No abstract

Digital predistortion (DPD) of a phased array requires that multiple transmit paths must be measured by a feedback (FB) receiver (Rx). In this paper, we propose a FB concept for DPD in a time-division-duplex (TDD) phased arrays. We use a single FB line to collect the waveform samples from the parallel transmit paths to the FB Rx. The TDD switches are used to enable and disable individual transmit paths. The feedback is calibrated by comparing the FB outputs from individual PAs to over-the-air (OTA) measurement reference performed with a frequency modulated continuous wave (FMCW) signal. The individual PA measurements are post-equalized before the DPD training to model the far-field signal. Three alternative strategies are considered for training the DPD through the calibrated FB line and compared with the OTA DPD. The performance is verified by OTA measurements of a 28 GHz phased array transmitter and with fifth generation New Radio waveform in terms of total radiated (TR) adjacent channel power ratio (ACPR), cumulative absolute ACP (CACP), and main lobe error vector magnitude (EVM). The best EVM and ACPR performance is achieved by the strategy where the individual PA responses are treated independently. The methods were comparable to the OTA DPD performance, achieving all < 37 dB TRACPR, −29 dBm/MHz CACP, and ≤ 7 % EVM.

Linearization of millimeter-wave (mmW) phased arrays is one of the key enablers for improving the system performance in terms of power, efficiency and linearity. However, phased array transceiver topologies that have multiple parallel nonlinear components with a shared digital input challenge the standard digital predistortion techniques. In addition, different analogue beamforming techniques complicate the linearization even further due to the fact that the signal nonlinearity has to be observed or modelled over-the-air (OTA) together with the impacts of antennas and even the directive mmW radio channel. The best linearization strategy depends on the system level targets of linearity such as error vector magnitude and adjacent channel power ratio which have slightly different nature when observed in the radiated far-field. In this paper, we present our view and the status of the literature on the topic of phased array digital predistortion. We highlight that the nonlinear distortion have a beam shape which may be different from the linear part of the beam. We also review the antenna array figures of merit describing the nonlinearity. Finally, we show an experimental example of OTA linearization of a 28 GHz phased array transmitter.

RF performance of 5G new radio (NR) millimeter wave (mmW) system will be characterized over-the-air (OTA) in 3GPP 5G NR performance and type approval testing. Total system Error Vector Magnitude (EVM) performance has not been standardized in 3GPP since mobile and base stations are certified separately. In this paper, we extend the OTA measured system EVM concept to cover EVM performance testing with beam steering for 5G mmW radio link. We show that the OTA measured system EVM inside of an electromagnetic compatibility (EMC) chamber can be directly converted to an expected link range, and this has been verified with outdoor measurements. The EVM measurements are performed for a set of beamforming directions to form an expected coverage area. The OTA measured system EVM results confirm that the 5G mmW Proof-of-Concept radio supports 5G NR 16-QAM and 64-QAM modulations as well as 256-QAM modulation, which is currently specified for sub-6 GHz, only. The maximum estimated range of the 5G PoC mmW link is 840 m with 16-QAM modulation and 150 m with 256-QAM modulation. The estimated cell coverage with ±15 degrees beam steering varies from 205 000 m2 to 6 500 m2 using 16-QAM and 256-QAM modulations, respectively. Usable beam width (BW) of the transceiver array is dependent on the system EVM requirement. It varies based on modulation, coding, and link distance. This phenomenon is called cell breathing, which is similar to any cellular system with adaptive coding techniques, although BW might be much narrower in 5G mmW systems.

Production rate plays an important role in industrial applications, which means higher demands for accelerations and speeds of the systems. The requirements for accuracy and repeatability are also increasing. A solution for these demands is a high-speed tooth belt linear drive; however, the drawbacks of system of this kind are non-linear friction and flexibility of the belt, which make the precision control of the system difficult. In this paper, the frictions and flexibility of the high-speed tooth belt linear drive are analyzed.

Digital predistortion (DPD) of a phased array requires that multiple transmit paths must be measured by a feedback (FB) receiver (Rx). This paper proposes a simplified FB architecture to be used for phased array DPD. A single FB line collects the waveform samples from the parallel paths to the FB Rx. The gain and phase of the common FB line is obtained by comparing the FB outputs to over-the-air (OTA) measurements. The overall DPD training is done by collecting the PA outputs with the common FB line, post-equalizing them to model the main lobe waveform and combining them to create the object used for array DPD. The DPD performance was verified by OTA measurements with 5GNR waveform and 28 GHz 8-path phased array transmitter. The DPD trained through the local FB line with the proposed calibration method achieved <-45dB ACPR which was close to OTA DPD performance.

Different assembly, printing and cutting applications demand often fully synchronized movement of multiple actuators. The linear tooth belt drive offers an inexpensive and fast solution for linear movement applications. In this paper the cross-coupled controller is implemented and tested with biaxial linear tooth belt drive system for motion synchronization. The elastic tooth belt set uncertainty in the system parameters and the quantitative feedback theory is applied to design controllers for the biaxial system. Due to an elastic belt stretching phenomena system accuracy is analyzed using two different feedbacks with cross-coupled controller -firstly values are measured from driving motors' encoders and secondly from belt drives' load carts.

In this paper, over-the-air (OTA) phase measurement and calibration method for a fifth generation (5G) millimeter wave radio frequency unit is presented. The phase error measurements are done for both receiver and transmitter. The measurement results are used to calibrate the individual antenna ports of the antenna array system so that accurate radiation patterns can be formed. In order to confirm the calibration, the radiation patterns are measured with a 100 MHz wide 28 GHz 5G New Radio communication signal. The measurements show that the calibration improves the maximum power level flatness of radiation patterns and reduces side lobe levels.