Communications systems designers have reached for a variety of different techniques to squeeze maximum capacity from minimum bandwidths. One of these approaches involves the use of multiple signals as part of a multiple-input, multiple- output (MIMO) antenna configuration. MIMO techniques are used in a number of newer wireless standards, including in IEEE 802.11n wireless local area networks (WLANs), IEEE 802.16-2004 Fixed WiMAX, IEEE 802.16e Mobile WiMAX, and 3GPP Long Term Evolution (LTE) cellular systems. But systems and components using MIMO present new challenges for test equipment suppliers.

Test equipment suppliers offer both individual instruments for signal generation and analysis as well as bundled systems. National Instruments, for example, supplies a WiMAX Test System that includes the firm's 6.6-GHz model NI-PXIe-5673E RF vector signal generator (VSG), the 6.6-GHz model NI-PXIe-5663E RF vector signal analyzer (VSA), and software programmed according to the different standards for performing fixed or mobile WiMAX measurements. The system, which can generate modulated signals from 85 MHz to 6.6 GHz, can be used for handset, base station, and component testing.

Agilent Technologies also supplies a full MIMO test system solution based on its model V2920A RF VSG, model V2820A RF VSA, model V2891A frequency upconverter, and model V2895A MIMO synchronization unit. The system can be configured for as many as eight channels with bandwidths to 80 MHz.

The model V2920A RF VSG is available in versions operating from 10 MHz to 4 GHz and from 10 MHz to 6 GHz with output power controllable from -130 to +13 dBm at 1 GHz. The model V2820A RF VSA is available in versions from 400 MHz to 4 GHz or 400 MHz to 6 GHz with better than -140 dBc/Hz phase noise at 300 kHz offset from a 2-GHz carrier.

Similarly, the R&S SMU200A VSG from Rohde & Schwarz can be equipped with two baseband generator boards and two fading simulator boards to create a full-featured MIMO test signal source. It can support 2 x 2 MIMO testing to 6 GHz.

Recently, ETS-Lingdren and Elektrobit announced a partnership to provide solutions for MIMO over-the-air (OTA) testing. Their new test solution combines the Elektrobit (EB) Propsim F8 MIMO OTA emulator with ETS-Lindgren's AMS-8700 MIMO OTA Test System, which enables characterization of MIMO devices from 700 MHz to 6 GHz.

Veriwave has introduced its WaveGen 3 x 3 MIMO signal generator as a means of replacing three separate signal generators operating at specific wireless bands, such as 2.4 GHz, 4.9 GHz, and 5 GHz. It does not require programming of inphase (I) and quadrature (Q) baseband waveforms, but allows an operator to select from standards-based waveforms stored in the instrument's memory. It supports channel bandwidths of 20 and 40 MHz and can control output power from -50 to 0 dBm.

A number of companies offer additional MIMO test solutions, including the E2010 Broadband Wireless Test Set from AT4Wireless, the 3920 digital radio test set from Aeroflex (www.aeroflex.com), the ACE MX MIMO Channel Emulator from Azimuth Systems, and a system based on the model MF6900A Fading Simulator and a model MD8430A Signaling Tester from Anritsu Company. The Anritsu solution makes use of baseband signal processing to emulate 3GPP LTE 2x2 MIMO fading effects.