Towards circulator-free multi antenna transmitters for 5G

2019 16th International Symposium on Wireless Communication Systems (ISWCS)

Jokinen

Leinonen

et al. 2019

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.

Section: Phased Array Figures Of Merit Of Linearity a Beamformedmentioning

confidence: 99%

Digital Predistortion Concepts for Linearization of mmW Phased Array Transmitters

2019 16th International Symposium on Wireless Communication Systems (ISWCS)

Jokinen

Leinonen

et al. 2019

“…First, the PAs of the array can be different due to the implementation tolerances, temperature gradient and process variations. Second, in circulator-free array implementations [4], the PAs sees a load which varies over the steering angle due to the finite antenna coupling [5]. Even if the PAs are identical, their input powers may differ due to the implementation of the mmW power division network with phase shifters.…”

Section: Introductionmentioning

confidence: 99%

Statistical Linearization of Phased Arrays Using Power Adaptive Power Amplifier Model

Khan

2019 IEEE 30th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)

Pärssinen

et al. 2019

Phased arrays used in millimeter-wave systems challenge the concept of power amplifier (PA) linearization by digital predistortion (DPD). This is due to the shared digital path and inaccuracies in analog beamforming and other component variations. However, the group behavior of multiple parallel nonlinear branches can be expected to be more predictable due to averaging effect compared to a single branch behavior. In this paper, we use a power adaptive nonlinear model to mimic the average behavior of a single PA and utilize the probability distribution of the input power of each individual PA to approximate the expected nonlinear behavior of the array over-the-air. The approximated array response is used for the DPD training. The simulation results indicate that the proposed approach provides good linearization performance for large arrays that have varying amplitude and phase weights.

“…On the other hand, decreasing the inter-element spacing from the half of a wavelength increases the coupling between antenna elements [8]. The finite antenna coupling causes challenges due to the circulator-free array architectures used in highly integrated mmW systems [9]. Large planar arrays can also be partitioned into two-dimensional aperiodic tiles to improve the peak sidelobe levels, directivity and aperture efficiency [10], [11].…”

Section: Introductionmentioning

confidence: 99%

Sidelobe Reduction by Subarray Stacking for Uniformly Excited mmW Phased Arrays

Javed

2019 IEEE 30th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)

Leinonen

et al. 2019

The performance of multi-user millimeterwave (mmW) systems is limited by relatively high sidelobe levels (SLLs) of antenna arrays. Per-antenna amplitude control can be used to adjust the amplitudes to reduce the SLL, but the reduction is often achieved at the cost of reduced transmitted power. Large two-dimensional (2D) antenna panels used in mmW phased arrays, however, allow the 2D antenna configuration to be reconfigured to reduce the SLL. In this paper, we present a simplified approach for sidelobe reduction by stacking multiple uniform linear arrays of different size to reduce the sidelobes across the horizontal plane. The approach is based on the relation between the number of antenna elements and the directions of null and sidelobe maxima. The sidelobe reduction is demonstrated by both simulations and measurements. The measurements are carried out in an anechoic chamber at 28 GHz center frequency using a 100 MHz wide modulated 5GNR waveform.