applied sciences Article Software-Defined Radio Beamforming System for 5G/Radar Applications Diogo Marinho 1,2,*, Raul Arruela 1,2, Tiago Varum 1 and João N. Matos 1,2 1 Instituto de Telecomunicações, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal; [email protected] (R.A.); [email protected] (T.V.); [email protected] (J.N.M.) 2 Departamento de Eletrónica, Telecomunicações e Informática, Universidade de Aveiro, 3810-193 Aveiro, Portugal * Correspondence: [email protected] Received: 2 September 2020; Accepted: 10 October 2020; Published: 15 October 2020 Abstract: Based on the flexibility of software-defined radio (SDR) techniques applied to an array of antennas, this article presents a beamforming architecture designed to operate in millimeter-wave bands (28 GHz), with possible applications in radar and 5G systems. The system structure, including its main constituents such as the radio frequency (RF) frontend modules, the radiating elements as well as the baseband processing on the host computer are widely described. Beamforming is achieved by digitally controlling the signals that feed the antennas. The experimental measurements performed in an anechoic chamber validate the proposed approach. Keywords: digital beamforming; SDR; 5G; radar; beam shaping; phased array antenna 1. Introduction The world is gradually undergoing the age of communications, facing an enormous density of traffic and connections, where everyone is online, people and objects, interacting with each other, through a multitude of applications [1]. The modern generation of mobile communications (5G) is launched, which brings new challenges and opportunities, and will allow the creation and integration of new networks such as the internet of things (IoT) and vehicular networks, in an increasing global coverage. These systems impose a set of new requirements such as high speed data transfer, low latency, high network capacity and high connections density [2], which involve the operation in a frequency range little used so far, in the zone of millimetre waves. Radio detection and ranging (RADAR) technology, that was mainly used for military purposes, recently has suffered increasing attention, and its application is nowadays widespread in sports, biomedical, military or in transportation systems. Radars are used for surveillance, navigation, localization, traffic control or for weapons guidance. Currently, with the evolution of vehicular networks, smart cities and other intelligent systems, more advanced radar technologies are being developed. In the near future, the extension of the radar concept is expected for two purposes, reflectometry and communications. The scenario of Figure1 is foreseeable, a panoply of interconnected systems sharing information, and experiencing a huge communications density, with high risk of interferences. Appl. Sci. 2020, 10, 7187; doi:10.3390/app10207187 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 7187 2 of 14 Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 14 FigureFigure 1.1. ModernModern environmentenvironment ofof multicommunicationmulticommunication systems.systems. RadarRadar technologytechnology isis requiredrequired toto filterfilter thethe environment,environment, focusingfocusing moremore accuratelyaccurately onon thethe targettarget oror targets,targets, asas wellwell asas toto mitigatemitigate interferenceinterference signalssignals fromfrom thethe surroundingsurrounding environment.environment. MultibeamMultibeam capabilities,capabilities, beamforming,beamforming, highhigh gaingain andand tremendoustremendous versatilityversatility andand reconfigurabilityreconfigurability areare importantimportant aspectsaspects forfor modernmodern radarradar systems.systems. Additionally,Additionally, mostmost ofof thesethese characteristicscharacteristics allowallow usus toto overcomeovercome propagationpropagation issuesissues raisedraised whenwhen thesethese systemssystems operateoperate atat higherhigher frequencies.frequencies. Thus,Thus, versatileversatile andand dynamicdynamic communicationcommunication systems systems are needed,are needed, with thewith ability the toability continuously to continuously adjust to the adjust applications to the inapplications which they in are which inserted, they maximizing are inserted, the maximizing quality of communication. the quality of communication. With additional signal With processingadditional capability,signal processing adaptive capability, antennas useadaptive new digital antennas architectures use new that, digital in real-time, architectures dynamically that, in adjustreal-time, the radiationdynamically pattern adjust of the the radiation array. These pattern systems of the have array. perception These systems of the have received perception signal of and