Aeroflex has added support for 4x2 multi-input multi-output (MIMO) to the 7100 Digital Radio Test Set for the R&D testing of LTE user equipment (UE) being designed with this feature.
4x2 MIMO is used adaptively to offer improved throughput in good signal conditions, and improved resilience in poor signal conditions. When the signal-to-noise ratio (SNR) at the UE is good, the device can make use of spatial multiplexing, where multiple information streams are transmitted simultaneously to improve throughput.
When the SNR is poor then transmit diversity is employed. This is where a single information stream is distributed across separately-encoded antenna ports to reduce the variations in SNR experienced by the UE, thus improving the cell coverage. Measurements are made both at the base station and at the UE and these are used to determine how many streams can be supported in the prevailing signal conditions.
‘This new software option means that single cell 4x2 MIMO emulation is now supported in a single 7100 instrument, allowing transmit diversity and spatial multiplexing to be set up easily and readily tested from a familiar graphical user interface,’ said Michael Thorpe, Product Line Manager at Aeroflex.
Option 7100-111 is a software license that enables 4x2 MIMO functionality and can be enabled in the field. Testing can be controlled using either command line interface (CLI) control or programming via Remote API. This new release of the software supports 4x2 MIMO measurements on LTE in FDD mode with bandwidths of 10 MHz, 15 MHz, and 20 MHz. It is planned that 1.4 MHz, 3 MHz, and 5 MHz bandwidths will be added in due course.
Fading and Additive White Gaussian Noise (AWGN) measurements are supported, using the optional integral fading and AWGN generator, with configurable cross-correlation between streams.
More about 4x2 MIMO and spatial multiplexing
There are two modes of operation for spatial multiplexing, closed loop and open loop. Closed loop spatial multiplexing uses feedback from the UE to determine the rank and the pre-coding matrix, chosen from a set of 16 values.
Open loop spatial multiplexing - referred to in 3GPP specifications as ‘large-delay CDD’ - cycles through a fixed set of four pre-coding matrices in consecutive resource elements. This latter type is employed for fast-moving users, where the overhead of the closed loop feedback cannot be processed quickly enough.
Aeroflex said that this release of the software supports open loop spatial multiplexing, with closed loop planned to be included in the next release.