LTE Test Mobile supports Beamforming and 4 x 2 MIMO

29 March 2011— Aeroflex announced that the TM500 LTE test mobile has increased the number of modes it supports to include user equipment (UE) beamforming and 4 x 2 MIMO, as specified in Release 8 of the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) standard.

The TM500 test mobile allows engineers developing LTE base stations (eNodeB) or physical layers (PHY) for eNodeB to perform beamforming and 4 x 2 MIMO (transmit diversity and spatial multiplexing) measurements either in the laboratory or over the air in a trial LTE network. Beamforming and transmit diversity techniques are used in LTE networks to improve cell coverage and spectrum efficiency. Dual-layer beamforming (Rel-9) can also boost cell average throughput by allowing multiple devices, under the appropriate operating conditions, to share the same base station resources.

The TM500 test mobile is the most widely used instrument worldwide for testing the performance of base stations, and this latest software upgrade reaffirms Aeroflex’s commitment to tracking each new development in the 3GPP standards ahead of the market requirement. It also represents an important milestone on the roadmap towards LTE-Advanced new transmission modes Designated as Transmission (Tx) Mode 7 in LTE Release 8 (Rel-8), beamforming is very important to achieving the best performance from LTE. Although the technique is mainly applicable to Time Division Duplex (TDD) modulation, the TM500 can support beamforming in both TDD and Frequency Division Duplex (FDD) modulation schemes. MIMO is applicable to both TDD and FDD, and the TM500 supports the 4 x 2 MIMO feature when operating in either mode.

“This latest upgrade to the TM500 enables it to support all the special measurements and test features that are required to verify the beamforming and 4 x 2 MIMO performance of the eNodeB,” commented Stamatis Georgoulis, product manager at Aeroflex Test Solutions. “It also prepares the TM500 to upgrade for dual-layer Rel-9 beamforming and LTE-A features as soon as these are required.”

The TM500 test mobile with beamforming support features channel estimation based on UE-specific reference symbols (RS) or demodulation RS (DM-RS). In over-the-air tests or using a fading channel simulator, it provides data on beamforming gain by comparing cell-specific RS and DM-RS power. This allows the engineer to assess the efficiency of the weighting vectors selected by the eNodeB. Advanced eNodeB designs may utilize different weighting vectors across resource blocks (RB), and for verifying performance of these eNodeBs, the TM500 provides a per-RB channel estimation.

About LTE Beamforming

Rel-8 LTE introduces seven new transmission modes, of which the basic ones are Tx diversity, spatial multiplexing and beamforming techniques. The network controls the configuration of the modes for each UE depending on the UE channel conditions, coverage and capacity requirements. Tx diversity and beamforming are aimed at increasing coverage, while spatial multiplexing is effective at boosting the data rates.

Beamforming techniques are employed in cellular communications to increase the received signal-to-noise ratio (SNR) at each UE, and to reduce inter-cell interference and hence improve both coverage and spectrum efficiency. This is achieved due to the increase in antenna gain when signals from multiple antennas add constructively to create a narrow-beam high-amplitude signal at the receiver – so-called ‘array gain’. The technique is performed using a channel-dependent weighting vector that pre-codes the signal across the antenna array. LTE beamforming is receiving particular attention in China, following the success of the beamforming application in TD-SCDMA.