the optimize received theirsignal radiation and optimize diagrams their by radiation changing thediagrams beam shapeby changing and beam the direction, beam shape suppressing and beam interferences direction, bysuppressing introducing interferences nulls in the by directions introducing of thenulls interference in the directions signals, of the changing interference the level signals, of side changing lobes, compensatingthe level of side for hardwarelobes, compensating impairments for and hardware finally, accommodating impairments and the finally, mutual couplingaccommodating effects that the canmutual change coupling the amplitude effects that and phasecan change of the transmittedthe amplitude signals. and Particularlyphase of the regarding transmitted automotive signals. radars,Particularly the authors regarding of [3 ,4automotive] present a goodradars, example the authors of the importance of [3,4] present of using a digitalgood beamformingexample of the in multiantennaimportance of systems using digital to reduce beamforming the power in received multiantenna in thedirections systems to of reduce interference the power signals, received placing in nullsthe directions in the radiation of interference pattern. signals, placing nulls in the radiation pattern. ThereThere havehave been been technological technological advances advances in this in field, this wherefield, low-costwhere mm-wavelow-cost mm-wave radars composed radars ofcomposed several antenna of several elements antenna integrated elements inintegrated single board in single and withboard high and resolution, with high resolution, have been presented.have been Inpresented. [5] is presented In [5] is an presented example ofan aexample low-cost of digital a low-cost beam digital steering beam receiver steerin (Rx)g phasedreceiver array (Rx) forphased IoT devicearray for connectivity, IoT device aconnectivity, cheap application a cheap to application get over the to communication get over the communication problems. In problems. [6], a frequency In [6], modulateda frequency continuousmodulated continuous wave (FMCW) wave radar (FMCW) is described. radar is described. This system This generates system generates multiple multiple digital beamsdigital withbeams high with gain, high low gain, side low lobe side level, lobe narrow level, beamnarrow width beam and width high and angular high angular resolution resolution control. Thecontrol. principles The principles of the digital of the beamforming digital beamforming applied to applied synthetic to aperturesynthetic radar aperture (SAR) radar systems (SAR) are systems shown inare [7 ],shown as well in as [7], the as improvement well as the inimprovement the resolution in achievedthe resolution regarding achieved conventional regarding radars. conventional radars.In [8 ,9], a wide variety of future applications are shown, as well as the progress that technology is facingIn in [8,9], reducing a wide the variety cost of of phased future array applications antennas. are Massive shown, antenna as well arraysas the usingprogress up tothat 128 technology elements, increasingis facing in performance reducing the and cost gain of phased of radar array communication antennas. Massive systems antenna are presented arrays using in [10 up], takingto 128 advantageelements, increasing of digital beamforming performance basedand gain on codedof radar aperture communication radar (CAR) systems technique are presented at 77 GHz. in [10], takingIn advantage [11–13], the of importancedigital beamforming of the beamforming based on coded spectral aperture efficiency radar (CAR) is demonstrated, technique at with 77 GHz. the cancelationIn [11–13], of undesired the importance interferences of the by beamforming placing nulls spectral in their directionsefficiency thatis demonstrated, can lead to a lowerwith the bit errorcancelation rate (BER). of undesired interferences by placing nulls in their directions that can lead to a lower bit errorIn rate [14 (BER).], there is a software-defined phased array radio operating at 28 GHz that uses software to controlIn [14], multiple there is a beam software-defined characteristics. phased However, array radio additional operating hardware at 28 GHz was that required, uses software a field to programmablecontrol multiple gate beam array characteristics. (FPGA) board forHoweve digitalr, control additional and an hardware Ettus B200 was mini required, software-defined a field radioprogrammable (SDR) for gate data array waveform (FPGA) board control. for digital In [15 control], a highly and an compact Ettus B200 28 GHzmini software-defined complementary metal–oxide–semiconductorradio (SDR) for data waveform (CMOS) control. integrated In [15], a circuit highly (IC) compact with multiple28 GHz complementary