5G Beamforming: How to Test Complex Beamformer ICs
Multiple input multiple output (MIMO) and beamforming are essential technologies to achieve IMT-2020 vision goals for 5G. They increase capacity and coverage in a cell to enable 100x faster data rates and 1000x more capacity than 4G.
Deployed with massive MIMO, multi-user MIMO (MU-MIMO) uses multiple antennas to transmit data to multiple users, thereby increasing cell capacity. Using MU-MIMO, 5G will transition from cell-based communications to beam-based communications. Beamforming is a special implementation of MIMO that uses multi-element antenna arrays to dynamically control the beam pattern. It applies specific spacing and phase/amplitude shifts between the antenna elements.
As the number of antenna elements increase and combine, the radiated energy becomes more focused, resulting in increased power delivery and signal-to-noise ratio (SNR) to the user. By applying a phase shift to the signal at each element, it is possible to change the direction of the beam away from an orthogonal orientation to the arrays. Through control of the phase shifts, electronic phase shifting enables rapid beam control without mechanical operation. The focused beams in beamforming maximize the user equipment’s (UE) SNR, improving the communication link for higher modulation coding schemes.
Figure 1 shows how to create beam patterns by applying more antenna elements and phase shifts.
Beamforming uses channel-state information (CSI) to calculate specific weightings for each antenna element. It applies real-time changes to optimize the signal for the target UE. The UE, in turn, identifies the channel characteristics and shares this information with the base station. The base station can change the phase and amplitude of the antenna elements to counter the effects of the channel conditions. This process offers better control of the transmitted signal. The signal is strongest for the intended UE, improving cell coverage.
Testing Beamformer ICs
Beamformer integrated circuits (IC) are at the heart of 5G communication systems. These multiport devices integrate multi-directional transmit (Tx)/receive (Rx) blocks into front ends, which are connected to the antennas. The critical elements of beamformer ICs must be tested thoroughly under linear and nonlinear conditions, and across the workflow from design and validation to manufacturing.
Beamformer ICs are complex devices. Design and test engineers need to make highly precise measurements at millimeter-wave (mmWave) frequencies and perform simulations at both the component and system level. Testing beamformer ICs requires:
- A multiport vector network analyzer (VNA) for S-parameter measurements
- A custom-switching test set for nonlinear S-parameters, such as distortion and noise figure
- The capability to generate and analyze signals across wide bandwidths
- Instrumentation with low residual error vector measurement (EVM)
- Vector calibration capability for accurate and repeatable wideband mmWave measurements
Facing significant technical challenges, engineers who develop and test beamformer ICs also are under extreme time pressure. Overcoming this challenge requires:
- Innovative ways to perform multiple measurements
- Measurement setup simplification
- Instrumentation with superior measurement speed
External switching test sets can enable multiple measurements for multiport/multi-direction beamformer ICs through a single connection. They can greatly simplify the overall measurement setup and save time by eliminating the manual reconfiguration of the test setup for each measurement.
Measurement speed is particularly important in the production phase of the workflow. Using a true multiport VNA eliminates the use of external test sets or switches while enabling faster and more accurate measurements at mmWave frequencies. High dynamic range, measurement stability, and fast sweep speed can further improve test reliability and reduce the cost of test.
For more information on MIMO and beamforming challenges for device engineers and how they can possibly be overcome, click here.
For more information on Keysight’s solutions for testing beamformer ICs, click here.