM

The cover story in the February 2012 issue of Test & Measurement World, “Use LTE channel emulation for mobile test,” features a technique for testing LTE and IEEE 802.11ac devices, both of which use MIMO (multiple input, multiple output) technology as the physical-layer wireless interface. MIMO increases data rates over previous single-stream wireless technologies by using multiple transmitters and receivers, setting up a multipath environment. The cover story focuses on beamforming, a technique for strengthening a signal by focusing a signal in a particular direction, and it mentions several models under consideration for simulating channel fading in the lab.

You can learn more about MIMO testing from two articles available in the “Designlines” section of the EE Times Website. “Test MIMO over-the-air with a two-stage method” by Allison Douglas (bit.ly/xFfeS7) in the “RF & Microwave Designline” explains how a reference antenna and MIMO device can be tested in an anechoic chamber for measuring the antenna pattern (figure). No chamber is needed at the second stage, where LTE protocols are applied to the transmission signals. Channel models such as those described in this issue’s cover story are then applied to the signals for throughput measurements.

In the first stage of the two-stage test method, a reference receiver and MIMO device operate in an anechoic chamber.

 
In “802.11ac Wireless LAN: what’s new and the impact on design and test” in the “Test & Measurement Designlines” (bit.ly/xDI7mo), Mirin Lew discusses the design and test challenges of applying MIMO to the emerging IEEE 802.11ac standard, which is an evolution of the IEEE 802.11n standard. IEEE 802.11ac increases throughput by providing signal bandwidths of 80 MHz and 160 MHz as opposed to the 40 MHz found in 802.11n devices. Because 802.11ac devices will use 256 QAM (quadrature-amplitude modulation), error-vector magnitude measurements will be more critical than they were for devices designed for previous WiFi standards. The article explains how to make the measurements with a vector signal analyzer. T&MW