More and more people rely on their wireless devices to manage email, social media, banking, and downloading or streaming videos and movies. In order to support these activities, consumers are demanding higher data rates and better signal integrity for their mobile devices. Wireless providers continue to improve connectivity and achieve higher peak data rates of their mobile communications systems to meet these growing demands. One solution being used more often involves the implementation of multi antenna techniques. Multi antenna techniques add system capacity by increasing the number of antennas at the transmitter, receiver or both. Specifically, they are implemented to achieve better spectral efficiency and increased peak data rates. The techniques include:

• Path diversity – uses multiple antennas at either the transmitter or the receiver to improve the robustness of the signal or the ability of the receiver to correctly receive the transmitted data.

• Spatial multiplexing - a technique used to transmit independent and separately encoded data signals (data streams) from each of the multiple transmit/receive antennas.

o MIMO (multiple input, multiple output) antenna technology places multiple antennas at both the transmitter and receiver. The data from each antenna at each end of the communications circuit are combined to minimize errors and optimize data speed. MIMO is used in many of the higher data rate wireless technologies such as LTE, LTE-A, WiMAX and WLAN 802.11n/ac. This

technique improves spatial efficiency and data through put for a single user.

Multiuser MIMO- sends data to multiple users simultaneously in the same frequency spectrum. This technique increases system efficiency rather than increasing data through put rate to a single user.

• Beamsteering or beamforming uses multiple antennas for directional transmissions and to steer a signal in the direction of a specific receiver. The same signal is transmitted from two or more spatially separated transmitters simultaneously. Magnitude and phase adjustments are used for spatial selectivity. This technique improves signal robustness and SNR at the receiver. Benefits of beamsteaming / beamforming include selectivity, interference management with increased gain and better SNR.

However, as the number of antennas increase, engineers are faced with system verification tests that are much more complicated. Validating multiantenna configurations present new challenges – such as the need to analyze the multiple transmit or receive chains simultaneously.Design and verification of MIMO configurations requires test systems with multi-channel synchronization.In beamforming applications, it’s critical to have precise timing and synchronization between channels and phase coherency to ensure proper inter-channel phase and magnitude measurements. Modular platforms like PXI are ideal for multi-channel synchronized test systems because of their scalability and ability to used shared resources for triggering and synchronization.

One example is a PXI test solution that canprovide time and phase synchronization to support MIMO and beamforming tests. Synchronizationcan be achieved using the PXI 10 MHz clock witha master module synchronizing with multiple slave modules. This configuration can be set formulti-channel waveform play or acquisition to start at the same time. A common clock reference provides time alignment but not phase coherence. Beamforming applications require phase coherency between channels to simulate real world simultaneous transmissions and measurements. Phase coherent signals must have a constant, relative phase at all instances in time. A phase stable relationship between generated signals or measurement channels can be achieved with phase coherent instruments to ensure multiple signals construct and destruct properly.One method to achieve true phase coherency is to use a shared local oscillator (LO) with each channel to ensure that all channels have the same phase properties. By sharing an LO, each downconverter in the analyzer or each modulator in the source share the same phase characteristics including phase error and the RF paths can be fully characterized given theconstant phase and channel to channel skew (delay in paths for each instrument). Keysight offers a time synchronous, phase coherent multi-channel test system, supporting up to 8x8. The Keysightsystem includes PXI vector signal generators (VSG) and vector signal analyzers (VSA) which share a common LO that can be used with up to eight VSA or VSGs.